Multifunction DAQ

cancel
Showing results for 
Search instead for 
Did you mean: 

CJC problems with SCXI 1102 + SCXI 1303

Solved!
Go to solution
I recently bought a SCXI-1600 (USB) data acquisition module in a SCXI-1000 (4 SCXI slots) chassis.
For a few simple temperature measurements, I have a SCXI-1102 installed in the first slot of the chassis, with a SCXI-1303 terminal block and I will use VI Logger.
 
As a first test, I'm using MAX to check if eveything works fine :
 
I configured a NI-DAQmx task including just a single thermocouple (K type) channel (channel 0)
My SCXI-1102 module is configured with "SCXI-1303" accessory, so that CJC can be turned on.
 
My problem is :
When I set CJC as "built in" and test the task, temperatures displayed are erroneous (thermocouple in ice + water displays about 13°C instead of 0°C) and there is noise of about 1,4°C (peak-to-peak).
But when I set CJC as "constant" (with a terminal block temperature of 24°C, which I previously measured with an external sensor), temperatures displayed in the test panel are ok and there is virtually no noise.
 
I tried another channel on the same module (channel 1) : same problem.
I tried it with a SCXI-1102C module : exactly same problem.
I tried another SCXI-1303 terminal block I just bought : same problem again.
I tried an old SCXI-1300 (one I found in an old cabinet in our lab) : now measurements are great with CJC turned on ! (virtually no measurement error and noise)
 
Can someone suggest reasons for my problem ? I start to think it might be a hardware problem on my 2 new SCXI-1303 terminal blocks (with serial numbers very close).
 
0 Kudos
Message 1 of 14
(3,069 Views)
Have you checked the gain and filter jumpers on your board? Do they match your MAX setup?
Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


0 Kudos
Message 2 of 14
(3,047 Views)
Just check this
 
the CJC type for SCXI 1303 is thermistor
The CJC type for SCXI 1300 is IC sensor
 
Which cjc type are you selecting in your application??
 
Regards
Dev
 
Message 3 of 14
(3,044 Views)

Hello Henrik, and thank you for your reply.

Could you explain what gain and filter jumpers are you talking about ? As far as I know SCXI-1102 have a fixed 2Hz lowpass filter and a (software-) programmable gain per channel.

0 Kudos
Message 4 of 14
(2,998 Views)

Hello devchander,

my SCXI-1102 board is configured in MAX as having a SCXI-1303 accessory (thus CJC is automatically adjusted). And of course I changed it to "SCXI-1300" when trying my old SCXI-1300 terminal block.

For now I'm not yet using the system in any application. I'm just checking if the measurements are working fine in MAX test panels... which answer is still... no 😞

0 Kudos
Message 5 of 14
(2,998 Views)

Hi Fabrice,

These recent discussions,

 http://forums.ni.com/ni/board/message?board.id=300&message.id=2228 

and http://forums.ni.com/ni/board/message?board.id=300&message.id=2312 

might give some pointers since they have also discussed about bias and pullup resistors.

Hope this helps

Regards

Dev

 

0 Kudos
Message 6 of 14
(2,996 Views)
Hey Dev !
Thanx again for your reply...
I have checked those discussions but haven't found any new informations, as I already had read several discussions (and the module user manual) about effects of bias and pull-up resistors on measurements accuracy.
 
As a reminder, in my case, offset and noise problems do only happen when CJC is set as "built-in". With a "constant value" CJC, measurements are accurate and virtually noiseless !
 
Fabrice
0 Kudos
Message 7 of 14
(2,993 Views)

Fabrice,

Do u have a spare SCXI 1303?? could u check with another scxi 1303 and see if u have the same offset?

Regards
Dev
 
Message 8 of 14
(2,990 Views)

Hehe 🙂 I had the same idea 😉

Yes I have both a 1303 and a 1102... but they are currently in use on a critical test bench and I can't take them to my lab to perform advanced controls in similar conditions before a few weeks.

But one thing I will do is go to that test bench and connect that "working" 1303 to my new 1102 without disconnecting the signals wires (thermocouples connected to a process) and check if I notice an offset in the measurements.

I will keep you informed...
 
regards,
Fabrice
0 Kudos
Message 9 of 14
(2,986 Views)
The "working" test bench was not is use today so I could perform the following tests :
 
- my chassis + my SCXI-1102 + the SCXI-1303 from the test bench = approximately same offset (I couldn't measure the offset accurately because I had no way to do a reference measurement)
 
- my chassis + the SCXI-1102 and SCXI-1303 from the test bech = same offset again 😞
 
And of course I know the SCXI-1102 and SCXI-1303 from the test bench are working fine together.
 
 
That all leads me now to think about a software problem related to calculation of CJC... I'll check my MAX / NI-DAQ versions and update everything that can be updated.
Let me know if you have any idea...
0 Kudos
Message 10 of 14
(2,982 Views)