What Is Thermal Monitoring?

Temperature is a fundamental indicator of how equipment and processes are performing. Excessive heat can point to friction from worn parts, overloaded components, or failing cooling systems, while unusually low temperatures can point to inefficiencies or issues in refrigeration or cryogenic processes. By continuously monitoring temperature trends, teams gain valuable insight into asset health—enabling proactive maintenance, ensuring product quality, and promoting a safer work environment.

^{Figure 1: Temperature Sensor}

Several types of sensors are commonly used to monitor temperature:

• Thermocouples—These sensors utilize the Seebeck effect. When two wires made of dissimilar metals are joined at one end (the measuring junction), a temperature difference between this junction and the other end (the reference junction) produces a voltage. This voltage is proportional to the temperature difference and depends on the specific metals used (examples include Types K, J, T, E). Thermocouples are rugged, inexpensive, and cover wide temperature ranges but require reference junction compensation, also known as cold junction compensation (CJC).
• Resistance Temperature Detectors (RTDs)—RTDs operate on the principle that the electrical resistance of a metal changes predictably with temperature. They typically use a fine wire (often platinum due to its stability and linearity) wound around a ceramic or glass core. RTDs offer high accuracy and stability over moderate temperature ranges but are generally more expensive and require an excitation current to measure resistance.
• Thermistors—These are semiconductor devices whose resistance changes with temperature. There are two types: Thermistors with a negative temperature coefficient (NTC) experience reduced resistance as temperature increases, while thermistors with a positive temperature coefficient (PTC) report increased resistance as temperatures rise. Thermistors offer very high sensitivity, making them ideal for detecting small temperature changes, and are relatively inexpensive. However, they have a limited temperature range and a nonlinear response compared to RTDs, which can complicate data interpretation. They also require excitation current.

^{Figure 2: Wireless Thermal Monitoring Process}

Components and processes exhibit distinct thermal signatures during normal operation. Deviations from these expected temperatures can indicate impending issues. Thermal monitoring systems use sensors, DAQ hardware, and specialized analysis software like NI LabVIEW to detect, convert, and analyze temperature data. Based on the analysis, maintenance can be scheduled or processes adjusted before problems escalate. Various setups facilitate data collection, including continuous online monitoring through wired and wireless systems, as well as offline monitoring.  

• Wired online monitoring—Sensors are connected with cables to a DAQ device and computer. This setup offers high reliability, real-time data, and less susceptibility to interference. However, installation can be complex, cables can be damaged, and redeploying sensors can require rewiring.
• Wireless online monitoring—Sensors transmit temperature data wirelessly to a gateway or DAQ device. This setup allows placement in hard-to-reach or hazardous locations without extensive cabling. Concerns may include battery life, wireless security, and potential signal range limitations or interference.
• Periodic (offline) monitoring—A technician uses a portable device to periodically measure temperatures at various points. This setup offers flexibility but is not continuous, relies on manual checks, and may involve placing personnel near operating machinery.

Interpreting thermal data involves reviewing the temperature information collected by sensors, often using specialized software. Analysis techniques using tools like NI DIAdem can range from simple threshold comparisons to trend analysis to more complex thermal modeling or imaging analysis. Potential signs of trouble, like rapid temperature increases, deviations from expected profiles, or inconsistent readings can be flagged for human review. Thermal monitoring systems can also be configured to trigger automated actions, like activating cooling systems, reducing load, sounding alarms, or shutting down equipment if critical temperature thresholds are breached.

Thermal monitoring is widely used across many industries on the factory floor, in processing plants, and in facilities management. Common applications include monitoring the following types of devices or processes:

• Bearings and gearboxes
• Motors and generators
• Engines and turbines
• Pumps and compressors
• Electronic components and cabinets
• Process fluids and pipelines
• HVAC systems
• Furnaces and ovens
• Server rooms and data centers
• Material curing processes

Temperature measurement is fundamental in the design, validation, and verification testing of new products and materials, such as testing electronics under load, engine component thermal cycling, and battery charge/discharge thermal performance. Engineers use tools like NI TestStand to automate sequences, ensure components operate reliably within specified temperature ranges, confirm thermal management systems are effective, and understand material behavior under thermal stress.  

Thermal monitoring can provide the following significant benefits:

• Reducing unplanned downtime from overheating or thermal failures
• Decreasing cost through predictive maintenance and optimized energy usage
• Enhancing safety by preventing fires or hazardous material conditions
• Increasing lifespan of machinery by operating within optimal temperature ranges
• Improving process control and product quality through temperature optimization

NI temperature input modules feature built-in signal conditioning essential for accurate measurements, including CJC for thermocouples, excitation for RTDs and thermistors, filtering, and amplification. Our software offerings, like NI LabVIEW, NI FlexLogger™, and NI DIAdem, allow users to acquire, analyze, visualize, and report temperature data, creating comprehensive thermal monitoring solutions.  

NI solutions for thermal monitoring offer several advantages over other approaches:

• Our long history of measurements in many applications means that the measurements you take with NI equipment are higher quality than hardware designed specifically for condition monitoring. NI products are more accurate, with more stable timing, and more reliable measurements.
• NI platforms are built on a concept of modularity, so systems are more efficient to design and easier to maintain over the lifetime of the application. Unlike fixed-personality systems, you can easily expand systems by adding modules to gain new channels or measurements.
• NI high-speed systems can capture all of the data, not just periodic bursts. This means you can record events that other systems miss.