Series HHT Hazardous Area Humidity/Temperature Transmitter

Series HHT Hazardous Area Humidity/Temperature Transmitter

Series RH-R Humidity/Temperature Transmitter

Series RH-R Humidity/Temperature Transmitter

Series 657 Relative Humidity/Temperature Transmitter

Dual Channel Design for Simultaneous 4-20 mA Output Signals

The Series 657 Relative Humidity/Temperature Transmitters provide two 4-20 mA channels to produce separate output signals for both relative humidity and temperature. These devices deliver ±2% accuracy for humidity and ±1°F for temperature measurements. Stainless steel probe can be easily mounted to most ductwork using either of the two optional kits below.

*NOTE: The configurator is only available for the Series 657C.

Product Applications

  • Cleanroom monitoring
  • HVAC/building control monitoring
Starting at $346.00
Grouped product items
Model Description Availability* Qty Price
657-1 Relative humidity/temperature transmitter. 1-3 days*
657C-1 Relative humidity/temperature transmitter. 1-3 days*


Dry clean air.
Relative humidity: 0 to 100%; Temperature: 32 to 212°F (0 to 100°C).
Relative humidity: ±2% (10 to 90% RH), ±3% (0 to 10% and 90 to 100% RH); Temperature ±1°F (0.5°C).
Temperature Limits:
32 to 140°F (0 to 60°C).
Pressure Limits:
1 psi (0.7 bar).
Compensated Temperature Range:
32 to 140°F (0 to 60°C).
Power Requirements:
10-35 VDC.
Output Signal:
2 channels each 4-20 mA. Loop powered on the RH channel.
Electrical Connections:
4 screw type terminals.
Mounting Orientation::
Mount in any position.
657-1: SS 5/16" x 10" (0.8 x 25.4 cm); 657C-1: 5/16˝ x 9-1/10˝ (0.8 x 23.1cm).
657-1: 5.5 oz (156 g); 657C-1: 10 oz (284 g).


  • Polymer film humidity and thin film RTD temperature sensors offer highly reliable and stable measurements
  • Remote mount housing offers installation flexibility (657-1)
  • Rugged die-cast aluminum housing is great for industrial applications (657C-1)
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Model Description Availability* Price
A-159 Mounting gland. Versatile adapter slips on any Series 160, 5/16" standard pitot tube made after Dec. 1990. Two-part stainless steel fitting slides over tube and provides permanent, secure mounting. Where duct interior is accessible, use the washers and jam nut supplied. For blind applications or in thicker materials, use model A-156 flange mounting plate. Once tube is adjusted to proper depth and angle, tighten smaller hex bushing to lock position. Graphite bushing inside assures leak-proof seal even at higher temperatures. TFE bushing also available. Note: For full insertion with this fitting, order next longer pitot tube. A-159 mounting gland is used for both duct mounting and flange mounting. 1-3 days*
A-158 Split flange mounting. Can be added to any Dwyer® No. 160 standard pitot tube. Cadmium plated steel. Gasket is pattern for mounting holes. Secure flange loosely to tube, adjust tube depth and tighten screws. Gasket of 1/16" Neoprene fits tightly around tube and against duct for leak-proof seal. Nuts, washers included. 1-3 days*