RPM / Tachometer System

[brettshelley]

Long time no post!

Anyhow, long day taking it's toll!

Anyone know of a simple ladder routine to calculate RPM based on a simple proxy connected to shaft reading a pulse a rev off the shaft. Have to calculate 10-40 rpm based off the proxy. Driving me nuts!

So, one proxy, 1ppr, 10-40 rpm to reach!!!

Tried timers, retentive, counters blah blah!

PLC L06 Automation Direct

Cheers... Brett

 

[bernie_carlton]

This implements what I described over at the AD forum.


PLC 06
// Rung 1
// Address 0
STR X0
PD C0
// Rung 2
// Address 2
STR C0
LD K6000
DIV TA0
OUT V2000
// Rung 3
// Address 6
STRN C0
TMRF T0 K6000
// Rung 4
// Address 10
END
// Rung 5
// Address 11
NOP

#BEGIN ELEMENT_DOC
"X0","Shaft Prox","","1 PPR"
"C0","One Shot Of Prox","",""
"T0","Pulse Timer","","Time in 1/1000ths of a second between pulses"
"V2000","RPM","",""
#END

 

[brettshelley]

Bernie,

I will give that a try!

Been bugging me for ages due to the slow rotation, before would use encoder for accuracy but customer wanted a cheaper solution! Same old!

So, instead had to use single proxy on shaft keyway!

Cheers...

 

[bernie_carlton]

Note that this will work prcisely because of the slow rotation. It would not be appropriate for much higher speed systems.

 

[Roy Matson]

Bernie,
For those of us not using Automation Direct could you describe your routine in plain English so it can be adapted.
Thanks
Roy

 

[bernie_carlton]

Again emphasizing that this is for low speed as brettshelley has noted, you will need the following as implemented on your particular PLC:

1. An up timer with the best resolution available but one which won't reach its limit in 1 minute. Make its preset the equivalent of 1 minute.

2. You will need a method of creating a one shot from the input signal. Again, refer to yoour PLC.


Here's the sequence:

The timer is merrily timing away, increasing its accumulated time.

The input signal happens. We create a one-shot pulse from that turn-on edge.

Using the one-shot we divide the preset of timer by the accumulated time of the timer and store the result in the 'RPM' register. (Note: take into account whether your division rounds or not.)

Again, using the one-shot reset the timer.

---------------------------------------------------------------------

And a correction to the documentation at the bottom of the DL06 code post above:

Time in 1/1000ths of a second between pulses

should have read

Time in 1/100ths of a second between pulses

(Got a little too wild with the zeroes)