Sensor buyers always need great value for money. This can mean high specification units built to last, or simply low cost temperature sensor assemblies.
The simplest probe arrangement comprises a sensing element, such as a Pt100 or thermistor. This is extended with cable to a termination requirement. The sensor as well as the cable to sensor connection are within a metal (usually stainless steel) closed one end tube. The probe is complete.
The cost components can be broken down to:
Thin film Pt100 elements are cheaper than wire wound sensors. Wire wound will always be slightly more accurate over a wider thermal span but for most applications this is trivial.
Nominal accuracy costs. Pt100’s are available as a standard F0.3 in BS EN 60751:2008 (which approximates to the old but familiar Class B) F0.15 or F0.1 increase the cost. The new standard has an even wider F0.6 definition which will be cheaper still
Thermistors are similarly price banded by tolerance. The tolerances are significantly wider than for resistance thermometers. Thermistors are cheaper than Pt100’s but the lack of standardisation can be an asset (to deter copies) or a problem if the sensor element becomes obsolete.
The extension cable can often be the dominant cost element in higher temperature assemblies. Cables made from PVC are very inexpensive, but have a temperature range limited to 70 or 105 °C depending on the PVC specification. Above that PTFE, FEP, PFA are available but may cost 5 times more than PVC. Adding shielding or braid increases cost further.
Thermistors, resistance thermometers and cables must fit into the closed one end protection tube. Around Ø 6.0mm is often practical. This tube is inexpensive, even in 316SS. Brass is occasionally used if the housing needs to be a specific machined shape. The housing is usually filled with a suitable filler like epoxy. Occasionally we sell even cheaper units without hot end enclosures.
The cheapest assemblies come in volume. Peak Sensors can utilise numerous automatic processes to reduce labour time. We have auto cable dereelers, cutters, strippers and welders.
Subsequent operations can include calibration, physical integrity tests, cold end plugs, serial marking or a range of other actions. If they are needed for the application then there is no choice. To maintain a low cost temperature sensor, specifiers must understand the cost components.