Control of Metering Pump

[Edric]

Dear all,

Now i'm doing a project for the aluminium strip degreasing line. There is a conductivity control for the liquid in the tank.

Control element: metering pump 315l/h with variable speed control motor(370W 1440rpm), upstream is Sinamic converter.
Measuring sensor: conductivity meter. JUMO.

The pump will feed the alkaline solution into the tank(22m3) and the conductivity in the tank will be controlled in the range 10~15 ms/cm.

Anybody have some experiece for it.

My plan is to control the on-off time(pulse, PID) for the pump in a fixed low speed, but i don't know whether it is allowed that the pump on-off in so short time( approx. 1 min).

Anybody have some suggestions or new idea for the control.

Thanks a lot!

 

[Manglemender]

A degreasing tank was included as part of a lithographic plate line that I worked on in Wenzhou about 4 years ago. My memmory is a bit rusty.

This needs to be a very slow control loop in real terms due to the volume in the tank and the time it takes for any addition of caustic soda to register as a change in the conductivity. I also seem to remember that the relationship between the amount of caustic sode and the conductivity is not a linear function.

At least you've selected a proper metering pump which is more than can be said for the clowns in Wenzhou.

I would suggest that you design the control loop in terms of litres per minute required and then control the pump accordingly. You will come to a minimum speed for the pump below which you will neeed to time pulse it as you suggested.

Nick

 

[shooter]

time pulse is no problem with a VFD this will limit the current.
your idea is good, you will need some time to spread the soda so stop pump before goal.
wait for a minute then check again for goal.

 

[Edric]

Thank you for your reply!

At least you've selected a proper metering pump which is more than can be said for the clowns in Wenzhou.

how about your case of the lithographic plate line, you don't have the dosing pump, then how do you control the conductivity, only check the feedback of the meter. And what do you mean of the in term of litres per minute, can you explain a little bit detailed. Thanks!

 

[Edric]

time pulse is no problem with a VFD this will limit the current.

would you explain a little bit for me, i'm not familiar with the drive system.

Thanks a lot

 

[Manglemender]

As I recall, the addition of caustic soda was governed by a valve on a pressurised supply (BAD IDEA!!!).

The system ran off two timers. If the conductivity level was too low then the valve would open for a pre-defined period of time (a dose) and would then close and remain closed for a further pre-determined time. If the conductivity was still to low then the sequence would start again.

Nick