In the second half of the 1980s, Fuji began to sell smart transmitters. At present, more than 500,000 FCX series products have been used in various industrial processes in the whole country. FCX series products adopt the "first gold floating mold box" structure of Fuji's Haochuang, which has excellent reliability and good performance. It is one of the pressure transmitters that are widely used in my country's petrochemical industry. On the basis of FCX series pressure transmitter, Fuji has developed FCX-AⅡ series products. This series of products is also based on the structure of "first gold floating mold box" (as shown in Figure 1), which adopts silicon microcapacitance sensor and newly developed detection circuit (ASIC) in the sensor unit to realize high-precision sensor unit and The temperature compensation unit of double temperature sensor, the accuracy can reach 0.1%, and the long-term stability is within 0.1% URL (measured for 3 years).
Fuji's silicon microcapacitance sensor adopts a symmetrical differential capacitance structure, and the electrodes of the upper and lower sensitive capacitors are drawn out through the conductive layer coated in the guide hole on the sensor. When the silicone oil fills the guide hole, the external pressure acting on the floating mold box is transmitted from the silicone oil to both ends of the sensor, and the silicon wafer is squeezed and deformed, thereby changing the distance between the capacitor plates and causing the capacitance to change. Another function of silicone oil is to act as a dielectric between the capacitor plates.
The main body of the sensor is made of single crystal silicon, and the side is an aluminum electrode, which is used to connect with the lead to transmit the capacitance signal to the outside world. The rest of the conductive parts of the sensor are made up of gold. The three plates of the differential capacitor are insulated by ceramic materials.
In the sensor electrostatic capacitance detection circuit, Fuji uses an ASIC mixed with digital/analog circuits, which not only realizes high-speed detection, but also reduces the detection error caused by electromagnetic interference in the circuit, while improving detection accuracy, long-term stability and reliability.
Another innovative technology of the FCX-AⅡ series transmitter is temperature compensation based on dual temperature sensors. Through the temperature sensor built in the sensor unit and the temperature sensor built in the electronic device, temperature compensation is performed on the sensor part and the circuit part respectively to improve the temperature characteristics of the transmitter.
