USB 9219 strain gauge

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I am using the NI-9219 USB to measure very small forces from a strain gauge but I'm having some difficulty in choosing the appropriate strain gauge. I have been suggested two different ones from Vishay. I have attached the spec of the two strain gauges that have been suggested. Would you be able to recommend one or the other for use with the NI-9219 to measure the displaecement of a beam by forces in the range of 10⁻⁵ Newtons?

thanks,

Jamie

[KostasB]

You can use the first strain gauge (Resistance=350Ohm) in quarter bridge configuration as the 9219 has 350Ohm quarter bridge configuration (page 2 of the attached manual). The excitation for the sensor will be 150mV.

More info on how to take straing gauge measurements is at the following tutorial:

http://zone.ni.com/devzone/cda/tut/p/id/7130

KostasB

NIUK Applications Engineering

[cfm]

Thanks Kostas,

Would that be the best one to use then? I was under the impression that the higher the resistance the better to measure small forces?

thanks,

Jamie

[KostasB]

Hi,

this is correct but you will then need to use a full- bridge completion, so you will need 4 strain gauges. All of them will be active. This will result in the most accurate measurements. If you would use a high resistance strain gauge in quarter -bridge completion, the system would not be balanced, so for 0 strain you would still get some voltage on the output.

I hope that helps,

KostasB

NIUK Applications Engineering

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So for a full bridge configuration would each of the 4 strain gauges need to be powered and read seperately, using 4 serperate channels of the module?

Jamie

[KostasB]

No, you would still use one channel and the strain gauges will be powered from the same internal source. So for 4 strain measurements you need 1x NI-9219 and 16 strain gauges . See the attached connection diagram implementing full bridge completion on the 9219.

KostasB

NIUK Applications Engineering

Message Edited by KostasB on 06-12-2008 09:03 AM

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brilliant,

thanks very much Kostas