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Dwyer Series HHT

Series HHT Hazardous Area Humidity/Temperature Transmitter

Dwyer Series HHT
Series HHT

Intrinsically Safe or Explosion-Proof Models

The Dwyer Series HHT Hazardous Area Humidity/Temperature Transmitter takes accurate measurements in the harshest of environments. The transmitter is offered in explosion-proof and intrinsically-safe versions depending on the application’s requirements. The explosion-proof model is offered with 4 to 20 mA output for humidity only. The intrinsically-safe version is offered with 4 to 20 mA output for humidity and temperature. Both versions have an optional two line alphanumeric display to show the current humidity and temperature.

The Series HHT humidity/temperature transmitter is excellent for offshore HVAC applications, dust and grain applications. Intrinsically safe models require an intrinsically safe barrier.

It is important to develop a routine schedule for replacing the RH/temperature sensor (part number A-451). The sensor should be replaced annually or sooner depending on application conditions.



  • Relative Humidity Range:0 to 100% RH.
  • Temperature Range:-40 to 140°F (-40 to 60°C).
  • Accuracy:±2% 10-90% RH, ±0.9°F at 72°F (±0.3°C at 25°C).
  • Hysteresis:±1%.Repeatability:±0.1% typical.
  • Temperature Limits:-40 to 140°F (-40 to 60°C).
  • Storage Temperature:-40 to 176°F (-40 to 80°C).
  • Compensated Temperature:-40 to 140°F (-40 to 60°C).
  • Power Requirements:For instrinsically safe models HHT-IX, 9.5 to 28 VDC. For explosion-proof models HHT-EX, 16.5 to 28 VDC.
  • Output Signal:4-20 mA, 2 channels for humidity/temperature models (loop power on RH).
  • Response Time:15 seconds.
  • Electrical Connections:Screw terminal block.
  • Conduit Connection:1/2″ female NPT.
  • Drift:<1% RH/year.RH Sensor:Capacitance polymer.
  • Temperature Sensor:Solid state band gap.
  • Housing Material:Aluminum.
  • Display:Optional 2 line alpha numeric, 8 characters/line. Temperature display is °F/°C selectable.
  • Display Resolution:RH: 0.1%: Temperature 0.1°F (0.1°C).
  • Weight:2 lb 8 oz (1134 g).
  • Enclosure Rating: NEMA 4X (IP66). Models HHT-EX: FM Explosion-proof, Class I Div. 1 Group B, C, D, Class II Div. 1 Group E, F, G, Class III Div. 1; Models HHT-IX: FM Instrinsically Safe, Class I Div. 1 Group A, B, C, D, Class II Div. 1 Group E, F, G, Class III Div. 1 T4.
  • Agency Approvals:FM, CE.



HHT-EUExplosion-proof humidity transmitter.No
HHT-EU-LCDExplosion-proof humidity transmitter.Yes
HHT-ITIntrinsically safe humidity/temperature transmitter.No
HHT-IT-LCDIntrinsically safe humidity/temperature transmitter.Yes
HHT-IUIntrinsically safe humidity transmitter.No