PID Control for pump problem

Hi guys,

I'm having a problem with one of my pump on my system which is working with a PID in my SLC5/03.

A brief explanation of my process
The liquid from a tank need to be pumped with this pump controlled with a PID
and should maintain the right pressure asked at the output of this pump.
For exemple if i ask on the HMI 5 PSI.. this pump should start and reach 5PSI and then modulate around it.

In Manual Mode, i have no problem to start this pump and reach all the speed that i need from 0-100%
The Speed feedback on my HMI seem to work properly with the real speed of my motor and Hz on my drive.
I tested 0%, 10%, 20% and 30% in manual
Im also prety sure the Pressure feedback is also good on my HMI

The problem i have, when i turn my pump in automatic mode, itsimply can't start, the speed feedback stay at 0% and even when i do a start in manual and reach my PSI and switch in automatic the speed feedback drop from 20% to 0% and my PSI drop to 0...

It just like that my PID doesnt really take care of my Process Value or do not modulate properly.

I also tried with a higher GAIN setting like 5.0 or 15.0 and it doesnt do anything better, rather than droppingto 0% if it's set too high it will ignore my PV and simply overshoot my PSI and keep rising it.

i posted also my PID and all SCP from my PLC
I can also confirm that there is 30 word between each PID...
N21:23 Actual pump
N21:53 Other Pump 1
N21:83 Other Pump 2

The pressure transmitter is 0-250PSI working in 4-20ma
http://www.gefran.com/pt/download/4175/attachment/en

And my drive is a Siemens Micromaster 440
6SE6440-2UE24-0CA1

If you guys have any suggestion or idea please let's me know

Thank you !

Post your .RSS file here. Zip it first.

Set bit "OL"

Why do you have the "output max" set at 30?

"Limit Output CV" set to yes.

It sounds like it's running direct control action (when PV < SP decrease the output), but needs to be reverse action (when PV < SP, increase the output)

I don't know how the PID setup interprets Control Mode E = SP-PV. Is that direct or reverse action?

danw said:

It sounds like it's running direct control action (when PV < SP decrease the output), but needs to be reverse action (when PV < SP, increase the output)

I don't know how the PID setup interprets Control Mode E = SP-PV. Is that direct or reverse action?

Click to expand...

See pdf (reverse action)

From what i saw in manual the output never need to be higher than 30% to reach the PSI needed, i would guess its the reason why i have a max setting there.
i guess i could put to yes the limit output CV

Unfortunately i dont have the right to post my .RSS or i would have done it.

From your PDF:
When cleared (0) - Reverse acting (E=SP-PV) causes the control variable to
decrease when the process variable is greater than the setpoint.

it seem to be the right control mode.



Could it be possible that i have a bad scaling on my output or something ?
If you watch my N21:23 SCP
my Input is like 38 ony my 0-16383 Scale
and my output is like 11235 on my 6242-31206 Scale
isnt it suposed to be proportional ?

Could it be possible that i have a bad scaling on my output or something ?
If you watch my N21:23 SCP
my Input is like 38 ony my 0-16383 Scale
and my output is like 11235 on my 6242-31206 Scale
isnt it suposed to be proportional ?

Click to expand...

With a value of 38 on a scale of 0-16383 rescaling it to 6242-31206 you get..

38/16383=.002319

.002319*(31206-6242)+6242=6299.8

Is something else writing to O:6.5?

Output scaling will depend on the output card you have and how you have it configured.

How are you controlling the output in the manual mode?

You should be writing to the PID's CV this will allow a bumpless transfer when going back to auto. See PDF..

Nop nothing else on my program is on the O: 6.5
only this PID is wirting on it.
i watched my output card is also configured in 4-20ma

i guess im going to give a try in forward acting

One of the problem i have right now i dont have any USB to DH485 adapter so i have to use my RS232/CP3 cable to go online which is the same than my HMI... so i cant use both at the sametime.

From what i can see, i dont have anything else controling my output N21.23 other than the PID so, my guess the percentage on the HMI for the manual that i want do directly into N21.23 when the PID is off.

Anyway i abit running out of time with this problem thanks for the help but i think im going to call someone local to help me solve the problem.

Mickey, thanks for the screen shot with control action definitions. Dan

I was abit in a rush rhe other day just wanted to take a min to thanks you for the support

Martindag said:

Anyway i abit running out of time with this problem thanks for the help but i think im going to call someone local to help me solve the problem.

Click to expand...

Please come back with your solution, once you solve it.

I will !