TABLE OF CONTENTS This chapter will help you understand and become familiar with other sensors that play a very important part in process control, but may not be encountered on a daily basis. The following are covered in this chapter:
Position, distance, velocity, and acceleration sensors
Rotation sensors using light and Hall effect sensors
Force, torque, load cells, and balances
Smoke detectors, gas, and chemical sensors in industry
Sound and light measurements
Sound and optical devices
There are many sensors other than level, pressure, flow, and temperature that may not be encountered on a day to day basis such as position, force, smoke, and chemical sensors but play an equally important part in process control in today's high-technology industries and/or for operator protection. These sensors will not be discussed in as much detail as the sensors already discussed. However, the student should be aware of their existence and operation.
Many industrial processes require both linear and angular position and motion measurements. These are required in robotics, rolling mills, machining operations, numerically controlled tool applications, and conveyers. In some applications it is also necessary to measure speed, acceleration, and vibration. Some transducers use position sensing devices to convert temperature and/or pressure into electrical units and controllers can use position sensing devices to monitor the position of an adjustable valve for feedback control.
Absolute position is the distance measured with respect to a fixed reference point and can be measured whenever power is...
