UNIVERSITY OF BATANGAS
COLLEGE OF ENGINEERING
ELECTRICAL ENGINEERING DEPARTMENT
HILLTOP ROAD, BATANGAS CITY
EE5L
INSTRUMENTATION AND CONTROL LAB
ACTIVITY NO.11
ANALOG ELECTRONIC INSTRUMENTATION
MEDRANO, ERVIN C.
EE3-3 / 1201541
ENGR.MELCHOR R. BARCENAS
INSTRUCTOR
MAY 14, 2021
I. OBJECTIVES
To differentiate the different functions of transmitter.
To know the proper way of using transmitter.
To accurately use the symbols of transmitter.
II. INTRODUCTORY PART
FLOW TRANSMITTER
Are sensors with an electrical transmission output for remote indication of flow rate.
The different transmitters are Ultrasonic, Paddlewheel: in-line, adjustable and fixed,
electromagnetic: adjustable, in-line and fixed, and turbine: in-line.
TEMPERATURE TRANSMITTER
A temperature transmitter is a device that connects to a temperature sensor to transmit
the signal elsewhere for monitoring and control purposes. Typically, the temperature sensor is
either an RTD, Thermistor or Thermocouple type sensor and will interface with a PLC, DCS,
data logger or display hardware.
PH TRANSMITTER
pH sensors and transmitters are used in many industries such as chemicals, water &
wastewater, food & beverage, pharmaceuticals, power plants, primaries and oil & gas. The
selection of the sensor depends on the application. Choose the glass sensor's diaphragm and
reference system according to your needs. Use ISFET sensors where glass breakage is
intolerable or media contain high amounts of organic solvents. Apply enamel sensors when
long-term stability and lowest maintenance are required.
REVERSE-ACTING I/P TRANSDUCER SIGNAL
A current-to-pressure transducer is used to convert a 4-20 mA electronic signal into a 3-
15 PSI pneumatic signal. This particular transducer is configured for reverse action instead of
direct, meaning that its pressure output at 4 mA should be 15 PSI and its pressure output at 20
mA should be 3 PSI.
PLC ANALOG INPUT SCALING
An Allen-Bradley SLC500 programmable logic controller (PLC) uses a 16-bit analog-to-
digital converter in analog input card to convert 4-20 mA signals into digital number values
ranging from 3277 (at 4 mA) to 16384 (at 20 mA).
CLAMP-ON MILLIAMMETER
One better way to measure a 4-20 mA signal without interrupting it is to do so
magnetically, using a clamp-on milliammeter. Modern Hall-effect sensors are sensitive and
accurate enough to monitor the weak magnetic fields created by the passage of small DC
currents in wires. Ammeters using Hall-effect sensors have are completely non-intrusive
because they merely clamp around the wire, with no need to “break” the circuit.
LOOP CALIBRATORS
Exist for the express purpose of 4-20 mA current loop circuit troubleshooting. These
versatile instruments are generally capable of not only measuring current, but also sourcing
current to unpowered devices in a loop, and also simulating loop-powered 4-20 mA
transmitters.
III. ANALYSIS
Models for hand calculation of semiconductor devices used in analog electronic
systems are further described. Junction and Schottky diodes, BJT, JFET and MOSFET
devices, as well as the frequency behavior of the basic one and two transistor amplifiers are
discussed. Photodiodes, LEDs and laser diodes are also presented. When I was going to read
this chapter, I was giving thought instinctively to the nowadays available Spice models
(Shockley for diodes, Ebers-Moll and Gummel-Poon for BJTs, Level 1 through BSIM3v3 for
MOSFETs), and Spice based programs for modeling and simulation of analog circuits (PSpice,
LTSpice, TINA Spice, XSpice, HSpice, Spice 3, Ngspice, Spice Opus, etc.). PSpice is the most
popular program and serves as an industry standard for simulation of analog circuits with
discrete components. Talking to device models, it would be very usefully to mentioned some
PSpice models for diode, BJT, MOSFET (only the simple Level 1 model since the advanced
BSIM3v3 and its later versions have a lot of parameters), and their model parameters. Some
important device characteristics can be also shown as a result of dedicated circuit simulation
schemes.
IV. QUESTIONS AND ANSWERS
1. What is NAMUR signal levels?
One of the intrinsic benefits of a “live zero” analog signal standard such as 4-20 mA is
that a wire break (open fault) can immediately be detected by the absence of current in the
circuit. If the signal scale started at zero (e.g. 0-20 mA), there would be no way to electrically
distinguish between a broken wire and a legitimate 0% signal value. In other words, the “live”
LRV point of a 4-20 mA signal provides us with a way to indicate a certain type of circuit fault in
addition to indicating an analog measurement during normal operation.
2. Why do we use shunt resistors to measure loop current?
Shunt resistor values are commonly very small, for their purpose is to assist in current
measurement without imposing undue voltage drop within a circuit. It is rare to find a 250 ohm
resistor used strictly as a diagnostic shunt resistor, because the extra voltage drop (1 to 5
volts, depending on the current signal level) may “starve” loop-powered instruments of voltage
necessary to operate. Shunt resistor values as low as 1 ohm may be found installed in 4-20
mA current loops at strategic locations where technicians may need to measure loop current.
3. Why do we use test diodes to measure loop current?
Another way to measure a 4-20 mA signal without interrupting it involves the use of a
rectifying diode, originally installed in the loop circuit when it was commissioned. A “test” diode
may be placed anywhere in series within the loop in such a way that it will be forward-biased.
During normal operation, the diode will drop approximately 0.7 volts, as is typical for any silicon
rectifying diode when forward biased.
