Strange values using SCC-TC02 in SCC-2345, please look att picture

[Johan.svensson]

Hi,

Use a SCC-2345 and one SCC-TC02 and one standard type K thermocouple. The result after each maesurment is -1908625864800603,25 ??

Notice that the program I use is the example in labview supplied by NI. I know that there is a thermistor inside SCC-TC02 for CJC, but at first I want to get it to return sensible values.

This should be simple, but is not,  I have been testing all I can think of, so please look at the pic and tell if anyting is wrong for my system... Anyone out there who had similar problems?

[devchander]

Did you choose a valid physical channel, cjc channel and cjc source as internal??

Plus there is one more example vi called SCC-TC0x.vi ( uses Traditional DAQ device drivers), try acquiring with this

( Note; you may have to reset Device if you have to use DAQmx functions after using traditional DAQ functions)

Also, grounding might be an issue. So, try connecting the ground of SC-TC02 to the SC-2345 ground.

[Johan.svensson]

Ok, to bad... I can't find that example-vi...

Could you post it here?

Will be back later to answer  your questions, after my luch 😉

[devchander]

Have you installed traditional (Legacy) NI-DAQ device drivers??

If you have, you will find this attached example vi

Note: it will work only if you have installed traditional DAQ device drivers.

[Johan.svensson]

Sorry for the late answer...

I don't have thoose drivers installed so it doesn't work.

But I was thinking, can't I use a normal voltage input instead and scale the value to represent a temp. based on K-thermocouple?

[devchander]

You mean without a cjc??

that will not give you a valid/ correct thermocouple measurement

[Norbert_B]

Johan,

since the 2345 is signal-conditioning, it does not digitze the data. So i have to ask which DAQ device you are using.
The next question is how you set up the whole testfixture. In general, you are measuring voltages. These voltages are very low, therefore you are using SCC (mainly for amplification and CJC). The voltages are then digitized by a DAQ device. This device specifies the resolution and speed of the acquisition. After the digitizing the values are binary values of a certain resolution (not equal to the DAQ-resolution!) which depends and are presented differently on the format you have chosen for the acquisition (e.g. DBL = 8 byte).
Small example: the resolution of the measured value is 1 byte = 11111111. If you would choose uint, the value would be 255. If you would chose int, the value would be -1. So you see, same binary pattern, two different values.
So please check if you are running in such an issue or if the measurement returns the wrong pattern. You could check with MAX for the value.
Another point is, like you already read is, that the CJC-channel has to be valid and return proper values.

hope this helps,
Norbert B.
NI Germany

[Johan.svensson]

OK, I will look into this and return with results

Message Edited by Johan.svensson on 09-25-2006 08:31 AM

[Johan.svensson]

DAQ Device is: PCI-6221

When I use max to read volts from channel ai7 (wich refers to socket J8, where SCC-TC02 och mounted) Max calibration tool shows -0,012 (temp probe free in the room temperature) and when I heat it up with my fingers 0,027.

I have tried the same test for channel ai15 wich should return the temp value from cjc termistor inside SCC-TC02. It shows 1,5 at room temp.

[Norbert_B]

Johan,

ok, these are the unscaled data fron the channels. But are they valid? You should try to create an apropriate DAQmx Task in MAX to check the scaled values (which means you would create a temperature task with CJC and the correct couple-type set). Are the values ok here?
If not: what about that CJC-value... 1,5 V seems a bit high for me, but i am no expert for termistors..... If you heat up the TC02, does this value change?

Norbert