what should the cjtemp measure

[Joey Wood]

In the SCXI 1102.VI if I measure the cjtemp what should it be? I am measuring around 894 deg c for a j type thermocouple using a TBX - 1303 is this coorect? If not what should it be and how do I correct it?

[Michael_S.]

Here is some information on the cjtemp reading and teh 1303 terminal block using an 1102 module.

Just scanning cjtemp at room temperature ~26 Deg C should yeild about 1.2V.

Here is the link to the Knowledge Base:

http://ae.natinst.com/operations/ae/public.nsf/fca7838c4500dc10862567a100753500/5ca3a774944ddbd8862564eb0060234b?OpenDocument

[Dave_Karon]

OK. You should be aware of whatever you are trying to use, so...
The CJC is measuring the temperature of the termination strip (actually the PC board(?) ) in the SCXI-1303, where the thermocouple leads are connected. In The 1303 they use a precision thermistor for the CJC sensor. The 1303 also has circuitry for open circuit detection.
In LV you address it with the SCXI address
"OBx ! SCy ! MDz ! cjtemp".
When converted to temperature, it should give you the temperature of the PC board in the SCXI-1303, close to room temp where the system is located. (~18�C-30�C??)
It seems like you are running into one of several possible problems or errors.
Your problem is in either hardware or software. Either your hardware is damaged or you have an error in your code.
In your original post on this, you said that you read 167�F when you expect to read ~202�F based on other sensors.
1. Are you actually reading the CJC?
1a. If so, are you converting it to deg? (from volts?)
1b. Does it change as you warm or cool the SCXI-1303?
2. Are you actually reading your TCs? Are you reading the correct channel(s)??
2a. Do they change when you warm or cool the TC junction? When the TC junction is sitting in the air, the TC voltage should be very close to 0.0(0.000000 V)
2b. Is the range (or gain) setting on your TC channel(s) reasonable? e. g.
+/- 50 mV or 20mV(FS)? 20mV will give you a type J TC temperature range of ~600�F (wow you did say bearing temps?) check your TC tables.
3. You have to take the CJC temp, convert it into EQUIVALENT volts for the type J TC, add it to the TC volts from your type J TC channel, THEN you convert it to temperature.

So, that should give you a few things to look at.
I still haven't heard from you whether you wrote your own program from scratch, or you are using the example program (vi) under SCXI examples, or you wrote your vi based on (one of) the example.
If you still don't get anywhere with this, try posting a copy of your vi.
I don't remember you saying which version of LV and which version of NIDAQ you are using.
From your earlier post(s) it looks like you are (or were) getting something of a reasonable reading from you TC.

Good luck
Dave