Flow meter selection issues
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I searched through some posts on forums discussing flow meters, and I also looked up information online; however, most of them were related to 4-20MA flow meters, which are used to measure flow rate. I’m looking for a flow meter that can measure cumulative volume, and the medium in question is water. For example, if I need 500L of water, I set this value in the PLC; then the valve is automatically opened. As water flows through the flow meter, once 500L has been collected, a signal is sent to close the valve, thereby achieving automatic control. I wonder if there is such a flow meter? A small amount of error is acceptable, but it should not be too large; for example, it should not exceed 1%. Please give me some advice, thank you
Create an accumulation module in the PLC, define its output as an intermediate variable such as 111.SM, then use 111.SM as one of the input values in the comparison module (high selection); with a comparison value of 500, an DO signal is generated to open the valve. The theory is as such; give it a try first, without changing the flow meter.
For this as well, it depends on the medium and the flow rate to determine the appropriate choice. Avoid speed-based methods; in that case, a mass flow meter is the better choice, though there are cost considerations. :lol
Flow meters; some of them also have an accumulation function, but this depends on the specific model. I recall that the Rosemount 8800D vortex flow meter had such a function. If it doesn’t have it, then accumulation can only be done at the AS station. In the PLC, this functionality needs to be implemented by writing custom function blocks.
Conclusion: The poster is not good at self-control.
With batch water inflow, orifice plate flow meters work fine
Ultrasonic flowmeters can also accumulate measurements, and a metering device can be used for output
Flow meters should all have cumulative functions; it’s necessary to choose ones with good repeatability – repeatability is absolutely crucial!
Original poster, ignore what those people above say – this function has nothing to do with flow meters. By adding an accumulation module to the PLC, it’s possible to accumulate values for any flow meter, as long as its measurements are accurate, and then close the valve.
Such flow meters have existed for a long time; they can be found online
OP, I understand what you mean. You’re not suggesting that the valve should be closed every time 500L is accumulated, because this approach won’t solve the issue related to the flow meter’s readings. You don’t need to use a flow meter; instead, use a small container with a capacity of 800L. Install a level gauge on this container, and use the height indicated by the level gauge to determine how much water has been accumulated. The valve can then be closed once 500L has been reached.