Humidity transmitter

1 use

The temperature transmitter is used for humidity measurement. In this article, a humidity transmitter is defined as a humidity measurement device that uses a humidity sensor for humidity detection, and converts the humidity sensor signal into a standard current signal and a standard voltage signal through a conversion circuit, wherein the humidity module product counts Into the product. [1]

Category 2

From the signal output interface is divided into 4 ~ 20mA, 0 ~ 10mA, 0 ~ 20mA, 0 ~ 5V, 0 ~ 10V, etc., or digital / frequency interface and other interfaces;

From the structure and installation form is divided into wall type, duct type, probe type;

The distance from the humidity sensor and the conversion circuit is divided into an integral type or a split type;

There are explosion-proof and other types of products.

3 basic principles

The humidity sensor is used for humidity detection. The temperature sensor is usually a polymer moisture sensitive resistor and a polymer humidity sensitive capacitor, and then the humidity sensor signal is converted into a standard current signal or a standard voltage signal through a conversion circuit.

4 Technical parameters

Humidity measurement range

Humidity measurement accuracy (pay attention to accuracy and measurement range/range relationship)

Humidity measurement signal output form

Humidity transmitter structure and installation

5 optional

Select according to measuring range

Can refer to humidity sensor selection, such as the entire measurement, the sensor needs to use capacitive type

Select according to accuracy requirements

See the humidity sensor selection, such as high accuracy requirements, the sensor is preferably capacitive, and the relationship between the accuracy and the measurement interval is selected according to the requirements, such as the use of humidity in the humid environment, select the transmitter with good humidity accuracy

According to the signal interface selection

Can choose 4~20mA, 0~10mA, 0~20mA, 0~5V, 0~10V, etc., or digital/frequency interface and other interfaces

According to the structural form and installation requirements

Indoor installation, choose wall type; air duct installation, choose air duct type.

About peripheral devices

Transmitters generally have the requirements of starting voltage, and the starting voltage is generally 7VDC or more. Considering the partial pressure of the sampling resistance and the line loss resistance, it is generally required that the voltage of the transmitter circuit power supply is greater than 12VDC.

Current interface humidity transmitter sampling resistance is generally less than 500 ohms

Voltage interface humidity transmitter load resistance is generally greater than 50K ohms

6 installation

Humidity transmitters are generally installed as close as possible to the location where the required humidity is measured. However, considering the relative humidity and the temperature (the same environmental system, low temperature and high humidity, low temperature and high humidity), the transmitter needs to pass a certain current. , Heat can be generated, ventilation problems must be considered, or the location of the humidity sensor in the humidity transmitter should be flushed down.