Calculate the Speed of a Conveyor in Feet\Min from a known Frequency.

Gear Reduction Box = 3.0
Drive Sprocket = 22 Teeth
Driven Sprocket = 88 Teeth
VFD = PowerFlex 40

I have a VFD controlling the speed of a conveyor. I am sending it a frequency from 0 to 60HZ. The customer wants to know the speed of the conveyor in Feet/Minute. So I have a Motor driving a Gearbox. The Gearbox drives the Drive Sprocket. On this Sprocket there is a chain that drives the Driven Sprocket. How do calculate Ft\min the conveyor is moving if I know the frequency? Thanks for your response.

More information required.

What is the nameplate speed of the motor, and the diameter of the driving drum.

If you calculate the RPM of the driven sprocket, and you know the diameter of the driven drum, then you can calculate the surface speed of the conveyor.

You forgot the driving sheave of the conveyer belt.

I suggest you look this up. You can find in Machinery Handbook. Give us your best effort and we can take a look at it.
Dan Bentler

480VAC, 3Phase, 60HZ, RPM 1725, F.L.A = 0.08.

Driven Drum Diameter = 24"

You forgot the driving sheave of the conveyer belt.

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Not heard this term before, did we mean the same thing?

I suggest you look this up. You can find in Machinery Handbook. Give us your best effort and we can take a look at it.

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Is going to be the only way you learn, drawing a picture will help immensly....

scottmurphy said:

Not heard this term before, did we mean the same thing?

Is going to be the only way you learn, drawing a picture will help immensly....

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I guess I use the term driving sheave and driving pulley interchangably. Machinery Handbook treats them the same in table of contents ie pulleys and sheaves V belt pp 2284 - 2336

Dan Bentler

Another way (which I prefer) to solve this problem is to use a handheld tachometer to measure and then calculate the scale factor in one step.

There will be slip in the motor and it may or may not match the nameplate...this can make a calculation based on the mechanical system less accurate than "calibrating" it with a hand-tach...plus, you don't have to go hunting down information like conveyor belt thickness and reducer ratios.

If you are using a speed command being sent to the drive for the known variable in your equation, be careful of the very low end of the speed range being non-linear in most cases. if you are using speed feedback from the drive, then you should have no concerns about using simple ratio math to create the result.

You want the easy answer that works and takes about an hour?

If so read on.

If not go back to the never ending list of questions and formulas.

Set the drive to zero adjust everything so the conveyor is not moving.

Set the drive to 60Hz.

read the surface speed of the conveyor , write that down. Use a digital hand held , the thing with the read out in feet / minute and a little wheel.

Repeat for every 10 Hz and then double check.

Use the numbers you wrote down in a SCALE with Parameters block and ouput the data to a read out or HMI.

If it has to be more accurate, order an encoder , install it on the conveyor drive shaft or use a prox switch to read pulses on the drive sproket on the conveyor.

Count the pulses and compare to the hand held device / use scale method.

Even after all the calculations you will find that you have to use this method to tweak the numbers, so why not just start with it?

1. Motor RPM = 1725 at 60 hz.
2. Gearbox reduction = 3.0
3. Sprocket reduction = Driven sprocket teeth (88) / Drive sprocket teeth (22)
4. Overall reduction = Gearbox reduction * Sprocket reduction
5. Final output RPM = Motor RPM / Overall reduction
6. Circumference of Driven Drum = Diameter 24 (in inches) * pi (3.14) / 12" (1 foot)
7. Final FPM = Output RPM * Circumference
8. Output speed = Freq. output of VFD / 60hz * Final FPM @ 60hz

This will only give you the calculated FPM on the surface of the Driven drum. You must also do as OkiePC stated in post #7 or dahnuguy in post #8 to get the actual speed.

tomwhite007_2008 said:

Gear Reduction Box = 3.0
Drive Sprocket = 88 Teeth
Driven Sprocket = 88 Teeth
VFD = PowerFlex 40

I have a VFD controlling the speed of a conveyor. I am sending it a frequency from 0 to 60HZ. The customer wants to know the speed of the conveyor in Feet/Minute. So I have a Motor driving a Gearbox. The Gearbox drives the Drive Sprocket. On this Sprocket there is a chain that drives the Driven Sprocket. How do calculate Ft\min the conveyor is moving if I know the frequency? Thanks for your response.

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see the drawing below. I made a mistake. Both Drive Sprocket and Driven Sproket are the same size. Please forgive my drawing. Thanks.

tomwhite007_2008 said:

see the drawing below. I made a mistake. Both Drive Sprocket and Driven Sproket are the same size. Please forgive my drawing. Thanks.

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None of that matters.

You need output of drive and scale to measured speed of conveyor, nothing in between the two matters.

If you need more accurate then you need a feedback device on the conveyor, which also needs its output scaled to the actual conveyor speed.

Spend all day calculating these numbers and then you will find out that the motor does not go 1725 RPMs at 60Hz and the gear reduction is not nominal and the belt on the conveyor slips etc etc etc.

If you realllllly need the actual conveyor speed , use a contact wheel that reads out in some analog format and yes even this will need to be scaled or adjusted to correspond to your specific system.

If this is a test question to see if you can figure the circ. of a circle and put it all together as an approximate answer, then "do the math" version.

1760 * 1 / 3 (Gearbox) = 586.7 rpm * (3.14159 * 2) (pi * D) = 3686 ft/min

This takes no account of: motor slip, belt slip or belt thickness.

Nick

Manglemender said:

takes no account of: motor slip,

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The motor slip issue might be dependent on the particular VFD.
Some VFD's have good speed control. ABB's ACS800 and ACS550 are an example of VFD's with excellent speed control when used in sensorless vector mode.

I get 903 fpm (15 fps) at motor RPM of 1725 and 890 (14.8 fps) at 1700 RPM.
If you want velocity per Hz divide above by 60.
Dan Bentler