Advantages of the NI 9237 Over the NI 9219 in Strain Measurements
Hardware: CompactRIO>>Analog Input Modules>>NI 9237, CompactDAQ>>Analog Input Modules>>NI 9219
Problem: I will be using CompactDAQ or CompactRIO to acquire data from a strain gage. My two options for modules are the NI 9237 bridge module and the NI 9219 universal analog input module. What are the advantages that the 9237 has over the 9219?
Solution: Some of the most notable advantages that the 9237 has over the 9219 are:
- Sampling Rate: The 9237 has a 50 kS/s sampling versus 100 S/s with the 9219.
- Excitation Voltage: The 9237 has several programmable values of excitation up to 10 V whereas the 9219 has a fixed value (2.0 to 2.7 V depending on the Bridge Type and Load Resistance).
- Remote Sense: If your sensor is far away from the data acquisition module, your measurement can reflect error due to lead resistance. The 9237 has inputs for remote sensing, high imput impedance lines that do not allow current flow and therefore see no voltage drop due to lead resistance. An accurate measurement at the sensor can then be made. The 9219 does not have these remote sense inputs so you may have additional error with the 9219.
- Voltage Range: The Nominal Range of the 9237 is +/- 25 mV/V, while the 9219 has a Nominal Range of +/- 500 mV/V for the Half Bridge configurations and +/- 62.5 mV/V or +/- 7.8 mV/V for Full Bridge configurations.
- Quarter Bridge Completion: Both the 9237 and the 9219 have built in resistors for half bridge completion. However, the 9237 has additional accessories for quarter bridge completion, the 9944 and 9945 screw terminal blocks. These accessories provide either a 120 or 350 Ohm precision resistor for use when working with a quarter bridge strain gage.
The 9219 has no such accessory and cannot therefore complete the Wheatstone Bridge. For quarter bridge measurements, the 9219 must rely on 2-wire resistance measurements. It therefore, is not as accurate and does not suport 3-wire quarter bridge measurements.
In summary, the 9219 universal module is great if you want to perform basic strain measurements that do not require a high sampling rate and if your sensor does not have Sense+ and Sense- outputs built in for connection to remote sense lines. The 9219 offers application flexibility and the possibility of reuse in the future since it is capable of several other types of analog input. If you do need a higher sampling rate, your sensor does have Sense+ and Sense- outputs, or you are interested in quarter bridge strain measurements, the 9237 is recommended.
Related Links:
Products and Services: NI 9237Products and Services: NI 9219Product Manuals: NI 9944/9945 Quarter Bridge Completion Accessory User Guide (Sept 2006)
Attachments:
Report Date: 08/21/2007
Last Updated: 06/10/2009
Document ID: 4CKH1L4G
