When the discussion turns to temperature sensing, thermocouples get most of the attention. For determining surface temperature, however, especially when the surface may be moving, rotating, or inaccessible, no high-tech instrumentation outperforms phase change indicators.

The drawbacks to electrical or electronic instrumentation include vulnerability to external factors such as static electricity, ionized air, humidity , and being dropped. Electronic devices also require trained operators with technical understanding and skill. Remote-reading infrared sensors present fewer problems but still need skilled operators.

Phase-change temperature indicators, in contrast, take advantage of precise melting points of different materials and are easy to use. Tempil's phase-change temperature indicators are made of materials with melting points calibrated to a guaranteed accuracy of 1%. There are more than a hundred temperatures between 100 and 2500F (38 to 1,371C) available to be chosen. The indicators do not read out an exact temperature. But by melting they let users know exactly when a preset minimum or maximum has been reached.

Phase-change indicators react within milliseconds, unlike thermocouple or probes that must reach equilibrium with the surface and have to compensate for heat conducted away from the region being tested. Phase-change materials, on the other hand, are in intimate contact with the surface being measured, and only need someone who can see that a dry chalk mark has melted or a label changed color.

Other advantages include no set-up, calibration or recalibration periods. They are also relatively immune to abuse, unlikely targets for pilferage.


Is a reversible lacquer that changes from bright red to deep maroon (almost black) at 150- 160F ( 66- 71C ), and back to red when it's cooled below 100F. It is widely used on hair curlers and curling irons as a "ready" indicator. It is also used as a warning or safety device that an item is too hot to touch,

See the ready dot !
such as hot water faucets, steam pipes, cooking utensiles, etc.
Chromonitor retains its color-changing ability indefinitely under normal usage conditions. Chromonitor is compatible with the following materials: polypropylene, polycarbonate, nylon, polyester, polystyrene, polyacetal, chrome plate, and stainless steel. It should not be applied to aluminium, rubber or plastics not approved by the factory.
---Tempilstik - Temperature Indicating Crayons
Tempilstiks indicators are made of materials that are guaranteed to melt within 1% of their rated temperature. Mark the workpiece before heating begins. The dry opaque Tempolstik mark will change to a distinct melted mark when the temperature rating of the selected Tempilstik has been reached. A few of the hundreds of uses for Tempilstiks include:
Determining surface temperatures during welding and metal fabrication including preheat, postheat, annealing and stress relieving. Determining operating temperatures of bearings, transformers, steam traps, molds, PC board preheaters, motors, electronic components, hydraulic systems, commercial irons, hot plates and heat exchangers.
---Temprobe - Temperature Test Kit
Temperature test kits consist of twenty 3/4" (19mm) temperature indicators with ratings from 125F/ 52C to 800F/427C and a special holder. They are intended for use by researchers, experimenters, technicians, and people who do other heat-related operations.
---Tempilaq - Temperature Indicating Liquid
Temperature Indicating Liquid is Tempilstik material suspened in a quick-drying inert vehicle. It is available in the same temperature ratings as Tempilstiks and with the same 1% accuracy. Tempolaq should be used on surfaces which cannot be easily marked with a Tempilstik, such as polished metal, glass, plastics, rubber, fabrics or electronic components.
---Tempil Pellet - Temperature Indicating Pellets
Are Tempilstik material in tablet form (7/16") or 11mm diam.) and available in the same temperature ratings. Their major applications include use in industrial ovens and furnaces, and on large heavy objects requiring prolonged heating, where Tempilstik or tempilaq marks might vaporize or be absorbed before melting.
---Tempstik Test Kit: - a professional's temperature indicating kit
Consists of twenty 2-1/2" (64mm) temperature indicators each with its own holder, with ratings from 125F/ 52C to 800F/ 427C. They are for use by welders who frequently weld different types of heat treated alloy steels in various thickness, and need to know precise preheat and inter-pass temperatures.
Are self-adhesive temperature monitors consisting of a heat-sensitive indicator sealed under a transparent heat-resistant window. The indicator circle turns from light grey to black at the temperature rating shown. Color change is not reversible and provides a history of the surface being monitored. Some applications include monitoring of surface or operating temperature of printed circuits, electronic components, motors, appliances, machines, etc.

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