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Plant Wide Controller (PWC)

Application | Overview | Features

The Plant Wide Controller is a state-of-the-art equipment sequencing, control and monitoring system.  It combines innovative ease of operation, communication and expansion capabilities with boiler plant control application expertise.


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Plant Wide Controller (PWC)
Plant Wide Controller (PWC)

  • Application

The PWC can be configured for an unlimited number of control applications. These configurations are the most common:

Lead/Lag Controller for Improved Steam or Hot Water System Availability: Automatic Sequencing ensures that the number of boilers in service meets hot water or steam demand.  Tripped equipment is automatically replaced with a standby unit.

Boiler Monitoring: Flue gas temperature, smoke opacity and boiler draft may be monitored and trended.  Warning alarms and burner safety shutdown interlocks may be included.

Unmanned Boiler Plants: Provides for off-site monitoring and control using internal modem or RS485 interface.  Serves as a  single plant monitoring point for Building Automation Systems and personal alphanumeric pagers.

Cooling Tower Optimization: Multiple Tower Cells are sequenced and fan speed controlled with wet bulb optimization.  Substantial fan and chiller electrical savings can be realized.

Improved E-Gen Fuel System Availability: Fuel pump standby sequencing, day tank level control and fuel storage tank level and leak monitoring.

Improved Steam System Availability: Condensate transfer and feed pump standby sequencing, Deaerator and Surge tank level monitoring, alarm and remote communications.

Coordinated Hot Water System Operation: Pumps, isolation valves, distribution pumps and temperature monitoring for reduced thermal stress and energy consumption.

Fresh Air Dampers, Air Compressors and Fans: Sequencing, monitoring, and control are based on the number of boilers online.  A single damper failure will not prevent a boiler from firing.

Custom configurations are available to suit virtually any application. 

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  • Overview

The Plant Wide Controller (PWC) is a state-of-the-art equipment sequencing, control and monitoring system.  The PWC combines innovative ease of operation, communication and expansion capabilities with boiler plant control application expertise.  Off-the-shelf, standard applications for boiler modulating lead/lag, cooling towers and air compressors can be expanded to include additional monitoring or control additional pumps, variable speed drives and valves.  Multiple communication protocols allow simultaneous communication to alphanumeric pagers, laptops via standard telephone lines and Building Automation System or SCADA Systems using a control network.  The PWC is a complete plant monitoring, control and communication interface.

Easy Installation: The PWC integrates a powerful Programmable Function Controller (PFC), I/O boards, hardwired and LCD HMI, power distribution, 24VDC power supplies, external communications, isolation relays into a single wall mountable controller.  No external control devices are required.

Easy to Operate: Large LCD Display, intuitive operation, setup, alarm / event summary and historical trend displays allow quick process assessment and maintenance monitoring.

Easy to Configure: PWC configuration tools maintain the look and feel of the PCC-III and offer advanced features.  The PWC uses an intuitive “Blockware” configuration language with multiple block outputs and special purpose “Super” blocks that greatly simplify complex logic such as Outdoor Air Reset and boiler sequencing.


Blockware: The PWC uses an intuitive “Blockware” configuration language.  Functions (AIN, PID, LOALM, F(x)... ) are simply copied into a configuration, and then the control signals are “wired” from block to block.  Preferred’s innovative PWC_Draw™ for MS Windows® uses a graphical, “drag and drop” interface.  It allows the user to print or plot Blockware drawings, and then download them to a PWC via a standard RS232 port.  Additionally, Blockware and displays may be edited from the spreadsheet style PWC_Edit™.

Multiple Block Outputs: Using the Analog Input Block’s “BAD” data quality output a user may switch a loop to manual control or initiate an alarm.  The PWC display and any block can access all block outputs.  Other available outputs include cold junction temperature, input is out of normal range,  pulser is missing pulses, input type selector switch position does not match the input type, etc,.

Super Blocks: The PWC provides a collection of special function “Blockware” to enable simplified implementation of complex control strategies.  The function Outdoor Reset Setpoint [ORSP] is used to save energy by changing a setpoint based on the outdoor air temperature.  A typical application is to use the ORSP to generate the Hot Water Setpoint for a Hot Water Heating System.  Another important energy savings block is the Scheduler block.  The Time/Date Scheduler [SCHED] compares the current Time and Date to the schedule defined by the entered parameters, and sets the schedule output to “1” during the “Normal” period, and to “0” during the “Setback” period.  Typically this function is used to conserve energy during low occupancy periods.  It can be used to “setback” hot or chilled water temperature setpoints, activate outdoor lighting, and other time or day of week, or date based control logic.

LCD Display Commissioning: Plant Wide Controller configurations are designed to allow commissioning to be accomplished from the controller mounted displays.  Project specific tuning displays may be created to present and group key “Blockware” parameters for field tuning.  Additionally, any block parameter may be edited from the front panel display using the “Parameter Edit” mode.  Laptop computers are only required when it is necessary to change wiring between blocks or add additional blocks. 

PWC_Edit™: The “point and click” simplicity of the PWC_Edit software makes “Blockware” configuration simple and intuitive.  The program uses a straightforward spreadsheet format with a convenient fill-in-the-blanks approach.  Each Block has an unlimited length “comments” field for clear documentation.  The “Blockware” data and comments can be printed to any MS Windows® compatible printer.  PWC_Edit offers fill-in-the-blanks style display generation.  Display text can be presented as either regular or bold.  Dynamic-text, softbuttons, status, numeric values, time values and alarms may be added to any display.  The Chart Edit display allows configuration of trace and chart selections using a menu style system.  The generated configurations are then easily downloaded using a standard RS232 DB9F cable.

PWC_Draw™: The powerful object-oriented CAD interface in PWC_Draw makes the program the ideal choice for rapid “Blockware” programming in a visual environment.  The program is built on a Visio® platform with extensive Visual Basic automation.  Standard functions are included in menus of pre-drawn figures for each PWC Blockware Function Type.  Functions are simply dragged onto the drawing page and connected with “Smart Connector” lines to interconnect the Blocks.  Block inputs are automatically generated by placing the Block connections.  Double clicking on any block allows the user to edit data within the Block.  Drawings can be saved as AutoCAD® drawings and can be printed on any MS Windows® compatible printer or plotter.  “Blockware” data can also be printed in the PWC_Edit tabular format. 

Historical Trend Display

Each Chart can display up to 4 traces, called ‘Pens’.  The bottom of the screen shows the symbol and name of each Pen.   Charts can be a mixture of analog and discrete data.  A specific chart is displayed by selecting a Menu line that is linked to the chart.  The PWC can save up to 32 analog values plus up to 32 discrete values every 1, 5, 15, or 60 seconds in the 32 Mb non-volatile memory.  The 32 Mb Historical Memory can store up to 1-6 months of data (number of points monitored, sample interval, and data compression ratio affect duration).

Pen Selection: Each "Pen" trace has a unique name, chart scale, and engineering units.  However, only one Pen Scale can be displayed at a time. The Up and Down Cursor Arrows may be used to display the desired Pen Scale.

Chart Cursor Readout: When a chart is first displayed, the Chart Cursor is located at the right hand edge of the screen.  Using the Numeric keypad Arrows the operator may move the Chart Cursor.  The number on the top line of the screen is the value of the currently selected Pen trace where it touches the Chart Cursor. Use the Cursor Up and Down Arrows to display the values for the other Pens.

Start Time Panning: Use the Cursor Left and Right Arrows to shift the Start Time backward or forward in time.  The time is shifted 7/8 of the span to provide chart display overlap. 

Changing Chart Span: Using the PAGE UP and PAGE DOWN keys, the operator may change the Chart Span between 8 minutes, 40 minutes, 2 hours, 8 hours, or 24 hours.

‘Span’, Start Time and Date Selection: When a Chart is selected, the first screen that appears is the “Setup Display.”  This display allows the operator to easily select “Span” (width), Start Time and Date. This screen defaults to the current time and date with a 40 minute wide chart.


Telephone Modem: The internally mounted Telephone Modem permits the PWC to “dial out” to an alphanumeric pager and allows a user to “dial in” to the PWC to view all displays and make tuning adjustments.  Selected alarms cause the modem to dial a pager service center telephone number.  A 20 digit phone number can include outside line codes, access codes, and pauses.  The modem uses the TAP protocol to send a text message to an alphanumeric pager. The message can include a 30-character facility name plus a 20-character alarm message.  Upon receipt of the page, the user can “dial in” to the modem to acknowledge the message. If the system does not receive a dial back acknowledgement or front panel Alarm Silence button “press” within 5 minutes (adjustable), the system will dial a second backup pager and re-send the alarm message. The system will log the time and date of all pages and acknowledgments in the Alarm/Event List.  Using PWC_Remote™ software, which is included with the Telephone Modem (option p/n 190604), a remote user is able to “dial in” to the modem to view any screen and remotely “press” any keypad button just as if they were standing in front of the controller. PWC_Remote™ software running on the user’s personal computer can “dial in” to any PWC site, and does NOT require site specific programs or custom configurations.

Control Network: The PWC includes an RS485 Modbus port to communication with Building Automation System (BAS), Building Management System (BMS) or Supervisory Control and Data Acquisition (SCADA) systems.

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  • Features
  • Programmable Function Controller (PFC)
  • Hardwired Panel
  • Easy To Configure


Case Size: 16½" H x 14½" W x 6¾" D

Enclosure Type:  Wall Mounted

Case: 7 Slot, (CPU + 6 I/O Slots)

Weight: 55 lbs


Operating Temp: 32° to 122° F (0° to 50° C)

Storage Temp: -20° to 150° F (-28° to 65° C)

Humidity Limits: 15 to 95% (non-condensing)

Enclosure: NEMA 1


Accuracy: 0.025% Analog I/O

Resolution: 16 bit input/12 bit output

Microprocessor: 32 bit, 128k EEPROM

Execution Cycle: Five per second

Time/Date Clock: (battery backed)

Operator Control Panel

LCD Graphic Display:  2.9" H x 5.1" W

Keyboard: Membrane, tactile feedback

Historial Data (Optional)

Displays: 8 or 40 minute; 2, 8 or 24 hour charts

Memory: Non-Volatile, 32 Mb.  48 points every 15 sec for 30 days, or greater with datacompression

Standard Lead/Lag: Menu style, “Fill-In-The-Blanks” setup.

Control Language: Function block style, 60 functions, 600 Blocks

Security: 2 password levels

Custom Blockware Configuration Software: PWC_Edit™ spread sheet based or PWC_Draw™ graphical, editor (Windows PC Required).


Control Network

Protocol: Modbus (ASCII or RTU mode)

Speed: 1200 to 38,400 baud

Type: RS485, optically isolated

Telephone Modem: Internal Card 33,600 baud, RJ-11 Jack, Data and Pagers

Printer Port: Alarms/Logs, DB25F connector

Programming Port 

Speed: 9600 to 38,400 baud

Type: RS232, DB9F connector


Input Power: 120 VAC (+/- 15%), 12A total, 0.7A internal Built in surge suppressors

Internal Power Supply:24 VDC @ 300 mADC for external use

Input/Output Specifications

CPU Board

Analog Inputs: Quantity, 2; Type, 4-20 mADC or -20°F to +300°F Thermistor

Relay Output: Quantity, 5; Type, SPDT, 8A, ½ HP, 120VAC

Hand-Off-Auto Relay Output (HOA-ROUT) Board

Relay Output: Quantity, 5; Type, SPST, 8A, ½ HP, 120VAC

Toggle Switches: Quantity, 5 Type, Hand-Off-Auto (hard wired) SPDT, 8A, ½ HP, 120VAC

LED Indicators: Quantity, 10; Type, “Call for Operation” and “Output Status”

Auto/Manual Analog Output (A/M-AOUT) Board

Analog Output: Quantity, 5 Type, 4-20 mADC or 0-135 ohm (any combination)

Toggle Switches: Quantity, 5; Type, Auto-Manual 

Control Dial: Quantity, 5; Type, 0-100% (Manual Potentiometer)

Bargraphs: Quantity, 5; Type, 0-100%, 10 segment

Discrete Input (DIN) Board

Digital Inputs: Quantity, 15; Type, 120 VAC, optically isolated

LED Indicators: Quantity, 15; Type, Status Indication

Analog Input (AIN) Board

Analog Input: Quantity, 8; Type, Universal, Switch Selectable as: 4-20 mADC, 2 wire Thermistor, -20°F to 300°F, Thermocouple Type J, 0-1200° F, 0-5 VDC, or Potentiometers Pulse, 0.01 – 4000 Hz, 0-15 VDC

LED Indicators: Quantity, 8; Type: Status Indication

Relay Output (ROUT) Board

Relay Output: Quantity, 8; Type, (2) SPDT, (6) SPST-NO, 8A, ½ HP, 120 VAC

LED Indicators: Quantity, 8; Type, Status Indication

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