PCIe-6738 - query on the number of physical output channels

[Vishnu4414]

As mentioned in the specifications of PCIe-6738 , it seems to have 32 output channels. But are these physical output channels, and if so. Can I precisely control the output voltage of each of these channels ?

[santo_13]

Yes, there are 32 physical channels. It depends on your definition of precision, but within the instrument specifications, for sure.

[Vishnu4414]

Hallo

Thanks for the reply 

I actually require , 16 channels basically. Each output channel should have a voltage range of (1mv to 4mv). With a voltage precision step of +-25 micro volts. Each channel should also supply a minimum of 2mA. The system should also have very low noise (primary requirement). As i read from the NI document i see a noise of 1mVrms. What are your thoughts.

Thank you

[santo_13]

I hope you realize that working in the mV range is challenging due to noise and the thermocouple effect at every junction.

The maximum offset error of 6738 is 2.9mV which is larger than your smallest signal to generate.

What are you trying to do with such a small signal?

[Vishnu4414]

Hallo 

Thanks for the reply.

Its required for a photon sensor application. Hence such low voltage and precision are required. 

If this is not the right solution , do you know any other alternatives that might help.

[santo_13]

You're dealing with high precision low voltage signals, not a lot of general-purpose instruments do those.

Will you be generating DC at those low voltages or AC? if AC, what frequency?

The alternate idea is to create your own precision attenuator circuit using OPAMP and precision resistors but you will have to do your own calibration to account for the variability in the external circuits.

How accurate do you want these signals to be? does absolute accuracy matter, or does just the step size matter?

[Vishnu4414]

Hallo Santo

Good Evening 

Thank you for the reply.

The output just have to be DC. Absolute accuracy also matters, but there is no specified range for that. It has to be accurate to the best scale possible as slight jitters can effect the measurement. The most important criteria is noise. A slight disturbance can effect the system in a bigger manner. 

I am aware that we can make our own custom circuits for this. But for immediate testing purposes we require something that we can buy. Do you have any suggestions ?

Thank you

[santo_13]

If your application is one of a kind, then there may not be a ready solution.

The Thermocouple simulation is an adjacent application that deals with mV, as the voltages are in a few mV.

https://www.pickeringtest.com/en-us/product/41-760-003-pxi-16channel-millivolt-thermocouple-simulato...

https://www.ueidaq.com/products/8-channel-thermocouple-simulator