proportional band

[g6ivang3]

hello this is my 1st post but I have read many on here. im a novice when it comes to plcs, I actually have no training. at my present job these duties where just handed to me for no apparent reason lol anyway getting to the point I read in another point about doing a proportional band approach instead of the more complicated PID

So im using
Rslogix 500
micrologix 1100 with 1762-if2of2 module
vegason 61 sonar sensor
acs550 abb vfd

what I have is a tank where the level is read by the vegason61 (4-20ma)what I need is for the vfd to slow down my pump when the tank is 20% and max speed when the tank is 80%.

 

[kamenges]

Proportional band is just a way of expressing the P-gain in a PID.

In many of the controllers you come across the proportional gain is expressed as a direct number in units of correction/unit error. This means an increasing number produces an increasing response.

Proportional band flips that on its head. By definition proportional band is the amount of error required to make the correction change from 0% correction to 100% correction. Given that definition this means an increasing proportional band will produce a decreasing response.

What you will be able to use as a controller will likely be determined by the amount of error you can live with.

Keith

 

[g6ivang3]

so in my rslogix 500 I will have to setup a pid then right? im still not sure how I would go about programming one sorry

 

[Peter Nachtwey]

so in my rslogix 500 I will have to setup a pid then right?

NO! Use the SCP block.

 

[ianavina]

and scp to do what?

 

[Mickey]

and scp to do what?

g6ivang3, ianavina same person?

http://www.plctalk.net/qanda/showthread.php?t=85265

http://www.plctalk.net/qanda/showthread.php?t=85851

http://www.plctalk.net/qanda/showthread.php?t=85829

 

[ianavina]

What?

 

[Mickey]

What?

Very similar questions. On all three threads.

 

[jtn]

What Peter is trying to say is do a straight line equation where the min speed is at 20% level and the Max speed is at 80% level. The SCP instruction does the straight line equation for you so that you don't have to do program in the math equation of y=mx+b.

 

[ianavina]

so a separate scp from the one im using to scale the tank level

 

[lauu]

 

[ianavina]

perfect but how do I make that happen in a scp. sorry guys my knowledge on this is very minimal