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Old January 10th, 2023, 07:15 AM   #1
parky
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Very old logic systems replaced

Just reminiscing about some of my early days of using PLC's, the first one I replaced was relay logic, this was a cutting press with 12 different cutting patterns, with probably a hundred plus relays, the paper diagram was about 20 feet long, many interesting features where some contacts were in the cold sides of the coils I must admit pretty clever in reducing the number of relays.
We replaced it with a SQD Symax 300, there was no way of putting contacts on the cold side of the coils so ended up being a long winded job, we had no idea what the patterns were, the guy that used to run it had retired & it had been in storage for a number of years. By carefully reproducing the logic without knowing how it worked, we plodded on, from getting the press running, trying all the switch positions we then could replace the mimic panel with the correct lettering for the switches & control buttons. Incidently, this was a babtism of fire, we were still working on it until nearly midnight on a christmas eve in the early 80's.
Another one was a system that had what only could be described as overgrown integrated circuits for example modules were about 4 inches by 3 inches & 1 inch high with multiple pins, from the descriptions on the modules it was deduced these were discrete transistor logic blocks encapsulated in epoxy resin. Fortunately there was an engineer who knew how this system worked & from his description came up with a program that worked.
Is there anybody out there that has come across a valve control system they had to replace ?.
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Old January 10th, 2023, 07:34 AM   #2
Manglemender
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I did once work on a pneumatic logic system but I guess you were thinking of thermionic emmission rather than pneumatics.

I also remember repairing a machine in the 80's built arround the descrete logic cards similar to what you described. It was a blow moulding machine that made plastic dustbins and a control cable had become entangled with the mechanics and severed which caused damage to many of the logic cards. Myself and another technician worked 36 hours straight to get it going again.
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Old January 10th, 2023, 07:47 AM   #3
parky
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Yes I did mean Thermionic valves, I also worked on a pneumatic system, but this was a small one, they are still in use today, they are simple but reliable & only require an air supply.
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Old January 10th, 2023, 08:46 AM   #4
cardosocea
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You're clearly older than me, I was in nappies for a lot of the 80's and parky's retired now... here you are talking about relay logic whilst I'm looking to replace a pneumatic temperature control on two reactors. LOL I wish there was more of the electric stuff to replace on my end.

The only electric signal I have is the resistance to pneumatic pressure converter that reads out the temperature in the reactor. The rest of the equipment is all powered with pneumatics, PID controllers included.

This being said, the first system to replace that I looked into and had a plan to put in place was a large industrial sewing machine that sewed patterns on duvets (company made everything you need for sleeping other than sheets and pyjamas).

It used this punched strip as the "program" for the pattern to sew and we had spare strip to replace one of the existing "programs" and then there was none made anymore that we could punch again. The module that read the strip would be "highjacked" and at every pulse to read the next byte the little board I programmed would turn on the correct outputs to simulate the reading of the holes in the strip.

Obviously, the correct way to do it would have been to get it overhauled and a modern control put on it, but money was very, very tight there.
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Old January 10th, 2023, 09:57 AM   #5
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Yes, I'm old, I also did some replacement panels for an engineering company, probably not that old as above but the overloads were oil filled dashpots, this is the first time I came across them.
I have opened up some of my earlier memories, as an apprentice printing engineer, I was tasked with coming up with an idea to replace a feed system, the original was a mangle type rollers driven by a motor with a timer, triggered off a dancing arm, once the dancing arm triggered the microswtch, the drive would feed celulose paper (like a massive multiply toilet roll) for a time, the problem was that the paper against the dancing arm would cause mis-registration of the print, also if the feed was too long it dragged on the floor also causing bad registration, I built a system using a light source & a photo resistor, driving a relay, this worked well, then I discovered difuse photo cells (never seen them before) what a revelation circa 1969.
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Old January 10th, 2023, 12:19 PM   #6
Ken Moore
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The oldest system I have worked on was an old Texas Instrument system, pre 500. I/0 modules only had 4 channels. There was a "LAM", panel mounted loop access module used to access and control the 8 built in PID loops. Programmed with a VPU. You could only see 3 ladder elements at a time. Had a print out of the program printed with a dot matrix printer, you did all you research, and edits on it first, the did the real program. Outputs would hold there last state while downloading changes. Later helped migrate it to Foxboro I/A DCS.

Back in the 80's did a lot of process control with TI products. When Siemens bought them out, I almost cried. My first exposure to AB PLC's for process control, was shocking. BTR/W to just handle analog signals, no built in loops, no structured text, no built in analog alarms.
It was a step backwards in ease of programming.
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Last edited by Ken Moore; January 10th, 2023 at 12:22 PM.
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Old January 10th, 2023, 04:24 PM   #7
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My first PLC's were Digital Equipment PDP-14's which were DEC PDP-8's with a modified instruction set. DEC then went to the Industrial 14 which was similar but with better design. Both of them were programmed in assembly language.
After the DEC PLC's we went to using Modicon 084's the A-B PLC-2 and eventually to the PLC-5, both programmed with AB's CRT terminal and magnetic tape.

Last edited by mendonsy; January 10th, 2023 at 04:39 PM.
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Old January 10th, 2023, 10:00 PM   #8
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The resin-encased transistors sound like Square D NorPak. Difficult stuff to understand but a true technology leader for a period of time. Mostly simple combinational logic but there were some things done with clocked flip-flops.I think Allen-Bradley had an equivalent - was it called Card-Lock or something like that?

The Square D field offices handed out NorPak logic manuals by the bushel baskets to people that were interested but didn't buy it. I wish I still had a copy. It was a very good thing for me to study in my early years of learning about digital logic.

The Model 300s were a pretty solid processor, especially in the UV Prom versions that kept the user program in UV erasable nonvolatile memory. We've got several of them that have been running well over 30 years in a corrections facility. The power supplies have been changed out, the staff solders triacs into the output modules, the plastic is getting brittle, but the CPUs keep going and going.

After the end the only things still running will be AB PLC-2s, Square D 300s, and John Deere 2-cylinder tractors. And nobody will know how to work on any of them.

There was an old bull and a young bull going over the top of a hill - etc - etc etc. My favorite joke now that I work with young bulls on startups. Had one situation where 2 young bulls had worked for a couple of hours trying to get a burner started. I walked in, found a failed 5 volt regulator, got a cell phone charger, and they were calling me 'McGyver' as the electrician put it in the panel. Walked out of the control room in 20 minutes quietly but doing the Old Bull strut. Enjoy it when you can.

I'm fortunate that I work with young bulls that are willing to work and listen and learn - and I can take a nap in the truck whenever the mood strikes me. I don't go to meetings, I don't do purchasing, and I don't talk to IT. I wish all old bulls that want it could be so blessed.
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Old January 11th, 2023, 03:46 AM   #9
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Hi Sparkies,

Any of you ever worked with the AUTOMATE 35 of Reliance & that heavy weight terminal the Haziltine 1500 that is used to program the PLC?
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Old January 11th, 2023, 04:34 AM   #10
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Quote:
Originally Posted by cardosocea View Post
You're clearly older than me, I was in nappies for a lot of the 80's and parky's retired now...
You're clearly older than me, I wasn't around at all in the 80's!

I remember being taught that being able to set up some diaphragm valves from the 1960's was very important and I think they had PID control through the pneumatics with a very complicated array of bellows and rockers. Never saw one of those valves after that course and later found out that it's not complicated at all to set up a diaphragm valve where the control is done externally.

I was taught the basics and programmed my first traffic lights on an SLC 5/04.

I've worked on a lot of older DC drives and some AC drives that use a clutch unit for variable speed, which I'm told were the best thing available until inverter drives were affordable. Every time I have to do some fault finding or setup on the older gear, I keep thinking just how much harder everything must have been a few decades ago.
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Old January 11th, 2023, 05:21 AM   #11
parky
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@Puddle: you were lucky traffic lights, my first experience with a PLC was being thrown on-site with a Square D programmer with a tape drive, the manual, the panel had been delivered & installed & it was up to me to get it running, so with the manual, a written description of how it was supposed to work & a set of drawings I was on my own, that was a babtism of fire.
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Old January 11th, 2023, 05:29 AM   #12
cardosocea
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This is interesting, my first interaction with a PLC was in University with an old OMRON CPU. The programming interface was a 16x2 character LCD with a keypad underneath with the instructions that were available to program it with.

More interestingly, so that we didn't just start programming the PLC in text (after all the interface we had only allowed us to write Instruction List), the teachers then made us write ladder logic and then convert it to Instruction List to input in the processor.

When I look back at it as well, it's amazing how the PLC programming progress happened. You had relay logic, first PLCs had no graphic interface at all, so logic was all input in text. We then had the first computers to create logic and display crude graphics, so we reverted back to ladder instead of progressing with text. I do believe this was also a timing issue between the first PLC and computers advancing to display graphics (even if crude), i.e. there wasn't enough time to port relay systems to logic until the first graphic editor appeared.

Still interesting though.
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Old January 11th, 2023, 05:34 AM   #13
parky
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Yes, in actual fact I did not have a tape at the begining, I wrote the program in ladder on a pad then entered that into the terminal, downloading was one rung at a time I believe press F8 twice to load, if you forgot you lost it. My first omron C20 or S6 was with a handheld so wrote it down in ladder then entered it in list, it was difficult to remember to keep the written ladder in snc with the code in the PLC.
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Old January 11th, 2023, 05:36 AM   #14
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Does replacing Rockwell with Codesys count?
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Old January 11th, 2023, 05:38 AM   #15
parky
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Not sure but definitely a good move
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