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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

UtilitySaver Boiler Retrofit Controller

The UtilitySaver Burner Control System is designed to minimize total energy consumption of a burner (both fuel and electricity usage). UtilitySaver combines the fuel savings of an Oxygen trim system with the electrical kWh savings of a Variable Speed Drive (VSD) FD fan. UtilitySaver is intended for installation on an existing burner with either a Jackshaft or parallel positioning combustion control system.


The UtilitySaver is the ideal retrofit controller for customers that want to add oxygen trim and VSD control to their boiler control system, but want to retain their existing flame safeguard system. It installs quickly and easily, reducing installation cost and maximizing the payback from efficiency improvements.

Customers that want to modernize their flame safeguard controls as well should see the BurnerMate Universal, Preferred’s new linkageless controller that combines flame safeguard, parallel positioning with oxygen trim control, and VSD control.


Our UtilitySaver Burner Control System is designed to minimize total energy consumption of a burner (both fuel and electricity usage). UtilitySaver combines the fuel savings of an Oxygen trim system with the electrical kWh savings of a Variable Speed Drive (VSD) FD fan. UtilitySaver is intended for installation on an existing burner with either a Jackshaft or parallel positioning combustion control system.

Standard Equipment:

  • UL Labeled, Wired and Tested Control Panel
  • PCC-III-ZG00 UtilitySaver Controller
  • VSD – FSG Interface Relays
  • ZP-20 Oxygen Probe
  • ZP Oxygen Probe Mounting Kit
  • Flue Gas T/C Assembly
  • Air Damper Actuator
  • Air Damper Mounting Kit
  • Fuel Valve Actuator
  • Variable Speed Drive
  • VSD Fuses
  • Field Wiring Kit
  • Instruction Manual

Optional Equipment:

  • VSD Full Speed Bypass
  • Pressure Transmitter
  • Temperature Transmitter

Maximum Electrical Savings: UtilitySaver maximizes VSD electrical energy savings by keeping the FD fan damper(s) 100% open from high fire down to approximately 30% firing rate (field adjustable). From 30% firing rate down to minimum fire, the damper ramps from full open to partially closed to assure maximum burner turndown is achieved.

Energy Efficient Burner Control: It is well known that VSD controlled variable speed fans provide significant electrical savings compared to fixed speed fans with a damper. In most cases, the annual electrical cost savings due to the VSD are approximately the same as the annual fuel cost savings due to the Oxygen Trim. Therefore, One UtilitySaver control system provides twice the annual savings, achievable with application of only O2 Trim or a VSD.

Internal Proportion Integral and Derivative (PID) Control Option: The firing rate is determined by a pressure or temperature transmitter, the setpoint (determined by the operator), and a PID control block. PID control ensures that the required setpoint is reached without “offset” (setpoint deviation).

Manual Air Trim Capability: Manual Air Trim Capability with automatic adaptive gain.

Integral Oxygen Analyzer Diagnostics: Specific diagnostic codes for rapid trouble shooting. Continuous cell impedance checking for cell health prediction.

Oxygen Trim Delayed: Oxygen trim is delayed for a period after light-off (adjustable) to allow stack Oxygen to stabilize.

Simple Auto/Manual Control: The Operator has a simple “Demand Auto/Manual” station on the front of the controller to allow Automatic or Manual control of the burner firing rate. In Automatic, UtilitySaver uses the existing 0-135 ohm (or 4-20 mAdc) firing rate control signal to modulate the burner firing rate. In Manual, the Operator uses the PCC-III “Up” and “Down” arrows to set the desired 0-100% firing rate.

Lightoff Position: Lightoff position is adjustable for wide turndown burners.

Fuel-Air Lead/Lag: The UtilitySaver’s “Electronic Jackshaft” control logic links the Fuel Valves, Damper, and VSD speed together. To provide low CO (gas) and smokeless (oil) load changes, the air increases before the fuel on a load increase, and the fuel decreases before the air on a load decrease.

Easy Commissioning Using “Learn Mode”: F(x) Characterizer curves are set up by manually positioning fuel and air for safe and reliable operation and optimum Oxygen level and then pressing the “STORE” button. Air and Oxygen Setpoint curves are simultaneously setup. This process can be repeated for a maximum of 11 load points. Independent curves for each fuel are automatically selected.

Automated Purge & Light-Off: The air and fuel automatically drive to purge and light-off positions under flame safeguard system direction. VSD “at speed” contact interlocks burner purge and light-off limits.

Modbus Communication Interface: An easy to setup RS485 MODBUS interface is available for off-site monitoring and control.

Commissioning Software: The PC3_Setup Commissioning Software is included with every UtilitySaver Burner Control. The PC3_Setup Commissioning Software is MS Windows compatible. The software uses an automated step-by-step procedure to assist the service technician with the setup of the fuel and air actuators, ZP Oxygen Sensor, variable speed drive and fuel/air profile. The Software is not required for operation, it is only required during commissioning, calibration and tuning. Using the PC3_Setup Commissioning Software is a step-by-step procedure.  Individual “Tasks” are selected and “Run” by “pressing” the “Run” pushbutton. When each task is initiated, a series of steps are carried out and the user is prompted as required.


  • Minimum Fuel And Fan Power Usage
  • Improved  Availability with Full Speed Bypass
  • Real Time Boiler Efficiency Display


Controller: PCC-III-ZG00

Input Power: 120 VAC (+/- 15%)

Actuator Power: 24 VAC

Enclosure: 16” H x 14” W x 10“ D, NEMA 12 Wall Mounted


Drum Pressure: 4-20 mADC (optional)

Flue Gas Temperature: T/C

Flue Gas Oxygen: ZP Probe

Plant Master: 4-20 mADC

Fuel Actuator Feedback: Potentiometer

Air Actuator Feedback: Potentiometer

VSD Speed Feedback: 4-20 mADC


Boiler Efficiency: 4-20 mADC

Fuel Valve Actuator: Triac

Air Damper Actuator: Triac

VSD Speed Demand:  4-20 mADC

In-Situ Oxygen Sensor, Model ZP

Insertion Length: 20, 30, 45, 65, 90″ Probe

Flange: 3″ 125 lb

Mounting Kit (190680): Flanges, nipple, coupling, gasket, bolts, nuts and washers, calibration tubing, compression fittings and isolation valve

Signal Cable Kit (190681)

ZP Cable: 70 ft of 7 conductor wire cable for ZP probe

T/C Cable: 70 ft of type J T/C shielded cable

Triac Output Cable: 100 ft of 3 wire shielded cable

Load Sensor Cable: 50 ft of 2 wire shielded cable

Boiler Efficiency Kit (104087C)

Efficiency: ASME “by losses” method efficiency configuration

T/C: Flue Gas Temperature Assembly, 104087D, with mounting flange


Fuel: SM series

Air: SM series

Mounting Kit (190682): Right angle mounting bracket for Damper Actuator, (3) Lever Arms, (4) ball joints, (2) 12″ threaded Links


Application: Supply a self contained Boiler Control System to provide both electricity and fuel savings within the limits of stable burner operation. The control system shall be microprocessor-based and suitable for wall mounting. All the logic required to ensure that pre-purge, postpurge, light-off, and burner modulate cycles are automated shall be provided.

Combustion Control: A parallel positioning control strategy shall position the fuel valve, combustion air damper and forced draft fan speed for minimum fan kWh usage, and shall continuously trim the fuel/air ratio based on measured flue gas Oxygen levels for minimum fuel consumption.  Systems that control forced draft fan speed based simply on burner windbox pressures are not acceptable. The system shall position the fuel and combustion air final control elements’ movement and VSD speed with “Position Feedback Cross-Limiting” to ensure that a safe fuel/air ratio is maintained under all load change conditions. Fuel/air ratio shall be established and adjusted by the use of a “soft” function curve relating fuel valve position to air damper position. Oxygen trim shall be accomplished by varying the fuel/air ratio and shall include separate characterizable Oxygen setpoint curves for both oil and gas fuels based on firing rate, and adaptive gain adjustment as a function of firing rate.  Fuel valve and air damper shall be modulated in response to an external Plant Master demand signal (existing or by others) or measured boiler drum pressure (or temperature) compared to setpoint.  At a minimum, the control system shall display the following: Boiler Firing Rate, Boiler Efficiency, Trim %, Flue Gas Oxygen Setpoint, Flue Gas Oxygen, Fuel Valve Position, Air Damper Position and VSD Speed. The control system shall include a dedicated, normally energized, fail safe relay output contact in the “running” interlock circuit of the flame safeguard that will cause a fired equipment shutdown in the event of: low Oxygen,  air damper actuator fault,  fuel valve actuator fault, VSD fault, or controller fault.

Variable Speed Drive (VSD) Bypass: The control system shall include Operator selectable variable speed fan and full speed fan (VSD bypass) air flow control modes. Under “Variable Speed” control, both the forced draft fan speed and the air flow control damper shall be used to regulate combustion air flow. Under “Full Speed” control, only the air flow control damper shall be used to regulate combustion air flow. The controller shall contain independent variable and full speed fan setup curves for each fuel. In the event of a Variable Speed Drive (VSD) failure, the burner shall trip, the Operator shall transfer the VSD bypass transfer switch and restart the equipment. The power transfer switch shall be interlocked with the controller for automatic selection of the setup curves. This function shall not require a service engineer to implement the changeover.

Boiler Efficiency Display: Real time boiler efficiency shall be calculated and displayed, thereby allowing the boiler operator to instantly identify inefficiencies and potential operational problems. The calculation shall be based on the ASME “by losses” method and must utilize real time inputs of boiler firing rate, flue gas Oxygen, flue gas temperature and fuel selected. Two sets of adjustable fuel chemistry data parameters shall be included, and firing rate scaled radiation losses shall be used for maximum accuracy. NOTE: Flue gas temperature element must be provided and installed at each boiler outlet.

Boiler Controllers: To assure system integrity, a pre-wired and factory-tested, microprocessor-based, multiple loop controller system shall be provided. The controller shall include process variable and “First – out” annunciator displays, two 50 segment bargraphs to display the controlled variable and setpoint and one 20 segment bargraph to display the loop output. Configuration and calibration data shall be stored on redundant non-volatile EEPROM memory modules. The backup memory module shall automatically download into the primary memory in the event of primary memory data corruption. All control logic, tuning, and fuel/air ratio curves shall be field configurable.  Provide one configuration tool or laptop computer per facility if required to allow field modifications to the controller logic.

Electric Actuators: Electric actuators shall be furnished complete with a position feedback retransmitter, limit switches required for flame safeguard interlock, suitable torque while rotating 90° in 30 seconds, and shall be designed for “lock in the last position” upon fault.

Flue Gas Oxygen Analyzer: Provide a boiler breeching mounted in-situ, zirconium oxide Oxygen analyzer for each boiler. Extractive or “Wet Cell” type Oxygen analyzers are not acceptable. The probe shall be of a suitable length for sensing the Oxygen level in the middle ⅓ of the breeching. All wetted parts shall be stainless steel. The Oxygen analyzer shall include a digital controller that performs continuous self-diagnostics with diagnostic codes for at least 10 common faults. The system shall automatically send the trim actuator to the ‘null’ position and trigger the alarm dry contacts in the event of an Oxygen analyzer fault. The detector shall be field replaceable without removing the probe from the stack and shall not require special tools. The analyzer shall automatically perform periodic detector cell impedance tests to be used by the operator as an indication of calibration shift. Analyzer calibration shall be pushbutton semi-automatic (no trim pots) with English language prompts and diagnostic messages.  Analyzer output shall be field selectable as 0-10% or 0-21% without field recalibration.  Analyzer shall be Preferred Instruments, Danbury, CT, Model ZP.

Variable Speed Drive: Provide a pulse width modulation (PWM) type VSD suitable for microprocessor-based digital control. The VSD shall accomplish stepless speed control by adjusting both the output voltage and frequency to the motor. The VSD shall utilize IGBT power semiconductor technology in the inverter section.  VSDs must be UL listed. Provide a NEMA 12 (NEMA 1 will not be accepted) enclosure for the VSD to protect it from dust and splashed water. VSD shall be designed for 104° F continuous ambient air temperature. The enclosure shall be completely self-ventilating with powered fans as required. The VSD shall automatically limit the rate of fan speed increase to that which will prevent an over current or over voltage trip in the event of a “STEP” speed increase of 0 to 100 %. The VSD shall include a line reactor or DC Link Choke to reduce rectifier peak currents, and reduce total harmonic distortion (THD). To extend motor insulation life, the VSD shall limit peak voltages. The “dv/dt” shall be limited to 900V/microsecond on a 500′ cable length between the VSD and motor.  VSD’s that do not include internal “dv/dt” limiting shall be provided with external filters. Provide a 4-20 mAdc frequency output that reflects auto-limited frequency rate of change for effective fuel/air cross limiting. A VSD mounted operator interface unit shall be provided. The operator interface shall allow configuration of drive parameters and display diagnostic information for troubleshooting as well.

Commissioning Software: Provide Commissioning Software along with the Boiler Control System. The software must be MS Windows compatible and shall provide an automated step-by-step setup with prompts for user manual action and help screens of the fuel and air actuators, oxygen sensor, variable speed drive and fuel/air profile. The software shall automate actuator, oxygen sensor and variable speed drive calibration and provide a graphical representation of air damper, variable speed drive and flue gas oxygen setup curves.  The software shall not be required for operation, but shall only be used during commissioning, calibration and tuning.

Communications: Each controller shall be equipped with an optically isolated RS485 communications data highway and shall allow: Auto/Manual mode change, setpoint change, variation of the manual output, sensing and silencing of alarms. Provide all equipment capabilities specified in this paragraph, even if a connecting SCADA system is not included in this project.

Quality Assurance: The system shall be factory manufactured and tested according to UL508A requirements (CSA C22.2 #14 for use in Canada). The control system shall be a Preferred Instruments, Danbury, CT, UtilitySaver.