Voltage drop when using small resistance myDAQ

[mvalente]

Hello. On my myDAQ I am using AO and the function generator to generate a square wave at 500 mv peak to peak signal. I am using AI and the oscilloscope to measure this signal across resistors. When I use a 1K ohm resistor I get a reading from the oscilloscope of a 500mv peak to peak signal. However when I switch to using a 10 ohm resistor I am only reading a 45mv peak to peak signal. I am wondering why I am getting this?

Thanks.

[WhiteA]

What Oscope are you using? Also, could you attach screenshots of what you are seeing please

[charlesy]

Hello mvalente,

The myDAQ's analog output channels have a current limiter on them that starts to clamp around 2.5 mA. In order to maintain 500 mV into a 10 Ohm load, the amplifier would need to source 50 mA. The AO channels are specified for 2 mA maximum load current, so keep your resistor larger than 250 Ohms for a 500 mV signal. If you need to drive a heavier load, consider adding an external buffer on your circuit.

I hope this helps,

Charles Y.

National Instruments