The torque is measured either by detecting the actual deflection of the shaft caused by a torsional force, or by detecting the effects of this deflection. The surface of a shaft under torque will experience compression and tension, as shown in Figure 6-4. To measure torque, strain gauge elements are typically mounted in pairs on the shaft, an indicator that measures the length increase (in the direction that the surface is under tension) and the other that measures the length decrease in the Other direction.
The first torque sensors consisted of mechanical structures equipped with strain gages. Their high cost and low reliability prevented them from obtaining a general industrial acceptance. However, modern technology has reduced the cost of torque measurements, while production quality controls have increased the need for accurate torque measurement.
POWER
POWER is the measure of the amount of work that can be done in a given time. In the example of the Work and Energy page, the guy who pushed the car made 16,500 foot-pounds of WORK. If he did that job in two minutes, it would have produced 8250 foot-pounds per minute of power (165 feet x 100 pounds ÷ 2 minutes). If it is not clear about WORK and ENERGY, it would be a benefit to review those concepts HERE.
In the same way that a ton is a lot of weight (by definition, 2000 pounds), a horsepower is a lot of energy. The definition of a horsepower is 33,000 foot-pounds per minute. The power that the individual produced by pushing his car through the lot (8250 ft-pounds per minute) equals ¼ horsepower (8,250 ÷ 33,000).
OK, everything is fine, but how do you push a car through a parking lot referring to rotary machinery?
Consider the following change in the handle and crank drawing above. The handle is still 12 "from the center of the shaft, but now, instead of being attached to the wall, the shaft now traverses the wall, supported by frictionless bearings, and is attached to a generator behind the wall.
Suppose, as illustrated in Figure 2, that a constant force of 100 lbs. It is applied in some way to the handle so that the force is always perpendicular to both the handle and the handle when turning the handle. In other words, the "arrow" rotates with the handle and remains in the same position with respect to the handle and handle as shown in the following sequence. (This is called a "tangential force").