Calculate the Speed of Conveyor.


Thread Starter

Mads Kusk Hansen

I'm working on a project, were I have a conveyor belt, driven by a Powerflex 40. I need to convert the value from hz to km/h, so can do some calculations another place in my plc program.

I have looked in their Quick Start manuel, to see if there was a constant I could multiple the hz with, but I could find any.

Any of you have any suggestions?

I advance, thanks for you help.

Bob Peterson

The drive does not know what the linear speed of the conveyor is. Ut only knows what frequency it is sending to the motor.

You will need to correlate the motor RPM at 60 Hz (presumably it is a 60 Hz motor) with the gear ratio of the conveyor system to figure out what the linear speed is.


Curt Wuollet

You need a way to equate RPM to velocity. This involves finding the speed ratios of any gearboxes or pulley arrangements to get the RPM of the actual drive roller. Then it's simply a matter of finding the circumference of the roller. For example: a 4inch roller has a circumference a little over 12" 4*pi. If it goes 100 RPM that's about 100 ft/min. then do the conversions. Or you can get an optical tachometer on Ebay for less than $15 and measure the drive roller directly. Then it's just scaling.

You state that you want to convert from Hz to linear speed in a PLC controlled system. A quick, easy way is to put a flag on the driven conveyor belt drum and monitor the time of one revolution. Using geometry, one can then determine linear speed. Simple math manipulation can scale this to whatever units you require.
The easiest way is to first calculate the linear speed of your belt. depending on how long it is, you might attach a reflector on one chosen point. then using a stopwatch find the time it takes to traverse back to the starting position while also noting down your motor speed/frequency, linear speed = belt length/time taken. If you carry out the same exercise for ten trials and you get a graphical plot of linear belt speed versus motor frequency.
The way to accurately find the speed of a conveyor is to measure the length then time it for 1 or several rotations.

Make a mark "Start" on the belt, measure with a long tape measure to a second point, advance the conveyor then measure from point 2 to a new point 3, and so on until eventually you come back to "start".
This is the length
Time how long it takes "start" to go one revolution
Speed = Length / time
If the belt is short allow it to go for several revolutions.

To measure the speed it's usual to monitor the tail pulley because it's not driven there will be minimal slip. A proximity switch is good for that.
Just to make it clear, what you need is the formula for this calculation, or the way to calculate in in a PLC?
In the PF40, parameter A099 is the "Process Factor", a multiplier that is applied within the drive to scale the output value to be something other than Hz. So basically you take the motor speed x the diameter of the drive wheel and any other factors in your power transmission to the belt and boil it down to a single value. You then apply that multiplier to the VFD Hz output in A099 so that the drive display, AND THE ANALOG OUTPUT, is scaled to become whatever your new engineering units are.

So as an example: .
The motor is 4 pole, 1425RPM base slip speed at 50Hz.
The motor is connected to a drive belt of 10cm diameter.
The other end of the drive belt is connected to a sheave of 100cm diameter, so there is a 10:1 speed reduction at the load shaft.
That load shaft is connected to a drum with a 1m circumference.

That means for each Hz of speed from the VFD, the load shaft moves .1Hz, and at 1m circumference, the conveyor speed will be 0.1m/second, x 60sec./minute = 6m/minute, x 60min./Hr = 360m/Hr = .36kM/Hr. So the factor to go from 1Hz to .36kM/hr is (.1 x 60 x 60)/1000 or .36, so if you enter .36 into A099, the display, and the output speed, will be in kM/Hr instead of Hz. You can then read Parameter d010 and get that number directly.
> In the PF40, parameter A099 is the "Process Factor", a multiplier that is applied
> within the drive to scale the output value to be something other than Hz.

I think JRaef2 nailed it but you might like to use my method of measuring the speed then apply a fudge factor to the indicated frequency and apply that to A099.