Pt100 RTDs wired into a head-mounted or DIN-rail temperature transmitter output a linearised 4-20 mA signal that travels long distances on a standard analog loop [S1][S2].
Thermal imaging cameras with direct analog output read surface temperatures from -20°C to 900°C in standard models and 450°C to 1800°C in high-temperature models, with hot-spot detection and switched line-scanning modes [S5].
Measurement scope: contact resistance vs infrared radiance
Pt100 sensors use a single platinum wire whose resistance changes with temperature, and the connected transmitter firmware converts that measured resistance into a temperature reading using a programmed resistance-temperature table [S1].
Thermal imaging cameras detect infrared energy in a separate part of the electromagnetic spectrum that visible-light cameras cannot see, with image detail defined by temperature differences rather than reflected light [S3].
This fundamental split drives almost every downstream decision in a process control loop: contact measurement is invasive and slow but absolute, while non-contact IR is fast and standoff but emissivity-dependent.
Pt100 RTD transmitter output path
Pt100 RTDs are typically constructed from a single platinum wire terminated at two leads that connect to a dedicated RTD input card or to a temperature transmitter outputting a standard 4-20 mA signal [S1].
The transmitter linearises the platinum-resistance curve into an industry-standard 4-20 mA current loop that can be transmitted over longer distances than a raw resistance signal, and the head is available in terminal-housing or DIN-rail form factors [S2].
Both the input card and the transmitter depend on firmware-resident resistance tables to convert the measured ohms back to engineering units, which is why sensor-to-transmitter pairing and lead-resistance compensation matter more than sensor accuracy alone.
Thermal imaging camera output path
Process-grade thermal imaging cameras include an automatic hot spot finder and direct analog output suited to manufacturing process applications, with switchable thermal-imaging and line-scanning operating modes [S5].
Standard camera bodies cover -20°C to 900°C while high-temperature models span 450°C to 1800°C, and the analog output typically mirrors the hot-spot or pixel value selected by the user [S5].
Compared with point IR thermometers that return a single reading, the imaging camera delivers a full radiometric frame per output cycle, which can be either digital (for an industrial PLC) or analog 4-20 mA keyed to a region of interest [S4].
Decision criteria that separate the two technologies
Four engineering criteria decide the contest: target temperature range, access (contact vs standoff), surface compatibility, and loop integration cost [S1][S3][S4].
Pt100 RTDs dominate the sub-zero to +850°C band, work only where a thermowell or surface probe can be installed, tolerate any non-conductive coating, and need a 2-wire, 3-wire, or 4-wire lead run back to a transmitter or a pressure transmitter-style analog input module [S1][S2].
Thermal imaging cameras cover ranges that include -20°C to 1800°C, never touch the target, are sensitive to surface emissivity and smoke/steam, and emit analog or digital video that drops directly onto a PLC or a 4-20 mA input on a flow meter rack [S3][S5].
Side-by-side specification comparison
Pt100 transmitters output linearised 4-20 mA over long cable runs [S2], process thermal cameras deliver -20°C to 1800°C coverage with direct analog output [S5], and OEM module sensitivity splits into 20 mK and 50 mK NETD grades on the same camera family [S3].
Pt100 with head transmitter: cost low; temperature band -200 to +850°C; surface fit requires thermowell; integration lead time typical 2-4 weeks for the sensor plus DIN-rail transmitter [S1][S2].
Thermal imaging camera with analog output: cost mid-to-high; temperature band -20 to 1800°C depending on model; surface fit standoff only and emissivity-sensitive; integration lead time 4-8 weeks for OEM modules with custom optics [S3][S5].
Sensitivity on the thermal side matters at low delta-T: 20 mK and 50 mK sensor variants are both available in the same module family, with the 20 mK unit resolving finer temperature differences on a static handprint image [S3].
Where Pt100 wins: contact, custody, low temperature
Pt100 RTDs are the right answer when the target is inside a pipe, behind a thermowell, or below 200°C where most uncooled IR cameras lose signal-to-noise, and when a 4-20 mA loop must be linearised to better than 0.1°C for custody transfer [S1][S2].
Industries running steam, glycol, refrigerants, and bearing housings default to Pt100 because the sensor can be inserted directly into the process and the 4-20 mA output is galvanically isolated from the field wiring by the head transmitter [S2].
Typical deployments include bearing temperature on rotating equipment, heat-exchanger outlet monitoring, and HVAC chilled-water loops, where a small industrial valve body can host an integrated Pt100 in a single thermowell port [S1].
Where thermal imaging wins: moving, hot, inaccessible targets
Thermal imaging cameras are the right answer when the target is moving, above 450°C, or physically inaccessible, and when the user needs a 2-D thermal map rather than a single spot temperature [S3][S5].
Process examples include hot-spot detection on a moving steel strip, kiln lining scanning, glass gob temperature, and rotary kiln surface monitoring, where direct analog output drops the reading into an existing 4-20 mA loop on a pressure transmitter-style I/O card [S5].
Switching the camera into line-scanning mode collapses the 2-D frame into a 1-D line of pixels, which lets a single analog output represent a scanned profile across the moving target [S5].
Limits, failure modes, and integration gotchas
Pt100 fails when the lead resistance is not compensated (long leads add series ohms that map directly to a temperature error), when the thermowell fills with process fluid, or when vibration cracks the platinum element [S1].
Thermal imaging cameras fail on low-emissivity polished metal unless a known-emissivity target patch is used, on dusty or steam-laden optical paths, and on targets inside a closed flow meter body where line-of-sight is impossible [S3][S4].
Both technologies share one integration trap: a 4-20 mA loop is a current loop, so a single ground reference must be maintained; mixing grounded and isolated transmitters on the same segment produces offset errors that are easy to miss until commissioning [S1][S2].
Sourcing, standards, and engineering checkpoints
Pt100 element classes (Class A, Class B, 1/3 DIN) and 2-wire, 3-wire, 4-wire lead configurations are defined by the international platinum resistance thermometer standard (IEC 60751), and the 4-20 mA linearised output is the long-distance industry-standard loop format [S1][S2].
For thermal imaging modules, datasheets should be checked for NETD (noise-equivalent temperature difference, with 20 mK and 50 mK variants both common in OEM modules), frame rate, spectral band (typically 8-14 µm for uncooled LWIR), and analog output type [S3][S5].
Engineering checkpoints before purchase: confirm 4-20 mA loop burden voltage at the longest cable run, confirm the IR camera's spectral response against the target's expected temperature range, and verify the PLC input card can accept either analog current or digital video depending on the chosen path [S1][S3][S5].
Two trackable signals to watch over the next procurement cycle: published sensitivity improvements on sub-20 mK OEM thermal cores [S3], and a second source of head-mounted Pt100 transmitters with extended digital protocols layered on top of the standard 4-20 mA output [S1][S2].