The NI 9217 and NI 9219 2-Wire RTD Support Hardware: CompactRIO>>Analog Input Modules>>NI 9217
Problem: The Operating Instructions for the NI 9217 and NI 9219 both explain how to connect and measure from a 4-Wire RTD and 3-Wire RTD. Do these modules also support 2-Wire RTD's? Solution: Both these modules do support 2-Wire RTD measurements. All you need to do is connect the excitation terminal to the positive RTD terminal and then the negative RTD terminal to the excitation return terminal. It is important to remember that 2-Wire RTD measurements will be significantly less accurate than 4-Wire or 3-Wire RTD measurements because the module does not internally compensate for lead resistance. The following diagram shows how to connect a 2-Wire RTD to an NI 9217. Connect the sensor to RTD+ and RTD- and then place a jumper between RTD- and COM. The module has the ability to internally connect RTD+ to 4-Wire EX.
Note: Since you are using three terminals on the front of the NI 9217, you must configure your DAQmx Task for a 3-Wire RTD configuration. The following diagram shows how to connect a 2-Wire RTD to an NI 9219. Connect the sensor to HI and LO and then place a jumper between EX+ to HI and LO to EX-.
Note: Since you are using four terminals on the front of the NI 9219, you must configure your DAQmx Task for a 4-Wire RTD configuration. If the 9219 is being used in NI RIO there is another option. The channels can be configured for 2-Wire resistance mode and the scaling from resistance to temperature can be performed in software. Related Links: NI 9217 Operating Instructions (November 2006) NI 9219 Operating Instructions (March 2007) Attachments:  - 2WireRTD_9217.GIF - 2WireRTD_9219.GIF
Report Date: 04/20/2007 Last Updated: 01/29/2008 Document ID: 48JC337E |
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