Need more inputs shoe-horned into an installed PLC
Need more inputs shoe-horned into an installed PLC
(OP)
Has anyone run out of inputs on a PLC and had to cobble up something to fill the need?
I have a PLC limited to 8 I/O modules and I already have the 8 and they're about 90% utilized and so I am not allowed any further modules. (Click with 8 modules already.)
I'm running two BIG compressors with all operational commands coming down from the PLC. But, I have only single high-side and low-side pressure sensors on each of the two compressors. If one of those sensors take a slow dump I could run the compressors into destructive running areas. I want to add some redundancy -triple redundancy- so I can discover a failing/drifting sensor and warn the staff while continuing with the winning voters while a replacement is hunted up and installed.
I was wondering if I could REASONABLY add a second CLICK CPU and then, via either Ethernet or serial, regularly Modbus over these extra eight analog inputs in as alternative values for voting and use?
Anyone tried this?
I have a PLC limited to 8 I/O modules and I already have the 8 and they're about 90% utilized and so I am not allowed any further modules. (Click with 8 modules already.)
I'm running two BIG compressors with all operational commands coming down from the PLC. But, I have only single high-side and low-side pressure sensors on each of the two compressors. If one of those sensors take a slow dump I could run the compressors into destructive running areas. I want to add some redundancy -triple redundancy- so I can discover a failing/drifting sensor and warn the staff while continuing with the winning voters while a replacement is hunted up and installed.
I was wondering if I could REASONABLY add a second CLICK CPU and then, via either Ethernet or serial, regularly Modbus over these extra eight analog inputs in as alternative values for voting and use?
Anyone tried this?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
xnuke
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RE: Need more inputs shoe-horned into an installed PLC
RE: Need more inputs shoe-horned into an installed PLC
That's actually what I'm going to try using the second Click for. I'll load it up with two 4 channel A-IN units and and have the CPU reading them and passing them across once a second and call it a day... I hope. LOL.
Dave; Are there commercial ones? They'd probably work if they'll ship analog inputs with fidelity.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
Whether it ends up cheaper in terms of equipment cost compared to another Click complete with IO, I'm not sure though.
EDMS Australia
RE: Need more inputs shoe-horned into an installed PLC
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Need more inputs shoe-horned into an installed PLC
X; Are you referring to the 'Protos X' stuff? Yeah, not inexpensive..
I spent a couple of hours last night wading around in the CLICK stuff and found they've finally written a very nice manual for it. An entire 30 page chapter on "Communications". It shows very simple inter-CPU communications are possible via any of the three comm ports. I also found they sell a CLICK CPU with Ethernet called an 'Analog Ethernet CPU' that comes with 4 analog inputs! That means I only need one CPU and one analog module which makes it even nicer. I can also use the second comm port on the second CPU to Modbus out to two condenser fan VFDs.
Thanks.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
RE: Need more inputs shoe-horned into an installed PLC
You need to maintain the analog loops while not reading as they take a while to settle down.
It sounds as though you have decided to off-load the analog inputs, if they are used to trip the compressor perhaps consider a hard wired trip handshake rather than relying on communications.
Actually why not just spring for some reliable pressure transmitters, any industrial transmitter will be as reliable as the PLC
RE: Need more inputs shoe-horned into an installed PLC
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
RE: Need more inputs shoe-horned into an installed PLC
We knew you'd get it, and were just, uh, well,,, let's say "indecisive" at the moment. Cheers!
.
(Me,,,wrong? ...aw, just fine-tuning my sarcasm!)
RE: Need more inputs shoe-horned into an installed PLC
Nothing safety oriented. Two things:
1) Ability to run with a failed part. Using the usually shelved spares, actually in service, to keep the system(s) running.
I'll install them.
Run both systems on their same original transducers and study the two new ones. Make some educated decision on a difference between the three sensors that should be deemed a problem. When detected it will notify the car manager and disregard the odd-man-out. One of the the remaining two sensors will be designated "in control" and the system will continue until a spare sensor is installed.
HCBFlash; :)
All the goodies are supposed to show up Monday! So the fun can start. Unfortunately the first thing is running 1" rigid conduit all over under the car to separate the VFD stuff from all the signal wires.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
If I understand correctly, you are installing 8 additional PTs to allow for a TMR configuration on your field instruments? Interesting approach, we have moved away from the "more is better" philosophy and use a variety of risk/failure analysis methods to determine design requirements.
Best of luck!
RE: Need more inputs shoe-horned into an installed PLC
These rail applications can be tricky because we're often in a moving train in the middle of frikken no-where. These cars often are dome cars with many dozen kW of glass since a large amount is perpendicular to the sun. Without refrigeration a car can become uninhabitable in literally minutes. Redundancy and agility in the control systems is required to prevent really expensive or massively embarrassing events from occurring. Imagine a small company has paid $30k for a five day fly fishing excursion and in the middle of Montana the car goes nova. It will always be in an Amtrak train but it isn't an Amtrak business. You suddenly need them to take your passengers... Or, they'll set you out on a siding in a car that's not habitable! The car has only guests and a car manager with very little technical abilities.
Nasty.
Hence the redundancy. Two power sources, Amtrak Head End Power (480V) or on-board generator.
Two refrigeration systems. Both feeding isolated halves of all evaporation coils. Each with their own condensers.
Currently they are both being controlled by a single PLC. Bad. Both are being controlled by single high-side/low-side pressure transducers. Bad.
We need backups. Since you can't step out at 90 mph you need them pre-installed. But wait! You can't know which one is bad with only two units when you can't run a meter and touch them. So the 3 up voting.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
RE: Need more inputs shoe-horned into an installed PLC
.
(Me,,,wrong? ...aw, just fine-tuning my sarcasm!)
RE: Need more inputs shoe-horned into an installed PLC
I got the VFDs in today so I can ultimately control the head pressures. Got control of the misters for disaster control. All the pressure transducers are in and - will never leak. Now if the flaky cable supplier (Teflon twisted pairs) who's failed to ship for over three weeks now, will get his head out of his nether region I can wire the sensors in.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need more inputs shoe-horned into an installed PLC
I would have considered separating protection and control. One Click for the protection of each system, and a third Click for overall control of both systems.
Any comments?
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Need more inputs shoe-horned into an installed PLC
To the two PLCs with some time to install them.
Not sure where I'd put a third one Bill. I still have to install two touch screen status displays.
I think the three PLCs scheme doesn't apply here in the case where all the systems are split so functions are covered and re-covered by the two PLCs. If one dies you still have most functions covered. Also this isn't 'life safety' so you probably don't need a PLC to call a complete halt and stop the hurtling truck or something.
Before you guys harass me about the wire dressing this is a work-in-progress..
Keith Cress
kcress - http://www.flaminsystems.com