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K type thermocouple with USB 6361 DAQ and SC-2345 connector block

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How do I configure my DAQ and connector block to read temperature via a type K thermocouple?

 

I have a USB-6361 DAQ (mass termination) and SC-2345 terminal block. I have strain gauge (full bridge) and feedthrough modules, but I'm not sure which module I need to use.

 

This NI tutorial (link) indicates setup is straightforward:

  1. Create a virtual voltage/temperature/thermocouple channel in MAX
  2. Select physical Analog input channel of DAQ
  3. Configure thermocouple type and CJC source & value

I'm confused by the last step. As I understand, CJC is an electronic correction applied by the DAQ to the thermocouple. This forum post indicates I can create a virtual CJC using my 6361's terminal block. However, this NI tutorial on creating a CJC via MAX does not mention any physical channels when creating a CJC channel--let alone the terminal block.

 

What do I do? Do I...

  1. Connect thermocouple via feedthrough and use virtual CJC as directed.
  2. Connect thermocouple via SG module (full bridge) and configure a physical CJC on one of the bridge's legs?
  3. Something else. You're overcomplicating it.

For reference, here is a pic of a similar thermocouple to mine.

 

aeroAggie_1-1635879660950.png

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I hope you're aware of the resolution achievable with the DAQ you're using for K-type thermocouple measurements.

 

For example, K-Type thermocouple generates 1mV at 25C, of course, you can measure this using the +/-100mV range of 6361 with a resolution of 3.052uV and accuracy of 33uV, this would mean that at 25C the measurement will be +/-0.8C.

 

In terms of CJC, SC-2345 does not have a CJC circuit available, unlike other accessories - you already know this.

 

My understanding is that you create a CJC by using one of the available AI channels connected to a thermocouple. If you have 8 channels, use these 8 channels as CJC and place that thermocouple at the terminal block and use the rest of the 7 channels in your application.

 

I don't think you need to use the full-bridge for TC.

Santhosh
Soliton Technologies

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Hi Santhosh, thanks for the response, especially regarding resolution.

 

Resolution

To be honest, I had not even considered the resolution. I'm trying to measure a brushless DC motor's winding temperature over 2-5 minutes. I expect temperature to go from room temp up to 150 degC (or maybe 200 degC), so I think +/- 0.8 degC will suffice for me.

 

Setting up CJC - correct me if I'm wrong

The 6361 has 16 analog input channels. I connect my K-type thermocouple to one channel, let's say AI3. In LabVIEW or MAX, I configure a measurement channel with AI3. Wherever LabVIEW or MAX asks for CJC source, I specify some unused analog input channel, say AI7. The software derives the temperature at AI7 and uses the voltage difference measured at AI3 to estimate the temperature at my motor. Correct?

 

I will give it a shot tomorrow.

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Accepted by aeroAggie

It looks like I need the thermocouple modules (SCC-TC01, SCC-TC02, link).

 

I think I misunderstood what the CJC tutorial (link) was explaining. It seems it's explaining how to use a second thermocouple as a reference point. It's not explaining how to use built-in circuitry on my USB 6361 DAQ or SC 2345 connector block as a CJC.

 

Correct? Any NI engineers that can verify?

 

 

 

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Santhosh,

 

I had not considered resolution, but +/-0.8 degC should suffice for me. I'm trying to measure temperature changes from 50 to 200 degC.

 

Just to be clear on CJC, are you saying I can use a second sensor (thermistor, RTD, thermcouple, etc.) hooked up to another analog input as the CJC?

 

All,

 

It seems I need to buy a thermocouple module, such as the SCC-TC01 (manual link)

It has a built-in thermistor that can function as cold-junction compensation (CJC).

I would plug my thermocouple into this module. I could then configure a temperature task in MAX that uses this module and its built-in CJC to measure temperature, correct?

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@aeroAggie wrote:

Santhosh,

 

I had not considered resolution, but +/-0.8 degC should suffice for me. I'm trying to measure temperature changes from 50 to 200 degC.

 

Just to be clear on CJC, are you saying I can use a second sensor (thermistor, RTD, thermcouple, etc.) hooked up to another analog input as the CJC?

 

All,

 

It seems I need to buy a thermocouple module, such as the SCC-TC01 (manual link)

It has a built-in thermistor that can function as cold-junction compensation (CJC).

I would plug my thermocouple into this module. I could then configure a temperature task in MAX that uses this module and its built-in CJC to measure temperature, correct?


Yes, you need another sensor on a spare channel to act as a CJC and place that sensor close to the terminal block of the thermocouple connector.

 

You can also purchase an accessory with a CJC sensor inbuilt and in that case, you will still lose one of the AI channels to read that CJC sensor.

Santhosh
Soliton Technologies

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