Constant resistance mode in electronic load

Question

I have this DC electronic load.

I am setting this electronic load to a constant resistance mode option - say 100 ohms - and turning the output ON.

When I measure the resistance across the electronic load terminals using a multimeter, I am not able to read the value as 100 ohms. I am getting high resistance values and it is showing as open circuit.

However, if I connect a power supply to the electronic load and ask it to consume a current equivalent of 100 ohms, the electronic load is consuming the required current from the power supply as if it was connected to a 100 ohm resistance across it.

• Power supply was set to 10V.
• DC constant resistance was set to 100 ohms.
• Current consumption to the power supply was 100mA.

So, actually, the electronic load seems to be setting a constant resistance of 100 ohms when I set it as such, but I am not able to measure using the multimeter. Why is that?

Answer 1

From the manual:

https://bkpmedia.s3.amazonaws.com/downloads/manuals/en-us/8540_manual.pdf

You need at least 1mA of input current for proper operation. Your DVM does not supply that much for resistance measurements.

Page 19:

How much current does your voltmeter supply? It's not readily found. However, I tried a simple setup here, and this is what I got for a 100 ohm resistor (0.3 mA):

Answer 2

The electronic load would do something like read the voltage at the output and draw a constant current based on a calculation of that voltage * 1/Rset.

Your multimeter provides, by design, only a tiny current, which is too low for the circuitry in the electronic load to read accurately. There should be some indication of the resolution of voltage/current measurement in the datasheet or manual.