The Defrost Sensor can measure the thickness of the frost layer on an evaporator. This measurement is used to initiate defrosting when needed and only when needed. The energy consumption increases when the evaporator is blocked with ice so the air can’t pass, and the ice insulates the fins.
Traditionally, evaporator defrosts are based on a fixed schedule; by basing the defrosting on an accurate measurement, defrost can be done only when needed. This can typically reduce the number of defrosting cycles by 50%.
Low temperature freezers
-60°C to 0°C
With insulation for low temperatures
-30°C to 0°C
-30°C to +10°C
Include temperature sensor
-60°C to +20°C
Special product for OEM
The sensors have two mA output modes:
Simple analog is designed to be controlled from a PLC, and the control parameters must be inside the PLC.
Smart analog is designed for control from the sensor – and this means all changes must be made in the box, and you must connect a PC to the box directly.
This means you must decide where to have your control system and how you like to control the system. Most customers choose the simple analog because the sensors are often challenging to reach.
In the simple analog you just get the mA signal, and you decide which mA signal you like to defrost. The signal will be 4 mA when you have no ice on the evaporator and when the temperature is lower than the setting (when the evaporator is defrosting and filled with water), so you should set it to -1°C to get a reasonable measurement.
The sensor also has a relay output and can control the fans, heater, and compressor directly from the unit.
The sensor consists of a control box, a coated steel wire, and a temperature sensor for some versions.
To determine frost accumulation levels, the sensor measures a change in capacitance between a coated steel wire and the evaporator fins.
The defrost sensor is based on the capacitive measuring principle, in which an insulated steel wire acts as one conductor, and the evaporator fins act as the second conductor. The sensor measures the ice thickness between the fins. The output is a 4-20mA analog or more advanced digital output to the control system. The digital output can be used directly to control the defrosting and includes a temperature sensor that senses when defrosting is completed.
The sensor can be installed on both new and old evaporators in less than an hour. It can even be installed when the system is in operation hence shutdown is not necessary. The electronic part is mounted on the evaporator’s frame by using 2-4 screws. The mechanical part consists of a thin coated wire mounted between the evaporator's fins where ice is built up. The wire is mounted using standard nylon cable ties or around the pipes. The HBDF sensor is available in 3 versions, with a 10-, 20-, and 30-meter wire. 10 m wire is usually enough to get a representative measurement. After the installation, the sensor should be calibrated/configured to the evaporator using the HB-TOOL (PC-based software tool), which can be downloaded from our website.
Ice Bank Sensor
The sensor can measure how much water is turned into ice in an ice bank. The measurement is done between a coated steel wire and the cooling pipe. The sensor is designed for ice banks with metal evaporator pipes.
Application: Freezer -30°C to 10°C
Product Code: HBDF
Application: Heat pump
Product Code: HBDF-OD
Application: Freezer -30°C to 0°C
Product Code: HBDF-Freezer
Application: Freezer -60°C to 0°C
Product Code: HBDF-LT