Highest analog value

I am using PLC5/40 in our Extrusion press. I have an application in which i need to extract the highest value of pressure.
Pressure inside our Ram cylinder changes from 11 bar to 250 bar.
But each cycle it will have different higest pressure but less than the maximum pressure of 250 bar.
I want move the highest pressure of the previous cycle and use that pressure minus some safety value for next cycle.

In one cycle pressure increases from 11 bar(minimum) to approx. 220bar(not standard every time) and from there it will regulate to 210 or less than that and will continue to reduce till the extrusion is complete.

Now i need a routine to extract the highest pressure value.


Many thanks

I assume you are referring to an aluminum extrusion press?

Peak min and max detectors are pretty easy to build in any PLC.

For a peak 'max' detector, you need a suitable trigger. Possibly use a bit that indicates 'Container closed' or 'Crush/Upset' or if you have an internal command relay label 'Extrude' that would work also. If your press has 'surge valves' or 'prefill' valves, I would make sure that you use a bit that is only true while these valves are closed, so that you are looking at true 'extrusion' pressure and not the pressure required to move the ram during rapid close, or during some auxiliary function like 'container close'.

Use a positive transitional one-shot contact from your 'trigger' to MOVE a zero value to some integer register that will hold your sampled value.

Next you need to put a normally open contact from your trigger in series with a 'GREATER THAN' instruction. The top node of the compare instruction should be the register for actual pressure. The bottom node should contain the peak value register.

At the end of this logic string put another move instruction. The top node will contain the actual pressure, the bottom node will contain the peak value.

The logic works as follows:

At the start of extrusion (or what ever you use for a trigger) a value of zero is initially written to your register that contains the peak pressure value. All the time that your trigger bit is true, your actual pressure will be compared to your peak value and if the actual is greater than the peak, it will write continuously over write the highest pressure value detected during the extrude cycle.

Since the pressure does drop off near the end of an extrusion cycle, the peak recorded value will be higher than the actual pressure so the value will not get over written.

Once your trigger event is false, the peak value will remain frozen, available for any other use. You can add optional logic, triggered by a negative transition one-shot to move the peak recorded value to some other register or data table if you need to further buffer this value.

I appologize for a verbal description of the logic instead of posting a sample diagram, but I never quite figured out how to post diagrams.

A peak 'min' detector is similar in concept but you write the largest value possible at the trigger transition (i.e. 32767 for an integer) and use a 'LESS THAN' evaluation to move the actual value to the 'peak' value. This isn't useful in your extrusion press but there might be other applications in which the minimum value needs to be recorded i.e. fluid level in a reservoir, lowest position reached for an axis, etc.

Aluminium Extrusion

Thanks Mr. Greg Gauper !!!

Yes you are right. Its working. I tried all that but since i had been sleepless for last 3 days i could not think anything on my own.

Yes you are again right. Its an Aluminium extrusion press. I hope you would have lots of experience on Aluminium extrusion press.

I never had any experience with Aluminium Extrusion press until three days before when on our customer called me to do program modification on his press.

First day it was realy frightening as they spoke in terms of press and no body came for my help.

Actually this what they said on my first day. They wanted to decrease their cycle time and so they showed me a chart in which actual pressure took long time to reach extrusion pressure.

They told me in terms of Upset and breakthrough. Upset was always fixed at 100 bar and also breakthrough was fixed at 100 bar. After break through pressure is reached Extrusion is started. So now it will move from 100 bar to 220 (+/- 20 bar). Upset happened first and then immediatley break through.at the end of break through extrusion started. After reaching peak pressure of 220 bar it goes into regulation where the pressure drops to some where around 150 bar and then extrusion stops and actual pressure goes to some where around 11 bar.

So they said they need to reduce cycle time. and the best way to do that is by bringing the breakthrough pressure to the peak pressure of previous billet minus saftey pressure of 10 bar. so for every cycle breakthrough pressure will be based on previous peak pressure minus safety instead of fixed 100 bar.

Also this case is applicable only for automode not for manual. and also not for 1st billet.

Now i was realy wondering what was realy causing the break through to happen fast. After so much of search i found that hydraulic pump on/off are the exact cause.

Whole program was using a subroutine file to all its operation and there are no out instruction all are move instructions. so that also delayed my search. At one point i was wonder what was causing a particular bit turn on and off as i could not find its output instruction. all i could find only NO and NC contact of that instruction. even i couldnot find it through cross reference for the word. Now after so much of search i found but. But i would like to know how you all do it. I mean to search for a particular word and its output conditions if its not present directly.

Now i am working on Valve container forward Ring outlet on/off logic. This seems much more worse than previous Break through pressure. I will certainly post here if i need your help again.

Many thanks