TABLE OF CONTENTS This chapter will help you understand the prime modes of signal transmission and familiarize you with the various methods of signal transmission and where they are used.
This chapter discusses the following:
Pneumatic signal transmission
Types of analog electrical signal transmission
Electrical to pneumatic signal converters
Thermocouple and resistive type devices and temperature signal transmission
The operation of the signal processor in signal transmission
Smart sensors and fieldbus
Programmable logic controllers (PLCs) and ladder diagrams
Telemetry signal transmission
Conversion of digital signals into analog signals for actuator control
Measurement of variables are made by sensors, conditioned by transducers, and then transferred to another location using a transmitter. In the case of process control, the accuracy of transmission of the value of the variable is very important; any errors introduced during transmission will be acted upon by the controller and will degrade the accuracy of the signal. There are several methods of transmitting data. The chosen solution will depend on the sensor, application of the signal, the distance the signal needs to be sent, the accuracy requirements of the system, and cost. Unfortunately, the accuracy of the system can be degraded by poor transmission.
The various methods of signal transmission are discussed in this chapter. Control signals can be transmitted pneumatically or electrically. Due to the needs of an air supply for pneumatic transmission, inflexible pluming, cost, slow reaction time, limited range of transmission, reliability, accuracy, and the requirements of control systems, electrical transmission is now the...
