VC-921 Calibration

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.


12.2 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.


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.