Model 657-1 Relative Humidity/Temperature Transmitter

Dual Channel Design for Simultaneous 4-20 mA Output Signals

The Model 657-1 Transmitter provides two 4-20 mA channels to produce separate output signals for both relative humidity and temperature. This inexpensive device delivers ±2% accuracy for humidity and ±3% for temperature measurements. The sensor employed in the 657-1 features a state-of-the-art integrated polymer film humidity sensor and a thin-film platinum temperature sensor to assure high reliability and rock-solid stability over years of continuous service. Stainless steel probe measures 5/16" x 10" (0.8 x 24.4 cm) and can be easily mounted to most ductwork using either of the two optional kits.

Product Applications

  • Cleanroom monitoring
  • HVAC/building control monitoring

Models & Ordering

Model Description Usually Ships Price Order
Ships: Next Day
Price: $288.00
Relative humidity/temperature transmitter. Next Day $288.00 Order


Humidity & temperature detection in air.
Relative Humidity: 0-100%; Temperature: 32 to 212°F (0 to 100°C).
Relative Humidity: ±2% (10-90% RH), ±3% (0-10% and 90-100% RH); Temperature: ±1°F (0.5°C).
Temperature Limits:
32 to 140°F (0 to 60°C).
Pressure Limits:
1 psi (.07 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 RH channel.
Electrical Connections:
4 screw type terminal.
Mounting Orientation:
Mount in any position.
5/16" x 10" (0.8 x 25.4 cm) stainless steel.
5.5 oz (156 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)


Model Number Description Usually Ships Price Order
Split flange. A-158 Split flange. Next Day $13.75 Order
Mounting gland with 1/2 A-159 Mounting gland with 1/2" male NPT. Next Day $28.00 Order

Product Literature


Catalog Pages



I'm looking for a dual temp. and humidity gauge for an 8" duct. I'm wanting to remote read the temp and humidity on the incoming and outgoing air to an ERV unit. The RHP-3M11-LCD was recommended to me, however, it is a direct read. What would be the correct instrument to remote read the temperature and humidity from a distance of 8 feet. The 8" duct is in the attic and I want to read the result in the down-stair hall. I don't want to record nor program the unit, just read the performance.
The sensor recommended would be the best option we have for sensing temperature and relative humidity for your application. We do not have any options with a remote display that could stretch as far as you are asking, nor are there any on the market to my knowledge. In every case, you would need to utilize a process output, in this case 4-20 mA, to transmit the readings to a remote display(s) which would accept the process signal(s). If you are just looking for a remote readout to go with the RHP sensor with no control functionality, then you could look at one of our panel meters, possibly the SPPM, DPMA, DPMW, or DPMP & DPML series panel meters. For assistance selecting an appropriate panel meter, please contact our technical support group at 219-879-8000.

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