Choosing pid?

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bottles
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Choosing pid?

Post by bottles » Fri Mar 30, 2018 11:41 pm

I've started looking at making a Herms system. But can't find what type of pid is required. I can see lots on evilbay or Amazon but can't work out what criteria are needed.
I've tried to find an explanation on pid's but only find out how the machine calculates but not how types vary. I've also seen posts about people buying pid's that they can't get to work.
How did you choose yours?
Andrew

Fil
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Re: Choosing pid?

Post by Fil » Sat Mar 31, 2018 12:23 am

#1 criteria is to ensure whichever make/model you select is that its suitable to control via a SSR (Solid State Relay) and not a mechanical contact relay.
The latter is more suited to electrical kilns as the switching is far less rapid than when employed for direct liquid heating the volumes we heat.

I am far from expert on the subject but do use pids myself and from what ive read the top end of the market is dominated by Auber and the chinese imports are mainly copies and clones of the Auber brand.

Personally i opted for the sestos brand which is a far east import based on the auber to the extent that the auber manual which is far more comprehensive applies almost completely to the sestos, the 2 main differences being the lack of Fahrenheit display options on the sestos, and a few differences in the actual codes for settings (notably probe types). So i read the Auber manual for context and refer to the sestos sheet for settings..
https://auberins.com/images/Manual/SYL-2352_manual.pdf
The one brand lots of folk had problems with when i was looking into the subject was rex though that may have had more to do with folk buying the mechanical relay version rather than the ssr version instead of operational issues??

However if cost is a factor and you need to do it on a budget these days considering you still need to add a ssr heasink and enclosure with suitably rated fex and plugs/sockets.. given a couple more sunday afternoons a diy arduino or esp8266 or esp32 or any similar cheap as chips soc solution could work out a lot cheaper. As a sonoff fan boy i noticed that there was a recent addition of Pid functionality to the open source Tasmota project which you can flash onto lots of cheap devices ;) pm me for links as its not a public branch (yet)..
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jaroporter
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Re: Choosing pid?

Post by jaroporter » Sat Mar 31, 2018 7:10 am

also some require 12/24V and some 230V to power the unit. obviously it doesn't matter at all which you get but it will affect your design. one might be more convenient than the other.
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Re: Choosing pid?

Post by sbond10 » Wed Apr 04, 2018 12:34 pm

As einbrew says make sure its a 240 volt job, i have a 12-24v one and either struggling to find a solution to bring in a single 240v ps drop it to 12v but then carry on to 240v to power an element. These are the problems you face if you pick the wrong pid

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PeeBee
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Re: Choosing pid?

Post by PeeBee » Wed Apr 04, 2018 3:12 pm

I got a mains AC PID recently. Fitting it the control box with a 1A mains supply, I read this thread and thought I'd check again: The mains supply is only for the PID, everything else is running on 12V. I should have got the 12V version of the PID for an easier life.

Just playing devil's advocate. There's nowt wrong with 12V versions as long as you don't have to specially arrange 12V just for it when everything else runs on mains.

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themadhippy
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Re: Choosing pid?

Post by themadhippy » Wed Apr 04, 2018 3:20 pm

i have a 12-24v one and either struggling to find a solution to bring in a single 240v ps drop it to 12v
Id test it on 18v AC ,measure the current draw,then calculate a suitable capacitor size to run it off 240v,but only if i was 100% sure it was safe to do so
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bottles
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Re: Choosing pid?

Post by bottles » Wed Apr 04, 2018 8:02 pm

Thanks for the explanation of choosing pids. Where do you buy yours from? I've been looking on evilbay and amazon.
Are there any uk web pages showing how to wire up pids? I'm planning on using this for a Hermes system.
Most of the information I can find explains how the pids algorithm control the output. Or talking about the system and how shiny and new, while name dropping suppliers. Missing any details of the build.
Andrew

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themadhippy
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Re: Choosing pid?

Post by themadhippy » Thu Apr 05, 2018 12:14 pm

Are there any uk web pages showing how to wire up pids?
what make of pid have you got as the connections on the pid maybe diffrent depending on manufacturer,but its very easy.
You must (must, must, must) earth all touchable electrical metalwork, use nuts, bolts and crimps to achieve this earth bond,
And if your in an earth free location?
this earthing has to be able to carry full load current until the fuse blows.
it needs to carry the full prospective earth fault current
You must fuse the live 230V connections.
Only if theres a reduction in the current carrying capacity of the conductor
Use and RCD on the circuit.
Almost every house will have an RCD fitted,if not i suggest its time for a rewire
many wire & cable specs don't specify current
so whats all those tables in section 4 of the iee regs for?
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Fil
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Re: Choosing pid?

Post by Fil » Fri Apr 06, 2018 1:47 am

This might be a lower cost option.. https://github.com/arendst/Sonoff-Tasmo ... ff-Devices

buy a £4 sonoff basic Image
and with a computer running a mqtt message broker and nodered, ( I use a £10 raspberry Pi ZeroW).. but you could use your pc or lappy you can use the above linked system.

you will need a usb ftdi/uart programmer and jumper wires to hook things up to reprogram a 4k7 ohm resistor and ds18b20 temp sensor(£2-3?) so all in all it should come in under £10, especially if shipped in from the far east..

now the sonoff basic device contains a standard mechanical relay not a ssr, but this implementations operation cycle is 1 x per second, so its not going to effect the high frequency switching the usual pid controller would, but i would suspect its more than reactive enough to satsify the needs of a small scale herms/rims system.. But no i have not tested it!!

the relay may exhaust its 100,000 or however many expected switches earlier in its life due to this sort of use but that is the £4 component, and it can still be used as a wifi sensor input device with a dead relay ;)
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