sense a roller speed

Have a application that involves a machine that we are getting that i have not see yet that will have a feed belt to feed material. The belt i was told is controlled by sometype of drive unit that has a speed pot that you adjust to control the speed. The speed of this belt is 0-10ypm.
I will need to know the speed this belt is running for a down stream piece of equipment.
Open to any suggestions as to best way to know the speed this motor is running.
I was thinking possibly a prox switches used to detect a screw mounted on one of the ends of the rollers and feed it into a plc and count the revolutions for a time period.
Was wondering if there was someway to mount sometype of contact type roller/sensor setup on the belt and have it feeding into a redlion type display to display the YPM and then get a 0-10v or 4-20ma signal out of the redlion type unit that i could feed into a plc and then scale that input to be the YPM range for the down stream equipment it will be connected to.
Does this make sense or am i way out in left field. Anyone that has ever done this type of application and would like to give some advice it would be greatly appreciated.
Thanks

Check on the model of the drive. Many drives have an analog output that can be programmed to represent one of several parameters including speed. The simplest solution would be to wire the drive's analog output (programmed to represent speed) to an analog input on your PLC.

I was thinking possibly a prox switches used to detect a screw mounted on one of the ends of the rollers and feed it into a plc and count the revolutions for a time period.

Click to expand...

Yes, that is an old cheap, simple method that works if the maximum on/off switching time of your prox is shorter than the time the target is seen by the prox. You might get by using a screw head, if your " 10 YPM" = 10 Yards Per Minute or 30 feet per minute or 0.5 feet per second of belt travel. If your conveyor pullys are 4" diamenter, that would be C = 2xPIxR = 12.56", or about 1 feet around, so you would need a speed of 1/2 revolution per second, or about 30 RPM. For that slow speed of a conveyor wheel, a screw head may keep your prox switch ON long enough for it to switch the PLC input.

As member OkiePC favors, a variation if the prox-speed method is to use a piece of reflective tape on the conveyor pully, and read it with the proper photoswitch. Then your target can be bigger with no danger of unbalancing the pully, as you can with a large metal target.

thanks for response.
about a year ago this same type situation came up and i was looking at mounting a encoder etc., but then it got dropped.
What i am thinking of doing is mounting a encoder on a roller that will turn when the fabric is turning and using a HSC in a micrologix 1400 determine the actual speed the belt is turning and use that to control the speed of the machinery we will build to run down stream. I have zipped the file and posted it. The machine that i will be trying to determine the line speed on from what i have been told is using some type of DC drives to control the speed of the belts that is just set with a pot on a operator panel. I have not actually seen the machine yet and since it is a very old machine with the old DC drives and pot i am looking at trying to sense the line speed it is really running for the future equipment. If someone has done this type of application and could take a look and just tell me if it makes sense or not or what suggestions to change would be a big plus. Thanks