ENTER COMPUTER-AGE PROCESS CONTROL

A modern computerized control room uses a Distributed Control System (DCS). The control hardware is DISTRIBUTED inside and outside of the control room.

Ground control to Major Tom.
Commencing countdown,
engines on.

("Space Oddity," by David Bowie, 1969)

COMPARING OLD AND NEW CONTROL ROOMS

The pictures in this PTOA Segment feature Control Board Operators at work in modern, computerized Control Room.

A modern, digitized Control Room has computers and computer screens and a Distributed Control System (DCS) of some type.

The word "distributed" is an accurate description; the hardware/software cabinets that rapidly relay data between the processing area and the Control Room are not necessarily located in the control room but rather distributed throughout the plant area.

A non-digital Control Room was featured in PTOA Segment #10. Each individual Controller, Indicator, Recorder or Alarm is mounted on panels that stretch across the length of the room.

The non-digital control room is much larger because each piece of control hardware is separately mounted into panels.

This Process Operator is recording a TI reading

No kidding! Behind each one of those Indicators, Controllers, Recorders, and Alarms are dedicated wires and components that relay information between the Control Room and the processing area.

Brilliant PTOA Readers and Students … meaning those who are reading the PTOA in the intended, sequential order … learned in PTOA Segment #2 that the Outside Process Operator in the nearby photo was recoding a reading from a local, field-mounted TI.

If that TI reading were to be "brought into the board" for the Control Board Operator to view, wires and components from the processing area to the control board would be required just to monitor that one process temperature.

HOW ARE THE COMPUTERIZED AND NON-COMPUTERIZED
CONTROL ROOMS ALIKE?

Both the modern and pneumatic type Control Rooms are currently in use in process industries.

Both types of Control Rooms use automated technology to centralize oversight of process status indicators, recorders, controllers and alarms.

Otherwise stated …

Functionally, both Control Rooms are identical.

Which means that in either type of Control Room, the Board Room Operator will interact with a Temperature Controller as described below. The Temperature Controller might be in an old-fashioned Control Room or in the latest DCS system:

1. Both Control Rooms are constantly receiving transmitted signals of some type from the processing area that represent the status of the PV Temperature of interest. Other controllers are receiving signals that relay the status of PV Pressure or PV Flow(rate) or PV Level.

2. The incoming signals from the field are converted into information and data that a human being can understand. That human being is a Control Board Operator.

Only when necessary, the Control Board Operator makes changes on the PV Temperature Controller to keep that process variable where it needs to be to make the desired products.

Spoiler Alert! Smaller changes made in the Controller's Automatic Mode will take more time to complete. Big, fast changes are made in Manual Mode … but are more disruptive to the entire process unit

This mom (Controller) is sending an output signal to the daughter using a signal that does not appear to be effective.

3.The adjustments that the Control Board Operator makes to the Temperature Controller are translated into an Output signal. The Output signal from the Controller is a command that the magnitude of the Temperature must increase or decrease.

4. The Output signal from the Temperature Controller is received by an Automatic Control Valve which is located in the processing area.

The Automatic Control Valve will either open a bit more or close a bit more to maintain Temperatures, Pressures, Flow(rates), and Levels where they need to be to make the desired products.

The nearby photo shows an Automatic Control Valve. PTOA Readers and Students will eventually learn all about ACVs! Stay tuned!

Take Home Messages: Both Distributed Control Systems (DCS) and non-digitized control rooms exist in processing facilities and PTOA Readers and Students might eventually work in either environment.

Both DCS and non-digitized control rooms centralize indicating, controlling, recording and alarming functions of automated process control.

Functionally, DCS and non-digitized control rooms are identical. The Control Board Operator/Controller interactions with input from and output to field instruments are identical in both environments.

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