Here is the google translated CAL procedure for the DM0660 (Dream Tech firmware) from the
datasheet. It looks like you can skip ranges etc. I did not care much for Kerry's translations.
12 Calibration process method
The following description of the calibration flow is based on the wiring
diagram of this manual. (See circuit diagram).
Button function assignment during calibration: SELECT: Skip / function
selection; HOLD: minus (-); The rest of the keys: plus (+)
12.1 Enter calibration mode
{J8 is disable EEPROM write-protect WP & MCU into CAL mode}
Short J8, boot into calibration mode. (Function switch must be placed in the
resistance (ohms) mode, and remove the DMM input probes)
12.1.1 Self-Check
After checking the IC internal circuit, CAL, LCD display, ADC code value, if
there is an error then display Err0 ~ 4, then shut down after the measurement
with the measured voltage divider whether the connection is short circuit, open
circuit, the size of the resistance is correct etc.
After the completion of self-check, and then re-boot, start the calibration
process, self-test is completed automatically save the relevant parameters to
EEPROM, buzzer BEEP sounded to indicate save complete. If it has already been
detected, press the SELECT key to skip this check.
12.1.2
12.2 Voltage correction (DC 500.0mV)
Function switch in DC millivolts.
The voltage output of the calibrator is inserted into the Vinput, the negative
terminal is inserted into COMMON, the calibrator output set to DC500.0mV, press
+/- to adjust display to 500.0mV. If you have already adjusted, press the
SELECT button to skip this step.
Voltage output value that can be used for correction: 100mV ~ 500mV (integer
multiples of 100mV), the recommended value is 500.0mV. Adjust the display value
to match.
The output of the instrument can be the same, the following steps are similar.
12.3 Resistance Correction (50.00Kohm)
Function switch in Resistance ohms.
Calibrator output 50.00Kohm, press +/- to adjust the display to 50.00 Kohm, If
you have already adjusted, press SELECT key to skip this adjustment.
Values that can be used for the correction of the output value: 10Kohm ~ 50Kohm
(integer multiples of 10Kohm). The recommended value is 50.00Kohm.
12.4 Capacitance correction (500.0nF, 50.00uF)
Rotary switch set to capacitance position.
Calibrator output 500.0nF, wait for the display is stable, press +/- to adjust
to 500.0 nF; Value used can be: 200nF ~ 600nF (100nF integer times), the
recommended value of 500.0nF.
Calibrator output 50.00uF, wait for the display is stable, press +/- to adjust
the display to 50.00uF. If it has been adjusted, press SELECT to skip this
adjustment.
The output value that can be used for correction: 20uF to 60uF (integer
multiples of 10uF), the recommended value is 50.00uF.
Note: The capacitor cal needs to adjust the above two points, directly output
the corresponding range capacitor value, the program will automatically switch
the range.
{EEPROM contains the zero correction stray capacitance value, edit that there}
12.5 Ambient Temperature correction (input actual ambient temperature) {DMM
cold junction temp}
Function switch in Temperature.
LCD display default value of 25C or the last adjustment of the ambient
temperature (non-current temperature) according to the environment at the time
of calibration.
Temperature, press +/- to adjust to the ambient temperature (adjustable range 0
~ 50C).
Note: If you do not adjust the LCD and the default display temperature is the
current ambient temperature, at this time need to press at least +/-
The whole time, if the previous adjustment does not need to adjust again, press
SELECT skip.
12.6 DC Current calibration (DC 500.0uA, 50.00mA, 5.000A ranges)
Rotary switch set to DCuA / mA / A for adjustment.
The correct current output of the calibrator is connected to the corresponding
input, the negative terminal is connected with the COMMON port, and the DC
current DC 500.0uA / 50.00mA / 5.000A, press +/- to adjust the corresponding
range.
Can be used to correct the output value:
uA: 100uA ~ 500uA (integer multiples of 100uA), the recommended value is
500.0uA
mA: 10mA ~ 50mA (integer multiples of 10mA), the recommended value is 50.00mA
A: 1A ~ 5A (integer multiples of 1A), the recommended value is 5.000A
Note: The basis of current measurement is the {shunt} voltage, so need to
adjust the voltage and then adjust the current, the following current clamp
calibration is similar.
{I think that means do not overload or clip the A/D on one range, compared to
others as this makes a CAL error condition}
12.7 AC Current clamp calibration
Rotary switch to current clamp function, and the appropriate current can be
input according to the range. Adjust the display to the standard output value.
It is recommended to output AC signal 60Hz adjustment, the range output
correction value is as follows:
6.000A: 1A ~ 5A (integer multiple of 1A), the recommended value is 5.000A
6.000A / 60.00A, 60.00A / 600.0A, 60.00A, 600.0A: 10A ~ 50A (integer multiples
of 10A), the recommended value is 50.00A
600.0A / 6000A, 6000A: 100A ~ 500A (100A integer times), the recommended value
of 500.0A;
Note: 1. Individual range in the correction can automatically shift to a small
level range, easy to output a small current to correct. Such as school
The positive 6000A file will be measured according to the measured value
between 600.0A / 6000A automatic shift, then the output can be adjusted to
500.0A,
Another example is 6.000A file will automatically switch between 600.0mA /
6.000A, can directly output 5.000A current to adjust.
2. Clamp meter current before the calibration should ensure that the full-scale
output signal is about 600mV (corresponding to 6000count),
Do not deviate too much, the signal may cause excessive overflow, the signal is
too small may cause the resolution is not enough.
12.8 Voltage range calibration
Rotary switch set to DC volts. If the range is set to: DC600mV / 6V / 60V /
600V / 1000V,
It is recommended to inject calibration values of: DC500mV / 5V / 50V / 500V /
1000V, can also set the appropriate parameters for other values.
Press the +/- to adjust the display to the standard output value, you can
calibrate the current range.
Note:
1. After the power-on self-test step (12.1) is completed, you can also go
directly to the corresponding function to adjust, if the rotary switch is not
changed
(PT2.7 ~ 2.4), short-press the Select button, you can ignore the current
adjustment, jump to the next adjustment. Default tone
The whole is 12.2 voltage, 12.3 resistance, 12.4 capacitance, 12.5 temperature,
and can be in the default resistance function finished
Into the adjustment without having to switch the transfer to the corresponding
function.
2. During the adjustment process, after entering the standard signal, wait for
the display to stabilize and then press the +/- key to adjust. Avoid output
beyond {A/D overload}
Allows the range of signals.
3. The voltage adjustment error will affect the current adjustment, [b]if the
voltage readjusted, the current also need to re-adjust. ***[/b]
4. Corrective process of the function of the file is not right, the signal
short circuit, open circuit or signal instability will make the adjustment
error or
So that the error becomes larger. Adjust the data if the deviation tolerance
(+/- 80%), and LCD display the most significant digits greater than 6 or
display
"OL" press the +/- key will not respond to the operation, the buzzer no sound.
The operation is normal and the correction data is correctly written to EEPROM
after the beep
The BEEP sounded, the data can change normally but the buzzer does not sound
indicating that the data is not properly saved, please re-adjust one Times.
If still invalid, please check the EEPROM connections, and that J8 jumper is
shorted.
5. Please do not adjust the data other than the recommended value.
6. After calibration is complete, make sure that the J8 CAL jumper is
disconnected and restart after power-up.
https://www.eevblog.com/forum/testgear/a830l-teardownreview-a-cheap-multimeter-with-a-mystery-
function/msg1600945/#msg1600945
lmester
Regular Contributor
Posts: 124
Country:
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A830L Teardown/Review. A cheap multimeter with a mystery function.
« on: June 11, 2018, 09:13:25 am »
First, the mystery function. This meter has a setting marked with mA (capacitor symbol) 1.5V on
the rotary switch selections. See the pictures. This is not a capacitance measurement function. Any
value of cap connected to the leads shows a value of 0. The probes have no voltage or waveform on
them when this range is selected.
I used A bench power supply to feed A current limited voltage into the probes. This showed that this
setting was actually measuring current in mA's with a voltage drop across the meter probes of 1.5V.
I've got no idea what use that this might have. A mA current scale with a 1.5V burden voltage??
Does anyone have any ideas what this selection does? This function may not be working properly on
this meter. That's possible since this meter is a really cheap piece of crap.
Review/Teardown:
Not much of a teardown. Only a few Phillips screws :-)
I shouldn't have purchased this multimeter. I have no need for a cheap meter. I just couldn't resist.
It cost only $6.00 with free shipping.
How can you sell a meter with all of these functions/features for $6.00? My Fluke 87 cost over
$300! My bench multimeters were purchased used and cost nearly as much.
Why is this meter so inexpensive? I've thought of several possibilities...
The economy of using an ASIC:
You can see from the pictures that the PCB has a COB with only a few discrete components. Mostly
SMD resistors.
The build quality is very poor:
When I pulled the package from my mailbox, I could hear something rattling around inside. There
was an extra screw loose inside the meter case.
The positive test probe tip came apart while I was pulling the probes out of the box. This exposed
the probe conductor. I'd guess It's about #22 wire. Check the picture. Bad things could happen
when using these probes with the 10A current range. "My probes are melting and my fingers are
sizzling :-)"
Banana jack conductors are rusty.
Piezo beeper is just dangling by it's leads.
Overload protection & safety:
This meter has a CE certification.
I've never done any research on the CE mark. What does this actually mean?
For this meter, I'd say that "CE" might mean "Could Explode" during an overloaded!
The manual lists a 500mA fuse for the low current range. The fuse holder pads are on the PCB but,
no fuse is installed.
The manual also says that it can handle A 250V RMS overload on the voltage and resistance ranges.
I might test this. First, set the meter to a resistance range. Next, put on a pair of gloves. Then,
place the meter far away from my body. Finally, Insert the probes into a 240V receptacle. Does it
go Boom! or, just show an overload?
The 10A current shunt also has no fuse.
They did trim the shunt resistance. Several crimps in the shunt wire to increase it's resistance are
visible. Amazing for a $6.00 meter! Someone actually did some calibration of this meter!
There is some good news for this cheap meter.
I did some tests on the DC Volt ranges.
It's manual claims .8% accuracy on DCV.
It met this spec out of the box. With A little tweaking of the only calibration pot on the PCB it was
much better. It was even consistent when switching between all DCV ranges.
I've not yet tested the Resistance, ACV or current functions.
"Mystery function" is a "battery tester", it applies a load of 42 ohms across the COM and V jack,
and displays in milliamps the short circuit current of a battery under test. A good 1.5v battery thus
(by Ohm's law) should produce around 35 mA.
