Hydrogen Detection Transmitters - HHDT

The HHDT Hydrogen Detection Transmitters can operate as "stand-alone" units or can be used in conjunction with a variety of controllers. They are housed in an explosion proof casing, operate on 14...24 VDC and produce a 4...20 mA linear output proportional to the gas (H2, O2, etc.) concentration. The wide power supply variation allows placing the transmitters away from the power supply due to attenuation of the signal (voltage drop) over distance. Minimum voltage at the transimitter is 14 VDC. The transmitter has been calibrated at the factory and is ready to be used.

Three-conductor cable is required for each sensor transmitter. These connections are made to terminals on the circuit board inside the explosion proof housing. The socket for this connection is included in the transmitter.

Easy to calibrate 'ZERO' and 'SPAN' by adjusting the onboard potentiometers. Automated calibration is available by using the HHDT in conjunction with an HMP series of  control unit.

There are 2 different types of sensor transmitters available: a standard transmitter and an intelligent transmitter.



Standard Transmitter

The standard transmitter is housed in an explosion-proof casing. It operates on 14...24 VDC which is supplied by a control unit or an external power device and produces a linear 4...20 mA output proportional to gas concentration. The 4...20 mA output is sent to the control unit which displays the corresponding gas concentration.

Manual calibration is "one man" and is accomplished via potentiometers located inside the housing. However, when used in conjunction with the HMP series controllers, automated calibration is also available. With this feature, calibration can be accomplished by simply applying gas to the sensor and letting the controller make all the necessary adjustments.


Intelligent Transmitter

The intelligent transmitter is a microprocessor based module. It comes equipped with a local digital display, thus providing a reading of the gas concentration at the sensor site itself. It operates on 14...24 VDC and, like the standard transmitter, it is housed in an explosion-proof casing. Interfacing with the instrument is accomplished by applying a magnetic wand to magnetic switches located on the front panel. Thus , all functions can be performed without removing the covers, meaning there is no need to declassify areas being monitored.

The intelligent transmitter is completely self-contained and can operate as a stand-alone unit. It does not require a control unit to operate. In addition to having a local digital display, it also has an automated calibration feature built into the unit and thus does not rely on the control unit for automated calibration. However, when used in conjunction with the HMP controllers, the controllers provides alarm processing and alarm relays, and also a central monitoring location for multiple sensor channels. The controller will provide power to the transmitter and accepts the 4...20 mA linear output from it.


Technical data 

Standard Transmitter Intelligent Transmitter


14...24 VDC 14...24 VDC

Current drain

170 mA max. (without sensor), 300...500 mA (with sensor) 100 mA max. (without sensor), 230...430 mA (with sensor)

Output current

4...20 mA non-isolated (isolated optional) or 100...500 mA 4...20 mA non-isolated (isolated optional) or 100...500 mA


-20...+60 0C operating, -40...+85 0C storage -20...+60 0C operating, -40...+85 0C storage


99 % RH, non-condensing

99 % RH, non-condensing


Magnetic wand activated switches

Span, zero, and heater pots


Flashing display and output current goes to 0 mA

Output current goes to 0 mA


Explosion-proof, class 1, Div. 1, Groups B, C, D

Explosion-proof, class 1, Div. 1, Groups B, C, D


115.32 (H) x 198374 (L) x 128.27 (W)

72.39 (H) x 225.37 (L) x 96.52 (W)


1.765 kg

1.32 kg