Traditional NI-DAQ (Legacy)
- Right-click Data Neighborhood in MAX and select Create New. Choose NI-DAQmx Task and click Next.
- Choose Analog Input as the Measurement Type.
- Select Voltage as the Measurement Type under Analog Input.
- Select Create New Local Channels.
- Select ai0 under the DAQ card that is connected to the SCB-68, then click Next.
- Type a name for the NI-DAQmx Task and click Finish.
- Under Custom Scaling, select Create New Scale.
- Select Linear Scale.
- Define a scale name and click Finish.
- Set the same corresponding m and b values as defined in Step 7 above (where slope refers to m, and Y-Intercept refers to b). Change the Scaled Units to deg F, deg C, or Kelvin, depending on which units you want. Then click OK.
- Set the input range to your desired values, keeping in mind that it is already scaled for you (for example, a good range for Celsius would be 0—100 degrees).
- Make sure that the terminal configuration corresponds to the dip switch settings on the SCB-68.
- Click Save Task and verify that the task appears under Data Neighborhood » NI-DAQmx Tasks. Click the task to highlight it. In the middle section, above the task description, choose Test to test the task.
- Click Start to start the acquisition. You see the ambient temperature the CJC is reading in the specified units.
- Right-click Data Neighborhood in MAX and select Create New. Select Virtual Channel and click Finish.
- Select Analog Input as the Virtual Channel type and click Next.
- Type a name and description for the Virtual Channel and click Next.
- Select Voltage as the type of sensor or measurement and click Next.
- Define the units as C, F, or K and enter a temperature range – one that will include ambient temperature if that is what you intend to measure – and click Next.
- Select New Custom Scale and define a scale name and description. Set the scale type to Linear Scale and click Next.
- Type in the following m and b values based on the units you chose in step 5 and click Next.
Celsius: m=100, b=0
Kelvin: m=100, b=273.15
Fahrenheit: m=180, b=32
- View the scale to confirm it is correct and click Finish. Confirm that the scale name is selected and click Next.
- Select the DAQ Hardware connected to the SCB, select channel 0, and set the analog input mode based on the switch settings on the SCB.
- Click Finish. Now the virtual channel appears under Data Neighborhood. When you right-click the virtual channel and select Test, you will see the ambient temperature of the CJC in the units specified.
The transducer used for cold junction compensation is a thermistor. It is calibrated to match the following equation:
TC = 100 * Vt
TK = TC + 273.15
TF = (9/5 * TC) + 32
where Vt is the temperature sensor output voltage. TC, TF, and TK are the temperature readings in degrees Celsius, Fahrenheit, and Kelvin, respectively.
These connection blocks have DIP-switches that will enable the CJC. Refer to your User Manual or User Guide DIP-switch settings. After setting the switches, the CJC transducer is connected to Channel 0 of your data acquisition (DAQ) card. If you are using Traditional NI-DAQ (Legacy), create a virtual channel in Measurement & Automation Explorer (MAX) that reads Channel 0 to see the temperature the CJC is reading. If you are using NI-DAQmx, you create an NI-DAQmx Task instead of a virtual channel.