Ramp soak

[AustinT]

Hi ,

I ran into a problem that should be trivial with the ramp function .  I am trying to ramp a value up or down at a preset rate between 0-100 .  When one input is on it needs to ramp up . If a different input is on it should ramp down .  I made two ramp soak functions with the nc contact from the input on the pause input . It does not work right when it gets to the end of the ramp . Can you think of a way to do this ?  Thanks

[ADC Product Engineer]

Please define "it doesn't work right..."

[AustinT]

I guess a better way to say it is it is not working right in this application.  When the position hits 100 it finishes the ramp and jumps back to zero . I would like it to ramp between 0-100 at a given rate depending on which one of two inputs are active .  The application is a hydro deflector . The two inputs either raise or lower the deflector at a gradual rate . When neither input is on it stays where it was left . The limits are 0-100

[AustinT]

I spoke with tech support at automation direct and it looks like ramp soak will not work .  I ended up writing my own ramp with a rolling 1 ms timer and an up down counter . The output of the counter is scaled to 0-100 to go in ry1 .  I could see a function similar to ramp soak being very handy if it could ramp a value up but did not go to the next step .  The jog input would be replaced by a variable that could decide which step was active . So in my situation, I would have two steps , one to ramp up and one to ramp down .  When I wanted to ramp up I would enable the block and write a 1 to the step selector . When I wanted to ramp down I would enable the block and write a 2 .  Disabling the input would leave the output of the ramps at the last position during the ramp before the enable was turned off

[davidbgtx]

Try This, worked in the simulator
RY1 is the position to send the deflector and you can have different speed for raise and lower by changing the counts/sec

[AustinT]

Hi , thank you for the reply . I look forward to trying this when I get back in the shop tomorrow.  So I tried almost the same thing without the init instruction .  Can you please explain what leaving out init to ry1 was doing ?

Thanks

[Mike Nash]

The example davidbgtx posted is "simply" setting the setpoint to itself, so it doesn't change the value when it starts at step one when the instruction is enabled.

The one issue I see while playing with it is using RY1 because it is not in a retentive range by default. So when the PLC goes to run, RY1 is reset to zero.

If you don't want this to happen, use another R location (R1 perhaps) then copy that to RY1 after the RAMPSOAKs. This will retain the current setpoint on first scan.

[AustinT]

Another question regarding the ramp soak .  What happens after the value Ramps to the final destination and no more steps are in place .  When I ramp a pid setpoint it leaves the value at the final ramped value but it seems like with ry1 it is going back to zero .
Thanks

[davidbgtx]

Another question regarding the ramp soak .  What happens after the value Ramps to the final destination and no more steps are in place .  When I ramp a pid setpoint it leaves the value at the final ramped value but it seems like with ry1 it is going back to zero .
Thanks

It remains where it stopped, be that 0, 100 or anywhere in between, how ever as Mike Nash said RY1 is not retentive and will reset to zero if PLC power is lost or taken out of run mode. I used RY1 in the example because you had, my advice is to take Mike Nash's advice and use a R location that is retentive.

[AustinT]

Thank you all for your replies