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Thread: JACE or Appication/PLC
09-28-2012, 09:19 AM #27
Okay so critical has different levels! I mean more along the lines of a boiler plant or chiller plant. Still not what the industrial world would call critical.
I guess what I was looking at is based on cost, which obviously varies based on who's buying and selling, a Spyder and a JACE can be competitively priced. As a building owner, why would I want the Spyder instead of the JACE? I'm not using this JACE as the front end, just simply an equipment controller."Fortunately, I keep my feathers numbered for just such an emergency." Foghorn Leghorn
09-28-2012, 10:01 AM #28Regular Guest
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Note to those new to the Controls forum.
Bashing of JCI and Loytec and others allowed and encouraged.
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09-28-2012, 10:57 AM #29Regular Guest
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- Feb 2012
Greetings to ControlMT. I would like to respond to this topic will confine my response to you. As such, my comments are directly solely to you out of a necessity.
I would realise a boiler and cooling plant on different levels of consideration in a BEMS.
For a program change I can see that the benefits of instant reloading in a boiler plant may not be necessary. Yet, in a cooling plant I can visualise many issues with the I/O cycling off and PID loops resetting when this is not advisable or desired. Or, that all the logic is in one place unless it is very carefully planned distributed. The downfall of an event based system could be this very point of where the control is executed. Even a device with high cycle rate or response timing could be lost due to the nature of the I/O as user Orion deftly points out. If the I/O is Modbus communication, then fast cycle times are not a consideration. It would be impossible for a fieldbus or even Modbus TCP to respond on network in 10ms or less. Such a timing comparison is reckless. But, if the I/O is directed connected via a higher speed, regulated internal bus then faster cycling rates can be advantageous for some operations such as lighting and sunblind integration and operation, or control of a generator. The ability to check twice for an error once is good practise.
From management and documentation level if a user is maintaining a standard PLC environment much of the programming is across vendors platforms so code can be shared. This ultimately gives options to an integration specialist to move to multiple vendors with largely the same code library. This is 100% in theory and 60% in reality. But, 60% is better than 0%. 0% means you have a single vendor offer. Scalable control offering is also a consideration. Can you obtain both small and large I/O counts with the same programming and features? Save engineer time.
Some PLC manufacturers products are very inexpensive but may lack for features found in building automation such as scheduling. What is expensive? And what is your labour time? Your service time? One thing I most certainly disdain is coming upon a controller which only has blinking lights. Blinking lights are better suited on a tree. I prefer a display interface locally. I place value for this, whereas another frustratingly not.
What I suggest is bring in some documentation and make some comparisons. Lastly, compare pricing and any costs associated with the product name. One popular PLC vendor I have used charges thousands for software. They do this because their name is big where others have no charge. Compare. You can assign any cost premiums, warranted or not.
09-28-2012, 02:02 PM #30
So let me ask this about what your shilling here....
Can you explain to me how none of the outputs are going to change state after this? All the PIDs are going to be at their same state?? What if they are removed, added, connected to something else??
Even IF the controller has some magic inside that saves states of everything, how would this be applied to modified logic?
This 10ms cycle time would be more of a curse than a benefit 99.9% of the time.
Gee <insert tech name here>, that program snafu managed to cycle the output on/off every 10ms and blew out the control relays, contactors, and pump couplings in record time..... If only I could only find a tech that can react in 500ms and kill the controller before the $hit hits the fan....Propagating the formula. http://www.noagendashow.com/
09-28-2012, 02:17 PM #31
>faster cycling rates can be advantageous for some operations such as lighting and sunblind integration
How fast do these blinds move? 180deg/sec? Are you adjusting the blinds as clouds go by?Propagating the formula. http://www.noagendashow.com/
09-28-2012, 08:50 PM #32
It the dis-information that invites the defensive responses ... if factual, then there would be nothing to defend.
This IO rebooting topic is a case in point.
Yes NDIO would reboot when a JACE reboots ... but some people make it sound like NDIO is utterly flaky and cant be relied upon...which simply isnt true.
They also make it sound like a JACE reboots every 5 minutes ...again simply not true.
Geez comparing a DX-9100 to a PLC is hilarious ( and subtly deft too ) Its almost like saying you should use a DX9100 instead of a JACE...clearly absurd to anybody that ever programmed a DX9100. Imagine ...every program change requires a download that takes about 3 minutes and every program change needs validation ... very funny because 'commissioning' yr new critical boiler plant would probably take about 10 downloads and likely still not be quite right.
BTW I programmed my first DX9100 about 20 years ago ...and tweaked my last one just last week.
Here, on one job JCI branch are still installing them. No, I am not exaggerating either!
Hello have they changed in 20 years ??? ... nup!
Lastly, and this is what is very annoying about this topic ... is why on earth would somebody load a mission critical application on JACE with NDIO ... you simply wouldn't do ...full stop.
You would load a 'critical' application on a PLC or stand alone controller and the JACE would be supervising. OMG...almost sounds just like a real control system doesn't it?
BTW ... and this is what keeps getting missed... the JACE is rarely the main controller itself. Usually it is little more that a web server and a repository for histories.
Sure a small job with an AHU and few pumps would likely end up in a JACE and some NDIO but it would be poor engineering to run yr critical app on the same device as everything else.
Only a Controls Imbecile would do that.
The issue here is the framing of the proposition.
These types of issues re: criticality and appropriate application of controls exist for ALL control systems irrespective of their brand. Some systems have better solutions that others, but realistically ALL of them will behave respectably if applied sensibly.
My big issue with all HVAC controls is that too often they are applied by fridgies and electricians who DO NOT have the requisite engineering skills. They get out there as 'Controls Guys' and start looking for 'one size fits all' solutions.
Originally I was a sparky myself (but I may have spent some time doing a little engineering) ...sorry for alienating some of you because of this statement...what Im trying to say is .... THINK THICKHEADS...THINK and ENGINEER things instead of trotting out some half-arse solution and then seeing how it flies.
And if Loytec and its stick of hot swappable IO makes all these issues disappear ... then I guess the product is gonna take the boiler world by storm heh?1 + 1 = 3 ( *** for very large values of 1)
...everybody wants a box of chocolates and long stemmed rose
09-28-2012, 09:06 PM #33
All that is important, is that IO and LOOPS and stuff go to a known state when rebooted or reprogrammed or whatever....AND that the clown that installed it has appropriately engineered the system to account for it.
Yr all playing semantics with the word 'critical' here ...
does critical mean ... continue to run without interruption?...or
does it mean...not doing something destructive in a reboot?
or does it mean ... engineering the control system appropriately???
...i started my working life in a steel mill ... worked in an engine casting and milling plant ... pointed Solar Concentrators to track the sun ... and of engineered more HVAC control systems and more PLCs than some people here have had hot-dinners.
I can say one thing ... for many of those applications I would never consider using a JACE ... and I certainly wouldn't consider using a Loytec anything either. Some of them, we built our own dedicated embedded controllers (LON based actually)
... get the question right first before applying half-arsed solutions.1 + 1 = 3 ( *** for very large values of 1)
...everybody wants a box of chocolates and long stemmed rose
09-28-2012, 10:01 PM #34
A boiler plant is not a mission critical system, likewise with chillers applied to HVAC and not process. I use Jaces for both plants with complete success.
I don't pretend to do NASA control. PLCS have their place. I simply use a Jace to benefit from integrating drives, burners, boilers, and chillers, and do the ancillary equipment sequencing with out the network traffic. (outside of the plant)
I do 1500-3000ton plants all the time.Intelli-Building = Less Stress, commissioned with diligence!
10-02-2012, 12:28 PM #35Regular Guest
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- Feb 2012
Greetings Orion242. I break my imposed ruling here but I will respond. I want to assure you I have not utilised the word "critical". Therefore, there is no way I play semantics with a word. I leave misappropriated assumptions and ramblings to others and their loutish behaviour.
If you have a sunblind stroke at 1000ms then to move 1% you may like to have 10ms cycle time rate not having a trick in place to account for faster timing. To answer your american inquiry, blinds can move the entire span in one second, and they will every time you need to raise them or lower them.
I do make a concession the aforementioned manufacturer in many cases lists their 10ms cycle time rate because they can deliver this rate. This is an affirmation that the product is well designed from a market position. Certain not a curse when you may desire it at times or the instant reload feature. I think your previous scenario is not indicative of a seasoned programmer that understands what he does. For such a seasoned programmer there is a benefit to instant reload to adjust many sequences, add features, adjust constants not exposed to the user - the list of advantages can be quite long on reflection. Why disparage features that enhance products?
10-02-2012, 01:43 PM #36
I think the biggest problem with using something like a JACE for direct equipment control, is the lack of segregation it tends to encourage. Using the above mentioned chiller plant example - The JACE's extensibility would lead someone to try to use one to control the entire chiller room (it's not just a JACE thing, our brand new chiller plant has a single Alerton VLX controlling the chiller room). The problem with this is fail recovery. If the controller goes down, what happens with the chiller enable point, what happens with the valves for the running AND the off-line chillers... what happens with the pumps.. the towers... etc. However, if instead, you had a very cheap and simple smart IO/application controller dedicated to each chiller, and IT controlled that chillers own valves and pumps, and all you had to do was load a request point into it from your sequencing controller, it would allow the global to fail, come down, reboot, etc, and not have an immediate impact on plant operations. Have some simple failover logic in the application controller that if it has not gotten an update watchdog from the global for a given time, you can then have it go to a desired failed state (either enabled or disabled, depending on the plant use/configuration).
10-02-2012, 02:23 PM #37"Fortunately, I keep my feathers numbered for just such an emergency." Foghorn Leghorn
10-02-2012, 03:51 PM #38
10-02-2012, 04:04 PM #39
Got it...I wasn't following fully that is what you meant. I was reading it as two seperate issues. Makes sense to me. Keep everything compartmentalized. It may cost a little more in the intial installation (labor) but long term I would think it to be less expensive to maintain/repair as part/components fail."Fortunately, I keep my feathers numbered for just such an emergency." Foghorn Leghorn