Controlling a proportional hydraulic valve?

Hello guys,
The processor is a SLC 5/04 using RSlogix 500.
Have a question about a proportional valve on our hydraulic system on one of our machines. At the moment there what is called a lower plate that moves up and down about 4'. The speed of this cylinder is controlled through a GUI interface and the up speed is only one speed, you set the speed in the GUI and then it runs at this speed constantly. The down speed is more controllable as it has 3 speeds on the down stroke. The actual problem that I have is that the proportional valve has always run at 99% and recently the valve amplifier started faulting, the root cause has been narrowed down to the pilot and proportional valve not moving in sync ( one moving faster than the other). We have these parts on order but there is a 5 week lead on it. What I want to do is to put a ramp in the program to make it move up starting around 40% and speed up as it goes until it gets to 99% just before it tops out. (This is to keep it from shooting straight to 99% from the jump) There is a potentiometer in the system to know exactly where it is in the stroke. I know I could use a series of timers and move commands to do this but, was wondering if I use a SCP (scale with parameters) command and set the par. At the below settings will it work ok?

SCP
Input I:2.0
Min 0
Max 10000
Min scaled 40
Max scaled 90
Destination N18:120

N18:120 being the interger where the speed from the GUI is moved, I:2.0 is the input from the potentiometer. I know I will need a TON above this rung with a 4 sec value (since the stroke takes about 4-5 seconds) the process will go through the TON and ramp from 40% to 90% in the first 3-4 seconds and then the move command from the GUI will take over and set the speed at 99%. I think it will start moving at 40% and as it moves up the speed will increase in a ramp fashion until it gets to 99% or the top of the stroke whichever comes first.

So this is my question and I hope I have given enough information to understand the process at this point. Please let me know your thoughts and if you need more info I will post it as soon as I can.

Thanks,
Mark Coates

If you want to ramp it up from 40% to 90%, then assuming that your 99% value in N18:120 is 32440 (32768 * .99), and half of that is 16220 (because 90% - 40% = 50%).

And since there are 4000 counts in a four second timer (at least in a Logix 5k), divide 16220 by 4000 (better yet, divide 16000 by 4000, and add the 220 to your starting 40%).

Soooo, if you take whatever is in your accumulator during the four second startup period and multiply it by 4 and add 13107 (your 40% starting point, or 13327 if you want to keep your numbers whole), you will ramp up kinda-sorta real close to 90% by the end of four seconds.

This is a linear ramp, which I imagine should be fine for what you are trying to do.

Arrrghhh...!

I just saw the min - max values. No matter, use these instead of 32768.

Ttt