Flue Temperature, Opacity and Draft Controller


The JC-23D2 provides all-in-one stack monitoring through combined Flue Temp, Opacity, and Draft Control Functions. All three processes are displayed on the highly visible LED touchscreen display and are fully configurable from the user friendly menu structure. The JC-23D2 works with Preferred’s 190851D and 190851S LED light source and sensor with auto-ranging and auto-calibration features. Each function can be enabled/disabled as needed.

  • Automatic Draft Control
  • Precision Outlet Draft Control
  • Firing Rate Feedforward
  • Floating Draft Control
  • PID Draft Control
  • Automatic Damper Sequencing
  • Damper Adjustable Start Position
  • High Draft Alarm
  • Modbus Communication with RS-485 and Ethernet capability.
  • Live Data Tuning Screen
  • High Flue Temp Alarm and Shutdown
  • High Opacity Alarm and Shutdown · Opacity Auto-Calibration and Auto-Ranging - explanation video here
  • NYC-BAR Opacity Shutdown Sequence
  • Overview and Features
  • Application
  • Specifications
  • Documents
Overview and Features

The JC-23D2 combines Preferred’s Flue Temp, Opacity, and Draft Control logic into one unit. Each control function is displayed on the home screens and can be enabled/disabled as needed. All setup and adjustments can be made directly from the LED touchscreen display and user-friendly menu structure. The JC-23D2 includes a 50 entry time and date-stamped alarm history and a 60 entry opacity calibration history.


Light Source and Sensor

The 190851S Light Source uses a long-life LED Lamp. The 190851D Detector has a large lens that dramatically reduces inaccuracies due to ambient light and misalignment.


Calibration is automated, there are no manual adjustments. During every Calibration, the Lamp brightness is automatically adjusted to suit the soot/dust build-up, alignment changes, and stack width.


The JC-33D2 can be configured to automatically do a calibration after the burner fan cycles Off. Calibration cancels out soot build-up on the optics and thus significantly reduces the need to frequently clean the Source window and the Detector lens. Auto-Cal reduces false alarms caused by typical burner light-off and shutdown soot deposits.

JC-33D2 Indicator / Alarm: At a glance, the bar graph indicates when maintenance is required before the burner shutdown occurs. Intuitive Menu navigation makes setup and adjustments easy. Modbus RS-485 and ethernet makes remote monitoring easy. The home screen can be set to show all three channels at once to quickly view opacity readings.

“NYC BAR” Sequence: This sequence is similar to the Standard Operating Sequence (above), but conforms to the New York City D.E.P. Bureau of Air Resources requirements. The alarm relay activates instantly and the shutdown relay delay is fixed at 120 seconds (not adjustable). The 190712 Light Sensor Alarm Test filter complies with NYC BAR requirements.


  • Automatic Draft Control for increased boiler efficiency and reliability.
  • Precision Outlet Draft Control for low NOx induced FGR burners.
  • Firing Rate Feedforward option is included and assures stable draft during load changes. Separate curves for up to two fuels.
  • Floating Draft Control mode is the easiest to tune. Floating Control can be used with any type of actuator or an ID Fan VSD.
  • PID Draft Control mode is included for those who prefer this type of tuning.
  • Automatic Damper Sequencing for purge, light-off, post-purge burner shutdown, and standby. Simple Flame Safeguard interface.
  • Damper Adjustable Start Position option is included for installations with excessively high draft during light-off.
  • High Draft Alarm with time stamped alarm and event history.
  • Modbus Communication with RS-485 and Ethernet capability.
  • Live Data Tuning Screen for more convenient tuning.


  • User Adjustable High Flue Temp Alarm and Shutdown Setpoints
  • User Adjustable Alarm Delay
  • Peak Flue Temp Monitored in Alarm History

The Preferred Instruments JC-23D2 3-in-1 Flue Temp, Opacity, and Draft Controller assures accurate measurement of Opacity and Flue Temperature of boiler stacks to monitor for optimum performance. The precise draft control is recommended for: Low NOx burners, Installations with a stack height exceeding 75 feet, installations with multiple boilers sharing a single stack. Typical applications include commercial buildings, schools, hospitals, apartment complexes, and industrial plants.



Power Supply: 120VAC +/-15%, 50/60 Hz, 26 VA

Case Size: 3 1/2 w x 7 9/16 h x 4 7/8 d

Enclosure Type: NEMA 12 Faceplate, Flush Mounting

Ambient Temperature: 32°-131° F (0°-55° C) Ambient

Digital: Color Touchscreen 4" High, 0.5% Resolution Bar Graph


Alarm Setpoints: Adjustable 5-50%

Light Source and Light Sensor

Calibration: Automatic, Off-Line

Spectral Response: PhotopicPeak and mean within 500-600nm

Angle of Projection: <5°

Operational Error: <5%

Span Drift: <2%

Zero Drift: <2%

Calibration Error: <1% (Linearity)

Response Time: < 10 seconds for 95% change

Sighting Distance: 1 to 8 Foot Smoke Duct, 3 to 10 Foot Optical Path Length

Wiring Distance: 500 FT. Max (16 Ga. Wire), 250 ft. Max (20 Ga. Wire)

Sensor Housing: ¾" Pipe Mount


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

Retransmission: 4-20 mA, 650 Ohm Load Max

Network Output: 4800-57600 Baud RS485 Modbus RTU, Ethernet TCP/IP


3-in-1 Flue Temperature, Opacity and Draft Controller JC-23D2 Specification

3-in-1 Flue Temperature, Opacity and Draft Controller JC-23D2 Instruction Manual