Acquisition of a flowmeter

[Andrea]

I would need to manage a flow meter to acquire the instantaneous water flow that passes through a pipe and flow management. I have found some low cost flow meters, but I don't know if it's like mine slimline MPS053 manages to manage it by displaying its value. Here below I attach the characteristics of the flowmeter:

Waterproof, Heat resistance, pressure resistance, cold resistance
Frequency: F = 4.5 * Q (L / Min) error: ± 2% (270 output pulses / liter)
Voltage: 3.5-24VDC, current can not exceed 10mA,
Maximum current: 15 mA (DC 5V)
Working voltage range: DC 5-18V
Waveform output: Square Wave, output pulse signal

[Sergio Bertana]

I did a search on the net and I found several flowmeters like the one of which I report the characteristics (Data sheet), are all objects costing around ten euros. They have a 3-wire connection (2 power supply) and signal output. I did not find if the output signal is push-pull or open collector, in any case it is possible to connect it to the digital inputs of the CPU module SlimLine.

For reading you can connect it to the counter input, but if the flow rate is low and consequently also the output frequency you can acquire the count by directly sampling the digital inputs (See topic). To calculate the flow, just count the pulses in time just like in this topic it was done to calculate the rotation speed of a motor.

[Andrea]

Thanks to the valuable advice given, I was able to create a program to manage the weeder by distributing the quantity of liters per hectare (or for any unit of measurement decided by the manager) in proportion to the speed, automatically closing the solenoid valve that manages the flow.

The wheel speed was taken by managing the columns of the wheel, which are six, with an inductive sensor. I used the rotational speed example program in revolutions per minute. The question that arises is, isn't it convenient, instead of using RPMs, to count the time between one pulse and the next, knowing the diameter divided by the number of columns?

[Sergio Bertana]

Right observation, two methods can be used to calculate the rotation speed of an axis.

Counting the pulses generated by a generator placed on the axis, as in your case, and by counting the number of pulses in a certain time you can determine the speed of the axis. This solution is suitable when the rotation speed is high (Many pulses in the sampling time). If the speed is slow there are few impulses in time and therefore an inaccurate acquisition occurs.

Measuring the time between one pulse and another, this solution is suitable when the rotation speed is slow. If the speed is high, the time between pulses is very short and therefore difficult to acquire.

Conclusions, if you want to split the hair in 4 you can manage both modes of acquisition, switching from one to the other based on the rotation speed.

[Andrea]

Thanks again for the suggestions I built this program to manage the weeder and above all I did it to take advantage of the dryer PLC in the months in which the system is switched off and unused so as to make the most of the potential of the PLC also to make people understand its great versatility.

If someone is interested I can send you the program made especially for the management of a weeder.

[Author]

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