calculating delay times

Hi guys. I'm having trouble wrapping my brain around something I've got to do in an upcoming project. First off, this will be a belt conveyor with the speed controlled by a VFD. A part will travel down the conveyor, pass a photo eye, then after an "on delay time" (after photo eye is first made), an output will come on, then go off based on an "off delay time" (after photo eye is clear). The operator will have the ability to enter the on delay time, the off delay time, and the belt speed percentage from an HMI. Simple enough so far.

But, this is what I'm having trouble with: When the operator changes the setpoint for belt speed percentage, the on delay and off delay times for the output must be recalculated by the PLC to compensate for the change in belt speed.

So far, I'm thinking that the on delay and off delay times that the operator enters need to be for when the belt is at full speed. Then that delay value will need to be scaled somehow based on belt speed to come up with a new delay value. So, what would be the best way to do this? Do I find the relationship between minimum belt speed and maximum belt speed (i.e. how much slower is minimum than maximum) to come up with a multiplier to apply to the delay time entered by the operator? What say you?

Thanks in advance.

By the sound of what you are wanting to do, is to actuate a device a fixed distance after the PE is triggered. This fixed distance being adjustable by the operator?

So if you know the speed of the belt in m/min, and the operator enters the distance past the PE that he wants the device to actuate at, then relate this distance to the belt speed to get your timer preset. (Distance/Speed) = Time.

The off delay time is the same principle.

New Timer Preset = Preset at Maximum * (Maximum Speed / Current Speed)

sacsac said:

First off, this will be a belt conveyor with the speed controlled by a VFD. A part will travel down the conveyor, pass a photo eye, then after an "on delay time" (after photo eye is first made), an output will come on, then go off based on an "off delay time" (after photo eye is clear). The operator will have the ability to enter the on delay time, the off delay time, and the belt speed percentage from an HMI. Simple enough so far.

Click to expand...

This sounds like "parts tracking" on a variable speed conveyor. If it is, save yourself some grief and use an encoder or prox sprocket-tooth combo if the speed is not too great.

Question: Is there a possibility that another part can pass in front of the photo eye before the first output comes on?

bernie_carlton said:

New Timer Preset = Preset at Maximum * (Maximum Speed / Current Speed)

Click to expand...

This is what I needed. Thank you.