Using RTDs with a 6036E

[jmarotta]

Is it foolish to attempt to use RTDs with a 6036E coupled with a CB68-LP board?  It seems like most people (NI included) use a SCXI driver for temperature measurements.  Does anyone know about incorporating a CB68-LP into their temperature measurements?  Any advice is welcome.

Thanks,

Joe

[jmarotta]

Ok, so after some soul-searching (read: research), I found a few examples of using RTDs, but they all seem to be centered around SCXI connector blocks.  Is there a way of connecting RTDs across a different connection without having to use a SCXI device?  I have a CB-68LP board, but it looks like I'll have to build an excitation circuit.  I also have a SCXI-1000 device with SCXI-1326 connectors, but I'm not sure if these are too outdated to use Labview 7.1.  Any ideas or advice from anyone out there in NI-land?

Thanks,

Joe

[Elizabeth W]

Hi Joe,

First of all, here are some useful resources on RTD measurements:

NI Developer Zone Tutorial: Temperature Measurement with a Thermocouple or RTD

You could possibly use your current hardware, although it would make your life much easier if you get hardware that is specifically meant for RTD measurements.  I could make some recommendations for you if you can tell a little bit more about your application (i.e. channel count, preferred connectivity - USB, PCI, etc.).  Or, you could contact your NI representative by going here.  This link will get you in touch with a knowledgeable rep from our sales department who can recommend the correct hardware for your specific needs and application.  Hardware specifically designed for RTD measurements can provide important signal conditioning such as excitation, amplification, isolation, and filtering.

If you decide to stick with your current hardware, you're correct that you'll need to provide your own external current excitation source.  If you decide to use SCXI, there are some SCXI modules that are capable of sourcing excitation current (for example, the SCXI-1581 is one).  You mentioned that you have SCXI-1326 connector blocks, but you didn't mention which SCXI modules you have.  Do you have any?  If so, what are they?  I can tell you if it would be possible to use these modules for RTD measurements.  

You can directly connect your RTD to the CB-68LP and perform the RTD measurements using the NI 6036E.  This measurement will be susceptible to noise since it is connected to an unshielded terminal block.  And once again, you will need to provide external current excitation.  If you do want to take this route, what type of accuracy do you need for the RTD measurements?  Also, what type of RTDs are you using?  We can investigate further and see if it is feasible to get the accuracy you need with the 6036E.  

Whichever route we chose, you can create a temperature input NI-DAQmx task in Measurement & Automation Explorer (MAX).  From there you can configure your measurement, see a connection diagram which shows you how to physically connect the RTD to the connector block, and test your setup.  If you'd like more information about how to do this, just let me know and I'd be happy to help.

I hope this helps.  If there is anything else I can help with then definitely let me know!

[jmarotta]

Hi Elizabeth,

Thanks for the help!

We're currently looking into a lower-cost replacement for a thermistor setup that we have in Labview.  Unfortunately, budgetary constraints require that this project work with our existing hardware (I also have access to an old SCXI-1000 to connect with the SCXI-1326).  This information helps, but it feels a little like I'm at the beginning of a longer road than I'd thought...

As far as accuracy for RTD measurements, ideally we're looking for about +/- 0.5 Celsius, so not terribly accurate.  We're using Omega's F3105 RTDs, with leads soldered onto them.  I think even without using the CB-68LP board, we might have some noise problems. 

I don't know if this clarifies anything; I'm having some trouble getting Labview 7.1's MAXexplorer to recognize the connector blocks we've got for the SCXI device.  I'm currently digging into the literature that you've linked to, as well as the product manuals for the SCXI-1000, but I'm getting a little lost.  Any further help is appreciated, and I would be happy to give you any more information that you'd need.

Thanks,

Joe

[hecmar.arreola]

The NI BNC-2120 connects to most of NI 68-pin devices and has a resistance measurement feature.  I have never used it with an RTD but I don't see why it wouldn't work if you were willing to use this in place of your pin-out.  I am sure there are commercially available RTD signal conditioners that will handle the power/filtering of the RTD and output a 0-10V (for example) signal proportional to some temperature that you can read using one of the analog input pins on your pin-out.