Model 614 Electrometer Instruction Manual Contains Operating and Servicing Information Sean‘WARRANTY Keithley Instruments, Ine. warrants this product to be free from defects in material and workmanship for a period of 1 year from date of shipment. Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batter- ies, diskettes, and documentation During the warranty period, we will, at our option, either repair o: replace any product that proves to be defective. To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio, You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation prepaid, Repaired or replaced products are warranted for the balance of the original warranty period, or at least 90 days. LIMITATION OF WARRANTY ‘This warranty does not apply to defects resulting from product modification without Keithley's express writen consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leak- age, or problems arising from normal wear or failure to follow instructions. THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE BUYER'S SOLE AND EXCLUSIVE REMEDIES. NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRU- MENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE OF THE POS- SIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAM- AGE TO PROPERTY. Keithley Instruments, Inc. «28775 Aurora Road + Cleveland, OH 44139 + 440.248.0400 « Fax: 440-248-6168 + utp:/www.keithley.com gnc 709-160 Pir econ 0969 040: R600 ‘eh ces Mn, Ronn 12 Yan ol Dees, Ma Beng 09RD RASS Fe 8610 ENA “Mr 8 cmon od Meine R620 IEA“ 118957 60-118 959649 We S Ginpuam hs a0iseMGiows tana owoeeteNeOa THUS Toa Sierlanb, ve RO. A863572 9077 a BBS 909 omModel 614 Electrometer Instruction Manual Test Instrumer Al rights reserved. Cleveland, Ohio, U.S.A. July 1991, Fourth Printing, Document Number: 31896 Rev. DSPECIFICATIONS VOLTAGE ‘TempenaTune ACCURACY (1 YEAR) "COEFFICIENT eee ctr @ 25°36 RANGE RESOLUTION _s\thrdg tigi) (rag aight /°C ov OW 08 = 20° 008% +2 a 2 sao Sas + 00s + Oza ay av boom + 13 Soos% 2 ota ven sopety med INMRR: Greater than 6008 a 50H? end 60H ‘CMAR: Greater than 12048 at DC, SOHs and 60H. INPUT IMPEDANCE: Greater thon 5x10 in parallel with 20pF. MAXIMUM OVERLOAD: 350V poak. CURRENT were 28°95°C MAXIMUM ANGE RESOLUTION srg gts) {srg apts SUPPRESSION ccunacy ym 2s A~S~SC*NS SECON tT Se 2p za WA Selo OT Fuss Salma. ropa “ipa TSS ts OT F03s 200A, "20nk—MUpA «OSM 2d OUR + Od SDA Zink WOR std ORR TO S20. room “tase a idm 820A, Zsa tne OS Fas GOT 03d ZA 2A WA OBR ts OI TOs 2A zona yA aR Ns Go S038 Fata INPUT BIAS CURRENT: Less than 60fA at 23°C. INPUT VOLTAGE BURDEN: Less than 200,V, PREAMP SETTLING TIME (to 1% of final value: pA, 0.6s. nA, Sms. A, 25s NMAR: pA and nA, 7068. pA, S548. At SOHz and 60Hz MAXIMUM OVERLOAD: pA and nA, 350V peak. #A, 75V peak RESISTANCE TEMPERATURE ACCURACY (1 YR.) "COEFFICIENT. {we2eC. OCH BIC | TEST RANGE RESOLUTION (trp? dint) $106 igis)/°C CURRENT zko 1 (OSHS AOD 03d TOA min 19 OSs as Os Od TOA wok? 0 9 OSS ad © GOSH 03d Mya ua NKR Sas DEK Cd TOOnm zon 10k 5 as Od Toomm zoowa = WORD tad OH 03d A, zen imo 20m 4 os Od Yona mao 0M) 20m Sas OE TO Opa 20060 OM 2.0% 4 28 SOS), MAXIMUM OPEN CIRCUIT VOLTAGE: 32V OC. MAXIMUM OVERLOAD: ka, 75V peak. MI, G2, 350V pesk CHARGE [ACCURACY (1 YEAR) eae RANGE __ RESOLUTION -(shrdg it) O20 101 Se + 5nd 2 nc swore eer 2 ne 186 Set td INPUT BIAS CURRENT: Less than 6OFA at 23°C. MAXIMUM OVERLOAD: 350V peak. GENERAL DISPLAY: Five LED digits with appropiate decimal point, polarity and loveioad indication, (CURRENT SUPPRESS: Active in Current mode; allows correction fr in ‘put eurents on any sven range CONVERSION TIME: 400m. 2V ANALOG OUTPUT: 2V out for full range input, Inveting in Voltage “and Resistance modes. Output impadance: 10ra. PREAMP OUTPUT: Provides a guard output for Voltage and Resistance Tmeaturements. Can be used as. ivering output or with external fed Back in Current and Coulomb modes. Output impedance: Tk. MAXIMUM COMMON MODE VOLTAGE: 500V peak. CONNECTORS: Input: Tiax. Output: Sway binding posts. ENVIRONMENT: Operating: 0°C 10 35°C up to 70% relative humiity ‘Storage: ~25°C to + 65°C, POWER: Line or battery operated. 105-125V or 210250V (switch se ‘ected, 90-110V avaiable. 60-60H2, BVA typical, 1BVA maximum during Fatty charge 0 hou operation fom full charge. 20 hours to recharae DIMENSIONS, WEIGHT: 127mm high x 216mm wide x 359mm deep (3 mB" x 1a"). Net weight 3.349 (7.2 bs.) ACCESSORY SUPPLIED: Mode! 6011 Talal Input Cable. ‘ACCESSORIES AVAILABLE: ‘Mode! 1019 Universal Rack Mounting Kit Model 8011 Input Cae Model 81024 Voltage Divider Probe {upto 200V with 614) Model §103¢ Vottage Divider Probe (up to 20kV wth 614) Model §108 Test Shiels Model §105 Resistity Chamber Model 8148 Trax Tee Adopter Model 6147 Trox to BNC Adaptor Medel 8167 Guarded Adapter Medel 6301 Gueraed Probe Model 614 Spectcation Addends 1. “When Properly Zerood” refers to reagustng the Volts Zero pot after seater than 1°C change in ambient temperature or every 24 hours. 2. Normal made rejection specification applies fr signal and noise of less than ful ange 3, "Preamp setting te to 1% of ira value” assumes a step input from Oto ful range. 4, Overall specifeations are valid for ovetload signals under tH ‘Model 614 storage time must be derated according to manufacturers ‘spectcation forthe BA-35 Battery Pack at temperatures above 25°C. 000 MAXIMUM STORAGE TIME — DAYSSafety Precautions ‘The following safety precautions should be observed before using this product and any associated instrumentation. Although some in- stroments mad scccesories would normally be used with non-be- ardous voltages, there ae situations where hazardous conditions may be present “This product is intended for use by qualified personnel who reeog- nize shock hazards and are familiar withthe safety precautions r- quired to avoid possible injury. Read the operating information carefully before using the product. ‘The types of produet users are Responsible body isthe individual or group responsible forthe we and maintenance of equipment, for ensuring that the equipment ‘operated within its specifications and operating limits, and for en suing that operators are adequately trained ‘Operators use the product for its intended function. They must te trained in electrical safety procedures and proper use ofthe instr ‘ment. They must be protected from electri shock and contact with hazardous live circuits Maintenance personnel perform routine procedures on the produt to keep it operating for example, setting the lin voltage or replac- ing consumable materials. Maintenance procedure are described in ‘the manual. The procedures explicitly state i the operator may pe form them, Otherwise, they should be performed only by service personnel, Service personnel are tained to work on lve circuits, and perform, safe installations and repairs of products. Only properly trained ser ‘vice personne! may perform installation and service procedures. [Exercise extreme caution when a shock hazard is present, Lethl voltage may be present on cable connector jacks or test fixtures, The ‘American National Standards Insitute (ANSD states that a shock hazard exists when voltage levels greater than 30V RMS, 42.4V peak, or 6OVDC are present. A good safety practice is to expect ‘that hazardous voltage is present in any unknown circuit before measuring. Users of this product must be protected from electric shock at all times. The responsible body must ensue that users are prevented, aceese andor inenlated fram every connection paint In some ees, Connections must be exposed to potential human contact. Product ‘users in these circumstances must be trained to proect themselves from the risk of electric shock. Ifthe circuit i capable of operating, ator above 1000 volts, no conductive part of the circuit may be exposed. ‘As described in the International Electrotechnical Commission (EC) Standard IEC 664, digital multimeter measuring circuits (e.g. Keithley Models 175A, 199, 2000, 2001, 2002, and 2010) are Installation Category I. All othe instruments signal terminals are Installation Category I and must not be connected to mains. Donot connect switching cards directly to unlimited power circuits, They are intended to be used with impedance limited sources. NEVER connect switching cards directly fo AC mains. When con- necting soures to switching cards, install protective devices to im. it fault current and voltage tothe card, ‘Before operating an instrument, make sure the line cord is connect ed © a properly grounded power receptacle. Inspect the connecting, cables, tes leads, and jumpers for possible wear, cracks, or breaks before each use. FFor maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test ALWAYS remove power from the entire test system and discharge ‘any capacitors before: connecting or disconnecting cables or jump- es, installing or removing switching cards, or making intemal changes, such as installing or removing jumpers. Do not touch any object that could provide a current path to the ‘common sie ofthe circuit under test or power line (earth) ground, Always make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the voltage being measure."The instrument and accessories must be used in accordance with its specifications and operating instructions orth safety ofthe equip- ‘ment may be impaired. Donot exceed the maximum signal levels ofthe instruments and ac- ‘cessories, as defined in the specifications and operating informa- tion, and as shown on the instrument or test fixture panels, oF switching car. When fuses are used ina product, replace with same type and rating for continued protection against fire hazard, ‘Chassis connections must only be used as shield connections for ‘measuring circuits, NOT as safety earth ground connections. you are using atest fixture, keep the lid closed while power is ap- plied to the device under test. Safe operation requires the use of a Tid imeriock. ata © sere is present connect ittosafety earth round using the site commend in he ner docmenttion, ‘the A\ symbol onan instrument indicates ha the usershoulde- fer the operating instructions located inthe manual ‘Toe AA symbot on an instrument shows that ican source ormes- sure 1000 vot or more ncluding the combined effet of noma Et crmmcon nods veka, Us smd lly pecan void persona const wih hese vag ‘The WARNING heading in a manual explains dangers that might result in persona injury or death. Always read the associated infor- ‘mation very carefully before performing the indicated procedure. ‘The CAUTION heading in a manual explains hazards that could damage the instrument, Such damage may invalidate the warranty. Instrumentation and accessories shall not be connected to humans, Before performing any maintenance, disconnect the line cord and all test cables, ‘To maintain protection from electric shock and fre, replacement cemponents in mains cireuits, including the power transformer, txt leads, and input jacks, must be purchased from Keithley Instru- ments. Standard fuses, with applicable national safety approvals, may be used ifthe rating and type are the same. Other components that are not safety related may be purchased from other suppliers as Jong as they ae equivalent tothe original component. (Note that se- Jested parts should be purchased only through Keithley Instruments to maintain accuracy and functionality ofthe product.) If you are tunsure about the applicability ofa replacement component, cll @ Keithley Instruments office for information, ‘To clean an instrument, use @ damp cloth oF mild, water based cleaner. Clean the exterior of the instrument only. Do not apply cleaner directly tothe instrument or allow liquids to enter or spill on the instrument Products that consist of a circuit board with n0 ease or chassis (e.g. data acquisition board for instalation into a ccmputer should never require cleaning if handled according to in structions, Ifthe board becomes contaminated and operation is af= fected, the board should be returned to the factory for proper chaningservicing, Rev. 299TABLE OF CONTENTS Paragraph Title SECTION 1-GENERAL INFORMATION Introduction Features ..... Warranty information | Manual Addenda : Safety Symbols and Terms Unpacking and Inspection Specifications . SECTION 2 - OPERATION 2.1 Introduction 2.2 Preparation for Use . - 221 Battery Power 222 Line Power. 23° Operating Instruction . 2.3.1 Environmental Conditions 2.3.2 Front Panel Controls 2.33 RearPanel Description... 2.4 Measurement Considerations 2.4.1 Guarding... wee 2.42 Ground Loops aoe 7 ao 2.43 Electrostatic Interface... 2.4.4 Thermal EMFs 2.5 —_Electrometer Measurements, 2.5.1 Voltage Measurement 2.5.2 Current Measurement. 253 Current Suppress 2.5.4 Resistance Measurement... 25.5 Charge Measurement 25.6 2V Analog Output... 25.7 —_ Preamp Output (External Feedback) - 26 —Electrometer Applications 26.1 Insulation Resistance ....... 26.2 High Impedance Voltmeter 263 — LowLeakage Measurements 26.4 Diode Characterization .. SECTION 3 - ACCESSORIES 3.1 Introduction 32 Model 1019 Rack 33 Model 6102A Voltage Divider Probe 34 Model 6103C Voltage Divider Probe 35 Model6104 Test Shield . : 3.6 Model 6105 Resistivity Chamber... 3.7 Model6011 Input Lead : 38 Model 6146 Triax Tee Adapter. 3.9 Model6147 Triax to BNC Connector 3.10 Model 6167 Guarded Adapter . 3.11 Model 6301 Guarded Probe . ..TABLE OF CONTENTS (continued) Paragraph Title Page SECTION 4 - PERFORMANCE VERIFICATION 4a Introduction... ces tebsetteseteeseetetteeeeenans fa 42 Environmental Conditions - cece (et 43 Recommended Test Equipment lat 44 Performance Verification Procedure lat 45 Initial Conditions..........0-e0ce0ressessseseeeeereareerens ces [ae 48 Volts Verification la 47 Current Verification Seen a2] 48 Input Current Verification 4-2] 49 Resistance Verification... voliilicensasisnsresesrrsrenrenerereree Selects [4 4.10 Charge (nC) Verification ia SECTION 5 - THEORY OF OPERATION 5a Introduction. 52 Input Preamplifier .- 53 Volts. 5a Resistance 55 Current and Charge « 56 Zero Check 57 Ranging Circuit . 58 Power Supply 58.1 Battery Charging Circuit 5.8.2 Battery Shutbown Circuit 5.8.3 DC to DC Converter 59 A/D Converter 59.1 ‘Auto Zero... 5.9.2 Signal Integrate... 6... esse eeeeceeceeseeeeeeeeeeeeree 5.93 Reference Integrate - 59.4 Zero Integrator . 595 Reference Cicruit SECTION 6 - MAINTENANCE 61 Introduction. ceccteteeees [ET 62 Recommended Test Equipment. arene ee le 63 Environmental Conditions . coliliiiiticnsonsnsensnens : on et 64 Calibration Procedure. cD feet 6.4.1 Power Supply Calibration... 6-1 6.4.2 Volts Calibration ie2| 6.43 Current and Resistance C ie-3 65 ‘Special Handling of Static Sensi le-3 66 Troubleshooting . \6-3 67 Battery Replacemer le 68 Fuse Replacement : mo aoe le 6a Line Battery Fuse Replacement cece . (65) SECTION 7 - REPLACEABLE PARTS 7A General... 7-7] 72 Parts Li 7-1 73 Ordering Information 7-4 74 Factory Service 7-1 75 ‘Schematic Diagrams and Component Location Drawings 7.129 210 21 212 213 214 a1 32 33 34 35 36 at 42 45 51 52 54 55 61 62 64 65 74 72 73 74 75 76 LIST OF ILLUSTRATIONS Title Model 614 Front Pane! Model 614 Rear Panel... Equivalent Input Impedance Model with Zero Check Enabled Unguarded Configuration Guarded Configuration . Ground Loop Configuration Ground “Tree” Configuration Voltage Measurement. ..... Constant Current Method Employed by the Model 614 ‘Technique for Measuring Resistance > 10'10 .... - Insulation Resistance Measurement Using the Model6167 - Constant Voltage Technique i : High Impedance FET Gate Voltage Leakage Current Measurement... Characterizing a Diode with the Model 614 Diode Curves Model 1019 Model 61024 Model 6103C. Model 6105, Model 6011 Model 6167 DC Volts Verification. Current Verification... Resistance Verification Resistor Standardization Charge Verification Model 614 Block Diagram. Basic Circuit Configurations. Volts Configuration Resistance Configuration Model 614 Preamplifier Configured in Current or Coulombs Model 614 Ranging Circuit . ‘Top Cover Removal and Ci Current Calibration . Battery Replacement . Exploded View Input Connector Assembly. Model 614 Electrometer PC-596 Component Location Drawing Dwg. No. 31886, Power Supply PC-596, Component Location Drawing Dwg. No. 31886 Display Board PC-597, Component Location Drawing Dwg. No. 31881 Model 614 Electrometer PC-596, Schematic Diagram Dwg. No. 31895. Power Supply PC-596, Schematic Diagram Dwg. No. 31895 Display Board PC-597 Schematic Diagram, Dwg. No. 31894Table 24 at 42 43 51 52 53 61 62 64 65 66 7A 72 73 LIST OF TABLES Tite Ohms Range for Test Current Performance Verification Equipment Resistance Verification... Feedback Resistors . Feedback Elements Model 614 Ranging Performance Verification Equipment Offset Jumper Setup : Model 614 Static Sensitive Device Power Supply Checks . Preamplifier Circuitry Checks. ‘A/D Converter Checks Cross-reference of Manufacturers Model 614 Motherboard PC-596 . Model 614 Display Board PC-597 Page (28 iat 42] 4-3 5-3] Es 5-6| 62 63] 6-4] 65] 7-2| 73 73)SECTION 1 GENERAL INFORMATION 4.1 INTRODUCTION ‘The Model 614 is an electrometer with 10% A sensitivity, and an input current less than 60fA at 23°C. Voltage sen- sitivity is 10,V to 20V with an input impedance of greater than 50T® (5x10). Resistance sensitivity of the Model 614 is from 19 to 2x10"0 using the constant current technique. Charge sensitivity (nC) is from 10fC (10 Coulombs) to 20nC (2x10* Coulombs). See Figure 1-1 and 1-2 for front and rear panel detail 1.2 FEATURES The Model 614 includes the following features: + 4-digit diaplay with appropriate decimal point. * 2V Analog Output - The 2V Analog Output provides an analog signal with a scale of 2V for Full Range at the display. The output impedance is 10k®. The signal is in- verted for the Volts and Resistance functions. © Preamp Output, that can be used as a guard in the Volts ‘and Resistance functions, and as an inverting output in the Current and Charge functions. The output im- pedance is 1k. This output can be used for monitoring the input signal in applications requiring a buffer amplifier, and can also be used with external feedback. ‘© Current Suppress, which is available in the Current mode, allows correction for input offset currents on any given range. Does not affect accuracy or drift. ‘* Each Range has the following: 1. Automatic polarity operation, minus sign displayed, plus sign implied. 2. Effective input overload protection. 3. Overrange indication (flashing 0000). 4. Decimal point positioned by range push button. * Battery pack standard. Complete portability. Full charge is maintained when the Model 614 is plugged in. Bat- teries at full charge will provide 10 hours of operation, * Line power can also be used. Switch over from battery power to line power is automatic. * Volts Zero sets “zero” on the .2V range and need not be readjusted on the other ranges. 1.3 WARRANTY INFORMATION ‘Warranty information is provided on the inside front cover of this manual. If there is a need to exercise the warranty, contact the Keithley representative in your area to deter” mine the proper action to be taken. Keithley maintains com- plete repair and calibration facilities in the United States, West Germany, Great Britain, France, the Netherlands, ‘Switzerland and Austria. Information concerning the ap- plication, operation or service of your instrument may be directed to the applications engineer at any of the above locations. Check the inside front cover of this manual for addresses. 1.4 MANUAL ADDENDA. Improvements or changes to this manual will be explained on an addendum attached to the inside back cover. 1.5 SAFETY SYMBOLS AND TERMS. Safety symbols used in this manual are as follows: The symbol con the instrument denotes that the user should gefer to the operating instructions. ‘The symbot on the instrument denotes that 1000V (or more may be present on the terminal(s). ‘The WARNING used in this manual explains dangers that, could result in personal injury or death. ‘The CAUTION used in this manual explains hazards that could damage the instrument. 1.6 UNPACKING AND INSPECTION ‘The Model 614 is inspected both mechanically and elec- trically before shipment. Upon receiving the Model 614 unpack all items from the shipping container and check for any obvious damage that may have occurred during transit. Report any damage to the shipping agent. Retain and use the original packaging materials if reshipment is necessary. The following items are shipped with all Model 614 orders: ‘A Model 614 Electrometer ‘A Model 614 Instruction Manual * A Model 6011 Input Lead * Optional accessories per request If an additional instruction manual is required, order the manual package (Keithley Part Number 31896-00). The manual package includes an instruction manual and all perti- nent addenda. 1.7 SPECIFICATIONS. For Model 614 detailed specifications, refer to the specifica- tions that precede this section, WWFigure 1-1. Model 614 Front Panel Figure 1-2. Model 614 Rear PanelSECTION 2 OPERATION 2.1 INTRODUCTION Procedures for operating the Model 614 for measurements of Voltage, Current, Charge and Resistance are contained in this section. Several practical applications are explained later in this section, 2.2 PREPARATION FOR USE 2.2.1 Battery Power ‘The Model 614 operates on either line or battery power. A rechargeable lead-acid pack is used in the Model 614, The pack will be charged (whether the instrument is on or off) in 20 hours from complete discharge. The Model 614 will Operate for 10 hours after full charge. When the pack is discharged, the instrument automatically shuts off and will not operate until line power is connected, If the battery is ‘completely discharged, line power operation may be delayed by 5 to 10 seconds. Switch over from line power to battery ‘operation is automatic, CAUTION Do not store the Model 614 with a discharged battery pack for more than six weeks at a temperature greater than 25°C or damage to the battery pack may result, For long term storage (more than one month) charge the battery pack for 20 hours on line operation. Maximum shelf life after a full charge is two years. 2.2.2 Line Power ‘The AC input line voltage required to operate the Model 614 is 105V-125V or 210V-250V. The recessed LINE VOLTAGE switch on the rear panel, selects either 105V-125V or 210V-250V operation. F102 is the line fuse and is rated at 1/8A, 250V, 3AG for both 105V-125V and 210V-250V operation, For units ordered for operation from 90V-110V. or 180V-220V, F102 is rated the same as for 105V-125V or 210V-250V operation. Switching from line operation to bat- tery operation involves removing the Model 614 from line ower. As long as the Model 614 is operating on line power, the battery pack is charged or maintained at full charge. The Model 614 operates from 50Hz or 60H2. WARNING When using line power, ground the Model 614 through a properly grounded receptacle before operation. Failure to ground the Model 614 can result in severe injury or death in the event of a short circuit or malfunction. When operating on battery power, maintain chassis common within 30V of earth ground. 2.3 OPERATING INSTRUCTIONS. 2.3.1 Environmental Conditions All_ measurements should be made at an ambient ‘temperature within the range of 0°C to 35°C, and with 2 relative humidity of less than 70%. To maintain low input current ( < 60fA), ambient temperature of up to 23°C is sug- gested. 2.3.2 Front Panel Controls 1. ON/OFF Switch—Depressing the push button turns the instrument on for either battery power or line power. Releasing this push button turns the instrument off. 2.1—Depressing this push button selects the Current func tion, 3. R— Depressing this push button selects the Resistance function. 4. V—Depressing this push button selects the Volts func- tion. 5.nC {nanecoulombs)— Depressing this push button selects the Coulomb (Charge) function, 6. UNITS— Depressing any of these push buttons selects the appropriate scientific units of the parameter being measured 7. RANGE—Depressing any of these push buttons selects the appropriate range and sensitivity of the parameter being measured. Example 1: The current to be measured is on the order of 154A, A. Select Current (I. B. Select Unit (uA). C. Select Range (20). Example 2: The resistance to be measured is on the order of soca, ‘A. Select Resistance function (Ri. B. Select Unit (G0), C. Select Range (20). 8. CURRENT SUPPRESS ON/OFF—Depressing this push button turns on the Current Suppress circuit Releasing it disables the Current Suppress circuit. 24NOTE Current Suppress is active only when Current function (I) is selected. 9. Current Suppress Potentiometer—When the CUR- RENT SUPPRESS push button is depressed, the cur- rent suppress potentiometer can be used to zero out, any input up to +2000 counts (except +200 counts fon the 2000 yA; nA or pA ranges to prevent input overload without indication }. NOTE ‘The Current Suppress potentiometer must be readjusted when the range is changed. 10. ZERO CHECK Depressing this push button places the Model 614 in the Zero Check mode by shorting the preamplifier feedback elements in the Current or Coulombs mode, or shorting the preamplifier input in ‘the Volts or Resistance mode. Releasing the button takes the Model 614 out of the Zero Check mode. The Zero Check feature allows internal offsets to be corrected and also protects the sensitive input circuitry from charge build-up during overloads, NOTE ‘The input impedance characteristics change when the ZERO CHECK button is de- pressed. See Figure 2-1. 7 7 x iy = 200 cunnent Cry = 205° RESISTANCE i = 200F vorrace y= 200" ncouLomas Figure 2-1. Equivalent Input Impedance Model with Zero Check Enabled. 11, VOLTS ZERO— Volts Zero adjusts the input amplifier offset. This is accomplished only in Zero Check, .2V range. Volts Zero Verification A. Turn the Model 614 on and allow it one hour for warm-up. B. Depress ZERO CHECK. . Select the Volts function and the .2V range. 1D, The Model 614 should display .00000 +1 digit. If the display is not .00000 +1 digit, adjust the VOLTS ZERO potentiometer R103 (small hole directly under the Input connector) to obtain @ displayed reading of .00000 +1 oa E.. The Model 614 input amplifier zero is now adjusted for all functions and ranges. NOTE Adjust Volts Zero only on the .2V range. ‘Adjustment on the .2V range guarantees a proper zero on all other functions and ranges. 12. Input—The input connector is a Teflon’ female triax connector. NOTE ‘The input connector must be kept clean to ‘maintain high input impedance. insulated CAUTION Do not exceed the maximum allowable input. Instrument damage may result. Maximum the speci the front panel under the appropriate tions, where the possibility of overloeds greater than 75V peak exist, be sure that HA (k0) is NOT depressed. 2.3.3 Rear Panel Description Line Plug—The line plug mates with a 3-wire line cord which provides connections to line voltage (high, com- mon and earth ground). WARNING When using line power, ground the Model 614 through a properly grounded eptacle before operation. Failu ground the Model 614 can result severe injury or death in the event of a short circuit or malfunction. WARNING When floating Input LO above 30V from earth ground, hazardous voltage will be present at the 2V Analog Output and the Preamp Output.2, FUSE— The fuse is rated at 1/84, 3AG, 250V. 3. LINE VOLTAGE Switch—The LINE VOLTAGE switch selects eitheS0V - 125V or 180V - 250V operation (see paragraph 2.2.2). 4. Chassis Ground Terminal— This terminal provides a Connection to chassis ground (outside shell of input con- rector). 5 LO— This terminal provides a connection to input LO through @ Th resistor (se rear panel schematic Figure 1.2). 6 Preamp Out—Preamp Out (V-9 Guard) can be used as 2 guard in the Volts and Resistance functions. In the Current and nCoulombs functions, it can be used as an inverting output. 7. 2V Analog Output—The 2V Analog Output provides an ‘analog signal with a scale of 2V for Full Range at the display. The output impedance is 10k®. The signal is in- verted for the Volts and Resistance functions. Example: With the Volts function selected and 1.9000V. applied, the front panel display reads 1.9000. The 2V Analog Output will read -1,9000. 2.4 MEASUREMENT CONSIDERATIONS 2.4.1 Guarding Guarding consists of surrounding the sensitive input with a conductor (the Guard) connected to a low impedance point which is at virtually the same potential as the high it pedance signal. For Example: A coaxial cable with a grounded shield and a voltage applied to the center conductor from a voltage source with a high internal resistance, has a reduced output voltage due to leakage resistance of the cable. If instead, the shield is connected to a low impedance voltage source of approximately the same potential as the high impedance source, leakage from the center conductor to the shield nearly vanish. Even though leakage from the outer braid to ground may be considerable, this flow is inconsequential, since the current is supplied by the low impedance source. ‘The unguarded configuration shown in Figure 2-2 illustrates how leakage resistance causes erroneous results, The ‘guarded configuration shown in Figure 2-3 illustrates how ‘guarding eliminates the problem. The Model 6167 Guarded Adapter implements this configuration, If long cables are used, the cable capacitance C, (shunting Ry) becomes significant. The time constant RC. deter- mines the settling time of the measurement. If R and C, are large (> 109 and > 20pF respectively) response time is slow. Guarding the high impedance node eli problem. (See Figure 2-3) As CABLE =ss RL fo Figure 2-2. Unguarded Configuration Guarded Ampitier ‘Mode! 614 Preamp Out NO CURRENT FLOWS THROUGH RL THEREFORE Eo=Es, Figure 2:3. Guarded Configuration 2.4.2 Ground Loops Ground Loops, that occur in multiple-instrument test set- Ups, can cause erratic or erroneous measurements. A hookup as shown in Figure 2-4 introduces errors in two ways. Large ground currents flowing in one of the wires will encounter small resistances, either in the wires or in the interconnections. This results in voltage drops which may affect the measurement. Even if the ground currents are small, magnetic flux cutting across the large loops formed by the ground leads, can induce sufficient voltages to disturb sensitive measurements. Ly SIGNAL LEADS. HSTROWENT INSTRUMENT INSTRUMENT c /(Teica. Ground toor ~ ‘CAUSES CURRENTELOW Sita StewaL ueAD POWER UNE GROUND Figure 2-4. Grounded Loop Configurati 23To prevent ground loops, the signal grounds on the struments should be interconnected to a central node resembling a tree (see Figure 2-5). Experimentation is the ‘simplest way to determine an acceptable arrangement. For extremely sensitive measurements, however, ground loops formed by capacitive coupling through the power transformer and power lines can be troublesome. In this case, the Model 614 can be isolated from the power line by utilizing battery power. INSTRUMENT INSTRUMENT INSTRUMENT POWER UNE GROUND Figure 2-5. Ground “Tree” Configuration 2.4.3 Electrostatic Interference Electrostatic interference occurs when an electrically charged object is brought near an uncharged object, thus inducing a charge on the uncharged object. Usually, this is not observed because low impedance levels allow the induced charge to quickly dissipate. However, the high impedance of electrometer measurements does not allow the charges to decay as rapidly and thus, erroneous or unstable readings may result. Erroneous or unstable readings may be caused in the following ways: 1. DC electrostatic field can cause undetected errors in the reading 2. AC electrostatic fields can cause errors by driving the ‘amplifier into saturation or through rectification that pro- duces DC errors. Electrostatic interference is first recognizable when hand or body movements near the experiment alter the electrometer reading. Pick up from AC fields can also be detected by observing the electrometer output on an oscilloscope. Line frequency signals on the output is an indication that electro- static interference is present. Means of eliminating electro- static interference include: 1. Shielding, is both effective and economical. Possibilities include: @ shielded room, a shielded booth, shielding the sensitive circuit and using shielded cable. The shield should always be a solid conductor that is connected to a circuit ground. Meshed screen or loosely braided cable could be inadequate for high impedances or in strong fields. The Keithley Model 6104 Test Shield provides shielding under these circumstances. Note however, that shielding can increase capacitance in the measuring circuit. 24 2. Reduction of electrostatic fields. Moving power lines away from the experiment reduces electrostatic inter- ference. 2.4.4 Thermal EMFs Thermal EMFs are developed when a junction of dissimilar ‘metals are at different temperatures. Low thermal connec- tions are used to minimize thermal EMFs. Crimped or cad- ium soldered copper to copper connections are ideal. 2.5 ELECTROMETER MEASUREMENTS 2.5.1 Voltage Measurement ‘The Model 614 is capable of making voltage measurements from high resistance sources (> 10°). Make voltage measurement as follows: |. Turn the Model 614 on. Depress ZERO CHECK. Select Volts function and verify Volts Zero (paragraph 2.3.2). |. Select the desired range. Connect the source to the Model 614. . Release ZERO CHECK, Take reading. NOTE Cable capacitance may increase the ‘measurement response time. See paragraph 24.1. CAUTION Do not exceed the maximum input. In- strument damage may result. ag a92000 9 Figure 2-6. Voltage Measurement2.5.2 Current Measurement ‘The Model 614 is capable of measuring current to 10°%A. The feedback ammeter technique is used to measure the current. Low voltage burden and errors caused by inserting the ammeter into the circuit are reduced. Because the Model 614 employs the feedback technique for measuring current, cable capacitance and leakage are not significant problems. In fact, input capacitance may approach 0.1F without degrading the measurement. Leakage resistance as low as 102 will not degrade instrument performance. However, it is essential that the input cable be kept station- ary during very sensitive measurements. Flexing or moving ‘even the highest quality graphite lubricated low-noise cable ‘ay generate hundreds of femtoamps of currents due to the iboelectric ettect. Make current measurement as follows: . Turn the Model 614 on and allow one hour warm up. Depress ZERO CHECK. Select Current Function. Select units (yA, nA, or pA). 5. Select range (20, 200 or 2k). Apply input and release ZERO CHECK, . Take reading. Displayed reading is in wA, nA, or pA depending on the units selected. Nem awnag NOTE After first turning on the Model 614 (after overload or after changing function), it may be necessary to allow the input to settle for about one minute before input bias current falls within specification. For severe overloads, several minutes may be required. 2.6.3 Current Suppress This feature is provided so that offsets can be nulled out to observe input current changes more conveniently. Currents Up to 200A, 200nA or 200pA can be suppressed depen- ding on the Units selected. To use Current Suppress: 1. Input a baseline current. 2. Depress CURRENT SUPPRESS button. Current function (i) must be selected. . Adjust Current Suppress knob until display reads zero, ‘Small changes in input signal can now be easily seen. To observe original baseline depress ZERO CHECK. Original baseline is now displayed but with opposite polarity. NOTE ‘Any time a range or units change is made, ‘the Current Suppress should be readjusted. 6. To turn off Current Suppress, release CURRENT SUP- PRESS button, 2.5.4 Re ‘ance Measurement ‘The Model 614 is capable of measuring from 19 to 2x10"9. For resistances greater than 2x10", it is recommended that {an external voltage be applied to’ the unknown and the Model 614 be used to measure the current through the unknown. As shown in Figure 2-8. For more information refer to paragraph 2.6.1. The Model 614 employs the cons- tant current technique to measure resistance. Refer to Figure 2-7. Measure resistance as follows: 1, Turn the Model 614 on, 2. Depress ZERO CHECK. 3, Select Resistance function (R). 4, Select Units (k2, M@ or GO) 5. Select Range (2, 20, 200) 6. Apply the input and release ZERO CHECK. 7 Take the reading. The reading is in k®, MQ, or GO depending on the Units selected. Figure 2-7. Constant Current Method Employed by the Model 614. Model 618 lsd in Cute fnetion) Figure 2-8. Technique for Measuring Resistance > tone NOTE Stability with inductive sources: When using ‘the Model 614 to measure resistances or voltages from sources having high Q series inductances, it may be necessary to bypass the inductance with a 0.01uF capacitor to prevent circuit instability. This situation may be encountered when attempting to measure the series resistance of an inductor above 10mHy. The 0.01uF capacitor pro- vides a low impedance shunt to the induc- tor. 252.5.5 Charge Measurement (nC) ‘The Model 614 is capable of measuring Charge from 10fC to 20nC. The Model 614 measures charge as a feedback coulombmeter. Measurements should be made as quickly as possible since electrometer bias current introduces time dependent errors. The error due to bias current is 60fC/sec maximum at 23°C. Measure charge as follows: |. Turn the Model 614 on and allow one hour warm up. . Depress ZERO CHECK. Select Charge function (nC). . Select Range (.2, 2 or 20). - Release ZERO CHECK. A small Zero Check hop may ‘occur. Less than 200fC hop is typical. On the .2nC range the effect of instrument input current can be seen. The display ramps at a rate of less than 60fC/sec (6 digits/sec).. 6. Apply input. The displayed reading is the amount of charge transferred to the input. If the reading does not settle the amount of charge being transferred to input is changing with time. This means current is flowing in to (or out of the Model 614 input. The current and charge can be related as follows: Q= IT = Charge in nanocoulombs Current in nanoamperes T= Time in seconds geene 2.5.6 2V Analog Output This output can be used to drive a chart recorder. In the Volts and Resistance functions the 2V Analog Output signal is inverted. WARNING When floating Input Low above 30V from earth ground, hazardous voltage will be present at 2V Analog and Preamp Outputs 2.5.7 Preamp Output This output can be used as a guard in the Volts and Resistance functions. As a unity gain amplifier (in Volts function) this output is typically within better than 10ppm of the input (excluding offsets). The output resistance appears between input LO and output LO rather than in the Preamp Out HI lead. This keeps the 1k® protection resistor out of the loop when using external feedback elements. The Model 6146 Triax Tee Adapter may be used to provide high impe- dance interconnections between input and external feed- back elements. External feedback can be used if non- decade or logarithmic gain is required, or if added Coulombs capability is necessary, 26 NOTE To use external feedback elements with the Model 614 simply pop out all the UNITS but- tons. This opens the feedback loop and allows external elements to complete the loop. This can only be accomplished in the Current (I) function. Connect the external feedback elements (Ror C) from Preamp ‘Out (rear panel) to the Model 614 input using the recommended shielded test box. 7 } Pro Ost Input 614 2.6 ELECTROMETER APPLICATIONS 2.6.1 Insulation Resistance The Model 614 can directly measure resistances up to 2x10"'9. Above 10°, or for cable length longer than three feet, the Model 6167 Guarded Adapter is recommended to allow quick and accurate measurements regardless of cable capacitance or cable leakage. The Model 614 uses the con- stant current measurement technique to measure Resistance. This means that the test current through the unknown is constant, but the voltage appearing across the ‘unknown depends on the resistance being measured. The Model 614’s low compliance voltage keeps the error due to the voltage coefficient of the unknown resistance small. A typical setup for measuring insulation resistance is shown in 614 sett Resistance I) ‘Guard To Rear Panel Preamp Out Figure 2.9, Insulation Resistance Measurement using the Model 6167.It is necessary to shield resistances greater than 1070 if a stable reading is expected. With the constant voltage method, the Model 614 is used as an ammeter to directly read the leakage current through the unknown resistance. This technique makes it possible to ‘measure insulation resistances up to 10. The voltage source is applied externally and the Model 614 is connected ‘as shown in Figure 2-10. The insulation resistance can be found using any test voltage and can be calculated from: ‘measure current on the Model 614. applied voltage. Example: V; (applied vottage) 100V, |; (measure current) 100v pA 109 ‘An application in design where this range of resistance is ‘common would be the measurement of printed circuit board resistance. Stray leakages between adjacent tape patterns often cause circuit problems. Using the Model 614 to measure these resistances it is possible to assess and cor- rect the problem. TT i “I [votsse Model Source] y, k Ga wy vx. 100M com fe $V —0 To rest ofthe ecu i fis 0 Vv Figure 2-11. High Impedance FET Gate Voltage ‘The error due to loading a high impedance voltage source with a voltmeter can be expressed as: ‘error = BS__x 100% Rs + Rin Where: Rs = Source Resistance Rin Input Resistance of Meter In this example, if a DMM with 10M@ input resistance were used: error = OMA 199% = 100M2 + 10Ma en I the high impedance DMM were used (Input resistance is 100ma. Seerror = —100Ma_ Tome + Tan x 100% = 9.1% error A 9.1% error is not tolerable in this case, therefore the DMM could not be used. The Model 614 is capable of measuring voltages up to 20V with greater than 5 x 10° in- put impedance. In this example, 100Mo Figure 2-10. Constant Voltage Technique 2.6.2 High Impedance Voltmeter ‘The Model 614 is a high impedance voltmeter with greater than 5x10%2 input resistance. Consider an example of 2 designer who wishes to measure the gate voltage on a preci- sion JFET amplifier with a gate impedance of 100MQ. The designer needs to measure this voltage to an accuracy of 196. Refer to Figure 2-11. %erro Soom eaioaa * 100% = .0002% error due to input impedance. ‘The input impedance is more than adequate for this applica- tion. The 4%-digit Volts resolution allows the designer enough precision to make use of the high input impedance. 2.6.3 Low Leakage Measurements: ‘The Model 614 is capable of measuring leakage currents to 10°%A (10fA). A typical example of low leakage measure- ‘ment is shown in Figure 2-12. 27614 Sot to Measure Current L=Leakage Current sv oc Power suppy) = *T era Figure 2-12. Leakage Current Measurement In this example, the leakage current of a JFET needs to be ‘measured. Even though the manufacturer may specify 1nA leakage at 30V, this test set up may show that at 18V (or other required voltage) the leakage current is much less. Use of a shielded test enclosure such as the Model 6104 would help keep the measurement quiet and stable. The cable used to connect the Model 614 to the JFET and the power supply is the Model 6011 Shielded Test Cable which is provided with the Model 614. Diode leakage (forward and reverse) can be measured in a similar way. The forward leakage (measured with voltage source set to less than 0.6V) can be measured using the Model 614. This is because error due to voltage burden is less than 0.1% with a 200mV source. High capacitance diodes (e.g. zeners) present no problem, since the Model 614 is insensitive to stray input capacitance up to 0.1uF. 2.6.4 Diode Characterization With the constant current ohms configuration of the Model 614, it is possible to plot the I-V (current voltage characteristics of a diode over several decades). Refer to Table 2-1 for the range vs test current available with the Model 614. Table 2-1, Ohms Ranges for Test Current RANGES TEST ‘SCALE CURRENT | FACTOR 20K0, 2k 100.8 a 200K 10 WA m1 ALL Mo 100A 1 ALL Go 100A 1 r= Test Curent cL OUT ue on Figure 2-13. Characterizing a Diode with the Model 614. ‘The displayed reading on the Model 614 represents the voltage V, when multiplied by the scale factor shown in Table 2-1. Figure 2-14 shows several examples of diodes whose curves ate plotted using the method described above. 004A 10008, Figure 2-14. Diode Curves,SECTION 3 ACCESSORIES 3.1 INTRODUCTION ‘Section 3 lists each individual accessory that is available for the Model 614 Electrometer. 3.2 MODEL 1019 RACK MOUNTING KIT The Model 1019 Rack Mounting Kit can accomodate one or lodel 614s. The dimensions are 132mm x 483mm 19").See Figure 3-1 Figure 3-1. Model 1019 3.3 MODEL 6103C VOLTAGE DIVIDER PROBE ‘The Model 6103 Voltage Divider Probe extends voltage ‘measurement to 20kV and has a 1000:1 division ratio. Ac- curacy is 5% of reading. Input resistance of 4.5 x 10"9 permits use with Keithley electrometers and other high im- edance multimeters. It requires the Model 6012 Coaxial to ‘Triaxial Adapter when used with the Model 614. Lead length is 0.8m (30"), See Figure 3.2. Figure 32. Model 6103C ‘3.4 MODEL 6104 TEST SHIELD ‘The Model 6104 Test Shield facilitates resistance, current or voltage measurements with either 2 or 3 terminal guarded connections. Voltage up to 1200V may be used. Model 6104 provides excellent electrostatic shielding, high isolation resistance and a means for easy connection to most Keithley electrometers and power supplies. Clips plug into banana jacks allowing user to fashion modified connections. Use with the Model 6147 Triax to BNC Adapter and the Model 4801 Input Cable. 3.5 MODEL 6105 RESISTIVITY CHAMBER ‘The Model 6105 Resistivity Chamber is a guarded test fi ture for measuring volume and surface resistivity. It assures good electrostatic shielding and high insulation resistance. ‘The chamber is designed in accordance with ASTM Stand- ard Method of Test for Electrical Resistance of Insulating Materials. Resistivity can be determined by measuring the current through a sample with a known voltage impressed. ‘The measurement can be calibrated in terms of surface or volume resistivity. The Keithley Model 6105 Resistivity Chamber has been designed for use with Keithley elec- trometers (Model 614) and an optional high voltage supply ‘such as the Model 247. See Figure 3:3, Figure 3-3. Model 6105 at3.6 MODEL 6011 INPUT LEAD ‘The Model 6011 Input Lead is a shielded, low-noise triaxial cable 0.9m (three feet long) terminated with alligator clips. This cable mates directly with the Model 614 input. The Model 6011 is a supplied accessories. See Figure 3-4 Figure 3-4. Model 6011 3.7 MODEL 6146 TRIAX TEE ADAPTER ‘The Model 6146 Triax Tee Adapter can be used to connect ‘multiple inputs to the Model 614 and allows easy connection of external feedback elements. 3.8 MODEL 6147 TRIAX TO BNC CONNECTOR ‘The Model 6147 Triax to BNC Connector allows the Model 614 to be used with all Keithley acessories and cables requir- ing BNC connections. 3.9 MODEL 6167 GUARDED ADAPTER ‘The Model 6167 Guarded Adapter reduces effective cable capacity by driving the inner shield of a triaxial cable at guard potential. See Figure 3-5. Figure 3-5. Model 6167SECTION 4 PERFORMANCE VERIFICATION 4.1 INTRODUCTION Performance verification may be done upon receipt of the instrument to ensure that no damage or misadjustment has ‘occurred during transit. Verification may also be performed ‘whenever there is question of the instrument's accuracy and following calibration if desired, NOTE For instruments that are still under warranty (less than 12 months since date of shipment), whose performance falls outside specifications at any point, contact your Keithley representative or the factory im- mediately. 4.2 ENVIRONMENTAL CONDITIONS Measurements should be made at 18-28°C and at less than 70% relative humidity unless otherwise noted. 4.3 RECOMMENDED TEST EQUIPMENT Table 4-1 lists all the test equipment required for verifica- tion. If alternate equipment is used, the alternate test equipment’s specifications must be at least as good as the equipment specifications listed in Table 4-1. 4.4 PERFORMANCE VERIFICATION PROCEDURE Use this procedure to verify the Model 614’s accuracy. If the Model 614 is out of spec, proceed to maintenance (calibra- tion) Section 6, unless the Model 614 is under warranty. WARNING sation should be performed by personnel using accurate and reliable test equipment. 45 INITIAL CONDITIONS. ‘The Model 614 must be turned on and allowed one hour for warmup. If the instrument has been subjected to extremes of temperature, allow sufficient time for internal temperatures to reach normal operating conditions specified in paragraph 4.2. Typically it takes one hour to stabilize a unit that is 10°C (18°F) out of the specified temperature range. CAUTION Do not exceed maximum input. Instru- ment damage may result. Maximum input is stated in the specifications. 4.6 VOLTS VERIFICATION Verity the vottage tunction as follows: 1, Depress ZERO CHECK and select Volts (V). 2. Select 0.2V range. Adjust VOLTS ZERO pot (R103) for ,00000 +1 digit on the display. 3. Apply input (see Figure 4-1) as specified in Table 4-2. Release ZERO CHECK. 4. Verify that reading is within specifications in Table 4-2. 5. Select remaining ranges and repeat steps 3 and 4. 6. Repeat steps 2 thru 5 with negative voltage. DC Volts Verification Table 4-1. Performance Verfification Equipment [item |" DescRIPTION ‘SPECIFICATION MFR | MODEL A DC Calibrator -19V, 1.9V, 19V .002% Fluke | 343A B DMM 5%-digit .01% (2V range) Keithley | 191 c 9.8x10°9 resistor £2%, <.19%/°C Keithley | R-289-9.869 D 1000pF Polystyrene £2.5% <100ppm/°C Keithley | C-252-.001 E Decade Resistor 19-10M® 03% ESI DB-62 atRANGE ‘APPLIED INPUT FROM ITEM A TABLE 4-1 ‘ALLOWABLE READING AT 18°C - 28°C 2v (0.19000V 18983 to .19017* av 1.9000V 1.8984 to 1.9016 20v. 19.000V 18.984 to 19.016 “See Volts Zero Verification (paragraph 2.3.2) 4.7 CURRENT VERIFICATION Make current verification as follows: 1, Select Current (I), 200A range and depress ZERO CHECK 2. Configure the DC calibrator (Item A), decade resistor (item E) and the Model 614 as shown in Figure 4-2. chassis Figure 4-2. Current Verification 3. Set the decade resistor to 10.00k9 and set the DC calibrator to 1.900V. 4, Release ZERO CHECK and verify that the display reads between 189.3 and 190.7. 5. Depress ZERO CHECK and select the 200nA range on the Model 614. 6. Repeat steps 3 and 4 using 10.00M2 and 1.900V. Verify the reading is between 189.0 and 191.0. 7. Depress ZERO CHECK and select the 2000pA range. NOTE Step 8 may yield erroneous results if Volts Zero has not been verified (paragraph 4.6). 8. Repeat steps 3 and 4 using 10.00M@ and .01900v. Verify that the reading is between 1871 and 1929. 4.8 INPUT CURRENT VERIFICATION Make input current verification as follows: NOTE ‘This must be performed at 23°C + 1°C. isconnect all cables from the Model 614 input. 2. Select Current (I), 20pA range and depress ZERO CHECK. 3. Connect Analog Output COM (rear panel) to Chassis Common. 4, Release ZERO CHECK. Allow one minute for the rea to stabilize, 5. Verify reading is less than six counts, Depress ZERO CHECK. 6. Disconnect Common, a Analog Output COM from Chassis 4.9 RESISTANCE VERIFICATION Make resistance verification as follows: NOTE DC Volts verification and Current verification must be performed before Resistance verifi- cation is performed. 1. Select Resistance (R), 20k9 range and depress ZERO CHECK. 2. Configure the Model 614 and the decade resistor (Item E) as shown in Figure 4-3. 3. Set the decade resistor {item E) to 19.000k2. Release ZERO CHECK. 4. Verify that the reading is within the limits specified in Table 4-3. Depress ZERO CHECK,5. Select the remaining ranges listed in Table 4-3. and repeat steps 3 and 4 with the appropriate inputs as given in Table 4-3. Table 4-3. Ri RANGE | INPUT | ALLOWABLE READING 18°C - 28°C. 20k2 | 19.00K9 18.89 to 19.11 200k2 | 190.0K9 188.9 to 191.11 20m2_| 10.00Mo 9.90 to 10.10 Figure 4-3. Resistance Verificat 6. Verify the performance of the G®? ranges using the follow- ing procedure: A. Standardize the 9.8 x 10°0 resistor as follows: (a) Select Current (I), 200A range and depress ZERO CHECK. (b) Configure the DC calibrator (Item A) decade resistor (item E) and the Model 614 as shown in Figure 4-4. (c) Set the DC calibrator to 0.1V and set the decade resistor to 10M2. (d) Release ZERO CHECK. Take note of the displayed reading (approximately 10.00nA). Depress ZERO CHECK. (e) Substitute the 9.8 x 1050 resistor (Item C) for the decade resistor (it may be necessary to shield the resistor to obtain a stable reading). Release ZERO CHECK. WARNING high voltage. Take care to prevent con- tact with live circuits which could cause electrical shock resulting in injury or death. (f) Dial the DC calibrator until the Model 614 display reads as in step (d). The calibrator voltage will be approximately 100V. {g) Divide the calibrator voltage obtained in step (f) by 10 +o obtain the value of the resistor in G2. Record this result, Depress ZERO CHECK. (h) Dial the calibrator to Zero. oy Lo. Chassis E19000099 2 2 9 | Chassis Figure 4-6, Resistor Standardization B. Select the 2062 range. Apply the standardized resistor obtained in step A to the input.NOTE It may be necessary to shield the resistor (connect the shield to input LO) to obtain a stable reading. Do not handle the resistor by the body. This will contaminate the resistor and yield erroneous results. It is advisable to connect this resistor directly to Input HI. ‘Any cables used to connect the resistor to the Model 614 must be guarded. See section 2.4.1. C.Release ZERO CHECK. Verify that the reading is the same asin step A (g), +2%. D. Depress ZERO CHECK. E.If the 209 range is in order, itis only necessary to verify input impedance (on Volts) to guarantee proper operation of the 20060 range. F. Input Impedance Verification, {a) Select Volts (V), 20V range and depress ZERO CHECK. (b) Apply 19.000V to the Model 614 from the DC calibrator. Release ZERO CHECK and note the reading, (c) Depress ZERO CHECK and place the 9.8 x 10° resistor in series with input HI lead. NOTE It will be necessary to place the resistor as physically close to the Model 614 input as possible. This avoids errors due to cable resistance. If cables cannot be avoided, guarding must be employed. See section 2.4.1. NOTE It may be necessary to shield the resistor {shield connected to input LO) to avoid elec- trostatic interference and noise. (4) Repeat step (b). Wait a few seconds before noting the reading. This will allow the reading to settle. (e) Compare the reading obtained in step (b) to the reading obtained in step (d). Verify that the readings are within four digits (4mV) of each other. 4.10 CHARGE (nC) VERIFICATION To confirm Coulombs operation, proceed as follows: 1. Turn the Model 614 on. Depress ZERO CHECK. Set the DC (Item A) calibrator to 00.000. 2.Connect the 1000pF capacitor, the calibrator, and the Model 614 as shown in Figure 4-5. 3, Select the 2nC range on the Model 614. Release ZERO CHECK, 4, Dial 1.0000 on the DC calibrator. 5. Verify that the display reads between 0.9500 and 1.0500 nc. 6. Depress ZERO CHECK and reduce calibrator output to 00000. Figure 4.5. Charge VerificationSECTION 5 THEORY OF OPERATION 5.1 INTRODUCTION The Model 614 Electrometer is a multifunction meter capable of detecting currents as low as 10%A, providing high input impedance (5 x 100) on Volts and measuring up ‘to 200G2 with minimal error. To accomplish this, the Model 614 includes a special preamplifier circuit which gives it the electrometer characteristics. A second stage voltage amplifier scales the preamplifier output so that the A/D cir- ‘cuit will receive 2V input for full range. Figure 6-1 shows an ‘overall block diagram for the Model 614. Preamplifier Input t To All Circuitry ‘Suppress i 5.2 INPUT PREAMPLIFIER ‘The Input Preamp is designed to provide high input impe- dance for the Volts and Resistance functions, and low input impedance (with 6 x 10%A input current) for the Current and Coulombs functions. Refer to Figure 5-2 for the basic circuit configurations provided for the different functions, The preamp becomes a high input impedance, unity-gain buffer amplifier in the Volts function. In the Resistance function, a boot-strapped voltage source in series with a ‘or drive a constant current through the Preamp Output Range Amplifier 2V Analog Output [wv common [|] rT + igure 5-1. Model 614 Block Diagram 61unknown, The voltage developed across the unknown resistance is proportional to its resistance. This voltage is, present at the output of the unity-gain buffer, and thus pro- vides an output voltage proportional to the resistance under test. In the Current (I) and Charge (nC) functions, the preamplifier is configured as a feedback current to voltage converter. Feedback resistor R is selected by the front panel buttons labeled yA, nA and pA. Each configuration will now be considered 5.3 VOLTS In the Volts function the Model 614 is configured as a high impedance unity-gain buffer amplifier capable of measuring Uup to 20V with >5 x 10° input impedance. Refer to Figure 5-3. The JFET pair Q104 is the sensitive input device. U102, Q101, A102, A104, CR101 and CR102; and associated com: ponents are configured as a high impedance buffer amplifier. CR101 and CR102 provide a constant current ‘mA bias for VR101 and VR102. Q101 and Q102 buffer this voltage and supply drive for U101 and U102. R113, C107, and R112 provide input protection without sacrificing stabili- ty. C101, C102, and C106 provide unity-gain frequency compensation to the amplifier. Resistors R115 and R116 are ‘2 matched pair, providing 30.A bias to Q104. If the input FET pair is ever replaced, reinstall jumpers W101 and W102 and follow the procedure for nulling the input offset voltage. This procedure is outlined in Paragraph 6.4.2. fo | Ly ven fe ew ‘CURRENT RESISTANCE vow vo=On oy cn Ye] 4 5 t “e |” vours acouLoMes Figure 5-2. Basic Circuit Configurations Figure 5-3. Volts Configuration 525.4 RESISTANCE ‘The Resistance function operates similar to the Volts func- tion, except that a reference voltage of 1V is generated by U101, VR101, and associated components. Potentiometer R101 sets this voltage which can be measured between TP1 ‘and TP2. Refer to Figure 5-4. R104, R105, C104, and C108 stabilize the reference. ‘The series feedback resistor is selected by the front panel buttons labeled k2, MQ, GQ. Table 5-1 summarizes this selection. [> Gros, v2 sna dicate Table 5-1. Feedback Resistors UNITS SELECTION | RELAY Rep Crp ka. K103- R121, (R108 on 2009) C112 ma. 102. R102, C111 Go K101_R117, C109 Figure 5-4. Resistance ConfigurationCapacitors C109, C111, and C112 provide frequency stabili- ty to the feedback circuit, No calibration is necessary for R120 and R121. However, R117 is a 9.8 x 10° HI meg resistor requiring calibration. This is provided by R114. Resistors R114 and R113 form a voltage divider at the amplifier output which makes R117 ‘look’ like its value is being calibrated. NOTE This calibration is done for the 2000pA range. Once it is set, the G0 ranges are calibrated. It is not touched during Resistance calibration. Resitance calibration Feedback R and C 2104, U102 and discrete components aig 27K Figure §-5. Model 614 P involves adjusting R101 and monitoring TP1 for 1.0000V +500uV. See paragraph 6.4.3 For the 200kf range, itis necessary to switch R108 in series with the resistor R121. This keeps the compliance voltage across the unknown below 2V, thus limiting the power dissipation. 5.5 CURRENT AND CHARGE When either the Current (I) or Charge (nC) function is selected, the input preamplifier configures itself as a current to voltage ampifier. Refer to Figure 5-5. Preamp Output mplifier Configured in Current or CoulombsIn this mode the output from the Volts input buffer is fed in- to U103 via R119 and C110. High voltage op amp U103 Serves two purposes: 1. Provides +20V swing necessary to cover all Current ranges. 2. Provides the inversion necessary for feedback current. ‘The supply voltages to U103 are regulated +32V and are discussed in paragraph 5.8.3. Since at DC U102 and U103 operate without local feed- back, the DC loop gain exceeds 10°. This means that the accuracy depends on the feedback resistor selected. To fre- quency compensate this circuit, multiple poles and zeroes are required. This compensation is provided by R102, C101, C103, R119, and C110. Note that the composite current amplifier circuit behaves like an op amp with a single pole for frequencies above 10Hz. ‘The appropriate feedback element is selected by the WA, 1A, pA, or nC buttons on the front panel. Table 5-2 isa list of the values selected. Table 5-2. Feedback Elements UNITS ELEMENTS, SELECTED | RELAY, SELECTED uA 103 R121, C112, nA K102 R120, C111 pA K101 R117, C109 nc. K104 C13 jure 5-6. Model 614 Ranging Capacitors C109, C111, and C112 provide frequency com- pensation and cancel the effect of cable capacitance on the input. These capacitors also set the preamp settling time, ‘The only feedback resistor requiring calibration is R117. This resistor is calibrated by R114 on the 2000pA range. The feedback relays K101- K104 are low-leakage devices displaying > 10% at environmental extremes. 5.6 ZERO CHECK ‘The Zero Check actuator is a mechanical spring, actuated by the ZERO CHECK button. when Zero Check isin, the In- ut impedance of the instrument changes. For more detail, ‘see Figure 2- Resistor R113 prevents damage to the instrument during Overload when Zero Check is operated. Resistors R112 prevents the use of the Zero Check function from damaging the input FETS. 5.7 RANGING CIRCUIT ‘The ranging circuit converts the output of the preamplifier into{@ +2V output for a full range input. Refer to Figure 5-6, ‘As seen, the circuit is a simple inverting amplifier with a gain oF 10, 1, or 0.1. The gain is selected according to the range buttons on the front panel. The following table summarizes, the gains selected 55Table 5-3. Gain Selection RANGE | RESISTOR | ADJUSTMENT | GAIN (LTS) | Rs, 2 [RI25 Ri24 70 2 | R129 R127 1 20 | R130 R131 ot ‘The only exception to Table 5-3 is the 200k range, which selects R129 and R127. This is required to scale the 2V full range from the Resistance converter as described earlier. U104, C114, and C115 comprise a high-performance chop- per amplifier which eliminates the zero adjust for this stage. C116 and R128 are the feedback elements in this circuit which set the gain (along with R, described above) and the response time at the 2V analog output. Q105 and Q106 pro- vide overload protection to this circuit. R205, R122 and R126 provide the suppression feature. Since this is an inverting amplifier, the output at the 2V analog output is inverted in Volts and Resistance. It is not inverted in Current and Charge, since it cancels the inver- sion the preamplifier provides. 5.8 POWER SUPPLY ‘The Power Supply can be broken down into several sections: * Battery Charging Circuit ‘Battery Shutdown Circuit, DC - DC Converter 5.8.1 Battery Charging Circuit The battery charging circuit is composed of U109, 0113, CR104, R141, R144, and C120. Transformer T101 and its associated components convert line voltage to 1BVDC (pre- sent at TP3) which is filtered by C123. This voltage becomes the input to U109, which is an adjustable 3-terminal reg- ulator. The output voltage from this regulator provides the float limit for the batteries of 9.5V. This voltage is set by R140. During charge the output voltage will be in the range of BV - 9.4V. The regulator will be saturated, which limits power dissipation. Maximum current drawn through the regulator is 600mA. When the batteries become fully charg- ed (float charge), U109 trickle charges the batteries. 56 During float charge the battery voltage is maintained at 9.5V. As long as AC power is applied to the instrument, the batteries are maintained at this voltage. Current drawn from the regulator during float charge is essentially the current re- auired to power the circuitry, which is 200mA assuming the instrument is turned on. When the AC line is disconnected, the voltage at the anode ‘of CR104 decays (in about five seconds) to zero volts. This causes Q113 to turn off, disconnecting the regulator from the circuit. Thus, the batteries cannot discharge through U109 and associated components. When the line is recon- ected, Q113 turns back on, and causes U109 to regulate. Capacitor C120 stabilizes U109. Battery fuse F101 will blow if the batteries are installed backwards or if a circuit fault develops which causes high battery currents to flow (> 2A). 5.8.2 Battery Shutdown Circuit ‘When the instrument is battery operated, it is necessary to limit the discharge level of the batteries to 7.4V. If this is not done, the ability of the batteries to hold 2 charge will be To accomplish this, a low voltage detector consisting of U107 and associated components is used. When the battery voltage is above 7.4V, the input to U107 (pin 2) is above the nominal threshold voltage of 1.15V. As soon as the battery voltage drops below 7.4V, U107 senses this and the output pin 3 (open collector) pulls low, turning on Q107 and shut- ting off Q109. This shuts off power to the instrument, To prevent chatter, and to guarantee that the instrument does not turn on again until the batteries are charged above V, R133 provides hysteresis of 0.6V (referred to the battery terminals). Capacitor C119 prevents oscillations during the switching of U107. 6.8.3 DC to DC Converter ‘The battery voltage is used directly to supply the input to U108, which provides a regulated SV to the A/D and display circuit. However, a DC to DC converter is required to con- vert the unipolar battery voltage into a regulated +32V and -BV required by the preamplifier. ‘The heart of this converter is T102, 0110, and Q111. The clock circuit generates 100kHz which is divided down by