Howto: PLC Reef Controller II

[gabe21804]

as far as I know I would only need about 8 digital outputs and about 4 analog inputs.
I you guys get the Siemens compact PLC for about $150 you'll be ready to rock in no time since the digital in/out puts are rated for 10A each.
And as far as I know there are PID loops available.

What version is this, and whats the cpu revesion? Also does it have the estand 1.0 bus on it to connect to other modules? What we really need is s7 programming cables, there are a few guys on here with s7's already but have not been able to find ppi programming cables.

 

[H20ENG]

I think the problems with lamp restrike after power outages are mainly with electronic ballasts. When they first start up, it pulses the lamp with high voltage to fire it up, then runs a constant voltage through it while running.
If the lamp has been running, that pulse will not restrike the arc. it will continue to feed normal "run" voltage to the lamp when in fact the lamp never started.
That was my take on it anyway.
Chris continues lurking and learning....

 

[javajaws]

I think the problems with lamp restrike after power outages are mainly with electronic ballasts. When they first start up, it pulses the lamp with high voltage to fire it up, then runs a constant voltage through it while running.
If the lamp has been running, that pulse will not restrike the arc. it will continue to feed normal "run" voltage to the lamp when in fact the lamp never started.
That was my take on it anyway.
Chris continues lurking and learning....

...and I've got electronic ballasts. Better safe than sorry...that's what they always say. Its not like it costs anything to implement the delay...except for a few bytes of memory that is.

On a side note, I notice my electronic ballasts generate minor electrical noise in my house (like static on TV, etc.)...will this cause the PLC any problems (I would think not...but better safe than...well, you know...)?

 

[gabe21804]

...and I've got electronic ballasts. Better safe than sorry...that's what they always say. Its not like it costs anything to implement the delay...except for a few bytes of memory that is.

On a side note, I notice my electronic ballasts generate minor electrical noise in my house (like static on TV, etc.)...will this cause the PLC any problems (I would think not...but better safe than...well, you know...)?

Don't put them in the same enclosure or near each other. I have mine in the canopy, and my plc near the stand. As long as there is some distance between the two you'll be fine.

 

[easttn]

The sale forum does not last an hour, If your into this thread please follow here
PM for any details.

 

[Stbringer]

Wow! Plc's at last!!
Will be HAPPY to offer any help on logic design for reefs, data collection, suggestions, etc.
One caution, most plc contacts are rated like 10a for a relay output. There is a catch though, and that is most contacts share a common.
This is not always the case, but often the sum of the contact amperage is greater than the amperage per common. In simple terms, the make/break characteristics of the relay contacts are collectively higher than the ampacity of the board traces that provide power to the line side of the contact. Again, not always the case, but in MANY cases.

I have seen a great many good ideas and implementations here, and am a bit behind. I was thinking of trying a tc/mv card or an RTD card for PH but never got around to checking the electrical characteristics of the probe.

It seems the S word is taboo here, but I am very experienced with accumulated data, data logging, and conversion to excel, etc. to plot reef params.

Again, just an offer for assistance, and I can definitely learn a thing or two here. PM me if I can help!

 

[Stbringer]

OH, don't know if this has been handled or not, BUT for those of you using backup power, always keep a digital input available for your normal power ok, and one for "backup power on". This will allow you to determine alternative logic for low power, etc. It may even be of use for the plc to switch back to standard power after a preset time saving the battery but sailing through repeated brownouts, etc.

For items like DIN rail, oiltight/watertight buttons and switches, check your local yellow pages for electrical distributors that carry Siemens/A-B/ etc. plc's. They will have it and more.

 

[inerratum]

Bump, dont want this project to die.

I have the programming cable on the way, thanks easttn, so I can finally start to get mine setup. Still need the thermocouple module and the analog in module but at least I can start getting the basic timers setup soon.

Does anyone have a link to thermocouples that are saltwater safe and will work well for this application?

 

[Stbringer]

I recommend a Type J thermocouple for the temperature range in this application. They are made of a juncture of Iron/Constantan and in the US color coded Red/Wht. In most applications that need isolation of the probe, a threaded thermowell made of Inconel is used. Others have small already encapsulated probes. Try www.omega.com .
Oh, for accurate readings, you will need thermocouple wire also. Copper wire introduces error and temperature resistivity differences.
I have only purchased for industrial applications before, guess I shoud get looking!

 

[jgwinner]

Wow, great thread! I bought some uC's a long time ago to build something myself but never finished the project.

These PLC's are programmed in 'ladder logic' or C code?

'soft start' would be nice too, is there a way to syncronize the digital out with a zero crossing?

== John ==

 

[javajaws]

They are coded with RLL (ladder logic). I'm not familiar with a "zero crossing"...what's that refer to (I'm assuming some phase condition on the AC line)?

 

[Stbringer]

Naw, most of the outputs are Triac anyway, and only switch on the 0 cross. The relays response, etc. and the time from output set high in data table to output table update to backplane pretty much rule out digitally programmed soft start... Unless you want to bang it a few times on the way to speed.

Most do ladder logic, statement logic, and Siemens has Pascal available. Some small off brands and other controllers may do the C.

 

[jgwinner]

Zero crossing means a timer signal from an optocoupler based on an AC in (usually the power supply). In other words, it would be a trigger whenever the incoming a/c hits 0. What you would do is latch a signal saying 'turn on' to the pumps, and then when the zero crossing triggers, actually turn on the outputs.

Some solid state relays do this automatically, which is handy. those are probably 5-10 bucks a piece, can't remember current prices. It's been a while since I looked at this stuff.

One thing I've always wondered is if you could run an aquarium pump on 'half speed' by only passing through say every other waveform (DC if you will) or doing 2 on 2 off kind of a thing. The zero crossing detector would allow messing around with that too.

Edit: Triacs don't wait for 0 crossing, they just don't turn OFF until you have a zero crossing. Triac's are two back to back SCR's which is a diode with an 'input' - once you pass in a signal to the input the diode turns on, permanently until you remove power. Handy little things, no heat disipation at all.

Dimmers use triac's that trigger 'on' somewhere halfway up the sine wave. They then turn off at the zero crossing. I've made dimmers for DJ's based on this.

== John ==

 

[Stbringer]

Oh, javajaws, yea, you hit it.. the ac as it crosses 0 on the up or on the down is the 0 Cross. Most solid state DC outputs are not limited by this, but the actual Hz you can get out of a plc is sort of flaky in most cases, as it relys on scan time, etc. Most of the industrial motor starters/vfd's that would be used with a PLC contain the soft start so they generally don't build that into em.

 

[Stbringer]

jgwinner, you know your stuff!
(Guess we are typin at the same time, and you are faster!)
Best thing might be to use the hardware for the soft-start if you can rig it.

 

[Stbringer]

jg, what about firing a triac output to a 1/2 wave bridge set for the upper half, then later kicking on another 1/2 wave bridge set for the lower half??? Been a long time since I did the board level (20yrs) but know the speed limitations of most plc response pretty well, even if using PII interrupts. If you know of some kind of rig that would take a PWM output and convert each pulse peak and valley as a 1/2 cycle trigger, some of the smaller units do have a pwm out...

 

[javajaws]

How important is soft start and zero crossing? What benefits would that give us?

 

[DJ88©]

Less wear and tear on anything you need to start up.

A good analogy is dropping the clutch in a car when the engine is at 3,000 RPM all the time. Something will wear out in time.

Listen to a maxijet powerhead when you plug it in. YOu cna lessen the "chatter" with a soft start.

 

[jgwinner]

I'm surprised these PLC's have such speed limitations. I had been working with a 68hc11 single board computer a while ago and it had the 0 crossing built in. Geez, maybe I should dig that project out of retirement.

The PLC project seems nice and easy though, most everything is built.

The soft start is apparently disputed somwhat - my understanding is that no matter how you start the pumps they 'clatter' but it definitly would increase eletrical noise in any event.

Digital relays usually have a 0 crossing built in, including the 'hocky puck' relays.

Thanks for the kind words Stbringer, been a while since I did any professional EE work. Mostly doing C++, Oracle, IT stuff now.

 

[Stbringer]

HAHA! PLC's are fast for most industrial needs, and you deserve the praise. You remember what most of us forget, and clearly at that!

Ya, will get some noise, but maybe save the impeller some wear.

Problem with these little magnet motors is they need enough kick to light off initially or they just vibrate...
You are the man to ask, so say we fire the AC output to an SSR, it will then inherently light off the pump(s) at the 0 cross? The plc code can do the latching on/turning off on internal timers no problem.

Most of the 16pt and even some 8pt ac outs are very low resistive current rated outputs. The ssr would allow easy switching of multiples, larger pumps, etc. with virtually no penalty to the ampacity of the output card itself.

I use SSR's from time to time for resistive heating applications...PID algo. in the PLC. Using an SSR on an output for the heater(s) would allow you to kill them for sure in the event of a runaway temperature event (stuck thermostat in heater).