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Signals and PLC · Glossary

What is Analog Scaling?

raw counts to engineering unitsSignals and PLC

Analog scaling converts the raw value from a PLC analog input into engineering units such as bar or °C.

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Analog Scaling Explained

The input card turns 4 to 20 mA into counts, for example 0 to 27648 on Siemens S7 cards. The program scales these linearly to the transmitter range.

Wrong raw limits or range values give errors at every point except where they happen to match.

Analog Scaling Formula

PV = LRV + (raw − rawmin) ÷ (rawmax − rawmin) × (URV − LRV)
rawcounts from the input card
LRV, URVengineering range
Example: S7 card 0 to 27648, range 0 to 10 bar, raw 13824: PV = 5.0 bar.
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Calculators for Analog Scaling

CalculatorAnalog Scaling CalculatorFree online calculator with formula and worked example.CalculatorADC Resolution CalculatorFree online calculator with formula and worked example.

Free Downloads

Free downloadIO List Template in Excel with Automatic I/O Count and SparesFree download in Excel and PDF.Free download4 to 20 mA Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Analog Scaling?

Analog scaling converts the raw value from a PLC analog input into engineering units such as bar or °C.

Why 27648 and not 32767?

Siemens leaves headroom above 100 % for overrange diagnostics.

Where should square root be applied?

In the transmitter or after scaling in the program, never both.

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