Pulse rate to line speed

[JeffKiper]

I am not seeing an easy way to do this. Am I just over thinking it or am I totally lost? Either way is OK as long as I can understand where I am going wrong.

Conveyor running from 10~20 FPM. I get a pulse every 8"

So if I wanted to calculate PPM (Pulses Per Minute) every 20 seconds. I would just multiply the pulses counted during a 20 second timer by 3??? Because 20 seconds is 1/3 of a minute.

Then take the PPM and multiply by 8 (8" per pulse). This will give me IPM (Inches Per Minute)

IPM divided by 12 (12" per foot) FPM

Do you have a better way of doing this or some other way that might help me see the light?

 

[bernie_carlton]

Even at 20 FPM that's only 30 pulses per minute or one every 2.0 seconds. Divide 40 by the time you get between each pulse. If your accumulator is in hundreths of a second then divide 4000 by the stored accumulator value. If you can do this in floating point then your answer will be accurate to about 3 places. You don't even have to wait 20 seconds.

Input -> oneshot
If oneshot then store the current accumulator and divide 40 (or 4000) by the stored accumulator for FPM
If not oneshot then run timer

[Sorry about the number of edits. Hard to think on Monday.]

 

[jseavers]

Another way I can think of doing it would be to keep track of the time in-between pulses and do your math from there.

 

[mendonsy]

OR ... simplify your math and multiply the pulse count by 2. (3x8/12)=2
I suspect you will need to do a bit of averaging on your number though. If you don't it will probably produce some erratic results.

 

[Lancie1]

Your math seems correct, but maybe your resolution will not be too good because you have to wait 20 seconds to get a new update. If you could figure out how to count pulses per every second, your reading would always be only 1 second in the past, instead of 20 seconds behind.

Looking at your minimum speed of 10 Feet/min, that scales to 2 inches/sec, so every 4 seconds your conveyor will travel 8 inches or more, and you should get at least 1 pulse. So you could set your timer to 4 seconds and count the pulses in every 4 seconds. (Multiply by 15 to calculate pulses per minute). That would greatly improve your accuracy and resolution.

If instead of measuring Pulses per second, your measure Seconds per Pulse, your calculation would be more accurate and would look like this (where T = Time in seconds for 1 pulse):

1 Pulse/T Sec X 8 Inches/Pulse X 60 Sec/1 Min X 1 Ft/12 Inch = 480/12T Ft/Min = 40/T Ft/Min

So if T = 4 seconds, the conveyor will be traveling 10 Ft/Min
If T = 2.67 seconds for 1 pulse, 40/2.67 = 15 Ft/Min
If T = 2 seconds for 1 pulse, the conveyor will be traveling 20 Ft/Min

 

[JeffKiper]

Even at 20 FPM that's only 40 pulses per minute or one every 1.5 seconds. Divide 30 by the time you get between each pulse. If your accumulator is in hundreths of a second then divide 3000 by the stored accumulator value. If you can do this in floating point then your answer will be accurate to about 3 places. You don't even have to wait 20 seconds.

Input -> oneshot
If oneshot then store the current accumulator and divide 30 (or 3000) by the stored accumulator for FPM
If not oneshot then run timer

Bernie where did the 30 (or 3000) come from?

 

[bernie_carlton]

Sorry Jeff, I started posting before I had thought it fully through. I kept editing it. See my last version.

If it is 2 seconds between pulses for 20 FPM then 'x'/2 = 20 or 40. (4000 if accumulator is in hundreths. Other numbers for other resolutions.)

 

[JeffKiper]

No problem Bernie. What is the 40 or 4000?

 

[JeffKiper]

It makes since for now.

I am trying to pack 3 weeks worth of work in to a week on the road. It never ends good when it doesn't start out good.

Thanks for you help

 

[bernie_carlton]

You're welcome. Again, sorry for the confusing edits.

And here's the units. Having measured the time (x) for one pulse:

1/x (Pulses/Second) * 60/1 (Seconds/minute) * 2/3 (Feet/Pulse) = 'Y' Feet/Minute

 

[JeffKiper]

Monday enough said

 

[Sioan]

Interesting! You mean calculate the "momentary" speed ... ?