reading RPM

I have a keyence KV-16AR and I was hoping someone out there in PLC land could give me a hand. I am trying to write a program that will allow me to read pulses from a motor and convert them into RPM.
I would appreciate any help I could get

Thanx

Just an Idea

(#Pulses/amount of time)*(60sec/1 min.)*(1 rev/how many pulses for one reveloution)

Example:

36 tooth sproket (36 pulses = 1 rev.)
you count 14 pulses in 3 sec.
Then
(14 pulses/3 sec.)*(60 sec/1 min.)*(1 rev/36 pulses) = 7.77 rpm

Or you coould time how long it takes to count 36 pulses in the above example and use the same equation.

You may know this already but to figure the RPM it is often better to time between pulses and figure RPM from that with each rotation rather than counting pulses for a time.

Example:
Pulse
...2 sec...
Pulse RPM = 30
...1 sec...
Pulse RPM = 60
...3/4sec...
Pulse RPM = 90

I think the above equation can be used either way. Its one of those days so I am prob. wrong.

Thanks,
Bob

It's basically a question of the frequency of the incoming pulses. If high number of pulses then you can count them for a fixed time period to get a direct relationship (higher the number of pulses per time period = higher rpm). Otherwise if the pulse frequency is very low then use the time between pulses for an inverse relationship (a greater time between pulses = lower rpm).

Thanks...Can you give me an example of how to lay this out in ladder logic. I managed to write a program that will read input pulses but it dosen't seem accrate.

Post what you have and we can go from there.

Tahnks,
Bob

THIS IS WHAT I CAME UP WITH THE HELP OF THE KEYENCE TECH SUPPORT. WE WERE BOTH GUESSING AT THIS SO I'M NOT SURE IF I'M EVEN HEADING IN THE RIGHT DIRECTION.



2002 CTH0
---| |-------------------------------------------------|0004|----

2008 1000
---| |-------------------------------------------------( SET )---

1000 #00001 T000 1000 1001
---| |------|ts000|---| |-----------------(RES)--(SET)----------

1001 #00999 T001 1001 1000
---| |------|ts001|---| |-----------------(RES)--(SET)----------

1000 3000
---| |------|DIFU|-----------------------------------------------
| 3001
---|DIFD|-----------------------------------------------

3000 CTH0 DM0000
---| |--------------------------------------(LDA)--(STA)---------

3001 CTH0
---| |------(RES)------------------------------------------------

2002 HSP
---| |--------------------------------------------|0004|---------

2002 DM0000 #00060 DM0001
---| |----(LDA)-------(MUL)-------(STA)--------------------------

--------------------------------------------------------------|END|

-------------------------------------------------------------|ENDH|

I can see that the text wasen't displayed right but you kinda get the idea

   Pulse                     One Shot

----| |------------------------(^)



  One Shot

----| |------------(Divide 600 by Timer Value)



------------|-----|--

            | TMR |

  One Shot  | 0.1S|

----| |-----|Reset|

            |_____|

This will find the current RPM and reset the timer with the leading edge of the pulse. Accuracy can be adjusted by moving the decimal And/Or creating multiple pulses per revolition and adjusting the math accordingly.

Does this motor have multiple pulses/rev or just one pulse/rev. If it is one pulse then DeserDog will work but if it has multiple pulse/rev I don't think it will. Again, it is one of them darn days. Fire at will. Time for a cold one.

Thanks,
Bob

Bob O said:

Does this motor have multiple pulses/rev or just one pulse/rev. If it is one pulse then DeserDog will work but if it has multiple pulse/rev I don't think it will. Again, it is one of them darn days. Fire at will. Time for a cold one.

Thanks,
Bob

Click to expand...

If it has 2 pulses per rev divide by half as much that's all. Have one for me!

One important point that you need to consider is whether a standard PLC input can keep up with the frequency an duration of the pulses. If your sensor is detecting a 'once-per-revolution' target on a shaft rotating at 1800 RPM, you get one pulse every 33.333 milliseconds. That shouldn't be a problem for most PLCs currently on the market. Just make sure that your target is in front of the sensor for a long enough time to be detected by the PLC.

However, you'd have a bit of a problem detecting that 36 tooth sprocket that BobO mentioned if it is rotating at 1800 RPM unless you use a high speed counter input.

Hello.

This program for only Keyence KV-**.

-- Frequency counter --

2002 HSP
---| |----------------------|0004|----
2008 #1000 DM1404 2305
---| |-------(LDA)--(STA)--( SET )----
2002 DM1405 DM0000
---| |----------------(LDA)--(STA)----

0004 --- Input Signal(Max 30kHz)
DM0000 --- Measurement Freq ( Hz )
Measure period --- DM1404 (#1000msec = 1sec)

RPM = multiply Hz by 60.

Hiro

Hiro, THis seems to work pretty well. My only question is where do I place the MUL #60 on the rung? Does it matter?