A quick question that I'm hoping someone here can help me with. What is meant by the nominal resistance of a strain gauge and exactly how does it affect how the gauge performs? I can find plenty on information on the commonly available nominal resistances of gauges but I can't find anything on exactly what it means and when you'd want to choose one over the other.

I need to choose an appropriate gauge for a project but the nominal resistance values have me confused.

Thanks in advance...

 

hi RM,
What is the project.?
ie: what are the specification requirements for the gauge output.?
E

 

Thanks for the quick reply. I'm building a device to measure the force put through the arm of a water crank. I haven't decided if I'm going to measure bending or shear strain yet, I'll probably try both and see which works better. I'm going to set the gauges up as a half bridge with two passive gauges for temperature correction.

 

hi,
OK.
The strain gauges I have used were completed load cell assemblies, either 350 Ohms or 1000 Ohms.
The nominal resistance value is the typical value, usually pulse/minus a very small tolerance.
If you are buying/using just the strain gauge elements, you should provide a method of nulling out any off load errors due to the small differences in resistance of the two elements.
For the passive resistor half of the bridge, use close tolerance high stability resistors.

If you post your final design, indicating the maximum mV signal output of the half bridge, we could use LTSpice to show the expected results
E

 

The nominal resistance of the gauge is simply the resistance of each gauge element under conditions of zero strain.

 

Thanks for the quick reply. I'm building a device to measure the force put through the arm of a water crank. I haven't decided if I'm going to measure bending or shear strain yet, I'll probably try both and see which works better. I'm going to set the gauges up as a half bridge with two passive gauges for temperature correction.

The nominal resistance of the gauge is simply the resistance of each gauge element under conditions of zero strain.

Indeed:

 

Micro Measurments (now part of Vishay) was a prime manufacturer of strain gauges and all the associated data and hardware. The link will get you to endless data about strain and how to apply strain gauges. Omega Engineering is another very good source for strain gauge data. Either will carry the gauges, data and resistors needed to complete the bridge.

Ron

 

Thanks everyone, you've been really helpful. One last question, when would you use a strain gauge of one resistance over another? I'm going to need to justify my choice of components. Thanks again

 

hi RM,
Not knowing your app, this PDF gives selection data.
Note page #13.

E

EDIT:
This is a very big PDF, but is comprehensive.
http://r.search.yahoo.com/_ylt=A7x9...ecsg.pdf/RK=0/RS=nk4K2EVrIL6Ap_UytoLKHnNh_5A-

 

Thanks Eric that's brilliant, a bit of bed time reading for me.
Thanks for everyone's help, it's appreciated.