STRAIN GAGE SIMPLE BRIDGE CONNECTION FOR TORQUE

STRAIN GAGE SIMPLE BRIDGE CONNECTION FOR TORQUE

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Interconnecting the elements of shear strain gages on a shaft for torque measurement can be sometimes confusing - finding which grids are in tension and which are in compression, and how they should be wired together to form the full bridge for torque only.
In this video, a simple method is described that is easy to follow. The grids of the shear gages , seen from left to right or from right to left, will have the sequence of tension-compression-tension-compression, depending on the direction of torque application. regardless of the direction, the wiring shown in this video will work .
The strain gages shown in this video are micro Measurements type S036R shear gages, having independent solder tabs for each element. The two tabs in the middle are shorted to connect to P+ and P-. An easier gage to use is the 187UV gage from Micro Measurements, which has a common center tab for both the grids.
An identical , but smaller in size, is the 062UV gage, for small diameter shafts.
A set of 4 bondable terminals such as the CPF-75C from Micro Measurements are used for making the interconnections. These are labelled as P+, S+, P- and S-. These can be in any order, as long as each terminal is connected to the gage tabs as shown.

The sense of the output signal with respect to direction of torque can be easily changed, by inter-changing the S+ and S- connections, either at the bondable terminals or at the instrument input connections.
In this video, the gages are connected to a Model P3 Strain Indicator an recorder from Micro Measurements - a highly stable and accurate instrument. The response of the gages are as expected.
A static calibration is required to be done, by applying a known torque, and setting the sensitivity of the instrument to read the torque in direct engineering units of Kg-meter, Neuton-Meter etc.

All are welcome to contact us for further details or clarifications.
Please see the links :
P3 Strain Indicator: http://www.vishaypg.com/micro-measurements/instruments/p3-list/
Shear gages: http://www.vishaypg.com/micro-measurements/transducer-class-strain-gages/
StrainBlog: https://www.strainblog.com/