IR Pyrometer vs. IR Cameras

Thermal Imager or Pyrometer: Should I make non-contact temperature measurements with a single spot infrared sensor or use an infrared camera with temperature measurement capabilities?

Two primary instruments dominate non-contact temperature measurement: thermal cameras and pyrometers. These technologies serve distinct purposes—infrared cameras capture thermal images across multiple measurement points to map temperature distributions over surfaces or areas. In contrast, pyrometers deliver precise, instantaneous temperature readings from single points without imaging functionality.

Historically, process industries, such as glass, metals, plastics, and paper manufacturing, have relied predominantly on cost-effective single-spot pyrometers. These pyrometers provided targeted temperature measurements using detector wavelengths optimized for specific materials: short-wave infrared for metal applications, mid-wave infrared for glass processing, and long-wave infrared sensors for ambient temperature monitoring of high-emissivity materials, such as plastics. During this period, thermal cameras remained prohibitively expensive and lacked the durability required for demanding industrial environments.

Recent advances in low-cost focal plane detector arrays have transformed this landscape. Modern infrared cameras can now leverage thousands of individual detector elements to measure temperature at any point within their field of view. Furthermore, process-grade infrared cameras have achieved price parity with traditional pyrometers while offering enhanced environmental resilience.

This technological convergence presents process engineers with a critical decision point: selecting between spot sensors and infrared cameras based on application-specific requirements. The following analysis examines the fundamental strengths of each sensor technology and provides practical guidance for selecting the most suitable sensor technology for temperature measurement applications.

When is an IR camera a better solution than a pyrometer?

• • When you do not know where the hot spot is.

Many process engineers need to know the hottest temperatures on a given part. Single spot sensors require the mounting and targeting a single spot, so the pyrometer delivers a temperature measurement of the spot framed by the sensor optics. An infrared camera can search the entire area on any part and report the highest (or lowest) temperature of the part. In short, a spot pyrometer is a good tool when the measurement spot location is precisely known. However, an IR camera is the right choice for detecting the hottest spot on a target when measurement target is not always at the same location.

• •  When more than one measurement is preferable.

Large plastic parts such as automotive bumpers or aerospace parts can have substantial temperature variations, which may signal significant process problems. An infrared camera with the right optics can gather hundreds of spot measurements on small and large targets. Numerous spot pyrometers can also be deployed, but mounting multiple infrared sensors in multiple locations and outputs can be complicated and expensive. Many engineers may also prefer to use an IR camera instead of contact thermocouples when monitoring dozens of locations in an area, such as an automotive engine compartment under test. Two inexpensive IR cameras mounted on either side of any target under test will gather thousands of temperature measurements, with the advantage of detecting the hot spots where a thermocouple may not have been positioned.

• •  When temperature gradients signal process problems.

Temperature gradients in many products produced in sheets (paper, glass, steel, plastic film, wallboard, etc.) are often monitored by infrared cameras or line scanning systems in manual mode. An operator adjusts dryers or heating elements based on color variations in an infrared image representing temperature differences. Multiple infrared pyrometers could gather numerous data points. Still, they would never deliver a comprehensive view and visual understanding of the gradual temperature variations on a product produced in a sheet-based manufacturing process. “Thermal Stripes” representing higher or lower temperatures become obvious with an IR camera, but would be missed if the pyrometer was not aligned with the stripe. Optris thermal camera and software can be converted to “line-scan mode” to capture temperature gradients across any sheet moving under the targeted line.

• • When the spot to be measured is very small.

Even when equipped with close-focus optics, accurate spot size measurements can be delivered with a pyrometer only on targets. Here, the distance-to-spot size ratio, also known as the D:S ratio or the distance-to-target ratio, is an important performance characteristic for infrared pyrometers. In the case of the long-wavelength domain, due to the used detector technology, current high-performance state-of-the-art pyrometers are limited to 75:1. This means that the diameter of the spot being measured is 1/75th of the distance from the pyrometer to the object. A pyrometer, which is positioned 75m away from the object, will measure the temperature of a spot with a diameter of 1m.

Due to the detector technology and detector size, a modern uncooled infrared camera with 17µm pixel pitch and commercial far-field optics achieves a superior distance-to-spot size ratio of 813:1.

The advantages of small spot sizes are even more dramatic when measuring tiny objects in microscope applications. If small targets need to be measured, IR cameras are a better option, as the distance-to-spot size ratio is a magnitude better.

When is a spot pyrometer a better solution than a thermal camera?

• • When budget restraints call for a very affordable measurement solution or a volume application.

Calibrated single-spot pyrometers that deliver accurate non-contact measurements on high emissivity targets can be purchased for the same price as industrial contact temperature instruments, making them the only non-contact measurement solution accessible to some users.

The least expensive pyrometer still costs roughly one-tenth of the price of the least expensive infrared camera.

• •  When the target material requires a wavelength response that is not available for an infrared camera,

Some materials, such as thin film plastics or metals under 450 °C, require special wavelength sensors that are not available as detector options for infrared cameras, making a pyrometer the better choice.

Some companies have been using single-spot infrared sensors with a specific wavelength response for many years and may need a replacement IR sensor that operates in the same wavelength to match historical data. An example may be a pyrometer for glass measurement, which is responsive at 5.0 µm. Since affordable thermal cameras are not available at this wavelength, replacing an older pyrometer with a new one that responds to the same wavelength may be the best option.

• • When space makes the placement of an IR camera impossible.

Thermal cameras are available in sizes as small as 36 mm (diameter) x 90 mm (length). Still, this size may be too large for some measurement requirements, which may include embedding a sensor into another instrument. A pyrometer can be packaged in a small sensor head of 14 mm (diameter) x 28 mm (length), making it the best solution for space-limited placements.

• •  When high operating temperature and harsh environmental constraints require the most durable technology.

Although many Optris thermal cameras can be used up to 70 °C without additional cooling, many industrial environments and machine integration demand a higher ambient temperature rating.

Small pyrometer sensor heads can also operate at ambient temperatures between 85 °C and 250 °C without cooling, making them the only solution for hot ambient environments.

Shock and vibration from process equipment can damage the shutter mechanism necessary for an infrared camera to produce accurate measurements. IR cameras are subject to vibration limitations described in IEC 60068-2. Most infrared pyrometers are solid-state sensors and can withstand higher shocks, as they typically do not have moving parts.

• • When simple integration to PLC & easy installation are important.

An autonomous operation is a special feature of the Optris infrared camera in the Xi series. There is no need for a permanent connection to the software or a computer. Only a few settings must be set in advance in the software. Combined with modern field bus systems such as EthernetIP, ProfiNet, or Modbus TCP, thermal cameras are easily integrated into existing PLC networks.

Nevertheless, additional software, which runs on additional hardware, for advanced image processing or very complex applications, might become a fundamental part of a customized solution. Addressing every pixel in the image, rather than using a single temperature value, drives the complexity of software solutions and hardware resources.

Pyrometers offer less complexity as, most often, only a single temperature value needs to feed a control application. All spot sensors in the Optris product line support common analog (voltage, current) and digital output standards such as EthernetIP, ProfiNet, ProfiBus, CANBus, ModbusTCP, and other serial communication as RS232 and RS485.

• •  When speed matters

Most IR cameras built for production environments cannot provide temperature feedback on targets below 450 °C that exceeds 8 ms. New detector materials for infrared pyrometers can respond to temperature changes as fast as 0.3 ms, making them the preferred solution for high-speed measurements on fast-moving targets or temperature testing with ultra-fast temperature transients. One exception to IR camera speed limitations is the short-wave cameras used for high temperatures, which deliver unique temperatures at a rate of one millisecond.

• • When special applications require ratio or two-color wavelength measurement

Some production processes produce substantial dust or other particulate matter in the sensor line-of-sight that attenuates the infrared signal emitted by the part to be measured. The resulting errors can be eliminated when outputs from two-color wavelength sensors are incorporated into a ratio temperature calculation.

These unique pyrometers offer less emissivity depending on the temperature method, which calculates temperature by comparing the intensity of infrared radiation emitted. These pyrometers are useful in various industrial applications, such as steel production, ceramics manufacturing, and glass processing. When emissivity is unknown, the optical path is attenuated by dust or the measurement is partly blocked.

• • When target temperatures are above 3000°C

Short-wave infrared cameras for high-temperature metal measurement typically measure up to 2000 °C. A special G7 thermal camera is now able to measure up to 3000°C. Short- or short-wave ratio sensors can be calibrated to temperatures up to 3500 °C. This is related to the working principles of some detectors, which are only available in pyrometers, including oversaturation of bolometers at high temperatures, and a superior dynamic range of analog electronics.

Conclusion and next steps:

Before deciding on a non-contact infrared measurement solution, the best practice is to decide which technology, infrared camera or pyrometer, best serves the application. The next step is to select the best sensor wavelength to optimize accurate measurements. Next to choosing the optic options that most efficiently frame your target or targets, the correct interface option needs to be selected.

Nevertheless, it is always a good idea to discuss the application with an Optris-trained application engineer, who ensures the selection of the optimal instrument to deliver accurate non-contact temperature measurements.

Our application engineers or distributor support these considerations with extensive knowledge.