Autor Thema: flowmeter, pid, totalizer errors HELP!  (Gelesen 11241 mal)

Offline rev667

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flowmeter, pid, totalizer errors HELP!
« am: August 25, 2011, 11:10:55 Vormittag »
Hi guys,

I have an application that sprays water onto material as it passes through a duct.

I have a small pump fed by a tank, the pumped water goes through a proportional valve controlled by a 0-10V signal. This then goes through a flowmeter which gives a pulse for every cc (1000 pulses per litre), this then feeds the sprayjet.

I am controlling the valve manually from the screen, with the flowmeter providing feedback for the operator. The flow required is in the range 1 to 4 litre per minute, the optimum flowrate is 2 litres per minute (33hz on the flowmeter). I have connected the flowmeter to both inputs I1 and I2.

Input 1 drives a frequency counter block to provide the litres per minute on the screen.
Input 2 drives a high speed counter for totalizing purposes.

I have 2 problems.

The first problem is that I would like to control the valve using a PID block, so the operator sets the flowrate and the valve is controlled by the PID loop. I have tried this but it always becomes unstable. Any advice would be welcome.

The second problem is the totalizer, it seems inaccurate when compared to the flowrate and the real evidence of the tank level. I suspect it has something to do with the high speed counter not working untill the input is higher that 4hz. Could I use a normal counter?

Any help would be very welcome.


Offline Urs

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Re:flowmeter, pid, totalizer errors HELP!
« Antwort #1 am: August 27, 2011, 08:25:39 Vormittag »
Hello rev667

Regarding the PID settings you could find further informations paired with training on a simulator under:

Usually it's helpful to deal only with P and I value and leave the D value 0 (inactive).

The D part is mostly only needed for complicated very fast acting prozesses.

Hope it helps.

Regards Urs
« Letzte Änderung: August 27, 2011, 09:58:38 Vormittag von Urs »

Offline Sam

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Re: flowmeter, pid, totalizer errors HELP!
« Antwort #2 am: August 31, 2011, 14:54:28 Nachmittag »
Hello Urs,

if you do not get all the pulses to easy-relay, there could be several reason. One thing is that you have to use only 24VDC models easy-relay, because 240VAC inputs cannot take pulses so fast. If you have 24VDC model, then check that in Systems Setting "Debounce" must not be activated. If this is activated, you lost pulses for sure.
I Hope these information helps you.