Question

Write an essay on different temperature measurement devices. Explain the operational principle of each device, its advantages and disadvantages, its cost, and its range of applicability. Which device would you recommend for use in the following cases: taking the temperatures of patients in a doctor’s office, monitoring the variations of temperature of a car engine block at several locations, and monitoring the temperatures in the furnace of a power plant?

 

 

Answer 1

Temperature measurement can be classified into following categories:

1. Thermometers

2. Probes

3. Non-contact

 

Thermometers :

1. Glass tube thermometers:

It measures the temperature by the expansion of the liquid.

 

Advantages:

i. It has more repeatability.

ii. Good accuracy.

 

Disadvantages:

i. It does not have high temperature capability and also very low temperature capability.

ii. Inserting the glass tube into a pressurized fluid will reduce the accuracy.

 

Ranges and accuracy:

i. Accuracy depends on the size and length of the hole.

ii. If smaller the reading increment, range is less.

iii. It gives fairly accurate results within the temperature range of -200 to 600°C.

iv. Parallax error.

 

Applications:

Temperature measurement of patient’s body.

 

Probes :

1. Thermistors:

It converts the change in electrical resistance with the temperature.

Advantages:

i. Small size

ii. Low cost

 

Disadvantages:

i. Self-heating

ii. If the current is very high, the resistor will dissipate energy in the form of heat.

 

Ranges and accuracy:

i. Very accurate and repeatable

ii. Lower the cost, worse the accuracy.

iii. If signals are low, external noise will unavoidable.

iv. The range depends on its ability to give reasonable resistance changes over a wide temperature change.

v. It is particularly useful in small temperature change environments.

 

Advantages:

Temperature of a car engine block at several locations.

 

Non-contact devices :

It operates on the radiation heat transfer measurement. By change in the radiation heat transfer, temperature can be measured.

 

Advantages:

i. Accurate and repeatable.

ii. High temperature measurement.

 

Disadvantages:

i. High cost.

 

Ranges and accuracy:

1. One can measure the temperature which are very distant and also which are very nearer.

2. Very accurate.

 

Applications:

Monitoring the temperatures in the furnaces of a power plant.

Temperature measurement can be classified into following categories:

1. Thermometers

2. Probes

3. Non-contact