HESAI Mini Digital V/A meter VC-288

Volt-amperemeter

DNS-VC288

 

The VC-288 digital volt/ampere-meter is front panel meter for general purpose with a build-in shunt. It’s based on a 8 bit micro-controller N76E003 from Novoloc and a LM358A dual Op-Amp.
The micro-controller works like a PIC and have a build-in 12-bit ADC. The Op-Amp I suppose is configured as two voltage comparators, one for the voltage and one for the amp measuring. The intern clock of the micro-controller are in the range from 10 Khz till 10 Mhz.

Specification:

Voltage range
Current range
Supply voltage
Supplay current
Voltage error
Current erro
Shunt spec.
Refresh rate
0,0v-100v
0-10 amp
4,5v – 24 v
< 20 mA
± o,1 %
± 1 %
Build in shunt
300mS

The module has a built in current shunt (for 10 Amps) which should make it easy to use. It has 3 smaller wires for connection to a power-supply en for measuring voltage. The power-supply is in the range 4.5 to 30 V. The black wire is the common and the red wire for the power-supply. The yellow in connection to the red measuring voltage.
The basic drawing are: The two “thick” red and black wires are used for the current measuring.
Beware: The shunt resistor is included in de common line!!
Surprised of the cost of the panel meter I bought 2 of them and test them in respect till the given specs.
Before I will give the result of the test I have done I can say that I’m be negative surprised of it. The voltage measure is quit good but the current measure is bad. If you see the shunt and the way it is construct you can imaged that this will not be given a good result.
The shunt resistance has a value around 6.2 mOhm and is visible on the photo. The shunt is made from silver plated copper of 1.5 mm. It’s understandable that a little different in soldering on the PCB will give quite big difference in result of the resistance.
While I’m not be able to present Graphics here I will give some result from measuring the current.
For measuring I have used:
– Power supply LN-303pro 3 Amp/30 volt dual based
– ELW 72812 universal measure instrument used as mVolt instrument

Measure
Vshunt in mV     Iload in Amp      Imeter reading
3,2                      0,5                    0,44
6,2                      1,0                    0,83
8,8                      1,5                    1,23
11,5                    2,0                    1,62
14,2                    2,5                    2,01
16,9                    3,0                    2,04

The linearity of the meter is very bad.

Because I want to have a meter from 0 – 1 amp I have change the shunt, in a resistance of 62 mOhm with special resistance wire of 1,5 Ohm/meter.
The range now is change from maximum 10 amp till 1 amp but the non-linearity still be. And still I do not know way but I think it is due to the OpAmp Bias current.
Further investigations we be done.