Question

present briefly two different ways/ techniques or devices and their advantages/ disadvantages to convert the sensed/ measured ambient air temperature into an electrical signal representation in a space heating system

Note: (no equations or calculations needed just general idea)

Answer 1

A device which converts ambient temperature into an electrical signal is called as transduces. Basically, a transducer is a device which converts one form of signal into another form of signal. Here a sensing element is converting the ambient temperature of surrounding into the electrical reading for further Processing

The examples of these devices are;

Thermocouples  

The thermocouple converts the temperature into the electrical energy at the point of the contact. It works on the principle that the metals have different temperature coefficient and when these two metals join together then the voltage induces, and this voltage is directly proportional to the temperature.

the advantages of the Thermocouple are:

• No external power required
• simple and rugged in construction
• cheaper
• support for wider temperature range etc.

the disadvantage of Thermocouple are:

• Non linearity
• least stability
• Low voltage
• Reference is needed
• least sensitivity etc.

Thermistor

The thermistor is a type of resistor whose resistance varies with the temperature. The resistance is measured by passing the small measured direct current, and this current causes the voltage drop across the resistance.

the advantages of a thermistor are:

• The thermistor has fast response over narrow temperature range.
• It is small in size.
• Contact and lead resistance problem not occurred due to large resistance.
• It has good sensitivity in NTC region.
• Cost is low.

the disadvantages are:

• They are non linear.
• Self heating
• Passive i.e. current source is needed.
• Fragile
• Limited support for temperature range.