Micrologix 1400 without battery

Hi all,

I have a hazardous area application for a pre-existing design that uses a Micrologix 1400. My HA panel supplier says I can't use the Micrologix 1400 as it has a battery in it.

Could I use a Micrologix 1400 with the battery removed? I should imagine that I will need to install a memory module and configure the PLC to load the project from the memory module each time it powers up?

I thought the battery was just to maintain the real time clock, not the program.

Ken Moore said:

I thought the battery was just to maintain the real time clock, not the program.

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Not used these controllers but the manual says:

Page 15 said:

Replacing the battery when the controller is powered down will lose all user application memory

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https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1766-in001_-en-p.pdf

Is it possible to mount the controller in a peripheral panel that's outside of the hazardous zone?

If it helps, Siemens S7-1200 is a very similar controller and doesn't have a battery, although I'm saying that not knowing the extend of documentation that would have to be changed.

This is something I have picked up
1400, 1200 suitable for use in Class I, Division 2, Groups A, B, C, D or non-hazardous locations only. So removing the battery might not be enough.

If the device is not certified for an Atex Area, it must be inside an EEx'd Box, or located in a safe area, you could use a purged enclosure but this have long purge cycles (30 mins ) if power is interrupted.. All Cables between Hazardous and Safe will need Glavanic barriers or protection based on Atex Rating.

The whole build will need to be Atex approved and certified, you won't be able to build this in a "shed" yourself.

Agreed, not just a purge but probably a positive pressure maintained in the enclosure, this would definitely need to be re-designed with all these factors addressed & the equipment within the area explosion proof. I did work at a gas pumping station, there are many other things you need to be aware of, for example not allowed to mount aluminium enclosures on steel due to galvanic corrosion, not sure now if this is due to possible explosion risk or just to stop the corrosion.

So what is the area rating? Class I, Div I?

After puzzling a bit I think I understand the issue: when power is removed from the 24V supply, there's still a small plug-connected power source that could in theory create a spark if disconnected. The User Manual even contains that boilerplate warning about hazardous atmospheres when connecting or disconnecting the battery.

The MicroLogix 1400 uses the same battery and connector as the classic SLC-5/0x controllers: 1747-BA. Its functionality is very similar to the SLC-5/0x controllers, in that the Real Time Clock and user program and data storage run off that battery while the controller is powered down.

SLC-5/0x controllers will hold the program and RTC for hours or days (sometimes weeks) with their onboard capacitor if the battery is removed. I admit I don't have experience with the MicroLogix 1400's "hold up time" but the user manual suggests it is short or nonexistent.

I agree that if you install a 1766-MM1 memory module and can accept the loss of RTC and ordinary volatile memory storage, you can remove the battery and run without it.

Ken Roach said:

After puzzling a bit I think I understand the issue: when power is removed from the 24V supply, there's still a small plug-connected power source that could in theory create a spark if disconnected. The User Manual even contains that boilerplate warning about hazardous atmospheres when connecting or disconnecting the battery.

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That's more or less it, the battery is an energy source that can't be isolated before opening the panel (and thus exposing that energy source to a potentially explosive atmosphere). The HA panel manufacturer said we'd have to go to a 5370 Compact Logix since they don't have a battery, and then it would be compliant. I asked him how that works, since they still have stored energy in the form of a capacitor-based energy storage module (like just about every modern PLC these days), and his response was "uh...it does?"

Ken Roach said:

I agree that if you install a 1766-MM1 memory module and can accept the loss of RTC and ordinary volatile memory storage, you can remove the battery and run without it.

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Great, thanks for the sanity check. I think we'll go this way.

To address all the other comments - I'm not building this panel myself, it's being built by a global industry specialist in HA applications that builds and certifies panels like this as a core part of their business. They just won't put a ML1400 in it unless I remove the battery, so I have to either find a way to make it work without the battery (i.e. memory module), or migrate the logic to a Compact Logix.

Make sure your HA vendor knows about the "NSE" versions of ControlLogix and CompactLogix that forego the RTC so they can have less the 200 microjoules of stored energy.

I'm not in the mining industry, but I understand that's a thing.

Also, you're tempting me to see if I can adapt the NTP client socket application to the MicroLogix 1400 so it can have an accurate clock despite not having a battery.

Ken Roach said:

Make sure your HA vendor knows about the "NSE" versions of ControlLogix and CompactLogix that forego the RTC so they can have less the 200 microjoules of stored energy.

I'm not in the mining industry, but I understand that's a thing.

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Ah, yes of course, I'd heard of those. Just out of curiosity, do you know how it handles the lack of a battery/ESM backup?

Edit: you said it right in your post - they just don't have an RTC. Although IIRC, the ESM is also used to transfer the user program to non-volatile memory on power down as well?

Ken Roach said:

Also, you're tempting me to see if I can adapt the NTP client socket application to the MicroLogix 1400 so it can have an accurate clock despite not having a battery.

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Hey, look, I found a picture of Ken!

can you place the enclosure outside the hazardous environment and use intrensic barriers?
i had to do this several years ago for a manufacturing process.
class 1, div 2.
we also had an enclosure inside the hazardous environment that was purged.
it only contained i/o wiring. when pressure was lost, a signal was sent back to the main enclosure to kill the i/o power.
we used seal offs and nema 4/4x enclosures.
james

James has got it in one, that is the way to go.

Unfortunately in this application we can't.

We have several solutions to make it work in the hazardous area, I was just wanting to make sure that the simplest one (remove the battery and install a memory module) would work as I expected it to.

It may work, however, it would then have to be re-classified for that catagory, something that RW would not do, you could probably not do as far as I'm aware that PLC is not classified to work in that environment, so you would be responsible should something happen, RW would not support you in any way regardless if it was a solution.