Base & Derived Units
Use coherent SI units where practical, and identify derived quantities such as pressure, force, power, frequency and electrical units correctly.
REFERENCETERMS / UNITS / STANDARDS / SELECTION
Sensor Engineering Reference: Terms, Units, Standards & Selection
Sensor engineering depends on consistent terminology, units, specifications and selection criteria. Measurement terms must be defined precisely, quantities must use the correct units, standards must be matched to their scope, and sensor selection must account for the measurement task, environment and receiving system.
Interpret datasheets by separating measurement terminology from operating limits, checking the quantity and unit, confirming the relevant standard or test basis, and verifying the sensor interface against the receiving system.
REFERENCE SCOPE5 GUIDES
- Terms
- MEASUREMENT LANGUAGE
- Units
- SI + CONVERSIONS
- Standards
- INDUSTRIAL CONTEXT
- Selection
- APPLICATION CHECKS
TERMS / UNITS / STANDARDS / SELECTION
COVERSTerminologySI unitsConversionsStandardsSpecificationsSensor selection
CORE REFERENCE GUIDES
Terminology, units, standards and selection answer different engineering questions.
Terminology defines what a specification means; units define how a quantity is expressed; standards define common requirements or test frameworks; selection checks connect those details to the application.
TERMINOLOGY01
Sensor & Measurement Terminology
Definitions for range, accuracy, precision, repeatability, resolution, sensitivity, hysteresis, drift, response time and other measurement terms.
OPEN →UNITS02
SI Units & Unit Conversions
SI base and derived units, prefixes, engineering notation and practical conversions used for pressure, temperature, distance, flow and other sensor quantities.
OPEN →STANDARDS03
Industrial Sensor Standards
Standards and specifications commonly encountered with sensor performance, protection, interfaces, electrical equipment and industrial measurement.
OPEN →SELECTION04
Sensor Selection Checklist
A structured engineering check covering measurand, range, performance, environment, mounting, process connection, output, wiring and controller compatibility.
OPEN →KOMPENDIUM05
Sensor Kompendium
A broad engineering reference connecting sensor types, signal interfaces, wiring, measurement terminology, calibration and sensor selection in one page.
OPEN →REFERENCE PATH
Define the term, confirm the unit, then evaluate the requirement.
Many sensor-selection mistakes begin before the device is chosen. A requirement such as “high precision” or “fast response” is incomplete until the relevant quantity is defined, the required numerical limit is stated and the operating conditions are known.
Datasheets may use similar words for different performance characteristics. Accuracy, repeatability, resolution and sensitivity describe different properties, while maximum range, overload capability and environmental limits describe different operating boundaries.
TERMUNITREQUIREMENTDATASHEETAPPLICATION
MEASUREMENT LANGUAGE
Common specification terms should not be treated as interchangeable.
The same sensor can have fine resolution, good repeatability and still have a larger absolute measurement error. Each term answers a different engineering question.
| Term | Engineering meaning | Why it matters |
|---|---|---|
| Range | The interval of input values over which the device is intended or specified to operate. | The selected range must include normal operation and relevant extremes without discarding useful measurement detail. |
| Accuracy | Closeness of an indicated or measured value to the accepted reference value under stated conditions. | It limits how confidently the reading can represent the actual process or machine condition. |
| Repeatability | Agreement between repeated measurements made under the same or closely controlled conditions. | A repeatable sensor can reveal small process changes even when a separate calibration offset remains. |
| Resolution | The smallest change in input or reported value that the measurement system can distinguish. | More digits or counts do not automatically mean better absolute accuracy. |
| Sensitivity | The change in output produced by a defined change in the measured input. | It connects the physical measurand to the electrical or digital response used by the receiving system. |
| Response time | A measure of how quickly the sensor output follows a change in the measured quantity. | A sensor can be accurate in steady conditions but too slow for a fast machine event or control loop. |
UNITS & NOTATION
Units are part of the measurement, not formatting added afterwards.
Engineering values should carry the correct quantity, unit and scale. Prefix errors and incorrect temperature or pressure references can change a value by orders of magnitude or change its physical meaning.
Engineering Prefixes
Prefixes such as milli, micro, kilo and mega scale the unit. Keep the symbol and multiplier consistent when converting values.
Reference Conditions
Pressure may be gauge, absolute or differential; temperature intervals differ from absolute temperature; flow may be volumetric or mass-based.
Unit Conversion
Convert the numerical value and the unit together, and preserve enough significant figures for the required engineering decision.
Before values are entered into PLC scaling, drawings, reports or specifications, verify quantity names, unit symbols, prefixes and conversions in the SI units and unit conversions reference.
STANDARDS CONTEXT
A standard defines a scope; it does not replace the device datasheet.
Industrial sensors can be affected by standards covering the sensing device, electrical interface, enclosure protection, environmental testing, machine safety or the larger control system. The relevant documents depend on what the device does and where it is installed.
Device & interface standards
These can define terminology, dimensions, electrical behaviour, test methods or communication requirements for a particular sensor or interface family.
- Confirm the exact edition and scope.
- Do not infer compliance from a similar product family.
- Check whether compliance applies to the sensor alone or to a complete system.
Installation & environment
Protection, EMC, hazardous-location, machinery and process requirements may apply independently of the sensor's measurement principle.
- Match the installation environment.
- Check enclosure, cable and connector limits.
- Keep product approvals separate from general design guidance.
Before citing a standard in a specification, verify its scope and engineering purpose in the industrial sensor standards reference; a standard name alone does not establish which requirement applies.
SELECTION CHECK
Review the complete measurement path before selecting a sensor.
A suitable sensor must measure the required quantity over the real operating range, meet the needed measurement performance, survive the environment and mechanical installation, and provide an electrical interface the receiving PLC, DAQ or instrument can use correctly.
Measurand & range
State the physical quantity, normal range, startup conditions, overloads, fault conditions and the useful measurement span.
Performance
Separate accuracy, repeatability, resolution, response time, bandwidth, hysteresis and drift according to what the application actually requires.
Environment
Check temperature, pressure, moisture, washdown, chemicals, vibration, shock, dust and any hazardous-area or safety constraints.
Installation
Confirm process connection, mounting stiffness, sensing geometry, insertion depth, orientation, cable routing and maintenance access.
Interface
Match supply, analogue or switching output, pulse or digital interface, wiring, grounding, shielding and controller input requirements.
After the measurement requirement has been defined, complete the sensor selection checklist before a specific part number is approved.
RELATED LIBRARY SECTIONS
Sensor selection connects terminology, signals and measurement performance.
Terminology and units define the requirement; sensing principles determine the physical response; signal interfaces carry the output; measurement concepts determine how the result should be interpreted.
Sensors
Sensor types and sensing principles organised by measured quantity and industrial application.
TYPES / PRINCIPLES / SELECTIONSignals
4–20 mA, 0–10 V, PNP/NPN, pulse/frequency and wiring interfaces between sensors and control systems.
OUTPUT / WIRING / INTERFACEMeasurement
Accuracy, uncertainty, calibration, scaling, sampling and other concepts that determine how measurement results should be interpreted.
PERFORMANCE / CALIBRATION / DATA