Basic Principles for Selecting Temperature Transmitters

Ⅰ. The role of temperature transmitter

The thermal resistance does not output signals itself, only reflects the temperature value. Temperature transmitter, specially used in thermal resistance or hot spot couple, converts the temperature into a current signal of 4-20MA. Generally, current controllers are directly equipped with corresponding temperature transmitter analog input modules, such as thermostats, PLC thermal resistance analog modules.

"The intrinsically safe thermocouple transmitter just converts the direct temperature signal (should belong to an analog quantity) into a digital quantity" is a wrong expression. Although some have this function, most of them directly convert temperature signals (depending on different types, there are resistance or voltage, like the voltage is millivolt that is a different signal type, or due to the different size range, some components cannot be identified, so they need to be converted) into analog (standard signals are generally easy to identify, and some also have digital communication functions ).

Ⅱ. The basic principles of selecting temperature transmitters

1. As for the system, 2 wire temperature transmitter system is preferably used to transmit a current signal of 4 mA to 20 mA.

2. The measuring range and temperature output signal of temperature transmitter correspond to the temperature measuring range set by the user.

3. The operation conditions and environment temperature requirements of temperature transmitter should depend on the specific location. A wide temperature zone must be chosen for outdoors in cold winter areas; the requirements can be not very strict in subtropical areas or indoors. It should be noted that when temperature transmitter in a safety automation system is measured at higher temperatures, the temperature at its module cannot exceed the specified range. Otherwise, a wall-mounted transmitter should be used, or a compensation lead should be used to lower the temperature;

4. The change of the power supply voltage of  temperature transmitter and the change of the load resistance have little influence on the measurement accuracy.