Chinese (Simplified)EnglishFrenchGermanHindiItalianJapaneseKoreanPortugueseRussianSpanish

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

JC-15D Flue Gas Temperature Monitor

The JC-15D Flue Gas Temperature Monitor is a microprocessor based indicating instrument with an optional heavy duty Thermocouple Assembly.


The JC-15D is used to monitor boiler efficiency (higher stack temperature translates into lower efficiency) and as a high stack temperature switch. According to the Hartford Steam Boiler Inspection and Insurance Co., “Three out of every four (boiler) accidents are caused by overheating, and 80% of the overheating losses resulted from continued firing with low water levels; despite the fact that boilers, …are equipped with up-to-date controls.”

When a boiler runs out of water, the stack temperature gets very high very fast. A high stack temperature switch can alert the flame safeguard system and shut down the burner before the boiler is damaged, and potentially prevent a boiler explosion.



The JC-15D Flue Gas Temperature Monitor is a microprocessor based indicating instrument with a heavy duty Thermocouple Assembly. Flue gas temperature is continuously displayed using a highly visible backlit LCD display. An intuitive bar graph display and alarm messages provide clear stack temperature status. Bar graph Scaling, Alarm Setpoints, and Time Delays are all field selectable. All adjustments can be made directly from the faceplate of the instruments by scrolling through user friendly, English language menus. The type J Thermocouple Assembly is constructed of a seal welded inconel sheath for corrosion protection, and can be directly installed in the boiler’s flue gas outlet. The unit includes a ½” male NPT process connection, cast iron head with thermal block, and ½” female NPT electrical connection 

Alarm Sequence: Bar graph and numeric displays continuously indicate the flue gas temperature (FGT). If the FGT exceeds the warning setpoint for more than 30 seconds (adjustable), the bar graph blinks, the WARNING message appears, and the alarm relay energizes. If the FGT continues to increase and exceeds the shutdown setpoint for more than 30 seconds (adjustable), the bar graph blinks, the SHUTDOWN message appears; the shutdown relay de-energizes and latches into “Manual Reset” mode. The burner shuts down if the JC-15D shutdown relay is wired into the burner interlocks. The shutdown Relay remains de-energized and the SHUTDOWN message remains on the display until the operator presses the RESET pushbutton.  The alarm relay can be used to activate an external bell or horn. The alarm relay de-energizes when the warning and shutdown alarms are both inactive. Alternately, pressing the JC-15D Alarm Silence pushbutton, or energizing the 120 Vac Alarm Silence input, or a Modbus command can de-energize the alarm relay in order to silence an audible alarm.


  • RS485 Modbus Communication
  • 4-20mADC Retransmission
  • 4 Digit Display
  • 200 Segment Bar Graph
  • Large LCD Graphic Display
  • Field Adjustable Using English Language Menus
  • Low Boiler Efficiency Alarm Message and Contact
  • Burner Shutdown Contact and Message


Power Supply: 120 VAC, +/- 15%, 50/60 Hz, 15 VA

Case Size: 8″H x 3.5″W x 7.5″D

Enclosure Type: NEMA 4 Faceplate

Ambient Temperature: +32° to 122° F

Displays: High Contrast LCD Display, 4″ high, 0.5% Resolution Bar Graph

Bar Graph Range: 0°-2000° F field adjustable

Alarm Setpoints: Two (2) Adjustable With Adjustable Time Delays


Input Types: Type J or Type K Thermocouple, Field Selectable

Accuracy: 0.005% Resolution, 0.07% Accuracy

Break Protection: Upscale


Relay: Two SPDT Relays 10 A Resistive, 8 FLA, ½ HP, 120 VAC

Retransmit: 4-20 mADC, 650 Ohm Load Maximum

Network: 1200 – 38400 Baud; RS485 Modbus, ASCII or RTU


Assembly: Type J Ungrounded

Probe Material: Inconel

Insertion Length: 20″

Connection: ½” MNPT


Provide a remote reading microprocessor-based flue gas temperature alarm and indicating instrument and a flue gas temperature sensor assembly for each boiler. The instrument shall provide a flue gas temperature display in engineering units, “Inefficient” operation warning indication, “Overheat” operating condition indication and alarm contacts. The Instrument shall continuously indicate flue gas temperature on a highly visible backlit LCD display. Provide an integral or separate 4 inch, 0.5% resolution (minimum) bargraph display in engineering units with visual alarm setpoint indication. Provide an “Alarm Silence” and “Manual Reset” pushbutton and two 10 ampere relays. The housing shall be panel mountable, fully gasketed with NEMA 4 front face. All adjustments shall be made from the front panel display in engineering units. No external configuration tools shall be required. The Instrument shall provide: cold junction compensation and upscale thermocouple break protection. The Instrument shall include alarm messages as follows: When flue gas temperature exceeds the “Warning” setpoint for more than 30 seconds (adjustable), the bargraph shall blink, and the “Warning” message shall appear and an “Alarm” relay energizes and if wired to an alarm circuit an alarm is activated. If the flue gas temperature continues to increase and exceeds the “Shutdown” setpoint for more than 30 seconds (adjustable), the bargraph blinks, the SHUTDOWN message appears, the “Shutdown” relay de-energizes and latches into the “Manual Reset” mode. If the “Shutdown” relay is wired into the burner interlocks, the burner shuts down. The “Shutdown” relay remains de-energized and the “Shutdown” message remain on the display until the operator presses the integral “Reset” pushbutton.

Provide a Flue Gas Temperature Sensor Assembly for each boiler. The sensor assembly shall include: iron/constantan ISA Type J thermocouple, inconel sheath, ½” male NPT process connection, cast iron head and a 20″ insertion length. Extension lead wire shall be one continuous length of 20 gauges ISA Type JX with PVC insulation. The assembly shall be installed in the boiler outlet before any damper or fan in accordance with manufacturers suggested installation instructions. The Instrument shall include a RS485 Modbus network interface and a 4-20 mADC retransmit output to communicate to a future Data Acquisition System (DAS) or Building Automation System (BAS). The Instrument 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 Flue Gas Temperature Monitoring, Control and Alarm System shall be Preferred Instruments, Danbury, CT, Model JC-15D, with 104087D Thermocouple Assembly.