Temperature Measurement & Calibration for Process Control

Explore why temperature is a critical measured variable in industrial settings, covering measurement methods, thermometers, and technologies used across heat transfer, boilers, HVAC, and welding.

Explore absolute zero and the four temperature scales—Fahrenheit, Rankine, Celsius, and Kelvin—and learn key conversion formulas and example values.

Explore heat transfer—including conduction, convection, and radiation—and how thermal equilibrium, heat capacity, and specific heat guide energy flow, using the q = m C (T2−T1) formula.

Explore how materials expand when heated and contract when cooled, and how linear and volumetric expansion coefficients describe the changes, with liquids showing volumetric expansion three times the linear coefficient.

Apply the linear and volumetric expansion formulas to compute L2 and v2 from L1, V1, alpha, beta, and temperature change, with copper as an example.

Explore liquid-in-glass thermometers, where liquid expansion moves a column in a sealed glass tube. Calibrate with a regulated water bath and use alcohol-based liquids and industrial metal-engraved scales.

Explore how bimetallic thermometers use differential thermal expansion in a two-metal strip, formed into a coil, to bend and drive a temperature pointer. Learn how alloy choices affect accuracy and range, and how the sensing bulb, bimetallic element, and switch function enable thermostats and boiler flame surveillance.

Explore field system pressure spring thermometers, including liquid filled, gas filled, and vapor pressure types, featuring a bulb, capillary, and spring, with calibration, installation tips, and response-time considerations.

Explore electrical thermometers and the operation of thermocouples, RTDs, and thermistors, including construction, applications, cold junction compensation, and measurement circuits for sensor selection.

Explain how thermocouples generate Seebeck voltage using dissimilar metal junctions and temperature differences. Describe cold junction compensation and the roles of the Seebeck, Peltier, and Thomson effects in thermoelectric thermometry.

Explore how cold junction compensation uses an isothermal block and thermistor to correct Seebeck voltages from J2 and J3, yielding accurate J1 readings.

Construct a thermocouple by welding wires, placing ceramic beads for insulation, and securing a termination block to press the tip against the thermal well, considering Seebeck coefficient and temperature range.

Choose thermocouple wires by grade, diameter, and material, noting precision, standard, extension tolerances, and compare common types such as Type K, J, and E for temperature measurement.

Discover thermocouple measurement circuits, from difference thermocouples and thermopiles to averaging assemblies, enabling temperature difference sensing, non-contact high-temperature measurement, and high-input-impedance multipoint recording.

Explore resistance temperature detectors, high precision thermometers that measure resistance changes to gauge temperature, offering accuracy in stable environments but thermocouples are preferred in high temperature or corrosive conditions.

Increase RTD resistance with heat. Coil wires around an insulator with a protective sheath to boost heat and require current or voltage, yielding a larger drop than a thermocouple.

Explore rtd construction from a wound platinum, nickel, or copper element sealed in glass to thin-film ceramic designs, noting platinum's -400 to 1200 degrees fahrenheit stability and thermowell use.

Thermistors are temperature sensitive resistors made from solid state semiconductors with lead wires sealed in glass. Most have a negative temperature coefficient, while some PTC variants are used in applications.

Explore how NTC thermistors, temperature sensitive resistors with resistance dropping as temperature rises, provide high sensitivity (-50 to -500 Ω/°F) for temperature alarms, but non-linear behavior requires lookup tables.

Explore how PTC thermistors show a rapid resistance rise at a switch temperature, enabling current limiting and self-resetting protection, with response influenced by heat capacity, dissipation, and ambient temperature.

Zero power sensing reduces self-heating errors in thermistor circuits by keeping current and power under 0.4 mW, achieving about 0.1°F accuracy, though thermistors remain slightly less accurate than RTDs.

Explore how infrared radiation thermometers measure temperature non-contact by converting emitted energy, and compare blackbody and graybody concepts for applications like fiber optic sensing, disappearing filament pyrometers, and thermal imagers.

Learn how infrared thermometers measure temperature by detecting infrared radiation and accounting for emissivity, reflectivity, and transmissivity. Explore the 8–14 micron band and the distance-to-spot ratio for accurate readings.

Explore how infrared thermometers use one or two color detectors with optics and circuitry to measure surface temperatures for process control, plus remote line scanners for continuous monitoring.

Explore disappearing filament pyrometers, non-contact high temperature measurements by matching brightness to the hot object. Understand emissivity, interference, and human perception, with a range from 1000°F to 10,000°F.

Thermal imagers use a two dimensional array of infrared detectors to map temperature. Radiometric imagers provide exact readings; non-radiometric show only images, aiding industrial diagnostics and building surveys.

Explore practical temperature measurement and calibration for process control, covering sensor response time, thermowells, thermocouples, Wheatstone bridge measurements for RTDs and thermistors, and the importance of calibration for accuracy.

Investigate response time in temperature measurement, define the time constant t for first-order processes, and show how heat transfer, mass, and initial-to-target differences reach 63.2% of the change.

Protect temperature sensors from heat, pressure, and chemicals with thermowells in industrial processes. Enable maintenance and calibration without shutdown via built up or bar stock thermowells.

Explore practical thermocouple measurement, including wire size, shielding, isolation, noise reduction, calibration, and break protection for accurate, reliable temperature readings across control systems.

Explore practical rtd measurements in thermowell installations, including three-wire and four-wire configurations with copper wire and lead resistance cancellation, and understand shielding, transmitters, and isolation for reliable readings.

Explore resistance bridge circuits, including Wheatstone bridges, to measure RTD and thermistor resistance with balanced and unbalanced configurations; learn how three- and four-wire setups compensate lead resistance while reducing self-heating.

Calibrate temperature instruments to prevent drift using dry wells, microbats, and blackbody sources for infrared thermometers. Verify transmitter outputs with 4 to 20 mA loops, adjusting zero and span.

Develop a solid foundation in how temperature is measured, interpreted, and calibrated across industrial settings, and look ahead to the next course on pressure measurement.