PLC Analog Scaling Calculator
Pick a common signal type or enter your own raw and engineering ranges — drag the slider to simulate a live analog input.
Automation workflowStep 1 of 5
- 1Scale analog
- Reject timing
- Takt
- Throughput
- OEE
Next workflow step
Continue to Conveyor Timing Simulator — Continue the guided sequence with your current context.
Try an example
Learn about this tool
What it is, when to use it, formulas, and common questions
What is this?
This calculator converts PLC analog raw counts to engineering units (and back) using linear scaling — the same math used for 4–20 mA, 0–10 V, and custom module ranges on Siemens, Allen-Bradley, Omron, and other platforms.
Instead of only showing a static formula, it includes a live slider so you can scrub a raw value and immediately see the scaled engineering reading. That makes it easier to verify HMI tags, NORM_X/SCALE_X blocks, SCP instructions, or handwritten linear equations during commissioning.
When do engineers use it?
Use it when wiring a new transmitter, checking whether a pressure/temperature/flow reading matches the field instrument, or debugging a “wrong” scaled value that is actually a min/max or raw-range mistake.
Common scenarios: 4–20 mA into a 0–27648 or 0–32767 integer range, 0–10 V modules, bipolar ±10 V, or custom raw mins/maxes after analog filtering. Also useful when training technicians on why raw 12000 is not “half” unless the raw span is centered the way you expect.
Formula
Eng = EngMin + (Raw − RawMin) × (EngMax − EngMin) ÷ (RawMax − RawMin) Raw = RawMin + (Eng − EngMin) × (RawMax − RawMin) ÷ (EngMax − EngMin) For 4–20 mA on many Siemens analog inputs (example): RawMin=0 (or 5530), RawMax=27648 for 0–20 mA / 4–20 mA configurations — always confirm your module’s actual raw endpoints in the hardware config.
Example
Example: scale 4–20 mA raw counts 4000–20000 to 0–100 PSI.
At raw 12000: Eng = 0 + (12000 − 4000) × (100 − 0) ÷ (20000 − 4000) Eng = 8000 × 100 ÷ 16000 = 50 PSI.
If the HMI shows 62.5 PSI at the same raw value, the PLC min/max or engineering span is wrong — not necessarily the transmitter. Scrub the slider here to find which endpoint mismatch would produce the displayed reading.
FAQ
- Why doesn’t mid-scale raw equal mid-engineering on 4–20 mA?
- Because 4 mA is often not raw zero. If live zero is 4 mA, the usable span is 16 mA. Mid-engineering (50%) corresponds to 12 mA, which is not the midpoint of a 0–20 mA raw range. Always scale with the true RawMin/RawMax for your module.
- Does this match Siemens NORM_X / SCALE_X or Allen-Bradley SCP?
- It uses the same linear interpolation those instructions implement. Parameter names differ by platform, but if your raw and engineering endpoints match the block configuration, the results should agree within rounding.
- What if my signal is non-linear?
- This tool is for linear scaling only. Thermocouples, RTDs with special linearization, or square-root flow transmitters need vendor linearization or a characterization curve — do not force them through a simple min/max scale without the correct transform.
- Can I use it to reverse-calculate raw limits?
- Yes. If you know a few engineering readings and the corresponding raw monitor values, you can sanity-check whether the configured RawMin/RawMax and EngMin/EngMax are consistent with the live slider relationship.