"So much pressure in the air (I know, I know)"

("Can You Get Away?," by F. Beverly, Mosley, and Tupac Shakur, 1996)

A SMALL, PNEUMATIC CONTROL ROOM

The above picture shows a Control Room Operator in a useful but old-fashioned control room that is still in service.

This Boiler Control Process Operator is responsible for keeping the boiler on a college campus safely and reliably operating. The hot water generated by the unseen Boiler is distributed via a Hot Water Header to sinks and showers and radiators throughout the college campus.

Hot water is a utility, like electricity. Utilities are extremely important because the entity that is using them cannot work without them.

However, many public utility systems have older control rooms because it takes a lot of money to upgrade to modern digital control systems.

Furthermore, the historical demand for hot water on campus would be well documented. There is less incentive to upgrade to swanky controls when there is less need for the newest and fastest Process Control instrumentation

 

PNEUMATIC CONTROL ROOM HARDWARE

Control room hardware examples do not make interesting pictures. That being understood, PTOA Readers and Students can scrutinize the Boiler Room Control Room to understand the how the individual components fit into a Pneumatic Control Panel.

PTOA Readers and Students were introduced to the concept of "pneumatic control" in PTOA Segment #9.

To be more specific,

"Pneumatic Control" means the instrument is powered by Instrument Air Pressure that ranges from 3-15 psi.

 

Control Panel Pneumatic Controllers

Below the clock that is installed in  the Boiler Control Room is a rectangle and below that rectangle are three boxes with black lines crossing over them. .

Each of the three boxes contains an Indicating Controller of some type.

Eventually every controller fails. And when an individual controller has to be removed from the panel above it looks something like the photo to the right.

PTOA Readers and Students also learned in PTOA Segment #9 that Control Board Operators and Outside Process Operators control "Process Variables."

If the PV Temperature is being controlled, the device shown in the nearby picture is a TIC. PTOA Readers and Students learned in PTOA Segment #8 about TICs. A nearby photo shows the open door of a "local control" Foxboro brand TIC.

No doubt the many brilliant PTOA Readers and Student noticed how much different the Control Panel TIC looked compared to the Foxboro TIC that was installed out where the pumps and pipes are.

 

Control Room Annunciator Alarm Panels

To the left of the clock in the Boiler Control Room is an Annunciator Alarm Panel.

The Alarm Panel shown has several separate rectangles with writing on them. Each rectangle is wired to light up when there is unexpected process behavior in the vicinity of where the input to the alarm originates. Maybe the level in a tank is too low or too high. Maybe a pump stopped working.

A loud audible alarm sounds when any one of the rectangles are lit up.

The Control Room Operator will acknowledge the alarm by pressing a button that turns off the audible alarm. Then the Control Room Operator will ask the  Outside Process Operator to go and investigate the problem and report back on the status of the plant in the area that is experiencing a problem.

The nearby picture shows a different Control Room Operator acknowledging an alarm originating from an Alarm Panel.  The design of this Control Room wraps the Alarm Panels around the top of the Control Room.

The alarm will not stop buzzing until it is acknowledged by the Control Room Operator. The light on the annunciator/alarm panel will not go off until the problem out in the processing area is fixed.

Note that Annunciator Alarm Panels are "general" alarms.  The root cause of the problem will require a human being to investigate. An individual Indicator or Controller would target the problem in the processing area.  However, Pneumatic Control Panels did not have sufficient room for each desired Indicator or Controller that Process Operators desired to have installed in the Control Panel.

 

Control Room Process Variable Recorders

Find the Annunciator Alarm Panel once again. There are actually four Alarm Panels that are visible in this Control Room.

Below each Annunciator Alarm Panel is a spool of paper which is recording one or more Process Variables (PV Temperature, PV Pressure, PV Flow(rate), and PV Level).

If the recorder is documenting the PV Temperature, then this device is a Temperature Indicating Recorder (TIR).

Pneumatic Recording devices have continuously moving rolls of paper  (kind of like a cash register). Pens record the operating conditions while the paper moves beneath them. The roll of paper changes color toward the end, alerting the Control Board Operator to install a fresh roll.

The job of the Recoding Instrument on the Control Panel is to record the trends and histories of Process Variables.

Situating the Recorder below the Annunciator Alarm Panel makes sense! Gazing at a bump in the trend line will give a good hint where to start looking for the upset in the processing area.

Below is a photo of a TIR that could be found in the Boiler Room Control Panel.

The TIR mounted in the Control Panel sure looks a lot different than the TR that would be found in the processing area.

Although Pneumatic Control instruments will be found in process industries, the modern Control Room and Control Room Panel does not rely on pneumatics for automatic instrument control.

One Big Exception: Pneumatic Control will be necessary when a spark from electronics could cause a safety concern.

 

Take Home Messages:  "Pneumatic Control" means the instrument is powered by Instrument Air Pressure that ranges from 3-15 psi.

Pneumatic Control Rooms do exist in process industry but have been replaced by more modern methods of Automatic Process Control.  However, Pneumatic Control will be used in areas that need to be "instrinsically safe." That phrase means Pneumatic Control is warranted when there is a concern that electronics could cause a spark, and hence an explosive reaction.

Control room hardware...like controllers and recorders... look different from the local controllers and recorders but perform the same function. 

Alarm Annunciator Panels alert Control Board Operators that something is wrong in the processing area. The Control Board Operator must acknowledge the alarm to keep it from buzzing.  The Control Board Operator will instruct the outside Process Operator to investigate the problem. The Annunciator Panel light will not go off until the problem is fixed.

©2015 PTOA Segment 00010
Process Industry Automation

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