(1) Thermocouple: The principle of thermocouple is that when two different conductors or semiconductors are connected into a closed circuit, if the temperature of the two contacts is different, the thermoelectric EMF will appear in the circuit and generate current.
The thermoelectric potential of the thermocouple depends not only on the temperature of the measuring end, but also on the temperature of the free end (cold end).
In order to ensure the measurement accuracy, an additional potential which changes with the temperature of the cold end is usually introduced into the circuit of the measuring instrument to compensate the temperature of the cold end automatically. Considering that the transmitter is usually far away from the measuring point, it is too expensive to use a more expensive thermocouple wire to lead from the measuring point to the transmitter. In order to save money, low-cost metals with similar thermoelectric properties at lower temperatures (below 100 degrees Celsius) are used in industry as substitutes for thermocouple wires in the low-temperature region, called compensating wires, so that the thermocouple wires can only be drawn below 100 degrees Celsius, and the rest of the length can be extended by cheap compensating wires. .
Thermocouple models are mainly K type, S type and B type according to the temperature range.
(2) Temperature Transmitter: The main function of input circuit of temperature transducer is temperature compensation and zero-point adjustment at cold end of thermocouple. The output circuit mainly converts the millivolt signal of the thermocouple into the standard signal (generally using the current signal of 4-20 mA), and transmits it to the temperature control unit behind.
(3) flow orifice: the function is to detect the differential pressure signal on both sides of the orifice plate.
(4) Flow Transmitter: The differential voltage signal detected by orifice plate is converted into current signal of 4-20mA and transmitted to flow control unit.
(5) pressure transmitter: the pressure signal detected at the pressure port is converted to 4 to 20mA current signal.
(6) thermal resistance: thermal resistance is temperature measurement based on the resistance of metal conductor with temperature. Thermal resistance is often used to measure temperature when the temperature is below 150 C because of the small potential of the thermocouple. Thermal resistance (PT100) is used to detect the temperature of the driving fan and the walking beam of the heating furnace. Thermal resistance does not need cold-end temperature compensation as thermocouples do, and the measurement accuracy is relatively high. It is suitable for temperature detection in the range of - 200 ~ +500 ~.
(7) Valve positioner: the flow controller output of 4-20 mA signal into gas signal, control the opening of the actuator. The valve positioner mainly consists of electrical conversion unit and position feedback unit.
(8) Pneumatic actuator: pneumatic actuator is an important part of the furnace combustion control system. It is powered by compressed air and consists of pneumatic actuator and regulating valve. The actuator is the driving part of the actuator. It produces thrust or displacement according to the signal given by the valve positioner. The most common part of the regulator is the regulator valve, which is operated by the actuator by changing the flow area between the spool and the seat to regulate the flow of media.
(9) electric actuator: consists of two parts: actuator and regulating valve. The control valve part and the pneumatic actuator are universal, but the difference is that the electric actuator uses the electric actuator, even if the motor is used as the power source to regulate the opening of the valve.