Contact temperature sensors are often described as simple devices. Thermocouples are indeed just two pieces of different metal joined at a measuring point. Resistance thermometers are almost as simple in principle. A good Temperature Sensor Design however will consider much more.
While the measuring component of an assembly is simple in principle, a good temperature sensor design must provide the sensing part with support, insulation, environmental protection, process connection and a termination point. Consideration toward adequate immersion and immunity from other sources of error are also needed. Anticipated sensor lifetime needs consideration as well as cost.
Design is always a compromise. Probes can be made very cheaply however this will impact on material selection and design complexity which can shorten probe lifetime and reduce accuracy. A simple example is the diameter of a Mineral Insulated Thermocouple. Thick probes, maybe Ø 6mm or Ø 8mm will be significantly more robust compared to a much cheaper Ø 1.0mm.
Design compromise does not only involve cost. Fast responding temperature sensors will have a low thermal mass, but robust sensors in rough, tough environments require thick sheath sections to resist abrasion or enough physical strength to absorb some knocks.
The application temperature directly affects material selection. The further a process temperature is from ambient increasingly restricts material choices. At the high extremes a sensor needs to be made of ceramic insulators and platinum alloys. These are no where near as cheap or easy to handle compared to polymer insulators and copper wires.
Sensing components are available in different nominal accuracies. Thermistors are often sold with a number of nominal accuracies from 0.5% to 5%. Resistance thermometers are available from 1/10th DIN to Class B. As you would expect, accuracy costs.
Once a probe is made, costs can still be incurred through appropriate testing. This can include calibration, response rate test, robustness (cable pull tests) or pressure test.
A probe has got to be fit for purpose. A good temperature sensor design will make the better compromise choices considering a balance of the constraints. Making a probe eternally robust and highly accurate cannot be done at minimal cost. It must be designed as well as possible to meet all constraints while minimising cost.
Peak Sensors only supplies temperature sensors. We welcome any enquiries for probes. To send an enquiry, please contact us.