Pump current indication
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When using variable frequency speed control, (1) does the variable frequency signal require a special controller to issue commands? Can a regular controller, such as one used in flow control circuits, directly send signals to adjust the motor’s frequency? (2) How can the speed change be seen on the DCS during variable frequency speed control? Can it be seen directly with the current indicator? Are there any reference materials?
Sure. The output of the flow control circuit is a 4-20mA current signal, and the frequency converter uses this 4-20mA signal to adjust the speed. A speed sensor can be installed to monitor the speed; however, measuring the current alone is not very accurate, as for a frequency-driven motor, when the speed is constant, the magnitude of the current is closely related to that speed
OP, which system are you using! The first question: It’s probably not practical to adjust the frequency of the inverter directly through the control circuit; it still needs to be done through controller programming! For the second question, it can be achieved using a speed sensor!
First question: What exactly is the controller of the traffic control loop that the original poster is referring to? Quadratic meter? PLC? As long as a 4-20MA signal is generated, it can be used to control the frequency converter. Of course, it depends on the control requirements such as stability, accuracy, and deviation, as well as the actual performance of the control system; if these requirements are not met, it is better to carry out signal processing and apply PID adjustments first. Although modern frequency converters generally have PID functionality, in practice performing the calculations within a PLC or DCS yields better results. Second, the inverter can output a 4-20MA signal on its own, and the user can configure it as a speed signal, eliminating the need for a speed sensor. But as a few people above have said, the conversion might not be accurate; it depends on your requirements. Better frequency converters use vector control technology, resulting in quite accurate feedback of the speed signal. Communicate with each other and make progress together.
Modern frequency converters generally come equipped with a 4-20MA feedback signal that is proportional to the frequency signal; by performing conversion, the speed signal can be obtained.