Free tool
4-20 mA Scaling Calculator
Convert current and voltage signals to measured values, find the PLC raw value and copy the ready-to-use SCL code.
Measured value
5
Signal
12 mA
PLC raw value
13,824
Share of measuring range
50 %
The value is within the valid measuring range.
Scaling in SCL (Siemens S7-1200 / S7-1500)
// raw 0 ... 27648 -> 0.0 ... 10.0
#value := SCALE_X(MIN := 0.0,
VALUE := NORM_X(MIN := 0, VALUE := #raw, MAX := 27648),
MAX := 10.0);This is a purely mathematical calculation. Always rely on the datasheets of your sensor and analog module and on your controller configuration. No warranty.
How 4-20 mA scaling works
A sensor with a 4-20 mA output maps its measuring range linearly to the current: 4 mA is the start of the range and 20 mA is the end. The formula is: value = range start + (I − 4 mA) ÷ 16 mA × (range end − range start).
Example: a 0 … 10 bar pressure sensor at 12 mA gives (12 − 4) ÷ 16 × 10 = 5 bar.
Common values at a glance
| Signal | Share of measuring range | Raw value | |||
|---|---|---|---|---|---|
| Siemens S70 … 27648 | INT160 … 32767 | UINT160 … 65535 | 12 bit0 … 4095 | ||
| 4 mA | 0 % | 0 | 0 | 0 | 0 |
| 8 mA | 25 % | 6912 | 8192 | 16384 | 1024 |
| 12 mA | 50 % | 13824 | 16384 | 32768 | 2048 |
| 16 mA | 75 % | 20736 | 24575 | 49151 | 3071 |
| 20 mA | 100 % | 27648 | 32767 | 65535 | 4095 |
Frequently asked questions
Why does the signal start at 4 mA instead of 0 mA?
This "live zero" lets you tell a wire break or sensor failure (0 mA) apart from a valid start of range (4 mA). It also allows two-wire sensors to draw their power from the same current loop.
What does the raw value 27648 mean?
Siemens S7-1200, S7-1500 and ET 200 analog inputs deliver values from 0 to 27648 in the nominal range. Above that, depending on the module, there is an overrange area up to a maximum of 32511. The exact behaviour is described in the manual of your analog module.
Which raw value range should I choose?
It depends on your analog module. Siemens S7-1200, S7-1500 and ET 200 use 0 … 27648. Other controllers and modules often deliver the full positive range of a 16-bit value (INT16: 0 … 32767, UINT16: 0 … 65535), and simple 12-bit converters deliver 0 … 4095. Pick the matching range or enter your own raw values. The datasheet of your module is authoritative.
How do I detect a wire break?
If the current falls below 3.6 mA, NAMUR NE 43 treats it as a failure. Many analog modules report this as a "wire break" diagnostic. Evaluate that diagnostic in your program instead of relying on the scaled value alone.
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