PLC Analog Scaling Calculator
Professional tool for industrial automation engineers. Instantly convert 4-20mA, 0-10V signals to physical engineering values.
Use a PLC raw-count preset
Presets set the input range. Verify the range for your module and configuration.
Edit the input or result to convert either way. Values outside the range are extrapolated.
You can edit this value to reverse the calculation.
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Generate PLC code (ST / SCL)
// Waiting for input to generate Structured Text code...Understanding PLC Analog Scaling
In industrial automation, analog signals (like 4-20mA current loops or 0-10V voltage) represent physical quantities such as temperature, pressure, or flow. To use these signals in a PLC program, you must scale the raw integer value into a meaningful engineering unit.
The Linear Interpolation Formula
This calculator uses the standard linear equation y = mx + b to perform both forward and reverse conversions. The formula used is:
Scaled_Out = ((Raw_In - In_Min) / (In_Max - In_Min)) × (Out_Max - Out_Min) + Out_Min
This is identical to the logic used in the NORM_X and SCALE_X instructions in Siemens S7-1200/1500, or the SCL instruction in Mitsubishi FX series.
Common PLC Raw Data Ranges
Different PLC manufacturers use different integer ranges to represent analog signals. Here is a quick reference table:
| PLC Brand / Series | Analog Resolution | Raw Integer Range (Int) |
|---|---|---|
| Siemens S7-1200 / S7-1500 | 12-bit / 13-bit | 0 to 27648 |
| Siemens S7-200 SMART | 10-bit / 12-bit | 6400 to 32000 |
| Mitsubishi FX3U / FX5U | 12-bit / 16-bit | 0 to 4000 (or 0-16000) |
| Allen-Bradley (Rockwell) | CompactLogix | 0 to 32767 |
| Omron CP1H / CP1L | High Resolution | 0 to 6000 or 0 to 12000 |
Frequently Asked Questions
How do I convert 4-20mA to pressure?
If you have a 4-20mA pressure transmitter measuring 0-100 Bar: Set Input Low=4, Input High=20, Output Low=0, Output High=100. If your multimeter reads 12mA, the pressure is exactly 50 Bar.
What is the raw value of 20mA in a Siemens PLC?
For standard Siemens analog input modules (AI), 20mA corresponds to the integer value 27648.
What are NORM_X and SCALE_X in Siemens TIA Portal?
NORM_X normalizes a raw integer value to a floating-point value between 0.0 and 1.0, based on a specified input range (e.g., 0 to 27648). SCALE_X then maps that normalized value to the desired engineering unit range (e.g., 0.0 to 100.0). Together, they perform the same linear interpolation as y = mx + b. For Siemens S7-1200 and S7-1500 controllers, these two instructions are the standard way to convert analog input signals into physical quantities like temperature, pressure, or flow rate.
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