PLC5 upgrade to Control Logix

Hey Cardosocea ,
Any chance you might be selling some PLC-5/25's and maybe a jumbo rack or two when it is all over?
MadPoet.

Correction.
I would be interested in acquiring, cheaply, some PLC-5/15's (not the 5/25.)

I would also be interested in getting a 16 slot I/O rack with the power supply and a couple few 120 volt AC 16 point I/O modules. (1771-0A0 and 1771-1AD B.)

We have one very old system running on the PLC-5/15 . . . Been running many years and has given us no problems . . . I've looked at upgrading but if I can get enough spare parts to replace everything (but the wires) I could sleep better and delay the 'day of reckoning'.

MadPoet.

Was on vacation, sorry.
I have 2 5/15 in use at the moment. A couple 5/25 and 5/40 are the ones I have most of.

The project will be done over a couple of years (I'm hoping 3, but a few people on the budget side of things mention 5). I will be looking at what the parts I have are worth as I no longer need them to sell them on, but that will be in a bit of time, I'm afraid.

The integrator I used to work for does a lot of PLC5 upgrades, the general plan there was to replace the PLC5 processors with ACN ControlNet adapters, and then map the IO into a new CLX processor. Once that has been completed and tested then planned switching out of racks to a current style of IO over Ethernet/IP.

RIO can be a pain with CLX depending which card you use but is also doable

The best solution is to just replace it all at once, though I've never seen a plant willing to be down for that long obviously.

The PLC5 conversion software can give you some butt ugly but functional code (have to fix/verify everything flagged with PCE). CLX is a terrible PLC5, don't try and make it into one

raffles said:

CLX is a terrible PLC5, don't try and make it into one

Click to expand...

There is one thing you need to be aware of, it depends if your application depends on it or not, and I've seen many where you wouldn't have thought it did, but it made a big difference.

PLC5 : Floats converted to Integers follow the "traditional" method of rounding - that is xxx.5 and above, round UP.

CLX : Floats converted to Integers follow the slightly unconventional rounding method where any "result" that ends in exactly x.5 rounds to the nearest EVEN number when stored in a destination Integer tag.

This rears its ugly head most times when you divide by 2, that's when you get the xxx.5 result... If the destination tag is an integer tag, the "round-to-even" algorithm kicks in, and you will get a different answer to the PLC5.

From memory they changed to iec floating point format with CLX from PLC5. If you have an HMI that is pointing at an address on a PLC5 and just change the driver to point at a CLX with a tag to match, you will see garbage. The mantissa and exponent are not in the same place. You'll either need to be swpb (swap bytes) or rework the HMI

raffles said:

The best solution is to just replace it all at once, though I've never seen a plant willing to be down for that long obviously.

The PLC5 conversion software can give you some butt ugly but functional code (have to fix/verify everything flagged with PCE). CLX is a terrible PLC5, don't try and make it into one

Click to expand...

In this case, each PLC controls a vessel and they are not on 24/7 which gives us an opportunity to do this. Also, because they are fairly simple. I may have problems with some of the vessels though.

The logic will be re-written in CLX format. One thing I noticed is that we have vessels that are already updated so it should be fairly straightforward on that front. There was a time and place for the PLC5 type of programming but that time has long passed and I certainly don't want to support a plant with Frankenstein code.

raffles said:

From memory they changed to iec floating point format with CLX from PLC5. If you have an HMI that is pointing at an address on a PLC5 and just change the driver to point at a CLX with a tag to match, you will see garbage. The mantissa and exponent are not in the same place. You'll either need to be swpb (swap bytes) or rework the HMI

Click to expand...

The HMI will have to be reworked for sure and I also noticed that some signals (particularly integers that go negative) aren't dealt with nicely by the comms driver. So I'm aware of those too.