Rig safety in case of Power failure

jonnybgood · Mar 25, 2012

Hi,
I have a setup where a piston presses a bearing in a copper block. After 5 cycles the rig has to stop operating for some maintenance and it wont start again until the technician perform the required duties and reset the system with a key-lock switch.

I implemented safety features like the latching etc. in case of power failure.

I wish to design my Ladder diagram in a way that if there is power failure, the counter would not reset and the operator can run the rig for 10 more cycles. What is the best way to implement this?

thanks

Tharon · Mar 25, 2012

What brand PLC are you using? Some of them don't reset counters on power failures.

jonnybgood · Mar 25, 2012

Mitsubishi FX1N

Eric Nelson · Mar 25, 2012

On the FX1N, counters C16 and up will retain their count through a power cycle.

See section 4.10 (PDF page 93) in this manual...

http://www.meau.com/Files/JY992D88101-D.PDF

-Eric

jonnybgood · Mar 26, 2012

"Battery backed/latched counters:
• Counters which are battery backed/ latched are able to retain their status information,
even after the PLC has been powered down. This means on re-powering up, the latched
counters can immediately resume from where they were at the time of the original PLC
power down."

thanks a lot Eric clearly explained

Lancie1 · Mar 27, 2012

I wish to design my Ladder diagram in a way that if there is power failure, the counter would not reset and the operator can run the rig for 10 more cycles.

This can be dangerous. Make sure you look at all safety concerns, and that dangerous equipment will not suddenly re-start automatically after a power failure. Otherwise, someone make think that they can enter a machine and do some maintenance while the power is off, not realizing that it is going to run when the power comes back on. In other words, be good and be smart, JonnyBGood.

jonnybgood · Mar 27, 2012

Your statements are of great interest to me. How is this issue tackled normally?
Can you give me any hints pls?

Lancie1 · Mar 27, 2012

How is this issue tackled normally?
Can you give me any hints pls?

Normally, your equipment should have all required (external to PLC) safety devices such as guards, door locks, interlock switches, safety stop, and emergency stop pushbuttons. Your PLC program should be written so that when power is lost, the PLC Run output drops out and will not reset until a human operator again presses a Start button. With all these things, if a power loss still presents a safety problem, then a back-up power supply is installed, either a battery backup with necessary charger, inverter, and power supply, or for large systems, an engine-operated generator and generator control panel.

Eric Nelson · Mar 27, 2012

I thought the problem was that the counter resetting was allowing the machine to run too many cycle between maintenance. In other words, if the machine ran 4 cycles and there was a power failure, the counter would reset to zero, allowing 5 more cycles, for a total of 9. In theory, this power cycling could be repeated over and over, allowing an infinite amount of cycles without maintenance.

Upon rereading, I am now confused (and concerned) about the "can run the rig for 10 more cycles" part. I thought it could only run FIVE cycles before requiring maintenance?...

-Eric

jonnybgood · Mar 28, 2012

thanks a lot. things are clear now

jonnybgood · Mar 28, 2012

'In other words, if the machine ran 4 cycles and there was a power failure, the counter would reset to zero, allowing 5 more cycles, for a total of 9. In theory, this power cycling could be repeated over and over, allowing an infinite amount of cycles without maintenance.'
you understood well. It may be I made a mistake.

Rig safety in case of Power failure

jonnybgood

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Tharon

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jonnybgood

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Eric Nelson

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jonnybgood

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Lancie1

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jonnybgood

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Lancie1

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Eric Nelson

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jonnybgood

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