Counts to Engineering Units

Hi Guys,
I am somebody who is fresh out of college and into my first Job. I am working with RTUs which have PLC capability.

I would like to understand, how the Analog input module converts the Raw Counts (Obtained through an A/D Conversion) into Engineering Units (EU)?
Is The relationship between Counts and EU always Linear? If not why?
I would really appreciate if somebody could explain or direct me to some good reference material on the internet

Thanks for your time.

Gaurav Tyagi

Are you asking how to convert raw analog input data to a unit representation?

Or do the RTU's Convert it into EU for you? If so could you please give us the product code of the unit.

Honga said:

Are you asking how to convert raw analog input data to a unit representation?

Or do the RTU's Convert it into EU for you? If so could you please give us the product code of the unit.

Click to expand...

Hi Honga,
Thanks for the reply,
Of-course the RTUs when specified with a suitable instrument Range and Units represent the Raw Counts in Engineering Units. What I really want to know is what sort of backend Calculation is done in the RTU or as a matter of fact on any other PLC for converting RAW counts to EU.
Thanks
Gaurav

The unit would do the following

Your Final value = (Analog_Input/Maximum_Input)*(Maximum_EU_Range - Minimum_EU_Range) + Minimum_EU_Range

Simply scaling the raw data to the range you entered.

See links below for some more good reading material on the subject of scaling.

http://www.ronbeaufort.com/y=mx+b_part1.pdf

http://www.ronbeaufort.com/y=mx+b_part2.pdf

Thanks mickey for the links. They have been really helpful.
I guess my question on linear relationships of Counts and Engineering Values is answered. However what I still don't get is why relationships can be non-linear. In what case the relationship will not be a straight line ( Y=MX+B )

Thanks

A transducer gives us an analog ('simulation' to use the original meaning of the word) of the external phenomenon. We may have already come to measure the external value by 'normal' means (a thermometer for temperature for example). It is easiest for us to understand a continuously changing phenomenon if we develop a scale which has a continuously spaced set of divisions. We develop this even if the phenomenon itself isn't linear (think of the decibel scale for sound, it is logarithmic).

Some phenomenon may be easy to translate by a transducer into an analog value which closely matches an already developed standard. Thermocouples for example, are non linear with respect to a temperature scale.

In other words, if the relationship is linear then great, it is easier to use. But the world was not set up for our convenience and we may have to put up with some non-linear measurements.