Analog Scaling Issues
Analog Scaling Issues
(OP)
I have this situation:
I have a seametrics ex215b flow meter with a seametrics ft420 totalizer with 4-20ma output.
I have interfaced this with a red lion signal conditioner to change the 4-20ma to 0-20ma.
I then have it wired into a Netbiter EC220 analog input which I set the dip switches for 0-20ma.
Now for the hard part, what vaules do I set for scaling?
where 0.00ma = 0 gallons per minute
and 20.00ma = 1400 gallons per minute
my question is what would my scaling and offset be?
min. flow in this 14" pipe is 134gpm, this is the rate at which the influent water begins to be measured... and the maximum is 1,400 gpm.
but I just cant seem to figure it out...here are some pictures of what I have going on.
I have a seametrics ex215b flow meter with a seametrics ft420 totalizer with 4-20ma output.
I have interfaced this with a red lion signal conditioner to change the 4-20ma to 0-20ma.
I then have it wired into a Netbiter EC220 analog input which I set the dip switches for 0-20ma.
Now for the hard part, what vaules do I set for scaling?
where 0.00ma = 0 gallons per minute
and 20.00ma = 1400 gallons per minute
my question is what would my scaling and offset be?
min. flow in this 14" pipe is 134gpm, this is the rate at which the influent water begins to be measured... and the maximum is 1,400 gpm.
but I just cant seem to figure it out...here are some pictures of what I have going on.





RE: Analog Scaling Issues
I don't really understand your question - or why you ask. Or did I miss something?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
Or if you need the conditioner and the PLC input must be 0-20mA then the scaling is -20%*1.25.
RE: Analog Scaling Issues
20mA.....should be scaled to full scale
signals below 4mA have electrical noise and is unreliable....this is an industry standard hence 4 to 20 mA.....?????
RE: Analog Scaling Issues
We used 0 - 20 mA for many years without (m)any noise issues. Using the 'bottom' 4 mA to supply the electronics makes wiring easier and also makes wire break detection possible.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
not that i'm suggesting that you are wrong...you might well be measuring something that is course in nature....but I would not pass any equipment off that used 0-20mA as a transducer signal for some type of measurement device....maybe you are talking about a signal at component level of the electronics ....but please make could you make some reference to a source other than "this is the way we do it"....your never to old to learn
RE: Analog Scaling Issues
I'm waiting for some more regulars to give their view...
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
RE: Analog Scaling Issues
The only thing is that you seldom see any 0-20 mA devices today because industry has standardized on 4-20 mA because of the benefits I mentioned before.
There is also the Hart protocol that doesn't work with 0-20 mA because it loses the 'carrier' when signal gets close to zero mA.
What you read about 4-20 mA and immunity to noise as compared to 0-10 V is valid. But it is just as valid for 0-20 mA. No difference in that respect between 0-20 and 4-20 mA.
We are seeing a modern myth being formed by an audience without perspective and technical/historical knowledge and that thinks that googling is the ultimate source of knowledge. It takes a bit more than googling - it also takes understanding of the underlying principles.
BTW, we honor correct grammar and spelling in these fora. And we use capital letters when needed.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
"Compatibility of Analog Signals for Electronic Industrial Process Instruments", known colloquially as "ISA 50".
relevant portion:
3.2 Transmitters
The standard output signal shall be of a constant current nature having a range of 4 mA to 20mA, dc (a 16 mA span).
3.3 Receivers
3.3.1 The standard current input signal shall be 4 mA to 20 mA, dc (a 16 mA span).
The committee's reasons, cited back in 1975, for 4-20ma were those cited by Skogsgurra. 4-20mA was already in widespread use throughout the process industries when the standard was issued.
There is some 0-20mA use in Europe, but there must, literally, be 10'a of millions of 4-20mA loop circuits in use throughout the world.
RE: Analog Scaling Issues
As for the comment "BTW, we honor correct grammar and spelling in these fora. And we use capital letters when needed."
I'm sure that your grammar is no reflection of your technical ability.....
RE: Analog Scaling Issues
Sorry if my bad English has caused you any inconvenience.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
RE: Analog Scaling Issues
But, this is not about who is more skilled. It is about, as you say, helping each other. And I think that I helped you out of a misunderstanding - or didn't I?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
but yes you have given me some food for though...thanks
RE: Analog Scaling Issues
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
Se dig omkring
RE: Analog Scaling Issues
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
RE: Analog Scaling Issues
'Se' is see, that's right.
'dig' is a form of you that means you are spoken to or told to do something. The neutral form is 'du'.
'omkring' means around you in a panoramic sense.
So, the short sentence means 'look around you' and that is why my answer may have confused you.
The way we say 'see you around' is 'Vi ses' which means 'We will see each other (sometime)'
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
Vi ses
I shall be starting a thread on how the recession is affecting engineering...mayby you like to pass some comments?
RE: Analog Scaling Issues
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
RE: Analog Scaling Issues
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog Scaling Issues
If someone doesnt mind taking a look I have it online @ www.netbiter.net
Login: KaufmanWWTP
username: maverick30
go to the configure device tab
then under Active Devices - look at the configuration tab, click on it
then click on visualization & logging tab click on it, then click on EDIT for the 0-20ma signal
What should the scaling be?? Offset??
I have it set at 2500gpm
134gpm is the minimum flow in the 14" pipe, I have it setup in the redlion signal conditioner as well 2500gpm hi setting.
Attached is a picture
RE: Analog Scaling Issues
RE: Analog Scaling Issues
RE: Analog Scaling Issues