Relative Humidity Controller

The CH Range of Controllers

Farm Electronics manufacture a range of 3 electronic relative humidity control units with remote sensing.  All controllers use the same humidity sensor Model HC_L, (0-10 volt industry standard) and two models of controller include visual readout of sensor RH% provided by a large-scale two digit red LED display.

The Farm Electronics relative humidity controllers have a wide range of applications in Agriculture and in Industry.  Agricultural uses include control of ventilation systems in grain stores, livestock housing and in the large scale storage of vegetable crops.  Industrial uses include control of heaters, and possibly fans, in printing, baking and general manufacturing areas.

Model CH1/CH2 Ten
Model CH1 operates with a single remote RH sensor and has a large red digital display of sensor RH% and a single pole voltage free changeover relay permits an automatic control function for any associated ventilation or heating device operated by its own starter mechanism.  Inbuilt “anti-hunt” timers provide a 10 minute minimum run and minimum off delay.

Model CH2 is identical to the CH1 but without the digital RH readout display.

Model CH6 Ten
Model CH6 is similar to the CH1 with a single remote sensor and digital RH display but this controller has two separate control circuits each with its own switch setting, identified as High and Low.  This permits the CH6 to control two entirely separate devices at different RH% control levels using the information from the one sensor.

By wiring the two relays in series the CH6 can provide a High and Low switching point within one circuit.  Associated equipment would then operate when the sensor indicated RH% above the Low setting and below the High setting.  In addition the relay control logic in the CH6 can be preset internally to operate on a differential basis.  For this purpose only the High relay is utilised.  The relay will engage when RH% is above the high set point and then remain on until the RH% falls below the Low set point.

The CH6 can also be fitted with a 4-Way sensor selection switch box.  This allows up to four sensors to be attached to the controller and permits the operator to select any one of these sensors for control.  The operator can also switch between the four sensors for display purposes,  selecting each in turn to read the sensor RH% on the digital display.  This is done without altering the controlling sensor selection.

Model HC-L RH Sensor

Technical Specification

 Mains Supply 110 or 240 volt AC
 Remote Sensor 0-10 volt output
 Sensor Element Capacitive
 Sensor Accuracy +/- 2.5% RH
 Operating Range Relay 10% – 90% RH
 Digital Display 1% resolution LED (not CH2)
 Temperature Range 0 + 50 degrees C
 Voltage Free Relay Single pole changeover
 1.0 amp 10 min anti-hunt delay (On & Off)


1) Remote sensor provides accurate and reliable measurements of ambient relative humidity
2)The sensor is separate from the main controller with plug in connection
3)A 6m cable is supplied as standard, but the sensor can be used up to a maximum of 100m away from the controller
4)The sensor element is protected by a bronze filter.  Regular replacement is recommended for best results
5)Accuracy and durability of the sensor is related to the working environment.  Regular service and re-calibration is recommended.
6)A LED indicator illuminates when the sensor RH% is below the set level
7)Anti-hunt time delays operate on relay circuits to prevent relay flutter.  A manual override switch is provided for test purposes.
8) All CH units utilise a 1.0 amp single pole changeover voltage free relay