Measurements beyond temperature
The same approach as the temperature page for seventeen quantities: how the instruments compare, what the standards require, how each one is calibrated, and calculators to try with your own numbers.
Pick a quantity
Temperature
RTDs and thermocouples, with a curve fit solver.
Open →02Humidity
Capacitive sensors, salt fixed points, dew point maths.
Open →03Pressure
Piston gauges, head correction and gauge grades.
Open →04Voltage
Multimeter accuracy, thermal EMF and loading.
Open →05Current
Shunts, burden voltage and clamp meters.
Open →06Resistance
4-wire measurement, temperature and standards.
Open →07Resistivity and conductivity
Cells, KCl standards, wire and four-point probes.
Open →08Mass
Weights, balances, OIML classes and buoyancy.
Open →09Dimensional
Gauge blocks, thermal expansion and Abbe error.
Open →10Torque
Wrenches, transducers and extension correction.
Open →11Force
Load cells, dead-weight machines and testing machines.
Open →12Flow
Gravimetric checks, K-factors and meter types.
Open →13pH
Buffers, electrode slope and temperature.
Open →14Time and frequency
Oscillators, counters, ppm and gate time.
Open →15Light
Lux meters, standard lamps and the inverse square law.
Open →16RF and microwave
Power, VSWR, connectors and waveguide to 75 GHz.
Open →17Millimetre-wave
Waveguide WR-12 to WR-3, extenders and path loss above 75 GHz.
Open →At a glance
| Quantity | SI unit | Primary realisation | Typical working standard | Common document |
|---|---|---|---|---|
| Temperature | degree Celsius (°C) | ITS-90 fixed points, SPRTs | Reference PRT, dry block, bath | ISO/IEC 17025, IEC 60751, IEC 60584 |
| Relative humidity | Dimensionless (%RH) | Humidity generators, dew point | Chilled-mirror hygrometer | OIML R 121, ASTM E104 |
| Pressure | pascal (Pa) | Piston gauge and mercury manometer | Digital reference gauge | EN 837, ASME B40.100 |
| Voltage | volt (V) | Josephson junction array | Zener reference, calibrator | IEC 61010 (safety), data sheets |
| Current | ampere (A) | From voltage and resistance | Shunt, calibrator | Data sheets, IEC 61010 |
| Resistance | ohm (Ω) | Quantum Hall effect | Standard resistors, bridge | Data sheets, ISO/IEC 17025 |
| Conductivity | siemens per metre (S/m) | KCl solutions and geometry | Standard solutions, cells | OIML R 56, ASTM D1125, ISO 7888 |
| Mass | kilogram (kg) | Planck constant (Kibble balance) | OIML weights, comparator | OIML R 111-1, R 76 |
| Length | metre (m) | Laser interferometry | Gauge blocks, laser | ISO 3650, ISO 3611, ISO 10360 |
| Torque | N·m | Lever arm and weights | Reference transducer | ISO 6789 |
| Force | newton (N) | Dead weights in local gravity | Reference load cell | ISO 376, ISO 7500-1, ASTM E4 |
| Volume flow | m³/s | Weighing and timing, provers | Master meter, weigh tank | ISO 4185, ISO 5167, OIML R 117 |
| pH | Dimensionless | Primary buffers, Harned cell | Certified buffers | ASTM D1293, ISO 10523 |
| Time and frequency | second (s), hertz (Hz) | Cesium atomic clocks | GPS-disciplined or Rb oscillator | ISO/IEC 17025 |
| Illuminance | lux (lx) | Cryogenic radiometer, V(λ) detectors | Standard lamp, reference meter | ISO/CIE 19476 |
| RF power and S-parameters | watt (W), ratio (dB) | Microcalorimeter, dimensional standards | Power sensor, VNA with cal kit | IEEE 287, ISO/IEC 17025 |
| Millimetre-wave | watt (W), ratio (dB) | Calorimeter, waveguide dimensions | Waveguide VNA extenders | IEEE 1785.1 |
Documents are listed as starting points. Editions change, so read the current version of any standard you rely on.