DSN-VC288 Voltmeter-Ammeter Review Using The Siglent SDM3045X Multimeter

In this video, I have reviewed the DS-VC288 panel mount voltmeter/Ammeter using the Siglent SDM3045X benchtop multimeter. The VC288 meter did not present acceptable readings, especially in the current measurement. It uses an LM358 Opamp which is not suitable for this purpose and it does not show a linear behavior. The SDM3045X multimeter was used as a reference. I have tested the voltage and current readings separately.

YouTube: https://www.youtube.com/watch?v=bleSXMaTR7s

The way I see it he has a car in one hand and a motorbike in the other. I would not expect a $3.00 3 digit meter to be on par with 5 digit one costing a lot more. From what I can gather he is using a 3 digit meter on the power supply as his reference for current, when he is comparing to a 3 digit unit. I do not have a clue where the LM358 Op Amp comes into play but I am assuming it is in the DUT. The op-amp is a highly linear device with its output voltage proportional to the input voltage, or Vout=A*Vin. An important property of the op-amp is that the open-loop gain, is a very large number (typically 106 to 1015). It is apparent the test setup is not very good and not capable of validating his statement. I would like to see the schematic for the test setup and the reference specifications before I believe that statement. I assume his test equipment is in calibration. What is the specified tolerance of the DUT?

You can buy a unit and do your tests. 3 digits accuracy of the panel meter does not cover such a huge error. with any test setup, both meters must show the same value (as close as possible) because whatever test is identical for both. That's all.

To be as close as possible start by defining what that indicates. Be sure your equipment can exceed that range by a factor of 10 and is in calibration. How many digits are significant. Accuracy is how close the measurement is to the true value. This is expressed as a percentage, e.g. ±1%. It means that any given reading can be in error 1% above or below the calibration curve. Standard analog multimeters measure with typically ±3% accuracy, though instruments of higher accuracy are made. Standard portable digital multimeters are specified to have an accuracy of typically ±0.5% on the DC voltage ranges. What you are asking is that both have the same error. If you want them to match then they need to be calibrated properly and do not expect all three digits to match, first two maybe but not 3 with what you are using.

gilshultz: To be as close as possible start by defining what that indicates. Be sure your equipment can exceed that range by a factor of 10 and is in calibration. How many digits are significant. Accuracy is how close the measurement is to the true value. This is expressed as a percentage, e.g. ±1%. It means that any given reading can be in error 1% above or below the calibration curve. Standard analog multimeters measure with typically ±3% accuracy, though instruments of higher accuracy are made. Standard portable digital multimeters are specified to have an accuracy of typically ±0.5% on the DC voltage ranges. What you are asking is that both have the same error. If you want them to match then they need to be calibrated properly and do not expect all three digits to match, first two maybe but not 3 with what you are using.

Yes, if you check the video, that is an accurately calibrated reference benchtop multimeter, the panel meter was also calibrated at the starting point. that's why the first value is correct because it was calibrated on that to match with the reference, however, the panel meter does not show a linear behavior for other input values and the readings deviate from true values, especially in the current reading which the error is huge, much bigger than 1%

Quick point, unless I am mistaken the internal resistance for the amperage reading is different for both meters, that would automatically give different readings with the indicated test setup. To be accurate current must be in series and voltage in parallel and read at the same time. What is the tolerance of the 3 digit meter and how many counts plus and or minus? I missed it, I did not see where the bench meter was calibrated. The fact that he calibrated it at a given voltage says it is correct at that voltage but not necessarily at any others. Did he calibrate the span (min and full scale)? Is the meter 1% (full voltage ± 1 digit). When calibrating you must have at least two points. Try this link for some background: https://www.apesoftware.com/help/calibration-procedures/digital-multimeter Yes my equipment is calibrated, tracked with traveling standards which are then calibrated by a properly rated lab at the intervolt specified by the manufacturer.

It does not make any difference if you read the voltage and current at the same time or not. You can power the meter and read the values, and of course, you can build a circuit to read both current and voltage at the same time or connect the power of the meter and voltage reading input to the same point, so it shows the voltage which is being used to power the meter, so that's not the problem. Calibration at two points? The calibration of the panel meter is performed using ordinary potentiometers, so if you calibrate at a low input value, then it deviates at the upper calibration point and vice versa. You can not match these two because the panel meter does not show a linear behavior.

I would suggest you read some books on basic calibration, analog instrumentation and analog circuits. If you understand what you read then you will understand what I stated. FYI I have been calibrating instruments to ISO/TS for a lot of years. I would suggest you get calibration manuals for several pieces of test equipment and follow how they are calibrated. Yes you will find some where they calibrate at one voltage probably the highest reading but realize the divider network has been calibrated, sometimes called span.

@hesam_m

Your report was closed N.F.A.

All you are being given are alternate views / outlook.

Bob.