Current measurement in nA range (+ noise preoblem) using NI 9203 and 9172

[wook]

Hello,

I see that from reading other posts that NI cDAQ 9172 produces some noise.  I'm trying to make a current measurement in nA range using NI 9203 which is connected to 9172 chassis.  When I take the readings using MAX without anything connected to any channels, I get bad noises oscillating between nA and uA range (which already exceeds what I'm trying to measure).  All the wiring seem to be correct.  I have a source that I'm trying to measure going into one of the ai channels, COM to the common ground, as well as the metal part of of the chassis to the common ground.  Is there any way to reduce the noise, perhaps using an external resistor? Thanks.

[LucaP.]

Hi wook,

I'm sorry to say that the 9203 is not made for measurements in the nA range! Even if you reduce most noise you'll not gonna measure signals in the nA Range with the 9203.

As you see in the specifications manual of the 9203, the accuracy is in the uA range.

Measuring signals in the nA range is not an easy task. You need a high accuracy measurement device like a DMM. For example the 4071 DMM.

[leonardolt]

Hello wook.

 Maybe you shou use a low noise pre-amplifier  to increase your input current level. With a couple of OA you can build one.

[Henrik_Volkers]

Keithley has some very good application notes about measuring in the µ,n,p range (V and I)

Good luck, if it's your first time 😉  else:

Have fun 🙂

Message Edited by Henrik Volkers on 07-09-2009 11:54 AM