TABLE OF CONTENTS This chapter will introduce you to instrumentation, the various measurement units used, and the reason why process control relies extensively on instrumentation. It will help you become familiar with instrument terminology and standards.
This chapter discusses
The basics of a process control loop
The elements in a control loop
The difference between the various types of variables
Considerations in a process facility
Units, standards, and prefixes used in parameter measurements
Comparison of the English and the SI units of measurement
Instrument accuracy and parameters that affect an instrument's performance
Instrumentation is the basis for process control in industry. However, it comes in many forms from domestic water heaters and HVAC, where the variable temperature is measured and used to control gas, oil, or electricity flow to the water heater, or heating system, or electricity to the compressor for refrigeration, to complex industrial process control applications such as used in the petroleum or chemical industry.
In industrial control a wide number of variables, from temperature, flow, and pressure to time and distance, can be sensed simultaneously. All of these can be interdependent variables in a single process requiring complex microprocessor systems for total control. Due to the rapid advances in technology, instruments in use today may be obsolete tomorrow, as new and more efficient measurement techniques are constantly being introduced. These changes are being driven by the need for higher accuracy, quality, precision, and performance. To measure parameters accurately, techniques have been developed that were thought impossible...
