Temperature Measurement errror

[aspired]

I am using a DAQ card 6052E, an SCXI 1121 , chasis SCXI 1000 and TBX 1328 for thermocouple and thermistor measuremtns.

I have gone through the process of configuring everything in MAX. However my temperature measurments using a thermocouple gave me a wrong figure of around 70C. To debug this situation I measured the CJC temperature( using a Labview example)which is around 56C ( when in fact the ambient temperature is around 27C.
Why is my CJC temperature wrong ?. Is the CJC broken?
Also, the cable SH32-32 cable assembly ( for connecttion between 1328 and 1121) came without the cable adaptor. Hence I direclty connected the TBX 1328 to the SCXI 1121 it fits perfectly well withut the adaptor. (You can see the december 2000 manual for T
BX 1328

http://digital.ni.com/manuals.nsf/websearch/22B262582673F346862569B300742094?OpenDocument&node=132100_US)
Could that possibly cause any error?

Can someone give me advice as to how to debug this error? Thanks!

[LesHammer]

> To debug this situation I measured the CJC temperature which is around 56C

The manual states that the CJC temperature thermistor range is 0 to 50 degC. If you are measuring 56, you either have a broken/loose connection, or a configuration error. My bets would be on the loose connection.

Les.Hammer@CompleteTest.com

[Jeremy_C]

What cable adapter are you referring to? The SH32-32A should plug directly from the SCXI-1121 to the TBX-1328. What about if you acquire directly from one of the channels without referencing the CJC? Does the voltage returned change with temperature change? Make sure that your reading responds to changes in temperature. If you are not seeing a response, then something isn't configured correctly or there is a bad connection somewhere. Double check your connections for any bent pins. Let me know what you find out.

[aspired]

I am reffering to the TBX cable adaptor on page 8 of the December 2000 manual of TBX 1328.

I dont seem to have any bent pins.

I tried your suggestion. The voltage doesnt change when the temperature changes.( in fact it is pretty constatnt )
Also in MAX when i try to set up the global channel/task I keep getting an error saying
Minimum Possible voltage value is -5mV and maximum is 5mV. HOwever i know that the SCXI has maximum output of +5V. ( and i have set the gain to 1000 )

I also tested the cable for connections. It seems fine.

I then tried to use a thermistor for temperature measurements. ON the TBX 1328 I connected the 2 ends of the thermistor to the + and - of the Channel 0 input.
Also I connected

EX0+ to CHo+
EX0 - to CH0-
( I d
ont know if this qualifies as a 2 or 4 wire configuration)
Then when I tried to set up a global channel, it told me that the mimum value should be 198C and Maximum 300C.
I doubled checked my jumper settings on the 1121
gain = 1000
Filter = 4hz
Current excitation = 0.15mA.
it is confiuged for " MTEMP' readings. ( i am using it in multipled mode)
I have tried several different sensors but to no avail.
I am at my wits end and dont know what do to. I had called up NI but their suggestions did not work.

[Jeremy_C]

Because the voltage doesn't change when the temperature of the thermocouple changes, that indicates that something either isn't configured correctly, or some of the hardware is damaged. Additionally, if you have specified a gain of 1000, both with the jumpers and in MAX, then the DAQ Assistant will limit your range to +/- 5mV. After applying the gain of 1000, you will be maximizing the +/- 5V range of the ADC. So, we need to start simply and try to figure out where the problem lies. If you have a simple break out box (SCB-68) that you can connect directly to the DAQ board, try connecting a battery or some known voltage source to make sure you can take direct readings. Once you've accomplished this, then connect up the SCXI chassis and connect
this known voltage source to a channel on the 1121. Configure that channel appropriately with jumpers and in MAX, and make sure you can read this known voltage. This process will tell us where to focus our energies. Also, what was the service request number for your interaction with support when you called in?