RVT80, RVT81 Humidity sensor

Application of humidity sensors RVT80, RVT81

Relative humidity and air temperature sensors RVT80 and RVT81 have a wide application:

Meteorological stations, monitoring of biosystems

Process monitoring in laboratories

Warehouse monitoring

Climatic chambers and drying plants

Universities, development and research workplaces

Intelligent building management

Museums, depositories and monuments

Basic description of hygrometers

hygrometers RVT80 and RVT81 are designed for measuring relative humidity and air temperature. In addition, the RVT81 hygrometer contains a Pt100 temperature sensor of accuracy class A, including measuring electronics.

the hygrometer is connected via the RS485 interface with the supplied cable with M12 connector to the M4016, STELA or Hydro loggers H1, H7, H40 recording unit. Both sensors communicate with the connected unit under the FINET or Modbus RTU protocol.

The delivery of the hygrometer can also include a radiation cover RK5 or RK7, which prevents the measured temperature from being affected by radiant heat and at the same time protects the sensor from direct exposure to rain and sunlight.

The cost-effective RVT80 hygrometer does not use an accurate Pt100 temperature resistor for air temperature measurement, but a combined semiconductor sensor for which the manufacturer declares a measurement accuracy of ± 0.3 °C for 25 °C with an additional possible error of ± 0.1 °C every 10 °C from declared reference values of 25 °C. For a large group of applications, this accuracy of air temperature measurement is sufficient.

Measurement of relative humidity

The RVT80 and RVT81 hygrometers use a combined compact sensor SENSIRION SHT85 for measuring humidity and air temperature, in which the manufacturer's declared accuracy of measuring relative humidity is better than 1.8% in the range from 0 to 80% RH and better than 3% in the remaining measuring range. from 0 to 100% RH. The relative humidity resolution is 0.1% RH.

Air temperature measurement

The SENSIRION SHT85 sensor also measures air temperature with an accuracy of ± 0.3 °C at 25 °C. The maximum possible error of the integrated temperature sensor increases with increasing or decreasing temperature and reaches a value of up to ± 1.5 °C within the limit values of its measuring range -40 °C to +80 °C.

For accurate air temperature measurements, the RVT81 hygrometer contains a Pt100-A temperature sensor and very precise and stable evaluation electronics taken from the TEP01 temperature probe. A typical temperature measurement error does not exceed 0.1 °C in the range from -20 °C to + 50 °C. In the entire operating range from -50 °C to + 80 °C, the typical temperature measurement error is less than 0.3 °C. High accuracy and stability of measurement allows the use of high resolution of the measured temperature, which can be set by the user in the connected recording unit. The probe works with minimal noise without fluctuations and with a resolution of 0.002 °C.

Measuring channels

The RVT80 hygrometer contains two measuring channels and the RVT81 hygrometer has three measuring channels. The first channel is always occupied by the measured value of relative humidity and the second measuring channel is occupied by the air temperature obtained from the compact sensor SHT85.

The third measuring channel (only for RVT81 sensor) contains the air temperature value measured by the Pt100-A temperature sensor.

Connection of RVT80 and RVT81 hygrometers to the recording unit

The measured value of relative humidity and air temperature is transmitted to the connected recording unit via the RS485 serial bus. This method of communication eliminates the occurrence of an additional measurement error on the analog input side of the recording unit and, in addition, allows the transmission of values from several measuring channels of the probe via one communication line. Another advantage of RS485 serial communication is the possibility of parallel connection of several hygrometers to one recording unit. The hygrometer communicates on the RS485 bus under the FINET protocol (Modbus RTU) and therefore it can be easily connected to all FIEDLER units (M4016, H1, H2, H3, H40 or STELA).

Measured data from these telemetry stations are automatically transferred (via GSM/GRS network) to a secure database on the Internet and accessible to an authorized user via a standard web browser (graphs, spreadsheets, data exports to the client's PC, reports and reports, ... ).

Mechanical design

The body of the RVT80 and RVT81 hygrometers consists of a plastic housing with a diameter of 16 mm and a length of 72 mm, in which all measuring, evaluation and communication electronics of the sensor are located. The hygrometer is equipped on one side with a circular connector of the M12 standard with a power and communication pair of pins. The other side of the body of the hygrometer carries a combined relative humidity sensor SHT85 and possibly a Pt100-A temperature resistor (RVT81).

The measuring sensors are covered with a simple breathable plastic cover with very low temperature inertia, which prevents mechanical damage to the sensors and at the same time does not affect the accuracy of the hygrometer measurement.

Usually, the hygrometers are placed in the radiation cover RK5 or RK7, which can be ordered together with the hygrometer from its supplier. A universal stainless steel holder is also part of the delivery of the radiation cover.

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