Is the External excitation pins on the NI 9237 internally regulated?

[OKors]

I'm wondering if the external excitation in the NI 9237 module is internally regulated.
If so, does anyone see anything wrong with wiring in a 15v AC/DC wall adapter?

[WillPwr]

Hello, OKors!

When using external excitation voltages with the 9237, no - it is not explicitly "regulated." The card merely measures the mV/V read from the sensor. However, the 9237 does have limits on the range of this incoming voltage, which cannot exceed 10V.

This is listed on page 29 of the 9237 Operating Instructions and Specifcations.

So no - you will not be able to connect 15V DC directly to the 9237. Please let us know if you have any questions on this!

[OKors]

okay, good to know.
So to be more specific, what's the best way to supply supplemental excitation voltage to this module?
I anticipate using all 4 channels which will need 10vEX for each sensor.

If I'm understanding the limitations of this module, most likely it will not handle 4x10vEX which would exceed the 150mW power output.

Going back to the "wall adapter" idea; would this still be a good solution? Obviously I'd have to get an adapter that was no more than 10v.

[WillPwr]

Customers typically use a high precision power supply to provide voltage to their sensors, but a wall adapter could work as long as you divide down the voltage properly between the sensors.

The 150mW rating is the maximum internal power the card can provide, so the concern would be exceeding the card's current ratings and listed 10V voltages.

In short, I would recommend using the internal excitation if you can get away with it. If not, use an external programmable power supply. If not, then make sure you aren't exceeding the card's specifications. 

Please let us know if you have more questions on this. Thanks, OKors!

[Process_Systems]

Just a couple of comments on the wall adapter idea. The short answer is DON'T. A raw, or even a regulated wall adapter is usually of marginal quality in terms of the components used, and the stability of the voltage output that can be expected. Any noise, drift, or other crud on the excitation will invariably end up modulating your transducer signal. The degree of interference will depend upon your physical input configuration, but in general, since the transducer signal is only mv, you really do not want anythiing else there to have to attempt to deal with.

Secondly, and this falls in line with the "quality", or the lack thereof, of the componets in the adapter. Since the daq module you are using has a 10 volt absolute limit, you might want to condiser using a liimiting clamp on the excitation supply terminals. Clamps are cheap; DAQ cards aint!

My two cents, for what they're worth.

Have a good one,

Dave