Endpoint-preserving pressure scaleInput fraction to output coordinate
Unit Converters
Pressure Scale Calculator
Translate a pressure reading between declared instrument and engineering ranges while exposing input fraction, spans, endpoint checks, and extrapolation status.
Scale rule: this page maps endpoints; it does not repair a nonlinear sensor, invert a hysteresis loop, or clamp an over-range input.
Mapped output-
Input fraction-
Input span-
Output span-
Endpoint check-
Range state-
PRESSURE SCALE
Translate a pressure signal without hiding extrapolation
The diagonal line is the declared endpoint map. The live marker shows the current pressure and its output position, while the table preserves the exact fraction used.
| Element | Value | Unit | Meaning |
|---|
How to use
Map pressure endpoints into a display or control scale
Use this calculator when the input and output ranges have a defined linear relationship, such as a transducer span mapped to a display percentage.
- Enter the live input and its pressure unit.
- Enter the calibrated input minimum and maximum, preserving their orientation.
- Enter output endpoints with their engineering meaning.
- Check the fraction before trusting the mapped result.
- Treat an extrapolated value as a signal-quality event, not as a valid in-range reading.
Scale fundamentals
What a linear map preserves
Calculation method
Use fraction, then apply output gain
r = (x − x₀)/(x₁ − x₀)y = y₀ + r(y₁ − y₀)in range iff 0 ≤ r ≤ 1Units stay with x and y; r has no unit.
Default substitution
x = 65 kPa, x₀ = 0, x₁ = 100, y₀ = 0%, y₁ = 100%. r = 0.65 and y = 65%.
Endpoint reconciliation
At x = 0 kPa, y = 0%; at x = 100 kPa, y = 100%. If either endpoint fails, the range definition or sign is wrong.
Deep dive: sensor behavior
Linearity is an assumption
Actual pressure transmitters can have polynomial error, dead zones, hysteresis, and saturation. A straight map is suitable only when the calibration record supports it.
Deep dive: reversed ranges
Descending scales are valid
A high pressure can legitimately map to a low display value when the control signal is inverted. Keep the signed spans rather than sorting endpoints.
Deep dive: out-of-range policy
Extrapolation should remain visible
Silently clamping an over-range pressure to 100% hides a sensor or process fault. The result must state that it is extrapolated.
Cases, limits, and glossary
Use mapping only within its declared boundary
Display conversion: a 0–100 kPa transducer maps to 0–100% load, so 65 kPa becomes 65%.
Inverted alarm: 100 kPa maps to 4 mA and 0 kPa to 20 mA; the negative output span is intentional.
- Does not calibrate the instrument or estimate nonlinearity.
- Does not apply temperature compensation or damp pulsation.
- Does not decide whether an extrapolated signal is safe.
- Key terms: span, gain, fraction, endpoint, interpolation, extrapolation.
FAQ
Is this the same as a unit conversion? No; it maps one range into another.
Why not clamp values? Because over-range information is operational evidence.
Can endpoints be reversed? Yes, if the signal direction is intentionally inverted.
What validates the line? A calibration or control specification that supports linearity.
Result interpretation
Read the mapped output together with fraction and range state
The mapped output is the coordinate produced by the declared endpoints; it is not a second pressure measurement. A fraction of 0 is the input minimum, 1 is the input maximum, and 0.65 means the live pressure is 65% of the signed input span. A negative fraction or a fraction above 1 is extrapolation and must remain visible.
- Mapped output: the live display or control coordinate.
- Input fraction: the dimensionless position used in the interpolation.
- Spans: signed endpoint differences that preserve an intentionally reversed scale.
- Endpoint check: confirms that both entered boundaries reproduce their declared outputs.
- Range state: separates interpolation from extrapolation or a zero-span definition.
Detailed calculation process
Audit the pressure scale from symbols through reconciliation
Use one pressure unit for the live value and both input endpoints. The output endpoints may use percent, milliamps, or a documented engineering index, but they must share one output unit.
r = (x - x0) / (x1 - x0)y = y0 + r(y1 - y0)x, x0, and x1 are pressures; y, y0, and y1 are output coordinates; r is dimensionless.
| Symbol | Meaning | Default | Unit |
|---|---|---|---|
| x | Live pressure | 65 | kPa |
| x0 / x1 | Input endpoints | 0 / 100 | kPa |
| y0 / y1 | Output endpoints | 0 / 100 | % |
| r | Input fraction | (65 - 0) / (100 - 0) = 0.65 | dimensionless |
| y | Mapped output | 0 + 0.65(100 - 0) = 65 | % |
- Confirm x0 and x1 are different and use the same pressure datum and unit.
- Calculate the signed input span: 100 - 0 = 100 kPa.
- Subtract the lower endpoint: 65 - 0 = 65 kPa.
- Divide like units to obtain r = 0.65.
- Calculate the signed output span: 100 - 0 = 100 percentage points.
- Apply the output gain: 0 + 0.65 x 100 = 65%.
- Classify 0.65 as interpolation because it lies from 0 through 1.
- Reverse-check both endpoints: x0 maps to y0 and x1 maps to y1.
Evidence and measurement
Freeze the endpoint definition
Take the live pressure, input range, output range, pressure datum, calibration revision, and signal direction from the same instrument configuration. Record whether the source is gauge, absolute, or differential pressure. A later transmitter rerange invalidates an earlier endpoint map even when the live number looks plausible.
Scope and limitations
What the linear map does not establish
- It does not measure sensor linearity, hysteresis, repeatability, or drift.
- It does not compensate temperature, elevation, pulsation, or pressure datum errors.
- It does not clamp or certify an extrapolated signal as safe.
- It does not replace a transfer function when the device uses a square-root or polynomial response.
- It does not prove that the selected output coordinate has the right operational meaning.
Practical examples
Two different scale decisions
Panel indication: a 0-100 kPa transmitter feeding a 0-100% display produces 65% at 65 kPa. The result is interpolation and both endpoint checks pass.
Reverse-acting alarm: a 0-100 kPa input mapped from 20 mA down to 4 mA produces 9.6 mA at 65 kPa. The negative output span is intentional and must not be sorted.
Key terminology
Pressure scale glossary
- Endpoint
- A paired input and output value that defines one boundary of the map.
- Span
- The signed difference between high and low endpoints.
- Fraction
- The unitless location of the live input within the signed input span.
- Gain
- Output-span change per unit of input-span change.
- Interpolation
- Mapping a value between the two declared endpoints.
- Extrapolation
- Extending the line beyond an endpoint without new calibration evidence.
Frequently asked questions
Is pressure scaling the same as pressure-unit conversion?
No. Unit conversion preserves one physical pressure quantity; scaling maps a pressure range into a separate display or control coordinate.
Can the input or output endpoints be reversed?
Yes. A negative signed span is valid when the instrument or control action is intentionally reversed.
Why does the calculator show extrapolation instead of clamping?
Clamping hides the fact that the live pressure is outside the calibrated range. The out-of-range state is operational evidence.
When is a linear map invalid?
Use another transfer function when calibration data show a nonlinear response, dead zone, saturation, or square-root extraction.
Important note
Before relying on this result
Verify sensor linearity, saturation, and signal conditioning separately.