TABLE OF CONTENTS There are many sensors other than those used for measuring fluid characteristics required in process control, and which are equally important. This chapter covers many of the varied sensors used to monitor position, motion, force, and light. The sensors discussed in this chapter include magnetic sensors, light sensors, accelerometers, ultrasonic sensors, load cells, and torque sensors.
Many industrial processes require information on and control of both linear and angular position, and rate of motion. These are required in robotics, rolling mills, machining operations, numerically controlled tool applications, and conveyers. In some applications, it is also necessary to measure and control acceleration and vibration. Some transducers use position-sensing devices to convert temperature, level, and/or pressure into electrical units, and controllers can use position-sensing devices to monitor the position of an adjustable valve for feedback control.
Position measurements can be absolute or incremental, and can apply to linear motion or angular motion. A body can have a constant velocity, or the velocity can be changing, in which case the motion will have an acceleration.
Potentiometers are a convenient cost-effective method for converting the displacement in a sensor to an electrical variable. The wiper or slider arm of a linear potentiometer can be mechanically connected to the moving section of a sensor. Where angular displacement is involved, a single or multiturn (up to 10 turns) rotational type of potentiometer can be used. For stability, wire-wound devices should be used,...
