AB Characteristic Curve Add-On or PAX Block

paul.palmer

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Oct 2020
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Does anyone know of an Add-On Inst. or PAX Block that can be used to develop a characteristic curve?

I have a Variable Speed Pump with a Current transducer. Trying to determine if that pump actually has flow.

For example:
@ 25% Speed; NoFlow=1.1A, Flow=1.3A; Therefore, Flow Good if Amps>1.2
@ 35% Speed; NoFlow=1.3A, Flow=1.8A; Therefore, Flow Good if Amps>1.5
@ 45% Speed; NoFlow=1.5A, Flow=2.0A; Therefore, Flow Good if Amps>1.8
and so on.

If there isn't a block, I guess it can done with a bunch of SEL and GRT blocks based on pump speed.
 
Does anyone know of an Add-On Inst. or PAX Block that can be used to develop a characteristic curve?

I have a Variable Speed Pump with a Current transducer. Trying to determine if that pump actually has flow.

For example:
@ 25% Speed; NoFlow=1.1A, Flow=1.3A; Therefore, Flow Good if Amps>1.2
@ 35% Speed; NoFlow=1.3A, Flow=1.8A; Therefore, Flow Good if Amps>1.5
@ 45% Speed; NoFlow=1.5A, Flow=2.0A; Therefore, Flow Good if Amps>1.8
and so on.

If there isn't a block, I guess it can done with a bunch of SEL and GRT blocks based on pump speed.


And that would be the way I would approach this, because it won't always be you looking at the code at 3 a.m. trying to figure out what's going on ....

I would start off with an unconditional OTL Flow_Good, then a series of LES LES rungs which OTU it if the conditions aren't met ... transparency !

EDIT : And don't forget to include "debounce" timers, 1 single current reading falling below the setpoint should not cause alarm ....
 
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Good point @daba, it may be a little more work, but definitely more transparent. This customer is wanting us to program in FBD as much as possible. That kind of adds to frustration as well.

I thank you and @drbitboy for the replies.
 
This customer is wanting us to program in FBD as much as possible.

What is wrong with customers ? FBD ! as the preferred language ?? There's no hope for the human race .....

But at least you've got the "as much as possible" Get-Out-Of-Jail card .....
 
Just had the thought that you could program this as an Add-On Instruction - in Ladder or STL, and "Source Protect" it...

Just saying ....
 
FGEN does piecewise functions. You'll want two of those though, flow curve and no flow curve, and LIM your pump amp draw between them.

It'd be more time consuming but perhaps better for clarity to brute force it. Also, I don't know what the application is, but adding instrumentation might open up avenues in the future.
 
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How is FGEN not "clear?" It is at a minimum concise. Is linear interpolation sufficiently advanced tech that it is considered magic?



It looks like there will not be a lot of segments, so the endpoint pairs could be included in the comments as well.
 
How is FGEN not "clear?" It is at a minimum concise. Is linear interpolation sufficiently advanced tech that it is considered magic?



It looks like there will not be a lot of segments, so the endpoint pairs could be included in the comments as well.

It's up to personal philosophy, which stance you take in the "write code meant for 5 year olds" versus "no one but me has any business in my PLC" eternal debate.

OP knows his audience. I know there are some clients for whom I will take the long way around every time.
 
It's up to personal philosophy, which stance you take in the "write code meant for 5 year olds" versus "no one but me has any business in my PLC" eternal debate.

OP knows his audience. I know there are some clients for whom I will take the long way around every time.


Bravo! Always program to your audience.
 
It's up to personal philosophy, which stance you take in the "write code meant for 5 year olds" versus "no one but me has any business in my PLC" eternal debate.

OP knows his audience. I know there are some clients for whom I will take the long way around every time.




I get that. It is depressing that any audience doesn't understand that elementary level of magic, but yeah, I get that.
 
How is FGEN not "clear?" It is at a minimum concise. Is linear interpolation sufficiently advanced tech that it is considered magic?

It looks like there will not be a lot of segments, so the endpoint pairs could be included in the comments as well.

There are many "educated" techs in factories that barely understand XICs and XIOs, that's why so many get put on the "Basic" programming courses. And then of course management feel they have been "trained" so rely on them.

There is a whole world of difference between being "trained" (as in just attending a training course), than being "trained" (as in attending and taking in the subject matter).

Everyone on an RA training course gets a certificate - but it's not an indication that they have understood or even taken in what was being taught. It just states they were there ....

In most training facilities it is often two people on a rig to do the practical exercises, and I have very often observed that it is one of the two doing the exercise, the other just observing, and pressing buttons when prompted. IMHO that is not training people, that is giving up your training expertise to the better of the group, who most likely does not want to help his lesser accomplished partner, but wants to "shine".

Very few courses, anywhere, do written exams on the final day to evaluate if the delegates have learnt anything, or even listened during class, but they get their certificates anyway, their bosses are happily confident their money was well-spent, but regrettably, and very often, not so...

I have delivered courses, after 4 days training on the subject matter, to OEMs working on GM plants that had used the software for over 4 years ! They were teaching ME how it worked !

This was a dark time for me, believing I was the "trainer", but at the end of the day we could have sat in the coffee shop every day, and they would still have known more than me. But they had to have their "ticket", which they paid for themselves... In this case there was an "exam" at the end of their 2-week (??) course, and needless to say the LOWEST score was 99% !! Go figure ! How is it possible for a trainer to deliver a 2-week course after 4 days training ??
 
I get that. It is depressing that any audience doesn't understand that elementary level of magic, but yeah, I get that.


The trouble with "magic" is that you must NOT reveal how you did it ....
 
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