Which expert has experience in using PLCs to control metering pumps for constant flow output? Please share your insights
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I’ve taken on a project in the petrochemical industry. The system setup involves using PLCs for PID control; the actuators are Mitrato metering pumps, and rack flow meters are used to provide flow feedback in order to achieve a constant flow rate. What issues should be considered in this system? How can pulsations be addressed? I would be very grateful for any advice from those with experience in this field!
Since it is a metering pump, there is no need to consider PID control, as there is a good linear relationship between the output flow rate of a metering pump and its rotational speed; as long as the speed remains stable, the flow rate will also remain stable. If high accuracy in flow rate is required, a frequency converter with speed feedback combined with motor speed measurement can be used; this approach provides higher precision in speed control and better results. The flow meter is used for flow correction or calibration.
I agree with the opinion of the student above. If there are pulses, should the flow meter be installed further away, or a buffer device placed in front of the flow meter?
I don’t understand what the flow rate is in liters per hour for the metering pump mentioned in the original question; it seems unnecessary to use a flow meter with such a large diameter for measuring it. There is a difference between electromagnetic metering pumps and hydraulic diaphragm pumps in terms of metering pumps, as well as in their control methods. Most hydraulic pumps are equipped with frequency converters, which raises the issue of the minimum starting frequency and minimum operating frequency of the motor. For example, with ordinary domestic motors, they start at 10 Hz, and at that point they deliver 20% of the output level that would be achieved at 50 Hz. There are also those equipped with an electronically controlled stroke regulator, which can effectively overcome the problem of the motor’s startup frequency blind spot. To overcome pulsations, manufacturers’ product lines usually offer pulse dampers as an option, but this is applicable only in situations where strict requirements are not placed on the adjustment period ； Due to the addition of dampers, there is a certain amount of pure lag, and even after the metering pump is stopped, fluid continues to be supplied into the process pipeline for a short period of time. Therefore, it is necessary to analyze each specific situation; factors such as which manufacturer’s pump to choose and whether there are fluctuations in the pressure of the process pipelines all affect the quality of regulation.