DAQ-Pad 6020E and SCB-68

[tcushing]

I am using the CJC on ch0 and I have a Thermocouple hooked up to Ch1 but I get unstable readings. The temp fluctuates about 5 to 10 degrees C. For example if I am reading ambient temp, my thermometer reads 21C but Labview reads anywhere from 16C to 23C. I have used MAX and the Continuous Temperature Measurement vi. I am a newbie and need some help. Thanks.

[Bill B]

Hello,

Thank you for contacting National Instruments.

If you are using the Continuous Temperature Measurement.vi, you will need to ensure that you have channel 0 set as the CJC channel and also make sure that you have the correct thermocouple type selected. More than likely, the reason your are seeing such a large drift is related to how you have the switches inside the SCB-68 configured. Please see page 4-3 of the SCB-68 User Manual for how to configure the switches correctly. If the switches are not set correctly, the CJC voltage will not be connected to channel 0 and the voltage measured on channel 0 will randomly float.

Let me know
if you are still experiencing difficulties with this issue after inspecting what I metioned above.

Regards,
Bill B
Applications Enigineer

[tcushing]

I am using the Continuous Temperature Measurement.vi and the switches are correct on the SCB-68. I have the VI set to T-type thermocouple and CJC set to channel 0. I am using Omega T-type 28 gauge thermocouples. The thermocouple is set to a Referenced Single Ended measurement set to channel 1.

[Bill B]

Hello,

You will need to use Differential mode when measuring thermocouples. Thermocouples are floating signals sources that should not be grounded. By grounding one lead of the TC, you will ruin your accuracy completely. Make sure that you have your board set to Differential mode and your SCB-68 configured as your accessory. Then make sure you have your TC connected correctly to your SCB-68. The blue lead of your T-type TC should be connected ACH1(#33) and the read lead should be connected to ACH9(#66).

This should improve your accuracy substantially.

Regards,
Bill B

[tcushing]

So what is the point in even having a Referenced Single Ended mode then. I have connected them up using Differential Mode and I get the same fluctuations. The SCB-68 has 16 channel RSE and I need 14. The sales guy for NI said it would suffice. If not, to use 14 channels does that mean that I need a 32 channel terminal block?