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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

Draft Range Transmitter Assembly

The Model JC-22XMTR Draft Range Transmitter Assembly is a field mountable boiler draft range transmitter and independent high pressure cut-out switch with a 5 second time relay.

Application

Furnace draft is typically a low range signal, and contains a great deal of pulsation and vibration. The JC-22XMTR draft transmitter is specially designed for furnace stack draft applications to filter this noise. Ordinary low range transmitters do not include this noise filtering.

The usage of the High Pressure Cutout (HPCO) versus the Low Draft Cutout (LDCO) is determined by the burner and boiler design. LDCO describes when the burner trips on a flue gas pressure rise above a negative cutout setpoint (i.e. -0.05” wc). HPCO describes when the burner trips on a flue gas pressure rise above a positive cutout setpoint (i.e. +0.05” wc). In both cases, the burner trips when the pressure rises. The difference is whether the cutout setpoint is negative or positive.

LDCO Usage

Atmospheric burners and older induced draft burners that rely exclusively on the negative pressure at the boiler outlet to suck the air and flue gas through the boiler. These systems require a negative pressure setpoint and the Model JC-22XMTR-LDCO.

HPCO Usage

Forced draft burners have a burner fan that generates positive pressure to push the air and flue gas through the boiler. These systems require a positive pressure setpoint and the model
JC-22XMTR-HPCO even if the draft control setpoint is negative.

If a boiler has a forced draft burner and also has an induced draft fan that creates a very negative draft, then a negative setpoint low draft cutout might be required. Consult the boiler or burner manufacturer.

Overview

The Model JC-22XMTR Draft Range Transmitter Assembly is a field mountable boiler draft range transmitter and independent high pressure cut-out switch with 5 second time delay relay.  The transmitter provides a 4-20 mADC signal for draft control and the time delay relay provides an isolated “High Pressure Cut-Out” contact for use in the Flame Safeguard Limit Circuit. The time delay feature helps avoid nuisance burner shutdowns due to momentary draft fluctuations. The transmitter is calibrated as +1″wc = 4 mA to provide fail-safe operation (damper opens).

Features

Enclosure: NEMA 12, Field Mounted

Transmitter

Range: +1″ wc to -1″wc

Output: 4-20 mADC (2-wire)

Accuracy: +/- 0.75% FS

Power Supply: 24 VDC

High Pressure (Low Draft) Cut-Out

Range: +0.15″ wc to +4.0″ wc, Field Adjustable

Dead Band: 0.09″ wc (Average)

Contact: 20 Amps/120 VAC +1″ wc to –1″ wc Draft Transmitter Range

  • +0.15″wc to +4.0″wc High Pressure Cut-Out Setpoint (Field Adjustable)
  • 5 Second High Pressure Cut-Out Time Delay Relay
  • Combination Draft Range Transmitter, Independent High Pressure Cut-Out with 5 Second Time Delay Relay In One Box
  • Single Draft Connection Saves Installation Cost

Specification

Provide a –1″wc to +1″wc, 4-20 mAdc boiler draft range transmitter and an independent high pressure cut-out with 5 second time delay. Instruments shall be provided with a dust-tight, splash-proof enclosure. The high pressure setpoint shall be field adjustable from +0.15″ wc to +4.0″ wc.  The high pressure switch shall be mounted and wired to a pilot light so as to illuminate when the switch activates and to a 5 second time delay relay so as to provide an isolated, 10 ampere contact for use in the Flame Safeguard Limit Circuit. The Draft Range Transmitter with time delayed high pressure cut-out shall be a Preferred Instruments, Danbury, CT Model JC-22XMTR.