NI DAQ device which can generate constant current

[ArpanKundu]

Hi,

I am in need of a DAQ device that can generate both positive and negative constant current. I will be using it to charge/discharge a capacitor repetitively. The DAQ 9265 seems to provide only positive constant current from 0 to 20 mA. So I can charge my capacitor with it but I cant discharge with it. Is there a DAQ device in the market that can solve my purpose?

Thanks 

[crossrulz]

The 20mA signal is because that is a standard signal for sensors in industrial settings.

For arbitrary current sources, you might want to look at a Source Mearsurement Unit (SMU).

[Henrik_Volkers]

If you apply the capacitor , why not a voltage controlled current source?

Current needed?

Ground referenced?

Bandwidth?

I like this idea:

http://www.edn.com/design/analog/4324499/Bipolar-current-source-maintains-high-output-impedance-at-h...

or for very small currents

http://www.linear.com/solutions/1185

[ArpanKundu]

Hi Henrik,

You are right. I can do with a voltage source like NI-USB 6351. That would produce a time varying current. 

But in the literature, they generally charge/discharge supercapacitors at constant current. 

So I was wondering if there was any instrument available which can generate, say +10 mA for a custom amount of time and -10 mA for another custom amount of time. There can also be some rest period in between the two.

[Henrik_Volkers]

IF you tell us what your basic goal is we migth find a simple solution 🙂

A simple curent limiter (say a resistor or more fancy a two pole current 'source' in a diode bridge to make it bipolar) migth be all it needs.

But such circuits have a burden voltage ... so, as more specs you tell, as better we can help 😄

[SteveD123]

As Henrik says, the first step is to specify what you want to do. If you are doing capacitor charge/discharge experiments then you need to look into the voltage that the constant current instrument is able to supply.

V=C/Q

So the voltage across your capacitor will increase as you charge it. As you mention the term "Super Capacitor" I assume that you want to store a large charge. So you need to check that the voltage capability of your constant current instrument meets your requirements as well as the current capability.