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Analog Signal Scaling Calculator

Convert a linear analog signal into engineering units using configurable input and output ranges.

This calculator can be used for voltage signals, current signals, PLC analog inputs, sensor outputs, and other linear control applications.

Calculate Engineering Units

The signal value corresponding to the lower engineering range.
The signal value corresponding to the upper engineering range.
The engineering value at the minimum signal.
The engineering value at the maximum signal.
The actual measured analog signal.
Examples: PSI, °F, °C, GPM, %, RPM.

Result

General Analog Scaling Formula

Linear analog scaling converts a signal from one range into another range.

Engineering Value = Output Low + ((Signal − Input Low) ÷ (Input High − Input Low)) × (Output High − Output Low)

The important idea is that the signal represents a percentage of its input span, and that same percentage is applied to the engineering-unit span.

Worked Example: 4–20 mA to 0–100 PSI

Suppose a pressure transmitter produces a 4–20 mA signal representing 0–100 PSI.

You measure 12 mA.

0 + ((12 − 4) ÷ (20 − 4)) × (100 − 0)
12 mA = 50 PSI

The 12 mA signal is halfway through the 4–20 mA range, so the corresponding engineering value is halfway through the 0–100 PSI range.

PLC Scaling Example

PLC analog input modules often convert a physical signal into an internal numerical value before the program converts that value into engineering units.

For example, suppose a PLC input represents a 4–20 mA signal using raw counts from 3277 to 16384.

If the raw input value is 9830, the same scaling concept can be applied:

Engineering Value = 0 + ((9830 − 3277) ÷ (16384 − 3277)) × 100

The result is approximately:

50 PSI

The exact raw-count values depend on the PLC platform and analog input configuration. Always verify the module's documentation before using a raw-count range.

The Key Idea: Percentage of Span

The most useful way to understand analog scaling is to think in terms of percentage of span.

First determine where the signal is within its input range:

Signal Percentage = (Signal − Input Low) ÷ (Input High − Input Low)

Then apply that same percentage to the engineering range.

This is why the same mathematical concept works for:

  • 4–20 mA signals
  • 0–10 V signals
  • 1–5 V signals
  • PLC raw counts
  • Sensor outputs
  • Position feedback
  • Pressure, temperature, flow, and level transmitters

Common Analog Signal Ranges

Signal Typical Use
4–20 mA Industrial instrumentation
0–10 V HVAC, BAS, controls, actuators
1–5 V Voltage representation of 4–20 mA
0–5 V Electronic and control applications
PLC raw counts Analog input module representation

Using Analog Scaling for Troubleshooting

When troubleshooting an analog control system, it helps to separate the problem into stages:

  1. Physical signal: What voltage or current is actually present?
  2. Input conversion: What raw value is the analog input module producing?
  3. Scaling: How is the PLC or controller converting that value?
  4. Displayed value: What engineering value does the HMI or supervisory system show?

Checking each stage independently can help identify where an incorrect value is being introduced.

Common Scaling Mistakes

  1. Using the wrong signal range. Verify the actual input minimum and maximum.
  2. Using the wrong engineering range. Confirm the transmitter or device's configured LRV and URV.
  3. Ignoring non-zero lower limits. A signal does not necessarily start at zero.
  4. Reversing the input range. Some systems intentionally use reversed scaling.
  5. Confusing raw counts with engineering units. PLC raw values are representations of the electrical signal, not the final process value.
  6. Assuming a correct signal means a correct process value. The physical instrument, wiring, input module, and scaling program can each introduce different problems.

Related Calculators

Engineering Note

This calculator assumes a linear relationship between the input signal and engineering range. Real-world instruments and control systems may use nonlinear characterization, square-root extraction, filtering, clamping, or other signal processing. Verify the actual device and control-program configuration when troubleshooting.