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Temperature transmitter selection
Jan 10, 2019

Temperature transmitter selection

Common temperature transmitters are divided into thermocouples, RTDs, and integrated temperature transmitters:

First, the thermocouple signal remote transmission temperature transmitter consists of reference source, cold junction compensation, amplification unit, linearization processing, V / I conversion, breaking even processing, reverse connection protection, current limiting protection and other circuit units. It is to compensate the thermoelectric potential generated by the thermocouple through the cold end compensation, and then the cap eliminates the nonlinear error of the thermoelectric potential and the temperature by the linear circuit, and finally converts it into a 4-20 mA current output signal to facilitate the remote signal. In order to prevent accidents caused by temperature control failure due to galvanic breakage in the thermocouple measurement, the transmitter also has a power-off protection circuit. When the thermocouple breaks or the connection is poor, the transmitter will output the maximum value (28mA) to turn off the power.

Temperature transmitter selection

Second, the thermal resistance transmitter is composed of a reference unit, an R/V conversion unit, a linear circuit, a reverse connection protection, a current limiting protection, a V/I conversion unit, and the like. After the temperature-measuring thermistor signal is converted and amplified, the nonlinear relationship between the temperature and the resistance is compensated by the linear circuit, and a constant current signal of 4-20 mA which is linear with the measured temperature is output after the V/I conversion circuit.

Third, the integrated digital display temperature transmitter is used with industrial thermocouples and thermal resistors, and adopts two-wire transmission mode (two wires are used as common transmission lines for power input and signal output). The integrated temperature transmitter converts industrial thermocouple and RTD signals into 4-20 mA, 0-10 mA output signals that are linear with the input signal or with the temperature signal. Can be installed directly on the thermocouple,

Temperature transmitter selection

The junction box of the thermal resistor forms an integrated structure with it. There are two types of integrated temperature sensors: one is a direct resistance signal, and the other is a temperature change.

Selection considerations:

1. The input signal and output signal transmission are in accordance with the Hart standard protocol communication;

2. The integrated temperature transmitter should take measures against radio frequency interference;

3, the temperature transmitter input and output are isolated, increase the anti-common mode interference capability, more suitable for computer network use, especially in high temperature environment;

4. Wiring method: According to different forms, there are two-wire system, three-wire system and four-wire system;

5. Display mode: LED, LCD can be set by pc or handheld operator to display any one of the field temperature, sensor value, output current and percentage;

6, working voltage: ordinary model 12v-35v, intelligent 12v-45v, it is best to choose the rated working voltage is 24v 7. Allowable load resistance: at rated operating voltage, the load resistance can be preferred in a wider range .

8, pay attention to choose a suitable temperature, humidity environment: a: ambient temperature -25-+80 ° C (conventional type) -25-+70 ° C (digital display) -25-+75 ° C (smart type) b: relative Humidity: 5%-95% 9. Influence of environmental impact coefficient: δ≤0.05%/°C.

10. Simple structure, no moving or elastic components, high reliability and low maintenance.

11, easy to install, easy to adjust;

12, special environmental applicability: such as high temperature, high pressure, strong corrosion and other medium environment, oscillation, etc., mechanical vibration f ≤ 50hz, amplitude ≤ 0.15mm; corrosive gas or similar environment;

13. Explosion-proof working environment, explosion-proof mode selection: N Normal non-explosion-proof I Intrinsically safe explosion-proof E Isolation explosion-proof 14. Predetermined installation method: input type, straight type, thread type, flange type........