Read 5th Hart Variable

Andrew_W

Member
Join Date
Oct 2009
Location
Edmonton
Posts
38
Good Afternoon All,

I'm trying to read a totalizer from a McCrometer flow meter into a 1769-L33ER processor via a 1769sc-IF4IH hart module, unfortunately McCrometer has made the direct flow totalizer the 5th device variable. Because its the 5th device variable, it isn't mapped to one of the 4 dynamic variables, rendering my normal AOI that reads the dynamic variables useless.

What is the easiest way to read the 5th device variable via hart? anyone have a AOI for this?

Thanks

Andrew
 
I am waiting with bated breath for an answer on this.


I fail to understand why the instrument manufacturer does not allow the user to map which variables are designated as the four HART 'dynamic variables'. Why such a top down view as to which are the easily obtainable HART values?
 
I am waiting with bated breath for an answer on this.


I fail to understand why the instrument manufacturer does not allow the user to map which variables are designated as the four HART 'dynamic variables'. Why such a top down view as to which are the easily obtainable HART values?

I don't know this brand, but deal with Emerson on a daily basis... price is one reason. You can see this in Emerson when you look at the 1700, 2700, x700 transmitter range... the 1700 is very limited in what you can get from HART, the top of the line, 5700 transmitter, allows you to do whatever you want. The price difference is considerable.

The other issue that I see is that HART commands aren't that common in IO cards, so going from the fact that you couldn't reset the totaliser with a HART command, you'd easily run into a point where the totaliser change during a dose is masked by the power that value is raised to in order to fit in a 4 byte FLOAT. It's not uncommon to see this in PLC applications too where you see a 165.43e+15 which doesn't seem to change.

The other reason may well be that the accumulator inside the flowmeter will be a long integer, but as far as I know, HART variables are floats, which would raise the point before.

I too would have loved to do this sort of thing, but now just count pulses for small quantities and integrate the analog signal.

I wonder though if this is a thing on Ethernet flowmeters... never tried one, but am curious.
 
Andrew_W:
If the 5th variable is hard to get , you can use TOT instruction.
I have checked several times that TOT data from PLC and totalizer info from flowmeter(HART) are almost the same value.
So it is worth a try.
 
Andrew_W:
If the 5th variable is hard to get , you can use TOT instruction.
I have checked several times that TOT data from PLC and totalizer info from flowmeter(HART) are almost the same value.
So it is worth a try.

I do this as well and it's good enough. The other thing to consider is that the biggest source of error in dosing applications is what happens when you stop the dose and also the length of time you're dosing since the flowmeter error is great at starting and stopping (so a 12 second dose is bound to have a higher error than a 12 minute one).
 

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