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Old May 13th, 2019, 07:33 PM   #1
kevoler
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how to monitor a pulse

I have an oiler that needs to be monitored. The oiler lubes a head bearing at a rate of 9 pulses a minute. If the pulses fall to 7 pulses/min or go over 11 pulses/min the head motor needs to shut down or start an alarm.

Oiler pulses are 24V DC

This is the way I am currently thinking. Covert the pulses to RPM and use a limit function block for the high and low limits. I don't know if this is possible and looking for input.

PLC= Modicon M340
Software=Unity Pro
Progamming Language=Ladder
PLC expertise=beginner
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Old May 13th, 2019, 07:51 PM   #2
Bullzi
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HI and Welcome to the Forum.
Quote:
This is the way I am currently thinking. Covert the pulses to RPM and use a limit function block for the high and low limits.
That isn't a bad idea.

How are you getting that "pulse"? From a mag switch? Cam Switch or ?? Depending on the switch and how it works you may need to put in some "debounce" timers into your program to keep from measuring more than one pulse every time.

Is the pulse rate constant? In other words do you get pulses every X seconds?

How long can the head turn with no pulses? How long can you go if there are too many pulses?

These are all things you will want to keep in mind when you design your program. You want to protect the equipment but at the same time keep nuisance alarms from happening. It is my experience that if you keep your shut downs too tight eventually they find a way to override the shutdown and that is when bad things happen.

Good luck and check back if you need more help.
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Old May 13th, 2019, 07:57 PM   #3
Gene Bond
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Why not just set and reset two timers every other pulse? One is timing or the other is...,If one times out, Bingo!
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Old May 13th, 2019, 08:02 PM   #4
kevoler
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Hi Bullzi,

[Good luck and check back if you need more help.]
I do need more help as I am new to plc programming I need some examples in Ladder on how to implement my plan.
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Old May 13th, 2019, 08:17 PM   #5
Steve Bailey
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How quickly do you need to react?
The quickest reaction would be to set up a timer that runs continuously and resets at each oiler pulse. If the timer's accumulated value is less than 5.45 seconds when you sense the oiler pulse, that's a rate greater than 11 pulses per minute. If the timer's accumulated value is greater than 8.6 seconds when you sense the oiler pulse, that's a rate less than 7 pulses per minute.
If you can wait up to a full minute before you react you could set up a counter to keep track of each pulse and reset it once per minute. If the count is over 11 or under 7 when it comes time to reset, you sound the alarm.
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Old May 14th, 2019, 09:09 AM   #6
Firejo
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I'd read the "pulses" as digital inputs tied to a counter, and have a timer running set to 1 minute. You could then use two rungs, each with a comparison FB, one if the counter's accumulator is below 8 and the other if the accumulator is above 10. The timer's done bit would be at the beginning of each rung and a discrete bit would be at the end. When the timer goes done if the counter is less than 8 or more than 10 then that rung would be true enabling it's bit. If neither bit is enabled then the timer and counter simply reset. If either one of the bits is enabled then you set the alarm.
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Old May 14th, 2019, 01:47 PM   #7
STEMAPPLICATIONS
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Usually the way I've seen it done and IMHO the most effective is to have a sensor on each line from the manifold to the machine. There are so many ways to sense pulsing that I won't even get into it but the basics are to have a discrete sensing device that has the pressure differential that you desire for low and high. Your pump is on a timer to deliver X volume of lubricant. Your high timer runs once the pump comes on and you have so many seconds to see the pulse from the line come on. If the timer times out, declare a leak. Your low timer runs once the pump is running AND a high pulse is detected and you have so many seconds to see it fall. If the timer times out declare a blockage. If the high timer triggers an alarm, the low timer alarm is over-ridden. So you need to know what the pressure rise and fall time is typical by observation of a properly running system. A good machine millwright/mechanic is your best partner to determine that.

That's the way I have either seen it done or corrected systems to do so.

Last edited by STEMAPPLICATIONS; May 14th, 2019 at 01:58 PM.
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Old May 14th, 2019, 04:50 PM   #8
wancues
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i do the same as firejo. count pulses. when time expires i use lim to check count
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Old May 15th, 2019, 02:53 PM   #9
JGax
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Quote:
Originally Posted by kevoler View Post
I have an oiler that needs to be monitored. The oiler lubes a head bearing at a rate of 9 pulses a minute. If the pulses fall to 7 pulses/min or go over 11 pulses/min the head motor needs to shut down or start an alarm.

Oiler pulses are 24V DC

This is the way I am currently thinking. Covert the pulses to RPM and use a limit function block for the high and low limits. I don't know if this is possible and looking for input.

PLC= Modicon M340
Software=Unity Pro
Progamming Language=Ladder
PLC expertise=beginner
I think your idea is great....
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