High temperatures: thermocouples
Exhaust gas, steam and metal temperatures in turbines and boilers are measured with base-metal thermocouples, mostly type K and increasingly type N. At 600 °C a type K thermocouple gives 24.905 mV and a type N 20.613 mV, both referred to a cold junction at 0 °C. The thermocouple calculator converts with the real cold-junction temperature and shows the tolerance class at the measured temperature.
Two things limit a thermocouple in this service. The standard tolerance grows with temperature: class 1 for type K is ±0.4 % of the reading above 375 °C, which is ±2.4 °C at 600 °C before any drift. And type K drifts with time at high temperature; the type K and type N pages describe the mechanisms and why type N holds its calibration better.
Extension cable must match the thermocouple type. A wrong or reversed extension cable produces an error that depends on the temperature of the junction box, so it changes with the weather and is hard to find.
Bearings and windings: RTDs on long cables
Bearing metal and generator winding temperatures are measured with PT100 sensors, often 100 m or more from the monitoring system. A PT100 reads 134.707 Ω at 90 °C. Over 150 m of 1.5 mm² cable, a two-wire connection would read about 9 °C high. With three wires and a 5 % mismatch between the leads the error falls to about 0.2 °C, which is why three-wire is the standard connection and why the conductors of one sensor must be the same size and length. The RTD lead-wire error calculator gives the error and the longest cable for a chosen limit.
Pressure
Steam, feedwater and lubrication systems are specified in bar, megapascals or psi depending on the supplier: 160 bar is 16 MPa or 2321 psi. The pressure converter converts between them. Whether a figure is gauge or absolute has to come from the document; at 160 bar the difference is under 1 %, at condenser pressures it is everything.
A transmitter’s installed accuracy depends on more than its reference accuracy. The transmitter accuracy calculator combines reference accuracy, ambient temperature effect and drift for the calibrated span.
Vibration
Rotating machines are assessed by the RMS vibration velocity on their bearing housings. For industrial machines from 15 kW to 50 MW, ISO 10816-3 and its successor ISO 20816-3 define zones A to D; 4.5 mm/s is the boundary between zones B and C for a large machine on a rigid foundation. The vibration converter shows the zone and converts between velocity, the acceleration a sensor reports and displacement.
That standard does not cover everything in a power plant. Large steam and gas turbine sets, hydro units and wind turbines have their own parts of the ISO 20816 series with different limits, and turbine shafts are also monitored for relative vibration with proximity probes. Use the tool’s zones only for the machine classes it names.
Loops across the plant
Transmitter cables in a plant are long and often warm. With 600 m of 1.5 mm² cable at 40 °C, the copper is about 8 % more resistive than at 20 °C. The loop power calculator includes the cable temperature when it checks the voltage left for the transmitter.
Outside the scope of this site
Proximity-probe systems, flue-gas analysis, flame detection and electrical protection are not covered here.
Updated October 11, 2026