PID how control SSR relay

[t0r3r0s]

Greeathings.

I need some help about how control ssr relay with digital inputs .

I use ssr relay for control temperature , in FB PID I dont see MB or O .

Have some solution about that. 

 

Thank you

[Flex727]

Sounds like you're trying to create a thermostat. PID control makes no sense for digital I/O.

[t0r3r0s]

4 minutes ago, Flex727 said:

Sounds like you're trying to create a thermostat. PID control makes no sense for digital I/O.

i finde controling ssr with pwm , ssr work 0 off 1 on , 

i cant belive they have module for Thermocouple but not module for controling ssr 

[Flex727]

Of course. Yes, PWM function blocks are available. Which PLC are you using?

[kratmel]

Maybe topicstarter

13 minutes ago, t0r3r0s said:

....how control ssr relay with digital inputs .

...must be digital output

[Gabriel Franco]

Use PWM function, using PID output as input for PWM block.

[t0r3r0s]

Just now, Flex727 said:

Of course. Yes, PWM function blocks are available. Which PLC are you using?

I use vision V280 for this project , i use IO16DIA3/RO16 , Module for thermocouple , analog output for valves .

[Flex727]

You'll use your PID to control the frequency or duty cycle.

[Flex727]

You'll need "High-Speed" outputs. Those aren't available on the IO-D16A3-RO16.

[t0r3r0s]

2 minutes ago, Flex727 said:

You'll use your PID to control the frequency or duty cycle.

 

1 minute ago, Flex727 said:

You'll need "High-Speed" outputs. Those aren't available on the IO-D16A3-RO16.

I know, only digital TO have high speed , only try with examples of kratmel

[kratmel]

what hardware used?

8 minutes ago, t0r3r0s said:

analog output for valves

[kratmel]

V350_PID simple demo.VLP

V120_PID_motorized_valve_output_with_physical_feedback.vlp

in Examples

[t0r3r0s]

26 minutes ago, kratmel said:

Maybe topicstarter

...must be digital output

MI 247 which value is ???

[t0r3r0s]

15 minutes ago, kratmel said:

V350_PID simple demo.VLP

V120_PID_motorized_valve_output_with_physical_feedback.vlp

in Examples

pid for valves isnt problem i have analog output module , but problem is vvith controling temperature , can you explane me hovv can i use pvvm scan

[Ausman]

1 hour ago, t0r3r0s said:

I know, only digital TO have high speed , only try with examples of kratmel

Others have mentioned the issue, but I would be particularly careful trying to run an SSR with relays in a PWM.  The relays won't like it and you'll likely do damage if the stream is fast.  Even just for experimentation you may have a problem.

cheers, Aus

[Joe Tauser]

Set your PID block up for Output Range Low = 0 and Output Range Hi = 1000.  This will give you an output of the PID block of 0 - 100.0%, which is what the lower PWM block input is looking for.

I think the PWM block is misunderstood, as the posts in this thread wander around a bit.  It can certainly be used to control a mechanical relay if applied properly, but as Aus points out you don't want it running too fast.  The first parameter (your MI 247 with triple question marks) is the total cycle time.  A total cycle time of one second is fine if you're driving the DC input of an SSR with a transistor output, but that's way too fast for a mechanical relay as Ausman points out.  If I'm working with a relay I typically use a 10 second cycle time for PID.

Now to answer your ??? question for the value of MI 247.  If you look at the Help on the PWM function block, you'll see that the "units" of the PWM block are 1 unit = 2.5 ms, which is totally confusing and not very intuitive.  But that's how it is.  So....

1 sec Cycle Time for direct SSR use 1 / 0.0025 = 400

10 sec Cycle Time for mechanical relays use 10 / 0.0025 = 4000

Also, don't be afraid to post your code so we're not bogged down in trying to guess what you're trying to do.  We don't know the whole story until we see it.

Joe T.

[Ausman]

Just for interest's sake some thoughts on relays.  I have copied in here some specs for a common relay Unitronics use.

Mechanical 50,000,000 operations min. (at 18,000 operations/hr)
Electrical 100,000 operation min. (at 1,800 operations/hr under rated load)

Note the large difference between what the relay mechanicals are capable of vs what the electrical contacts are capable of.  MTBF is something that designers often (inadvertently) overlook.

I find it amazing that a relay maker will say their unit is OK to do "1800 operations/hr under rated load", when clearly if you run the relay at this allowed rate your possible (not guaranteed, look at MTBF definitions) run time for your machine is a whole 55 hours!  No-one in their right mind wants to build a machine for a client that will only run that short time before needing the relays changed.   Of course the relay maker would love you to be changing their product so frequently, but it's all a bit silly.

Relays are absolutely perfect for some operations, but durability is important.  Some of my machines over 25 years old have had one relay set change in their entire 24/7 life because they only switch tiny currents once or twice a day. 

Also look carefully at VA ratings vs other power specs of the relay you are looking at using.  I've mentioned this before on the forum.  You will often get "conflicting" info and it is a trap I fell into many moons ago by simply going on the amp rating , only to find units failing early because the actual VA rating is miniscule.  eg   rated voltage  240V ac,   Amps 2A,   VA 10W.    Also don't forget resistive vs inductive differences.

Tread carefully, Young Skywalker.  Advice seek and specifications all look you must. 

cheers, Aus

 

[t0r3r0s]

On 3/4/2020 at 12:31 AM, Ausman said:

Others have mentioned the issue, but I would be particularly careful trying to run an SSR with relays in a PWM.  The relays won't like it and you'll likely do damage if the stream is fast.  Even just for experimentation you may have a problem.

cheers, Aus

Have you some other solution ???

[Ausman]

Sadly, as Flex has already said, what you need is not available on your hardware.  You need to go to

https://unitronicsplc.com/io-expansion-modules/

and scroll down a bit to find I/O Expansion Modules for Vision, peruse what is available and what suits best that has solid state outputs.  In doing this you also need to check the specifications for the various modules, making sure that they are capable of what you want to do.  You do this by going here:

https://unitronicsplc.com/support-technical-library/

Some have higher switching rates than others.  For instance the I/O TO16 which might be the cheapest way to get it has a max frequency of 20Hz on resistive.  But if you go to an EXF-RC15 which links via UniCAN you can get 5Hz -200kHz.  It all comes down to careful consideration of the most practical and cost effective way of achieving everything needed.  In doing this, I always keep potential future replacement costs in mind as well.  If you have expansion and physical rack space, a few separate modules doing the same thing as one more complex module are often a better way to go.

You could also consider a snap-in, but I haven't really offered that up as I think it will be cost prohibitive in your scheme of things.

cheers, Aus

[Joe Tauser]

On 3/5/2020 at 1:17 PM, t0r3r0s said:

Have you some other solution ???

First, post the model and make of your SSR so we can truly know what you are using.  Most SSRs use a DC trigger signal of 3-30 VDC, which is why others keep recommending a transistor output to drive them. 

This is not totally necessary, it just works better.  You can certainly drive a typical SSR by switching a 24 VDC signal through a relay; you just have to slow it down with a longer cycle time on the PWM block.  Did you read my above post?

Joe T. 

[Ausman]

True enough, Joe.  It all depends on what t0r3 actually needs to do.  Because he asked, I have perhaps incorrectly assumed he realised his switching rates weren't suitable for a relay. 

Warning...digression.   If it were only us oldies in the 90s, I'd say do all the hacks I did back then by opening things up, finding the electronics that drove the relays in the first place, and direct coupling into that to avoid mechanical restrictions.  I had to do it a few times because of hardware restrictions on what was available then.  But of course I'm not suggesting that now!  I had an LG system that was still working umpteen years after I did this, until some goose remounted the enclosure and filled it with swarf that trickled down b/n the pcb and case.  "It's stopped working, Aus". 

But at least that wasn't as bad as the "maintenance guys" who attached something onto a big aluminium heatsink in a loco that had printing all over it saying "Do Not Drill or Mount Anything on this".   Hundreds of thousands of dollars later it eventually got going again. This is not a fib, it was in a government run workshop I was working near at the time.       🐒 's.     Sorry...most monkeys are pretty smart.    

Digression end.  Maybe we should start something in the lounge along the lines of the most astoundingly stupid truly happened control things people have seen.

cheers, Aus

[t0r3r0s]

On 3/7/2020 at 6:40 AM, Joe Tauser said:

First, post the model and make of your SSR so we can truly know what you are using.  Most SSRs use a DC trigger signal of 3-30 VDC, which is why others keep recommending a transistor output to drive them. 

This is not totally necessary, it just works better.  You can certainly drive a typical SSR by switching a 24 VDC signal through a relay; you just have to slow it down with a longer cycle time on the PWM block.  Did you read my above post?

Joe T. 

Greeatings .

 

I use Fotek SSR-40 DA this relay have input 3-30VDC , i read all your post and i vvill try vvith pvvm like you say