Editing Instrumentation (section)

===Automatic process control===
[[File:Industrial control loop.jpg|thumb|Example of a single industrial control loop, showing continuously modulated control of process flow]]
In the early years of [[process control]], process indicators and control elements such as valves were monitored by an operator, that walked around the unit adjusting the valves to obtain the desired temperatures, pressures, and flows. As technology evolved pneumatic controllers were invented and mounted in the field that monitored the process and controlled the valves. This reduced the amount of time process operators needed to monitor the process. Latter years, the actual controllers were moved to a central room and signals were sent into the control room to monitor the process and outputs signals were sent to the final control element such as a valve to adjust the process as needed. These controllers and indicators were mounted on a wall called a control board. The operators stood in front of this board walking back and forth monitoring the process indicators. This again reduced the number and amount of time process operators were needed to walk around the units. The most standard pneumatic signal level used during these years was 3–15 psig.<ref name=Anderson>
{{cite book
 | last = Anderson
 | first = Norman A.
 | title = Instrumentation for Process Measurement and Control
 | publisher = CRC Press
 | edition = 3
 | pages = 8–10
 | year = 1998
 | isbn = 978-0-8493-9871-1
}}
</ref>