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Knowledge Of Selection Of Transducer Sensors And Safe Use Of Transducers

Aug 24, 2020

Knowledge of selection of transducer sensors and safe use of transducers

In daily work, what should be paid attention to when selecting the inverter? First of all, we must know that the inverter can not be used normally under any circumstances, so it is necessary for the user to have more knowledge about the load, environmental requirements and the inverter. There are seven points of attention:

  1. Long-term low-speed rotation, because the motor generates higher heat and the cooling capacity of the fan is reduced, it is necessary to increase the reduction ratio or switch to a 6-level motor to make the motor run near a higher frequency.

  2. The installation location of the inverter must meet the requirements of the standard environment, otherwise it will easily cause failure or shorten the service life; the distance between the inverter and the drive motor is generally not more than 50 meters, if a longer distance is required, the carrier frequency must be reduced or increased The output reactor option can operate normally.

  3. Selection of load type and inverter:

The load driven by the motor is different, and the requirements for the frequency converter are also different.

  4. Fans and pumps are the most common loads: the requirements for the inverter are the simplest, as long as the inverter capacity is equal to the motor capacity (air compressors, deep water pumps, sediment pumps, and rapidly changing musical fountains need to increase the capacity) .

  5. Crane load: This type of load is characterized by a large impact when starting, so it requires a certain margin for the inverter. At the same time, if the elbow is put under the heavy object, there will be energy feedback, so the brake unit or the shared bus method should be used.

  6. Uneven load: Some loads are sometimes light and sometimes heavy. At this time, the inverter capacity should be selected according to the heavy load, such as steel rolling machinery, crushing machinery, mixers, etc.

  7. Large inertial loads: such as centrifuges, punches, and rotary kilns in cement plants. Such loads have a large inertia, so they may oscillate when starting, and there will be energy feedback when the motor decelerates. A frequency converter with a larger capacity should be used to speed up the start and avoid oscillation. Cooperate with the braking unit to eliminate the feedback power.

Second, eight precautions for using the inverter

  1. Vibration and shock. When the control cabinet equipped with the inverter is subjected to mechanical vibration and shock, it will cause poor electrical contact. At this time, in addition to improving the mechanical strength of the control cabinet and staying away from vibration sources and shock sources, vibration-resistant rubber pads should also be used to fix vibration-generating components such as electromagnetic switches outside and inside the control cabinet. After the equipment has been running for a period of time, it should be inspected and maintained.

  2. Electrical environment, physical environment, and ambient temperature. When the temperature is too high and the temperature changes greatly, condensation is likely to occur inside the inverter, and its insulation performance will be greatly reduced, and it may even cause a short circuit accident. When necessary, desiccant and heater must be added to the box.

  3. Working temperature. There are high-power electronic components inside the inverter, which are easily affected by the operating temperature. The product generally requires 0~55℃, but in order to ensure safe and reliable work, you should consider leaving room when using it, and it is best to control it below 40℃ . In the control box, the installation of the inverter should strictly comply with the installation requirements in the product manual, and it is absolutely not allowed to install heating elements or components that are easy to heat up close to the bottom of the inverter.

  4. Prevent over-voltage at the input. The input terminal of the inverter power supply often has overvoltage protection, but if the high voltage at the input terminal lasts for a long time, the input terminal of the inverter will be damaged. Therefore, in actual application, it is necessary to verify the input voltage of the inverter, single-phase or three-phase, and the rated voltage of the inverter. Especially when the power supply voltage is extremely unstable, there must be a voltage regulator device, otherwise it will cause serious consequences.

  5. Corrosive gas. If the concentration of corrosive gas in the use environment is large, it will not only corrode the leads of the components, printed circuit boards, etc., but also accelerate the aging of the plastic devices and reduce the insulation performance. In this case, the control box should be made into a closed structure , And ventilate

  6. Prevent electromagnetic interference. Due to the rectification and inversion of the frequency converter during operation, a lot of interference electromagnetic waves are generated around, and these high-frequency electromagnetic waves have certain interference to nearby instruments and instruments. Therefore, the instrument and electronic system in the cabinet should be made of metal shell to shield the interference of the inverter to the instrument. All components should be grounded reliably. In addition, shielded control cables should be used for wiring between electrical components, instruments and meters, and the shielding layer should be grounded. If electromagnetic interference is not handled well, the entire system will often fail to work, causing the control unit to malfunction or damage.

  7. The correct grounding of the inverter is an important means to improve the sensitivity of the control system and the ability to suppress noise. The smaller the grounding resistance of the grounding terminal E (G) of the inverter, the better. The cross-sectional area of the grounding wire should not be less than 2mm2, and the length should be controlled within 20m. The grounding of the inverter must be separated from the grounding point of the power equipment, and cannot be shared. The shielding layer of the signal input line should be connected to E (G), and the other end must not be connected to the ground, otherwise it will cause signal fluctuations and make the system oscillate. There should be electrical connection between the inverter and the control cabinet. If the actual installation is difficult, copper core wires can be used for jumper connection.

  8. In the inverter, there is generally a lightning absorption network to prevent the intrusion of instant lightning and damage the inverter. But in actual work, especially when the power cord is introduced overhead, the absorption network of the frequency converter alone cannot meet the requirements. This problem is particularly important in areas where lightning is active. If the power supply is overhead incoming lines, install a special frequency conversion lightning arrester (optional) at the incoming line, or pre-bury steel pipes 20m away from the inverter for special grounding as required by the specification. protection. If the power supply is introduced by a cable, a lightning protection system in the control room should be prepared to prevent lightning from entering and destroying the equipment. Practice shows that the problem of lightning strikes can basically be solved effectively.

  If you want to buy an inverter with confidence, you must understand the basic knowledge of the inverter sensor and the knowledge of safe use if you want to use it. This will not only work better, but also extend the working life of the inverter sensor!

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