ROTRONIC HM4 - Manual (Page 5)

E-M-HM4-V0_08
ROTRONIC AG
Bassersdorf, Switzerland
Document Code Unit
HM4 Humidity and Temperature Probe with
Heated Sensor
Instruction Manual
Document Type
Page 5 of 41
Document Title
© 2014; ROTRONIC AG E-M-HM4-V0_08
1.1 Scope
This manual is valid for the HM4 probe series with firmware version V1.1. The low-order digit of the firmware
version stands for minor changes, e.g. correction of errors, that do not influence the main functionality of the
device.
1.2 Background Information on the Principle of Measurement
In environments with high humidity (>90 %RH) near saturation point there is a risk of condensation forming on
the humidity sensor. To avoid resultant incorrect measurement, the sensor can be heated above ambient
temperature to avoid condensation. The same applies for outdoor measurements in mist or high levels of dew.
The probes in the HygroMet4 series from ROTRONIC (HM4) measure temperature and humidity
simultaneously. Formation of condensation on the capacitive SMD humidity sensor can be prevented by raising
the temperature above ambient temperature, thereby enabling accurate humidity measurements even when the
measurement environment has already reached dew point (100 %RH).
Pt100 temperature sensor
Inside: Evaluation electronics with AirChip3000 and real-time clock
Heated SMD Thermo humidity sensor
DRAFT