Improving Accuracy of Raw Value to Final Value Engineering Units

This article describes an alternative configuration of the “ratio” conversion method, rather than the “formula” method. This approach relies on actual measurements instead of theoretical value ranges. As a result, it provides more accurate Final Values that are specific to a particular sensor.

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Overview

Analog measurements typically fall within a current range of 4–20 mA (represented as 4000–20000) or within voltage ranges such as 0–5 V, 0–10 V, etc. These ranges represent the minimum and maximum values that a sensor can measure—referred to as the sensor’s raw values. In principle, these raw values can be converted into appropriate engineering units using a ratio.

For example, if a 4–20 mA sensor is used to measure distance (e.g., water level), you can express that distance as a percentage of the total range rather than in units like inches or millimeters. The ratio 4:20 mA corresponds directly to a percentage range of 0:100. Therefore:

• 4 mA = 0%

• 20 mA = 100%

Any value between 4–20 mA can be interpolated proportionally.

Current Value	Percentage Value
4 mA	0%
8 mA	25%
12 mA	50%
16 mA	75%
20 mA	100%

This same ratio-based method can be used with any engineering unit, provided the final value range is definitive or fixed.

For example, for a pressure sensor with a range of 0–50 psi, the 4–20 mA input range maps directly to 0–50 psi:

• 4 mA = 0 psi

• 20 mA = 50 psi

• Intermediate values scale accordingly

These ratios define the theoretical relationship between a sensor’s raw value (current or voltage) and its final value in engineering units.

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More Accurate Ratio Definition

Instead of relying on theoretical limits, you can define a more accurate ratio using actual measured values.

If you know any two data points—each consisting of a current or voltage reading and its corresponding engineering unit—you can redefine the ratio to reflect these real-world measurements.

Example:

• At 4.8 mA, the actual pressure is 12 psi

• At 10.2 mA, the actual pressure is 28 psi

From this, you can define the ratio 4.8:10.2 as equivalent to 12:28 psi.

This method results in a ratio that is grounded in measured performance, rather than relying solely on the sensor's theoretical range.

To apply this method, enter the known values into the formula definition tab of the configuration interface.