Transmitter characteristic analysis and important role

Sensors and transmitters play an important role in instrumentation and industrial automation. Different from the sensor, the transmitter generally has a certain amplification effect, in addition to converting the non-electricity into measurable electricity. This article briefly describes the characteristics of various types of transmitters for use by users.
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 directly install the temperature probe in the junction box, thus forming 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 the temperature and the resistance. After the V/I conversion circuit, a constant current signal of 4-20 mA linearly related to the measured temperature is output.
The thermocouple temperature transmitter is generally composed of a reference source, cold junction compensation, amplification unit, linearization processing, V/I conversion, burnout processing, reverse connection protection, current limiting protection and other circuit units. It is the thermal potential generated by the thermocouple through the cold junction compensation and amplification, and then cap the linear circuit to eliminate the non-linear thermal potential and temperature 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 limiting 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, also known as the difference transmitter, mainly by the pressure measuring element sensor, module circuit, 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.
Pressure transmitter measurement schematic shown in Figure 3. 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 very high amplification and can cancel out the 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.
Pressure transmitters can be divided into two general pressure transmitters (0.001MPa to 20MP3) and differential pressure transmitters (0 to 30kPa) according to the pressure measurement range.
Third, the level transmitter
1. Float Level Transmitter Float type liquid level transmitter is composed of magnetic float, measuring conduit, signal unit, electronic unit, junction box and mounting parts. Generally, the specific gravity of the magnetic float is less than 0.5, and it can float on 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, which can reliably protect the power supply and make the two The secondary meter is not damaged.
2. Float type liquid level transmitter Float type liquid level transmitter is to change 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 use the on-site key to perform routine setting operations 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 in a 4-20 mA or 0-10 mA current mode.
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 a liquid level or 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 a basic 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 surrounding 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 the volume filial, lighter, and cheaper. Ultrasonic transmitters can be used for level. Level measurement and flow measurement of open channels, open channels, etc. can be used to measure distances. 6. Electrode pH Transmitter The pH Electrode Transmitter is an industrial online analytical instrument that integrates PH detection, automatic cleaning, and electrical signal conversion. It is a pH 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 oxide. 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 appropriate values ​​of germanium, antimony trioxide, and aqueous solution are all 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. After the amplified PH signal and the temperature compensation signal are superposed, the differential conversion circuit is added. Finally, the 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 detect 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 operating 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 linearly related to 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.

Nickel Alloy Welding Wire\Welding Consumables

Nickel-based alloy wire owns good resistance to high reactive gases, caustic resistance medium and acid corrosion performance, and also owns high strength, good capability of shaping, hot and cold forming and welding deformation. Therefore it is widely used in petroleum chemical industry, metallurgy, atomic energy, ocean development, aviation, aerospace to solve the problem that general industry, stainless steel and other metals, non-metallic materials engineering corrosion problems could not be solved,it is a very important kind of corrosion resistant metal materials. Nickel based alloys are nickel based alloys that contain alloy elements and which can be resistant to corrosion in a number of media. To classify the chemical composition characteristics, mainly nickel, nickel copper alloy, nickel alloy, nickel chromium molybdenum (Nie Mutie) (iron nickel alloy), nickel chromium molybdenum (including Ni Cr Mo alloy and Ni Cr Mo Cu alloy) and nickel iron chromium (both iron nickel alloy) and other types of. Pure nickel welding wire ERNi-1 for welding of 200, 201 nickel alloy and nickel plated steel plate; steel and nickel dissimilar materials welding; steel surface surfacing.