SCXI-1125, TBX-1328, Mulitplexed Mode, built-in CJC DaqMx issue

[KeithB]

We have the following:

SCXI-1001 chassis connected to the PC through a PCI-MIO-16XE-10.

Slot 1 has an SCXI-1125 module with a TBX-1328 terminal board w/ DTEMP switch soldered. This runs in multiplexed mode.

When I create a traditional channel for a K-Type thermocouple, and select Built-In CJC, the temperature reads correctly, ambient temp.

When I create a DAQmX global virtual channel temperature channel, select K-type thermocouple, and Built-In CJC....the value reads like -250. The daqMX instrument is setup with the proper accesory listed.

I am using daqmX 8.6.1 presently. Any thoughts on the cjc correction not working right in daq-MX/daqassistant setup?

KeithB

Test Engineer, Hawaii Fuel Cell Test Facility

[mallorim]

Hi KeithB,

Welcome to the forums! A reason you might be encountering this behavior is because you are attempting to use both drivers to communicate with your DAQ device, but the drivers might need to be reset to use the device between tasks. To reset the drivers for Traditional NI-DAQ, open Measurement and Automation Explorer (MAX) and go to "Devices and Interfaces", then right-click "Traditional NI-DAQ (Legacy) Devices" and select "Reset driver for Traditional NI-DAQ." This can be seen in the screenshot below. If you want to use the NI-DAQmx drivers with your DAQ device instead, right-click the device under "NI-DAQmx Devices" and select "Reset Device."

Please let me know if reseting the device does not remove this error.

Regards, Mallori M.

Message Edited by mallorim on 04-09-2008 03:02 PM

[KeithB]

I went ahead and reset the Daqmx devices....including the DAQ card, SCXI-Chassis, and the module. Still same issue using the built-in CJC, it offsets the temp down to -250C. 

If I go directly to the module under DaqMx devices, I can open the test panel and read the '*_cjtemp' channel voltage, which is a 1.91V-0.65V output for 0-50C. The voltage read directly from the module test panel is around 1.21, which corresponds well with the temp in the accessory block.  If I enter this as the 'constant' cjc vlaue the probe reads ok.

Can I setup the cjc channel as a global virtual channel and reference that channel as a work around?  I just can't figure out where I can assign the physical channel '_cjtemp' to a virtual channel in daqmx.

Appreciate the help.

[mallorim]

Hi Keith,

Did you also try reseting the Traditional DAQ devices? Or only the DAQmx Devices?

The Knowledge Base Document: How to Create a CJC Virtual Channel for Use with Thermocouple Virtual Channels discusses how to set up a channel for you CJC which you can try, but I do not know if this will take care of the issue. Try it and let me know how it goes. I will keep looking from this end and see if I can't find the cause.

Regards, Mallori M.

[KeithB]

I tried reseting them both, only one, different order's etc....no change.

As for creating a virtual CJC channel:
It seems that daq assistant isn't letting me address the SC1MOD1/_cjtemp channel.

Only when I go into the SCXI Module Test Panel,  the channel shows up as last in the list, ai0, ai1, ....ai7, _cjtemp. When I go through DaqAssistant in NIMAX, I only have access to ai0 to ai7 of the module.

So programatically I can create a virtual channel for SC1MOD1/_cjtemp using the raw DaqMx vi's and typing in the physical channel name (not daq assistant), and then use the thermistor conversion vi to get the correct temperature, but I can't create a global virtual daqmx channel in MAX for the channel.

If I could programmatically create the channel, but have this also show up as a global virtual channel, that would work, but I don't think this is possible.

I am also trying to export the configuration to a text file, and change the listing for the physical channel of a ai voltage channel to the _cjtemp, but it just gives an error.

Intriguing error, old hardware, new APIs!!!!

Appreciate you following up with me.

KeithB




Message Edited by KeithB on 04-10-2008 09:58 PM

[mallorim]

Hi Keith,

Something to check might be the the switch S1 on your TBX-1328 is in MTEMP mode. When I tested this here on similar hardware, I saw similar unexpected behavior when the switch was set to DTEMP mode, which is not supported as can be seen on page 10 of the Installation Guide.

Regards, Mallori M.

[KeithB]

Well the problem has been solved.

In the SCXI Chassis 1, DAQmx configuration, the communicating device was set as Module 12. Once I set this back to module 1 the CJC temp correction is applied correctly in the global virtual channel.

I did not have to switch the TBX-1328 from Dtemp to Mtemp.

Thanks for the tips and assisting me in working through this.