Lesson 4 - Process Instrumentation
This lesson takes a closer look at process instrumentation. Whilst it explores the basic operations of manual instruments, it primarily focuses on the instruments that can be used in process control. It also investigates in more depth the instrumentation commonly used within the brewery.
Position Instruments
Position instruments play an important role within control systems.
We will not cover these instruments in too much detail, as there are many different types. They range from very basic mechanical switches (often referred to as limit switches), to electronic switches, to intelligent instruments that can even pick up a specific tag (a tag is any form of identification that can be read by a device).
Proximity switches are the most common form of these instruments. They are widely used, especially to indicate whether pipe routes are correctly set up or whether valves are open or closed. They are also used as safety interlocks in cases where vessel manholes are opened, or when a machine guard on a machine is opened. It is important to understand what position they are really in and what will happen if they fail. Valves often only have one proximity switch, which means they will only indicate that the valve is fully open or fully closed; therefore a sticky valve may escape detection.
Figure: Comparison of position switches