Flow Conversion

redviper · Dec 13, 2011

Hey All,

Have a little project in which I am metering Liquid Nitrogen in kg/hr. We only have the instantaneous flow rate available and the client would like to see the daily total.

System is an AB Control Logix.

Looking for very accurate data.

Thx,

K

redviper · Dec 13, 2011

*update

using "totalizer" pre-defined data type.

bce123 · Dec 13, 2011

Looking for very accurate data

How would you define VERY ACCURATE?
Does your flow meter have a totalizer?
If not What is your sample rate and what is your total scan time of the plc?

redviper · Dec 13, 2011

Very Accurate.....from client.....is +/- 1%

No totalizer on the meter.

Last Scan is at 27ms avg at 31ms.

We will use that totalizer pre-define data type tonight and will trend the instaneous over 24 hours compare and see if we are out to lunch or not.

danw · Dec 13, 2011

There are various sources of error, and A-B does a good job noting the timing issues for totalizers.

I'd do a very careful read of the totalizer comments (more than just the one below) in this A-B publication:

http://literature.rockwellautomation.com/idc/groups/literature/documents/wp/logix-wp008_-en-p.pdf

MichaelG · Dec 13, 2011

have you looked at the analog input RPI rate??

oops You also need to look at
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1756-um009_-en-p.pdf

RTS and RPI combine - read page 24 of the above manual
Also need to know the rate that the sensor is updating the analog output

Flow Conversion

redviper

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bce123

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danw

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MichaelG

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