6221, AI current, External Shunt Resistor. Getting started with Swept Sine (SVT)

[Kentmey]

Hi,

I am trying to read the current going through an RC (10kohms, 1 uF) circuit (connected to DAQ AO 0 outputing 2V, and to the AI O reading that voltage, and AI 1 reading the generated current).

The purpose is to use the getting started with Swept sine (from sound and vibration toolkit). Basically, it is doing impedance (or Z-meter, depending on how you call it).

Yet, on the DAQmx configuration, it says " external shunt resistor" with a Default value of 249. What does this mean, do I need to connect somehow a shunt resistor?

And this default value has a direct influence on the Nyquist diagram generated by this VI.

Please let me know if you have faced this issue already.

Kentmey.

[johnsold]

Kentmey,

How do you expect to measure the current?  The 6221 only measures voltage, so the simple way to get the current is to measure the voltage drop across a resistor.  The 249 ohm value is commonly used for measuring the current in 4-20 mA current loop systems.

If you are only looking at a series RC circuit and nothing else is connected, just measure the voltage at each end of the 10 kohm resistor.  The current is the difference divided by the resistance.

Lynn

[Kentmey]

True 🙂

I though the DAQ could measure current too, which was confusing me.

Thanks, I'll try that soon 🙂