current measurement

[kt2]

i'm planning to use an e series card to measure current. does anyone know what the minimum current range is that can be accurately measured?

[gbush]

Which E Series card?
Be careful when reading current. You can cause many problems if you don't connect into the circuit properly. You can easily cause ground loops that goof up everything.

What are you trying to monitor and how?
If you are using a sense resistor, what value?

Then you can define resolution.

[kt2]

The card: NI PCI -6036E. I'm applying pulses of different voltage (approx. 600mV to -400mV) to an electrode and I'm going to measure the resulting current for each pulse. The current will be in the nA-uA range. Basically, the operation will mirror that of a potentiostat. Am I correct in presuming that I'll need a resistor connected in series with the electrode in order to measure the current flowing through it.

[gbush]

Next round of questions :)))
What is the period and duty cycle of the pulses?
The card you have will gather 200KS/sec for one channel. More channels, slower scan.
The Pulse source, can it handle additional load?
Many times they are sized with very little "extra current".
What is the impedance of the electrode?
You want to have a large enough resistor to be able to read the nAmps, but you don't want the resistor to be the main load of your circuit.

Welcome to the real world of instrumentation!

[kt2]

Thanks for quick reply. The period is 1s, the duty cycle is 0.5. I was hoping to use analog output vi with some while loops to generate the pulse because i need labview to both supply and adjust the voltage applied to my electrodes. I don't seem to be able to adjust pulse amplitude using the generate pulse ci. The electrodes will have an impedance in the kOhms range. Therefore, I was planning to use a resistor in the kOhm range (e.g.1kOhm).

[gbush]

The generate pulse vi 's use the counter output to transmit the pulse. Counters, like digital outputs don't vary the output amplitude. You will need to use the analog output of the card. That limits you to a 5 mAmp total current output. Ideally, your sense resistor should be 1/100 of your load. If your electrodes were @ 10Kohms, then your sense resistor should be 100 ohms. This would give you readings from your sense resistor in the +/- 6 mVolt range.

[kt2]

you've answered all my questions and halved my project time! thanks!