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Preferred Instruments

Preferred Instruments manufactures microprocessor based controllers, instruments, and electric actuators for combustion and process applications. Preferred Instruments also manufactures oil tank gauging and leak detection equipment. A major component of the Instrument group sales is from control systems integration and personal computer based Supervisory Control and Data Acquisition systems. Preferred Utilities' industrial factory is located in Danbury, CT

Chief Dispatcher Boiler Plant Master Control System

The Chief Dispatcher boiler plant master provides lead lag control for up to ten boilers. It monitors a common steam header pressure or hot water temperature transmitter and provides on off, and modulating control of burner firing rate.


The Chief Dispatcher plant master optimizes boiler plant performance and helps extend boiler life for Cast Iron Sectional, Finned-Tube, Firebox, Flexible Tube or Firetube boilers . It can be applied to steam plants, hot water plants, and to hot water plants with condensing hot water boilers.

The Chief Dispatcher brings on the optimum number of boilers to meet plant demand, and optimizes the firing rate of each boiler to minimize fuel consumption.

 It communicates with the building or facility via Modbus, Ethernet (with converter) and can dial an alphanumeric pager.


The Chief Dispatcher is an advanced boiler sequencing, communication and monitoring system. The Chief Dispatcher combines innovative ease of operation, communication and expansion capabilities with boiler application expertise. Off-the-shelf, standard modulating lead/lag applications can be expanded to control circulating water variable speed pumps and isolation valves while monitoring the flame safeguard and boiler control systems. Multiple communication protocols allow simultaneous communication to alphanumeric pagers and the Building Automation System or local devices.

“Smart” Boiler Sequencing: Boilers are automatically sequenced on/off to ensure that the number of boilers in service meets hot water demand. If any boiler fails to start when called, or if a boiler trips during operation, the Chief Dispatcher immediately starts another boiler to replace the “Faulted” boiler. The operator may manually select the Lead boiler or allow the Lead Boiler to rotate automatically. Additionally, the total number of boilers in service may be set automatically or manually as selected by the operator or all boilers may be shutdown by a Building Automation System “Enable/Disable” contact input.

“Hard Manual” Backup: Hard wired control switches and dials provide simple manual control for easy troubleshooting and service. Each boiler has an individual firing rate bargraph, “Manual” firing rate output knob, and “Auto/Manual’ switch.

Modbus Communication Interface: A factory configured RS485 Modbus interface is available for Building Automation or SCADA system monitoring and control.

Building Automation System: A remote Hot Water Supply (HWS) temperature setpoint is set by either a Modbus or 4-20 mADC Building Automation System (BAS) Outdoor Reset input signal.

Historical Trending: Easy to use four pen charts allow quick system assessment and maintenance monitoring such as hot water temperature and boiler operating hour trends. Up to 32 analog values plus up to 32 discrete values can be stored every 1, 5, 15, or 60 seconds. The historical memory can store 1 to 6 months of data (number of points monitored, sample interval, and data compression ratio affect duration).

Firing Rate Output: Boiler Firing Rate Analog Output Cards may be ordered as ‘-P’ = 0-135 ohm or ‘-I’ = 4-20 mADC.

Telephone Modem: The internally mounted Telephone Modem permits the Chief Dispatcher to dial out to an alphanumeric pager and allows a user to dial in to the Chief Dispatcher 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 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. Using PWC_Remote™ software, which is included with the Telephone Modem, a remote user is able to “dial in” to the modem and 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 Chief Dispatcher site.


  • Steam, Hot Water, and Condensing Hot Water Boiler Control
  • Pre-engineered for quick delivery and affordability
  • Communicates to alphanumeric pagers and Building Automation Systems


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 Temperature: 32° to 122° F (0° to 50° C)

Storage Temperature: -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

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

Memory: Non-Volatile, 32 MB. 48 points every 15 sec for 30 days, or greater with data compression


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 (optional): 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%), 12 A total, 0.7A internal Built in surge suppressors

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


Note: the following specification pertains to the JC-CDHW hot water boiler version of the Chief Dispatcher. Click the “Contact Us” or “Find a Representative” link to discuss your application with a boiler controls engineer and obtain the right specification for your project. 

1. Application

Supply a fully integrated boiler control system to coordinate the operation of two (select up to ten) fully modulating hot water boilers in order to maintain the Hot Water Supply (HWS) temperature at setpoint. The control system shall be microprocessor-based and suitable for wall mounting.

2. Boiler Modulation

The control system shall incorporate a HWS header temperature PID control scheme. Boilers shall be modulated in “Unison” (all at the same firing rate). Modulation signals shall be 4-20 mADC or 0-135 ohm (as required by the boiler) and shall be electrically isolated channel-channel and channel-ground.

3. Hot Water Supply (HWS) Temperature Setpoint

When the HWS Temperature control loop is in the “automatic” mode, the control system shall establish the HWS temperature setpoint based on the time of day, day of the week and the outside air temperature. When in “manual” mode the operator may set the HWS temperature via a front panel display. All temperatures and time/date data must be field adjustable through “fill-in-the-blanks” style displays. Alternately, the control system shall accept a 4-20 mADC outdoor air temperature reset setpoint signal from an external Building Automation System (BAS).

4. Boiler Sequence

The control system shall utilize both HWS temperature and boiler firing rate percent to start and stop the boilers and shall minimize the total number of boilers in operation. The controller shall start and stop boilers when the HWS temperature is outside the adjustable temperature limit for longer than the adjustable time delay. In order to minimize header temperature deviations, the control system shall start and stop the next boiler when the “lead” boiler is at an adjustable firing rate limit for longer than the adjustable time delay. The control system shall monitor both boiler lockout and limit circuits to automatically skip over those boilers that are powered down for maintenance, tripped or otherwise will not start. The lead boiler shall either automatically rotate on a time of day, day of week (or month) schedule, or shall be manually selected by the operator. The boiler shall be run at low fire for warm-up for a preset low fire hold time. The base load ramp rate shall be field adjustable. The Control System shall reduce the firing rate to a minimum before stopping a boiler to prevent accumulation of fuel in the furnace.

5. Operator Controls, Trends, Indications and Alarms

The control system shall include a 16 line x 40 character (or greater) LCD display for boiler sequence control and status, alarm and event summaries, and setup menus for easy operation, tuning and troubleshooting. Alarms, events and operator actions shall be logged with Time/Date stamp and English language description. The control system shall include a minimum of 200 point memory. The control system shall include a minimum 100 x 150 pixel historical trending display or paperless chart recorder or other videographic hardware to permit the logging of at least 32 data points for at least 45 days. Provide a minimum of 4 “pens” per chart with 8 minute thru 24 hour chart “width” selections available.

6. Reliability

Include hard wired backup stations to permit manual operation of the plant should the control system require service. Manual operation must be possible when the microprocessor is not functioning. Hard wired “Hand-Off-Auto” control switches must be wired directly into every boiler and pump Start/Stop circuit. Each 4-20 mADC or 0-135 ohm modulating control output must include a hard wired manual backup station with Auto/Manual switch, output control knob and output level indicator (bargraph, analog meter or digital display).

7. Communication

The Control System shall have the ability of simultaneously communicating to a Data Acquisition System (DAS), Building Automation System (BAS) or Building Management System (BMS) via RS485 Modbus protocol and to a Personal Computer and an alphanumeric pager via standard telephone lines. The individual boiler limits, lockout, start/stop, warm standby, and firing rate status shall be readable. Header setpoint, plant firing rate, boiler quantity called to start, boiler selected as lead and all setup parameters shall be readable and writable.

8. Quality Assurance

The control system shall be manufactured and labeled in accordance with UL508 requirements (CSA C22.2 #14 for use in Canada). Inspection and labeling shall be supervised by UL or other OSHA approved Nationally Recognized Test Lab (NRTL). The control system shall be a Preferred Instruments, Danbury, CT,