Connecting 2, 3, and 4 Wire RTDs to My Data Acquisition Card

Updated May 24, 2018

Reported In

Hardware

  • Multifunction I/O Device

Issue Details

I have a 2-wire, 3-wire, or 4-wire Resistance Temperature Detector (RTD) that I want to connect to my data acquisition (DAQ) device. What do the different color wires on my RTD mean, and how do I physically connect them?

Solution

RTDs typically come in red/black or red/white color combinations:
  • Red: Excitation
  • Black: Ground
  • White: Ground
The following connection diagrams illustrate how to connect various RTD types to your DAQ device.

4-wire RTD Signal Connection

Connect each of the red leads on the positive side of the resistive element to the excitation positive and channel positive on the DAQ device. Connect the black (or white) lead on the negative side for the resistive element to the excitation and channel negative on the DAQ device. (The two additional leads from a 2-wire RTD increase the attainable accuracy.)

3-wire RTD Signal Connection

Connect the red lead to the excitation positive. Jumper the excitation positive to the channel positive on the DAQ device. Connect one of the black (or white) leads to excitation negative and the other to channel negative. 

Note: Some hardware has internal 3-wire configuration compensation and does not require the jumper lead from CH+ to EX+ (NI 9217 for example). These units will make this connection internally. Check the specification manual for the particular device you're using.

2-wire RTD Signal Connection

Connect the red lead to the excitation positive. Use jumper wires between the excitation positive to the channel positive on the DAQ device .Connect the black (or white) lead to the excitation negative. Jumper the excitation negative to the channel negative on the DAQ device. 
 

 

 

 

Additional Information

If you are unsure which wires are connected to which side of the resistive element, you can use a digital multimeter (DMM) to measure the resistance between the wires. ~0 ohms indicates the leads are attached to the same node. A resistance close to the nominal gage resistance (typically 100 ohms) indicates that the wire leads are on opposite sides of the resistive element. Alternatively, check with the manufacturer to see if they have a suggested way of connecting the RTD to the DAQ.

Note: Reference the specifications manual for your particular RTD to determine its required excitation level.

It is not recommended to use a USB-6008, USB-6009, or any M, E, or S series cards for temperature measurement because RTD's require a current excitation source. These devices will not be able to provide this current excitation, so you will need an external supply. National Instruments offers devices for RTD measurements that can provide the current excitation and acquire the temperatures in one module. These solutions come in a variety of form factors, including USB or Wi-Fi. See Products & Services: RTD Measurement Devices.

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