PLC Analog Scaling Calculator
Professional tool for industrial automation engineers. Instantly convert 4-20mA, 0-10V signals to physical engineering values.
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Input (Raw Signal)
Output (Engineering Value)
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// 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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