How do I measure temperature in an industrial process?

Industrial temperature measurement uses sensors inserted into or mounted on the process to convert thermal energy into a readable signal. The most common sensor types are thermocouples (two dissimilar metal wires joined at a tip that generate a small voltage proportional to temperature — rugged, inexpensive, and covering the widest range from cryogenic to over 3,000°F), RTDs (Resistance Temperature Detectors — a platinum element whose resistance changes predictably with temperature, offering higher accuracy and stability than thermocouples but at a higher cost and a narrower range up to ~1,200°F), and bimetal thermometers (a mechanical dial indicator using a coiled bimetallic strip — no power required, used for local visual indication). For non-contact measurement, infrared pyrometers measure emitted thermal radiation and are used where sensors cannot physically touch the target. The sensor output is typically sent through a temperature transmitter that converts it to a standard 4–20 mA signal for the PLC or DCS.

What is the difference between a thermocouple and an RTD?

Thermocouples and RTDs are both sensors that measure temperature, but they work differently and have distinct strengths. A thermocouple generates a millivolt signal based on the temperature difference between its measuring junction and the reference junction — it is self-powered, very rugged, responds quickly, and covers an extremely wide temperature range (some types reach 3,200°F+). However, thermocouple accuracy is typically ±1–2°C and the signal can drift over time. An RTD uses a precision platinum element whose electrical resistance increases linearly with temperature — it provides much better accuracy (±0.1–0.5°C), excellent long-term stability, and a more linear signal, but it costs more, is more fragile, requires an excitation current, and is limited to about 1,200°F. Choose a thermocouple when you need wide range, fast response, or low cost in harsh environments. Choose an RTD when accuracy and stability are the priority, especially in the –200°F to 1,000°F range.

How do I choose the right thermocouple type for my application?

Thermocouple types are designated by letter (J, K, T, E, N, R, S, B) and each has a different temperature range, accuracy, and chemical compatibility. Type K (chromel-alumel) is the most widely used general-purpose thermocouple — it covers –328°F to 2,282°F and works well in oxidizing atmospheres. Type J (iron-constantan) is popular for lower-temperature applications up to about 1,400°F and is common in plastics, rubber, and older equipment, but it is not suitable for oxidizing environments above 1,000°F because the iron wire oxidizes. Type T (copper-constantan) offers excellent accuracy at low temperatures down to –328°F and is used in food, pharmaceutical, and cryogenic applications. For very high temperatures (up to 3,200°F), noble metal types R, S, and B use platinum-rhodium wires but are expensive. Select the type based on your temperature range, the atmosphere or media the thermocouple will be exposed to, the required accuracy, and compatibility with your existing instrumentation.

What is a temperature transmitter and do I need one?

A temperature transmitter is a device that converts the low-level signal from a thermocouple or RTD into a standard, noise-immune output signal — typically 4–20 mA analog or a digital protocol like HART — that can be transmitted over long cable runs to a PLC, DCS, or recorder. Without a transmitter, the raw millivolt signal from a thermocouple is very susceptible to electrical noise, especially in industrial environments with VFDs, motors, and welding equipment nearby. A transmitter amplifies and conditions the signal close to the sensor, dramatically improving signal integrity and measurement accuracy. Transmitters also provide linearization (correcting the non-linear thermocouple signal), cold-junction compensation, sensor burnout detection, and diagnostic information. You need a transmitter whenever the distance between the sensor and the control system is more than a few feet, when accuracy matters, or when you need to integrate the temperature signal into a 4–20 mA loop or digital fieldbus network.

What is a temperature switch and when would I use one instead of a transmitter?

A temperature switch is a device that opens or closes an electrical contact when the measured temperature reaches a preset value — it provides a simple on/off signal rather than a continuous measurement. Temperature switches are used for protection and alarm functions where you need to trigger an action at a specific temperature threshold: shutting down a motor if bearing temperature exceeds a limit, activating a cooling fan when a cabinet gets too hot, triggering an alarm if a tank heater overheats, or interlocking a process to prevent operation outside safe temperature limits. Use a temperature switch when you only need to know whether temperature is above or below a set point and need a reliable, independent safety device. Use a transmitter when you need to continuously monitor the actual temperature value, trend it over time, or feed it into a control loop. In many critical applications, both are used together — a transmitter for monitoring and control, and an independent temperature switch as a safety backup.

Temperature Measurement, Instrumentation and Control - Dwyer

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Thermocouples and RTDs

Thermocouples and RTDs are the most common temperature sensors in industrial processes. They provide accurate readings for control systems, recorders and safety interlocks.

Sensor Types

Thermocouples – types J, K, T, E, N, R and S for wide temperature ranges
RTDs – Pt100 and Pt1000 for high accuracy
Mineral insulated sensors – rugged and bendable
Head-mount assemblies – with transmitters and terminal blocks
Surface and probe sensors – specialized mounting

Choosing a Sensor

Thermocouples handle higher temperatures, while RTDs offer better accuracy and stability. Specify sheath material, length, diameter and connection. Use matching extension wire.

Centro supplies thermocouples and RTDs for temperature measurement.

Temperature Accessories

Temperature accessories help your sensors and instruments read accurately and last longer. Thermowells, fittings, connection heads and extension wire protect sensors from the process and make installation and replacement simpler.

Accessories Available

Thermowells – threaded, socket weld and flanged wells protect sensors from pressure and flow
Compression fittings – adjustable sensor insertion depth
Connection heads – house terminal blocks and head-mount transmitters
Thermocouple and RTD extension wire – carry signals back to the controller
Connectors and plugs – quick disconnects for sensors

Choosing Accessories

Select thermowell material and length for the process, with the tip in the flow, and check the wake frequency calculation for high-velocity lines. Use extension wire that matches the thermocouple type to avoid reading errors. Head and enclosure ratings should match the environment.

Centro carries temperature accessories to complete your sensor installations.

Heat Exchangers

Heat exchangers transfer heat between two fluids without mixing them. They heat process liquids, cool oils and hydraulic systems, recover waste heat and condense steam, and they're used in nearly every process and HVAC industry.

Heat Exchanger Types

Shell and tube – rugged, high pressure and easy to clean
Brazed plate – compact and highly efficient for clean fluids
Gasketed plate and frame – expandable and easy to service
Double-wall and sanitary exchangers – for potable water and food processing
Air-cooled exchangers – reject heat without cooling water

Sizing Information

To size a heat exchanger, you'll need both fluids, their flow rates, inlet and outlet temperatures, allowable pressure drop and operating pressure. Fouling fluids may call for shell and tube or wide-gap plates. Material choices include stainless, copper, titanium and nickel alloys.

Centro can help you size and select a heat exchanger matched to your process conditions.

Thermowells

Thermowells protect temperature sensors from pressure, flow, corrosion and abrasion. They also let you remove sensors for replacement or calibration without draining or shutting down the process.

Thermowell Types

Threaded thermowells – common for general service
Socket weld and weld-in – high-pressure installations
Flanged thermowells – easy removal and corrosive service
Sanitary thermowells – tri-clamp for food and pharma
Tapered and stepped stems – strength and fast response

Choosing a Thermowell

Select material, insertion length, bore size and connection. For high-velocity flows, perform a wake frequency calculation to avoid stem failure.

Centro supplies thermowells for temperature sensors and thermometers.

Bi-Metal Thermometers

Bimetal thermometers are widely used temperature measurement devices that employ a bimetallic strip to indicate temperature changes. These thermometers consist of two metal strips, typically made of different metals with different coefficients of thermal expansion, bonded together. The metals expand or contract at different rates as the temperature changes, causing the bimetallic strip to bend. This bending motion is then translated into a rotational movement displayed on a calibrated dial to indicate the temperature. Bimetal thermometers are known for their simplicity, durability, and cost-effectiveness. They are commonly used in various industries and applications requiring reliable temperature monitoring, such as HVAC systems, automotive, food processing, and industrial processes. Bimetal thermometers offer advantages such as wide temperature ranges, resistance to shock and vibration, and ease of installation. They are available in different sizes and configurations to suit specific application requirements. With their robust construction and accurate temperature indication, bimetal thermometers provide a reliable and cost-effective temperature measurement solution in various industrial and commercial settings.

Related categories: Thermometers | Industrial Thermometers

Temperature Transmitters

Temperature transmitters convert thermocouple and RTD signals into a stable 4-20 mA or digital output. That makes temperature readings more accurate and less prone to noise over long cable runs.

Transmitter Types

Head-mount transmitters – install in sensor connection heads
DIN rail transmitters – panel mounting
Field-mount transmitters – with displays and enclosures
HART and smart transmitters – diagnostics and remote configuration
Isolated transmitters – prevent ground loops

Choosing a Transmitter

Match the input type (thermocouple or RTD), range and output. Consider accuracy, isolation and hazardous area approvals. Integrated sensor-transmitter assemblies simplify ordering.

Centro supplies temperature transmitters and assemblies for process measurement.

Temperature Switches

Temperature switches open or close a contact at a set temperature to start fans, stop heaters, trigger alarms or shut down equipment. They're simple, dependable temperature protection.

Switch Types

Mechanical switches – bulb and capillary or bimetal
Electronic switches – adjustable set points and displays
Limit switches – high-limit safety shutoff
Explosion-proof switches – hazardous areas

Choosing a Switch

Select range, deadband, contact rating and sensor style. Use thermowells for pressurized systems. Manual-reset limits add safety.

Centro supplies temperature switches for equipment protection and control.

Thermometers

Thermometers give simple, reliable local temperature readings in pipes, tanks, boilers and HVAC systems. They work without power, so they're a dependable backup to electronic sensors.

Thermometer Types

Bi-metal thermometers – rugged dial thermometers
Industrial thermometers – glass and digital models
Adjustable angle thermometers – easy viewing
Thermowells – protect stems and allow removal

Choosing a Thermometer

Select range, stem length, dial size and connection. Use thermowells in pressurized systems. Choose stainless construction for harsh environments.

Centro supplies thermometers and thermowells for industrial and HVAC use.

Shop by type: Bi-Metal Thermometers | Industrial Thermometers

Temperature Sensors

Temperature sensors measure heat in processes, equipment and buildings. They're the most common measurement in industry and are critical for quality, safety and efficiency.

Temperature Sensor Types

Thermocouples – wide ranges and fast response
RTDs – high accuracy and stability
Thermistors – sensitive, low-cost sensing
Infrared sensors – non-contact measurement
Surface and immersion probes – suit installation

Choosing a Sensor

Select by range, accuracy, response time and installation. Use thermowells in pressurized lines, and match extension wire for thermocouples.

Centro supplies temperature sensors and assemblies.

Temperature Controllers

Temperature controllers are devices used to maintain and regulate precise temperatures in different processes and environments. Temperature controllers monitor the temperature of a system and compare it to a set point, making necessary adjustments by activating heating or cooling mechanisms to achieve the desired temperature. They are widely used in applications such as manufacturing, HVAC systems, food processing, and laboratory environments. Temperature Controllers help improve product quality, enhance energy efficiency, and reduce operational costs. Modern temperature controllers often come with advanced features like digital displays, programmable settings, and remote monitoring capabilities, making them versatile and user-friendly tools for maintaining optimal temperature conditions.Not sure which input, output or panel size you need? Our team can match a temperature controller to your sensor, heater and control requirements.

Industrial Thermometers

Industrial thermometers are specialized devices used to measure temperature in various industrial applications. These thermometers are designed to withstand harsh environmental conditions and provide accurate temperature readings in industrial settings. They are constructed with durable materials, such as stainless steel or ruggedized plastic, to withstand high temperatures, pressure, and vibrations. Industrial thermometers come in various types, including bimetallic thermometers, gas-actuated thermometers, infrared thermometers, and digital thermometers. They are used in industries such as manufacturing, oil and gas, HVAC, and food processing, where precise temperature control is critical for operational efficiency and safety. Industrial thermometers offer features such as wide temperature ranges, high accuracy, and corrosion resistance. They are often equipped with protective features like IP ratings or explosion-proof enclosures to ensure safe and reliable operation in hazardous environments. With their ability to provide reliable temperature measurements, industrial thermometers are crucial in process control, quality assurance, and monitoring critical temperature parameters in various industrial applications.

Related categories: Thermometers | Bi-Metal Thermometers

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Temperature Measurement, Instrumentation and Control - Dwyer

Sensor Types

Choosing a Sensor

Accessories Available

Choosing Accessories

Heat Exchanger Types

Sizing Information

Thermowell Types

Choosing a Thermowell

Transmitter Types

Choosing a Transmitter

Switch Types

Choosing a Switch

Thermometer Types

Choosing a Thermometer

Temperature Sensor Types

Choosing a Sensor

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