Different types of temperature sensors
Designers of temperature monitors to alarm, log or protect equipment or areas can be built with many different types of temperature sensors. The type of sensor a manufacture of a temperature monitors chooses is usually determined by his best guess as to where the monitor is to be used by the end user as well as his familiarity with the alternatives.
The application usually determines the type of sensor
If he is building a monitor that will be used to monitor a refrigerator he might choose to use a thermistor because it has a high degree of accuracy over a narrow temperature range. However if he is building a temperature monitor to alarm a cryogenic freezer he will almost certainly choose a thermocouple or an RTD.
Choosing a thermocouple instead of an RTD could be based or price since a thermocouple is normally much less expensive than a RTD. Neither an RTD or Thermocouple has good linearity and will require a lot of engineering and additional circuitry in the finished product.
Analog vs. Digital
The choices of temperature sensors has expended in recent years to provide more choices for the design engineer. For centuries all temperature sensors were ananlog devices. Analog sensors include the liquid-in-glass thermometers, and bi-metal strip thermometers, which are very low cost, are not extremely accurate and almost impossible to incorporate into multi-purpose instruments. Analog sensors also include thermistors, RTDs and thermocouples, each of which have their plusses and minuses as shown in the table below.