Sensors and transmitters play an important role in the field of instruments, meters and industrial automation. Different from the sensor, the transmitter generally has a certain amplification effect, in addition to converting non-electrical energy into measurable electricity. The following briefly describes the characteristics of various types of transmitters for your reference.
First, integrated temperature transmitter Integrated temperature transmitter generally consists of a temperature probe (thermocouple or thermal resistance sensor) and two-wire solid electronic unit. The solid-state module is used to mount the temperature probe directly in the junction box to form an integrated transmitter. Integrated temperature transmitters are generally classified into two types: thermal resistance and thermocouple type. Thermal resistance temperature transmitter is composed of reference unit, R/V conversion unit, linear circuit, reverse connection protection, current limiting protection, V/I conversion unit and so on. After the temperature-resistor resistance signal is converted and amplified, the linear circuit compensates the nonlinear relationship between temperature and resistance. After the V/I conversion circuit, a constant-current signal of 4-20mA linearly related to the measured temperature is output. The thermocouple temperature transmitter is generally composed of a reference source, a cold junction compensation, an amplifying unit, a linearization process, a V/I conversion, a burnout processing, a reverse connection protection, and a current limit protection circuit unit. It is the thermal potential generated by the thermocouple through the cold junction compensation and amplification, and then by the linear circuit to eliminate the thermal potential and temperature of the nonlinear error, and finally amplified into 4 ~ 20mA current output signal. In order to prevent accidents caused by temperature control failure due to galvanic disconnection in thermocouple measurement, a power failure protection circuit is also provided in the transmitter. When the thermocouple breaks or fails to connect properly, the transmitter will output the maximum value (28mA) to make the meter cut off the power.
The integrated temperature transmitter has the advantages of simple structure, saving lead wire, large output signal, strong anti-interference ability, good linearity, simple display instrument, solid module moisture resistance, reverse connection protection and current limit protection, and reliable work. The output of the integrated temperature transmitter is a unified 4-20mA signal; it can be used in conjunction with a microcomputer system or other conventional instruments. Can also be made of explosion-proof or fire-proof measuring instruments.
Second, the pressure transmitter Pressure transmitter is mainly composed of load cell sensors, module circuits, display head, case and process connections and other components. It can convert the received gas, liquid and other pressure signals into standard current and voltage signals to provide secondary instruments such as alarm indicators, recorders, and regulators for measurement, indication and process adjustment. The measuring principle is: the process pressure and the reference pressure act on the two ends of the integrated silicon pressure sensitive element, respectively, and the differential pressure causes the silicon wafer to deform (the displacement is very small, only μm level), so that the silicon wafer is made of semiconductor technology. The full-dynamic Wheatstone bridge outputs an mV-level voltage signal proportional to pressure, driven by an external current source. Since the silicon material has excellent strength, the linearity and variation index of the output signal are both high. At work, the pressure transmitter converts the measured physical quantity into a mV-level voltage signal and sends it to a differential amplifier that has a high amplification and cancels temperature drift. The amplified signal is converted into a corresponding current signal by voltage-current conversion, and then subjected to a non-linear correction. Finally, a standard current-voltage signal having a linear relationship with the input pressure is generated. The pressure transmitter can be divided into two general pressure transmitters (-100Pa~120MPa) and micro differential pressure transmitters (0.1~1.5kPa) according to the pressure measurement range.
Third, the level transmitter 1, float type liquid level transmitter Float level transmitter consists of magnetic float ball, measuring catheter, signal unit, electronic unit, junction box and mounting parts. The magnetic float generally has a specific gravity of less than 0.5 g/cm3 and can float above the liquid surface and move up and down along the measuring tube. The catheter is equipped with a measuring element, which can convert the measured liquid level signal into a resistance signal proportional to the change of liquid level under the action of external magnetic flux, and converts the electronic unit into 4-20 mA or other standard signal output. The transmitter is a module circuit, which has the advantages of acid resistance, moisture resistance, shockproof, anti-corrosion, etc. The circuit contains a constant current feedback circuit and internal protection circuit, so that the maximum output current does not exceed 28mA, so it can reliably protect the power supply and make two The secondary meter is not damaged.
2, floating type level transmitter Float type liquid level transmitter is to change the magnetic float to buoy, which is designed according to Archimedes buoyancy principle. Float type liquid level transmitters use tiny metal film strain sensing technology to measure liquid level, boundary level, or density. It can be used to perform routine settings* via on-site keystrokes while working.
3, static pressure or level transmitter The transmitter uses the principle of measurement of hydrostatic pressure work. It generally selects the silicon pressure pressure sensor to convert the measured pressure into an electric signal, and then compensates by the amplifying circuit and the compensating circuit, and finally outputs the current by 4-20 mA or 0-10 mA.
IV. Capacitance Level Transmitter Capacitive level transmitter is suitable for industrial enterprises to measure and control the production process during the production process. It is mainly used as liquid level or powdery granular solid material level for conductive and non-conductive media. The long-range continuous measurement and indication. The capacitive level transmitter consists of a capacitive sensor and an electronic module circuit. It uses a two-wire constant current output of 4 to 20mA as the base type. After conversion, it can be output in three-wire or four-wire mode. The output signal is formed as 1 to 1 5V, 0 ~ 5V, 0 ~ 10mA and other standard signals. The capacitive sensor consists of an insulated electrode and a cylindrical metal vessel equipped with a measuring medium. When the material level rises, the dielectric constant of the non-conductive material is significantly smaller than the dielectric constant of air, so the capacitance changes with the height of the material. Transmitter module circuit consists of reference source, pulse width modulation, conversion, constant current amplification, feedback and current limiting unit. The advantage of using the pulse width modulation principle to measure is that it has a low frequency, interference with ambient radio frequency, good stability, good linearity, and no significant temperature drift.
V. Ultrasonic Transmitters Ultrasonic transmitters are divided into general ultrasonic transmitters (without headers) and integrated ultrasonic transmitters. Integrated ultrasonic transmitters are more commonly used. The integrated ultrasonic transformer consists of a watch head (such as an LCD display) and a probe. This transmitter, which directly outputs a 4 to 20 mA signal, assembles a miniaturized sensor (a probe) and an electronic circuit. Make it smaller, lighter, and cheaper. Ultrasonic transmitters can be used to measure liquid level, level, open channels, open channels, etc., and to measure distances.
6. Electrode pH Transmitter 锑 Electrode pH Transmitter is an industrial online analytical instrument that integrates PH detection, automatic cleaning, and electrical signal conversion. It is a PH value measurement system consisting of a tantalum electrode and a reference electrode. In the measured acidic solution, a germanium trioxide oxide layer is formed on the surface of the germanium electrode, so that a potential difference is formed between the germanium surface and the germanium trioxide. The magnitude of this potential difference depends on the concentration of trioxotide, which corresponds to the appropriate level of hydrogen ions in the acidic solution being tested. If the appropriateness of yttrium, yttria and aqueous solution is taken as 1, the electrode potential can be calculated using the Nernst formula. The solid module circuit in the pH transmitter consists of two major components. For the sake of safety in the field, the power supply uses AC 24V to power the secondary instrument. In addition to supplying power to the cleaning motor, this power supply should also be converted into a corresponding DC voltage by the current conversion unit for use by the transmission circuit. The second part is the measurement transmitter circuit, which sends the reference signal and PH acidity signal from the sensor to the slope adjustment and positioning adjustment circuit so that the internal resistance of the signal can be reduced and adjusted. The amplified PH signal and the temperature compensated signal are superposed and then converted into a conversion circuit. Finally, a 4-20 mA constant current signal corresponding to the PH value is output to the secondary meter to complete the display and control the PH value.
Seven, acid, alkali, salt concentration transmitter acid, alkali, salt concentration transmitter by measuring the conductivity of the solution to determine the concentration. It can continuously monitor the concentration of acid, alkali and salt in aqueous solution in the industrial process. This transmitter is mainly used in boiler water treatment, chemical solution preparation and environmental protection and other industrial production processes. The working principle of the acid, alkali, and salt concentration transmitters is: within a certain range, the concentration of the acid-base solution is proportional to the size of its electrical conductivity. Therefore, as long as the measurement of the conductivity of the solution changes, the concentration of acid and alkali can be known. When the measured solution flows into a dedicated conductivity cell, if the electrode polarization and distributed capacitance are ignored, it can be equivalent to a pure resistance. When there is a constant voltage alternating current flowing, the output current is linear with the conductivity, and the conductivity is proportional to the concentration of acid and alkali in the solution. Therefore, as long as the solution current is measured, the concentration of acid, alkali and salt can be calculated. The acid, alkali, and salt concentration transmitters consist of a conductivity cell, an electronic module, a display meter, and a housing. The electronic module circuit is composed of excitation power supply, conductivity cell, conductance amplifier, phase sensitive rectifier, demodulator, temperature compensation, overload protection and current conversion.
VIII Conductivity Transmitter It is a process instrument (integrated transmitter) that measures the ion concentration indirectly by measuring the conductance value of a solution, and can continuously detect the conductivity of an aqueous solution in an industrial process on-line. Because the electrolyte solution is the same good electrical conductor as the metal conductor, there must be an electrical resistance when the current flows through the electrolyte solution, and it is in accordance with Ohm's law. However, the resistance temperature characteristics of liquids are contrary to those of metal conductors and have negative temperature characteristics. In order to distinguish from the metal conductor, the conductivity of the electrolyte solution is represented by conductance (reciprocal of resistance) or conductivity (reciprocal of resistivity). When two electrodes that are insulated from each other form a conductivity cell, a current loop is formed if the solution to be measured is placed in between, and a constant voltage alternating current is passed through. If the voltage size and the electrode size are fixed, the loop current and the conductivity have a certain function. In this way, measuring the current flowing in the solution to be measured, the conductivity of the solution to be measured can be measured. The conductance transmitter has the same structure and circuit as the acid, alkali, and salt concentration transmitters.
Nine, smart transmitter Intelligent transmitter is a sensor and microprocessor (microcomputer) phase structure. It makes full use of the microprocessor's computing and storage capabilities, and can process sensor data, including conditioning of measurement signals (such as filtering, amplification, A/D conversion, etc.), data display, automatic correction, and automatic compensation. The microprocessor is the heart of the smart transmitter. It can not only calculate, store and process the measurement data, but also adjust the sensor through the feedback loop to make the collected data the best. Because the microprocessor has a variety of software and hardware capabilities, it can accomplish tasks that traditional transmitters are difficult to accomplish. Therefore, the intelligent transmitter reduces the manufacturing difficulty of the sensor and improves the sensor performance largely. In addition, the intelligent transmitter also has the following features:
1. With automatic compensation ability, software can automatically compensate sensor nonlinearity, temperature drift and time drift. Can be self-diagnosis, after the power can be self-test sensor to check the sensor is normal, and make judgments. Data processing is convenient and accurate, and data can be automatically processed according to internal procedures, such as statistical processing, removal of abnormal values, and the like.
2. With two-way communication capabilities. The microprocessor not only receives and processes sensor data, but also feeds information back to the sensor to adjust and control the measurement process. The information can be stored and memorized, and the sensor's characteristic data, configuration information, and compensation characteristics can be stored.
3. With digital interface output function, the output digital signal can be conveniently connected with computer or field bus.