Strain gages on the drive shaft for torque measurement

[wmcgonegal at rr.etc.ncr.doe.ca]

>There exist slip ring assemblies that allow one to gage up a drive 
>shaft. 

At out facility we have several torque measuring devices.  To get the 
excitation voltage to the rotating strain gage and the signal back to 
the signal conditioner, a non-contact rotary transformer is used.  One 
set of coils rotates near a stationary set.  Excitation voltage is fed 
through one set of coils and the signal voltage is fed back through 
another set.  The excitation voltage is an AC signal (3kHz).  The 
signal coming back to the signal conditioner is also AC with an 
amplitude proportional to the torque.

There are a few chassis dynamometers at our lab that have in-line 
torque transducers that use this type of set up to measure torque.  
The transducer is mounted between the dynamometer power absorption 
unit and the rest of the dynamometer.  There is also a car, here, 
equipped with "torque wheels" that uses rotary transformers to get the 
signals to and from the strain gages.  Instead of having the strain 
gage on the drive shaft, this car has an adapter plate that bolts 
between the hub and the tire (one for each of the drive wheels).  The 
plates have the appropriate strain gages so that torque can be 
measured.


Will McGonegal
Electrical Engineer
Mobile Sources Emissions Division
Environment Canada
wmcgonegal at rr.etc.ncr.doe.ca