The hottest intelligent transmitter is a paper-mak

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Intelligent transmitter -- a kind of paper automation instrument that "keeps pace with the times"

Hu song, senior engineer, once served as the chief of the measuring instrument section of Minfeng paper mill and the Standing Committee member of the automation professional committee of China paper society

key points: This paper introduces a new generation of transmitter, which is very different from the previous analog transmitter and has been put into use in various paper mills. The working principle of intelligent transmitter and some new problems in its use are introduced for the reference of relevant personnel in paper mills when selecting and using

key words: intelligent transmitter; working principle; Accuracy; Range migration; Communication

at present

at present, some paper mills in China use torque balanced DDZ-II instruments in production. With the development of computer technology and its application in production, ddz-iii instrument with unified signal of 4 ~ 20mA (1 ~ 5V) with computer replaces DDZ-II instrument. The development of semiconductor integration technology has led to the emergence of all electronic instruments with better performance and higher accuracy. In recent years, with the development of network technology and digital communication technology, people have added intelligent modules to all electronic instruments, and a new generation of intelligent instruments has been born. As far as I know, most of the new projects have adopted intelligent instruments

1 working principle of intelligent transmitter

at present, because computers not only completely replace the role of regulators in automatic control systems, but also greatly exceed the functions of regulators, we only introduce the working principle of intelligent transmitters

at present, as far as the current intelligent transmitter is concerned, it can be generally summarized as: diffused silicon resonance type, diffused silicon strain type, capacitance type, etc

1.1 diffused silicon resonant transmitter

at present, Yokogawa EJA series is taken as an example. On a single crystal silicon chip, microelectronic machining technology is used to make two H-shaped resonant beams with exactly the same shape and size at the center and edge of its surface, and they are located in a micro vacuum chamber, so that they are not in contact with the filling liquid, and ensure that they are not affected by air resistance during vibration. Figure 1 shows the structure of silicon resonant beam

Figure 1 the structure of the silicon resonance beam can make the joint height between plates

Figure 2 shows the self-excited oscillation circuit of the silicon resonator

at present, the silicon resonance supplier can provide free maintenance services in time for all kinds of equipment failures. Vibration can be processed through a unique hybrid molding process. The beam is in the magnetic field provided by permanent magnets, and forms a positive feedback loop with transformers, amplifiers, etc., so that the resonance beam can oscillate in the loop. Figure 2 shows the self-excited oscillation circuit of silicon resonator

at present, when the upper and lower surfaces of monocrystalline silicon are under pressure and form a pressure difference, deformation will occur, the center is under compression force, and the edge is under tension. Therefore, the two H-shaped harmonic

vibrating beams feel different strain effects respectively. As a result, the frequency of the central resonant beam decreases due to compression force, and the frequency of the edge resonant beam increases due to tension. In this way, the two H-shaped resonant beams convert the differential pressure and pressure signals into frequency signals respectively, send them to the pulse counter, and then directly transmit the difference between the two frequencies to the CPU for data processing, which is converted into the 4 ~ 20mA DC output signal corresponding to the input signal by the d/a converter, and superimpose a brain/hart digital signal on the analog signal for communication. Figure 3 shows the working principle of EJA intelligent transmitter

Figure 3 shows the working principle of EJA intelligent transmitter

at present, the built-in characteristic correction memory in the capsule assembly stores the correction data of the ambient temperature, static pressure and input/output characteristics of the sensor. After CPU calculation, the transmitter can obtain excellent temperature characteristics, static pressure characteristics and input/output characteristics

1.2 diffused silicon strain transmitter

at present, take Foxboro i/a series as an example. A very sensitive Wheatstone bridge is formed on a single crystal silicon chip by using the integrated circuit diffusion piezoresistive technology to diffuse boron into the lattice structure of the silicon chip. The back of the silicon wafer under the bridge is etched to the thickness of the corresponding measurement range by chemical etching method, and then the completed silicon wafer is bonded to the borosilicate glass or alumina substrate, and then the isolation diaphragm of various anti-corrosion materials is welded to the top of the sensor silicon wafer. Fill the gap between the isolation diaphragm and the silicon wafer with silicone oil or fluorine oil under vacuum

at present, in the application of gauge pressure and differential pressure, it is necessary to pierce a hole on the borosilicate glass substrate to the hole cavity behind the silicon wafer as the pressure inlet

at present, when pressure is applied to the integrated circuit silicon chip, stress is generated on the bridge resistance, and the piezoresistive effect formed by the pressure changes the resistance value on the bridge arm, so

generates a voltage proportional to the pressure. When the bridge excitation current is 1.0mA, the typical range of the bridge output corresponding to the full-scale pressure is 75 ~ 150mV. The bridge output signal and temperature sensor signal in the sensor module are directly transmitted to the electronic module including the signal processing circuit and microprocessor for data processing, and are converted into the 4 ~ 20mA DC output signal corresponding to the input signal by the d/a converter, A FSK modulation information based on FSK frequency shift keying technology is superimposed on the analog signal for digital communication. See Figure 4 for the block diagram of intelligent transmitter

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