There are three principles and methods for selecting the sensor of the photocoupling relay RF

　　First of all, we must have a thorough investigation and thorough understanding of the nature and characteristics of the controlled loop and the requirements of the optocoupler relay RF sensor. Secondly, the various characteristics of the light-root relay RF sensor itself - principle, conditions of use, technical parameters, structural process characteristics and specifications, etc., to achieve a comprehensive grasp and careful analysis; From the comprehensive consideration of advanced nature, rationality, availability and economy, the correct selection and use of optical coupling relay RF sensor is made. The principle of correct selection of optical coupling relay RF sensor should be specifically: (1) The main technical performance of optical coupling relay RF sensor, such as contact load, operation time parameters, mechanical and electrical life, should meet the requirements of the whole system; (2) The structure type (including the installation method) and the overall size of the optical relay RF sensor should be suitable for the needs of the conditions of use; (3) Economic rationality.

　　As the first step in selecting a photocoupling relay RF sensor, it is to determine its application classification, thus selecting a type of photocoupling relay RF sensor that has been successfully applied under a given condition, and then following the steps to make the selected photocoupling relay RF sensor most suitable for the specified application. How to choose the photoelectric relay RF sensor?

　　(1) Determine the type of optical coupling relay RF sensor according to the input signal

　　The nature of the input signal is different for the optical coupling relay RF sensors with different operating principles or structural characteristics. For example, the thermo-optical coupling relay RF sensor is a photoelectric coupling relay RF sensor that uses the thermal effect to operate; Acousto-optic relay RF sensor is operated by sound effect; The electromagnetic optocoupler relay RF sensor is controlled by the electromagnetic suction generated by the current through the coil to realize the contact opening and closing. This requires the user to first select the type of optical coupling relay RF sensor according to the nature of the input signal. For example, when reacting voltage, current or power signals, choose voltage,

　　Current or power photocoupling relay RF sensor; The reaction pulse signal may have polarity requirements

　　When, the sensor of pulse and polarized photocoupling relay RF should be selected.

　　(2) Here, a brief introduction to the difference between voltage and current optical coupling relay RF sensors for users to choose correctly. In terms of working principle, both are electromagnetic optical coupling relay RF sensors, there is no difference. However, from the design of the optocoupler relay RF sensor, there is a difference between the two. The magnetic circuit system of the photoelectric relay RF sensor is considered as IW=C, that is, when the coil inductance changes due to the armature action during the operation of the photoelectric relay RF sensor, the loop current value will not be affected. The current is determined by the larger impedance of other circuit components in the loop. The influence of coil impedance of the sensor on the impedance of the whole loop is negligible. Therefore, the number of turns of the coil wire of the general current current relay RF sensor is small, and the inductance and resistance are small, so the coil current is larger. A constant current value is supplied to the sensor coil of the current optics relay RF. Voltage optocoupler relay RF sensor coil input signal is a relatively constant voltage value, generally the power supply voltage directly added to the coil or through the network assigned to it with a constant voltage value. Therefore, the loop current depends mainly on the coil impedance and generally does not involve other loop components. In order to minimize its shunt effect on other branches, the general wire is thin, the number of turns is large, the inductance and resistance are large, and the coil current is not large.

　　(3) When selecting a current or voltage photocoupling relay RF sensor, there must be relative circuit conditions. Current optocoupler relay RF sensor requires constant current source circuit conditions, that is, the circuit has a large impedance in series with it, and its own impedance has little effect on the circuit current. Voltage optocoupler relay RF sensors require a constant voltage. The current optical coupling relay RF sensor is used as a voltage optical coupling relay RF sensor, because its coil resistance is small, it is easy to burn out the coil, and even cause a short circuit of the power supply. If the voltage optocoupler relay RF sensor when the current optocoupler relay RF sensor is connected in a series of coils in the line, due to its large impedance will significantly change the original loop parameters, because the coil does not get enough current and the optocoupler relay RF sensor does not operate.

　　It is worth noting that AC optically coupled relay RF sensor coils are generally less able to withstand overvoltages than direct flow optically coupled relay RF sensors. In the sensor coil of direct-flow photocoupling relay RF, the current increase rate caused by the increase of applied voltage is low. This is because the temperature rise of the coil causes the resistance of the coil to rise. However, in the AC photocoupling relay RF sensor, the increase of applied voltage causes the increase of current, and also causes the increase of coil resistance, which will cause further saturation of the magnetic conductive parts, so that the inductive reactance and then the impedance will be greatly reduced. The result is that the coil current increases at a faster rate than the applied voltage, so overheating due to the applied overvoltage is more likely to occur than the direct-flow photocoupling relay RF sensor.

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