"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 (Pneumatic) Control Room that is still in service.  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.

The funny thing about utilities is that they are essential, yet hardly ever get the attention they need. Many public utility systems have older control rooms because it takes a lot of money to upgrade them to modern, digital control systems.

Furthermore, the historical demand for hot water on a college campus would be easy to predict. There is less incentive to upgrade to swanky controls when the process ... like generating hot water ...  is easy to control.

 

PNEUMATIC CONTROL ROOM HARDWARE

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

To recap:

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

PTOA Readers and Students can scrutinize the nearby photo of a Boiler Room Control Room to understand the how the individual components fit into a Pneumatic Control Panel

Find the Pneumatic Controllers
in the Control Panel

Below the clock that is installed in the Boiler Control Room is a rectangle.

Below that rectangle are three boxes which appear at first glance to be bisected with black lines. These are board-mounted Pneumatic Controllers.

Eventually every Pneumatic Controller fails.  And when an individual controller has to be removed from the panel, it looks like the nearby photo of a Pneumatic Indicating Controller.

The descriptor "indicating" means that the Control Board Operator can easily observe the current value of the Process Variable that is being controlled.

Oops!

Fred is confused by the term "Process Variable." Fred, you need to reread PTOA Segment #9 to remember that the term "Process Variable" applies to the PV Temperature, PV Pressure, PV Flowrate, or the PV Level.

PTOA Readers and Students also recently learned in PTOA Segment #8 that "T" is used when the PV Temperature is being controlled.

Assume that the Pneumatic Controller unit above is a TIC, a PV Temperature Indicating Controller. The Control Board Operator could easily read the current value (and recent history) of the PV Temperature that is being controlled by viewing the indicated temperature that the recording pens have drawn on the paper.

The nearby photo is a Foxboro brand Pneumatic Indicating Controller.  Assume the PV being controlled is Temperature which would mean this is also a TIC.

This Foxboro pneumatic TIC model would be located out "in the field," meaning amongst the pumps and pipes ... and perhaps a Boiler.

The door to the "local control" Foxboro brand TIC is open. Each of the hardware components shown plays an important role controlling the PV Temperature.

Both of the Pneumatic Indicating Controllers shown perform the same job, albeit they look very different.

 

Find the Annunciator Alarm Panels
in the Pneumatic Control Room

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.

For example, maybe the level in a tank is too low or too high. Maybe a pump has 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.  Historically, 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.

 

Find the Process Variable Recorders
in the Control Room

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 rotating 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.

 

Your Mentor is old enough to have worked with Pneumatic Controllers and instruments. PTOA Readers and Students will next learn how Control Rooms have been modernized to become more efficient with computers and digitization.

One Big Exception: Pneumatic Control will still be necessary in process services that require a spark free, intrinsically safe environment.

 

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 "intrinsically 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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