Temperature Sensors: Selection Criteria

The most important criteria for selection of temperature sensor is its required range. The range in temperature within the universe varies from zero of black space to that of nuclear fusion deep within the stars which corresponds to billions of degrees. But the practical range on earth can be considered from 1 deg. R to 20,000 deg.R, which is tremendous and cannot be covered by a single sensor. 
Therefore, one of the restrictions on temperature sensors concerns the temperature  range over which it can stay reasonably accurate. From range, we can shortlist the available sensors that can be used for our applications. After range there are various other more or less equally important criteria like accuracy, uncertainty and cost. Inspecting these briefly, the user can determine if the sensor meets his requirements or not. Thus we can finally select the sensor which suits best for our applications. Sometimes, we may face a situation where are constraints are too harsh and we are unable to come down on a single sensor for our application. In such a scenario, we may need to relax a few constraints which might not affect the process or measurement in a significant way. With a vast variety of available sensors, though, such a situation rarely occurs.
When we finally decide the type of sensor we may need to study its further classifications and its available variations and the description of design in detail.
If some of the features are unacceptable to the user or the process, we may need to change our choice.
Temperature sensors should be selected to meet the requirements and limitations of specific applications. The parameters which the applications demands like temperature level, nature of information required (point or average temperature) and the nature of process environment should be determined.  The most difficult temperature measurement applications are those where high temperatures are to be detected within a hostile environment, such as that which exists within a fluid-bed coal gasifier. By referring the table below, we can get closer to the type of sensor we desire.

Temperature Sensor Selection Table.
Source: Process Measurement and Analysis, B.G. Liptak.

In the above table,

D: In Development
L: Limited
F: Fair
G: Good
E: Excellent
P: Protective well required (Reduces speed of response)
A: Detects the average temperature of an area.

For example, G(D) refers to a device which is a good selection for a particular application, but it may not be commercially available or may be rarely available.
The table must be read as follows.
First select whether the requirement is a point measurement or an average of multiple readings, which needs to be taken sometimes for better accuracy or for constantly changing readings.
Next check whether the environment in which the sensor or the instrument on which it is located is a part of hostile environment. Hostile environments refers o the processes such as fluid beds, where the sensor may need to face mechanical impact of high velocity solid particles.
Then we need to check for thermal interference if any. It may occur due to thermal refractories or temperature differences between the carrier gas and the solid particles it contains.
For further analysis like span, accuracy, cost, stability, we need to study and understand the classification of each of the above classes as they vary with each type.