ramping analog output

help, trying to ramp analog output 1746-no8i one channels sends pressure valve for hydraulic pressure I want to increase pressure at a given rate. I have looked at the manual and can set configurations, but does pid have to be used for a simple ramp up? anyone have some ladder logic examples

Depending on the processor and firmware level you are dealing with there is a ramp instruction (RMP). I have never used it but it may be an option.

Here is a pseudo-code concept for a ramp if the RMP doesn't do the trick for you.

 

IF (Target > RampedValue)

     

     RampedValue = RampedValue + RampRate

     IF (RampedValue > Target)

 

          RampedValue = Target

 

     END_IF

 

END_IF 

 

IF (Target < RampedValue )

     

     RampedValue = RampedValue - RampRate

     IF ( RampedValue < Target)

 

          RampedValue = Target

 

     END_IF

 

END_IF 

This is just a linear ramp but you can change anything at any time and it won't cause it any trouble.

Keith

If I understand correctly, I have done this by simply scaling a timer and feeding the acc value into the analog output. For example...start a TON when you want to start ramping. The timer might go from zero to 100,000 which could be scaled zero to 100% with the analog output raw values. The timer PRE is the actual length of time you want the ramp to take from 0 to 100. Hope this is clearer than mud.

ramping issue

golferjam said:

help, trying to ramp analog output 1746-no8i one channels sends pressure valve for hydraulic pressure I want to increase pressure at a given rate. I have looked at the manual and can set configurations, but does pid have to be used for a simple ramp up? anyone have some ladder logic examples

Click to expand...

the RMP function did work with sending the result to the analog output. it also has different ramps besides linear.

thanks for the idea

bluenoser337 said:

If I understand correctly, I have done this by simply scaling a timer...

Click to expand...

If you use this method, be sure to clamp the timer.ACC at the timer.PRE (or the result).

The timer ACC can be a few ms greater than the PRE resulting in a final ramp value greater than 100% of what you intend.

I use this frequently...

Example:
(Insert ramp start logic here) -> TON T4:0
DIV
...Source A: T4:0.acc
...Source B: T4:0.pre
...Destination: F8:0
GRT
...Source A: F8:0
...Source B: 1
......MOV Source: 1 Destination: F8:0

Then F8:0 becomes a multiplier that will ramp from 0.0 to 1.0 over a period determined by T4:0.pre

Insert a GRT T4:0.acc T4:0.acc -> MOV T4:0.pre T4:0.acc before the divide...Or: After the divide, clamp F8:0 to 1.0.

If you know the final value you are ramping toward and it does not need to "self correct", then you should not need PID.

Just multiply F8:0 by your final raw value and send it to the card.

On the other hand PID may provide useful features too.

Paul

y=mx+c
Y=analog output
m=Rate of increase or decrease
x=time interval !!
c=offset if any

Given the time frame in which the required output
should be achieved m can be calculated
Or
Given the m, time interval will differ.

Will this wont solve the problem?