accommodate several sensors at once. The ice point is designated as a secondary standard because its accuracy is ±0.005°C (±0.009°F), compared to ±0.001°C (±0.0018°F) for primary fixed points. commonly used with secondary SPRTs and industrial RTDs, the Comparison calibrations, thermometers being calibrated are compared to calibrated thermometers by means of a bath whose temperature is uniformly stable. Unlike fixed point calibrations, comparisons can be made at any temperature between and 500°C (–148°F to 932°F). This method might –100°C be more cost-effective since several sensors can be calibrated simultaneously with automated equipment. These electrically heated and well-stirred baths use silicone oils and molten salts as the medium for the various calibration temperatures. 2.3.3. Element types There are three main categories of RTD sensors; Thin Film, Wire-Wound, and Coiled Elements. While these types are the ones most widely used in industry there are some places where other more exotic shapes are used, for example carbon resistors are used at ultra low temperatures (-173 °C to -273 °C). are widely available and are very inexpensive. They have very Carbon resistor elements reproducible results at low temperatures. They are the most reliable form at extremely low temperatures. They generally do not suffer from significant or strain gauge effects. use a wire coil minimally supported within a sealed housing filled with Strain free elements an inert gas. These sensors are used up to 961.78 °C and are used in the that define SPRT’s ITS-90. They consisted of platinum wire loosely coiled over a support structure so the element is free to expand and contract with temperature, but it is very susceptible to shock and vibration as the loops of platinum can sway back and forth causing deformation. have a sensing element that is formed by depositing a very thin layer of Thin film elements resistive material, normal platinum, on a ceramic ; This layer is usually just 10 to 100 angstroms (1 to 10 nanometers) thick. This film is then coated with an epoxy or glass that helps protect the deposited film and also acts as a strain relief for the external lead-wires. Disadvantages of this type are that they are not as stable as their wire wound or coiled
accommodate several sensors at once. The ice point is designated as a secondary standard because its accuracy is ±0.005°C (±0.009°F), compared to ±0.001°C (±0.0018°F) for primary fixed points. Comparison calibrations, commonly used with secondary SPRTs and industrial RTDs, the thermometers being calibrated are compared to calibrated thermometers by means of a bath whose temperature is uniformly stable. Unlike fixed point calibrations, comparisons can be made at any temperature between –100°C and 500°C (–148°F to 932°F). This method might be more cost-effective since several sensors can be calibrated simultaneously with automated equipment. These electrically heated and well-stirred baths use silicone oils and molten salts as the medium for the various calibration temperatures. 2.3.3. Element types There are three main categories of RTD sensors; Thin Film, Wire-Wound, and Coiled Elements. While these types are the ones most widely used in industry there are some places where other more exotic shapes are used, for example carbon resistors are used at ultra low temperatures (-173 °C to -273 °C). Carbon resistor elements are widely available and are very inexpensive. They have very reproducible results at low temperatures. They are the most reliable form at extremely low temperatures. They generally do not suffer from significant or strain gauge effects. Strain free elements use a wire coil minimally supported within a sealed housing filled with an inert gas. These sensors are used up to 961.78 °C and are used in the SPRT’s that define ITS-90. They consisted of platinum wire loosely coiled over a support structure so the element is free to expand and contract with temperature, but it is very susceptible to shock and vibration as the loops of platinum can sway back and forth causing deformation. Thin film elements have a sensing element that is formed by depositing a very thin layer of resistive material, normal platinum, on a ceramic ; This layer is usually just 10 to 100 angstroms (1 to 10 nanometers) thick. This film is then coated with an epoxy or glass that helps protect the deposited film and also acts as a strain relief for the external lead-wires. Disadvantages of this type are that they are not as stable as their wire wound or coiled
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