Specifications

70
2"
Figure 28 Bead type thermistor ((Permission is granted under the GNU Free
Documentation License, http://en.wikipedia.org/)
Different temperature sensors have a wide range of temperatures pre-designed
within each IC chip for manufacturing and functionality purposes. In Florida, we
would generally want a temperature sensor to have a range of temperatures from
40 or 50 degrees F to probably 90 degrees F. That way we can preset the
thermostat as to what temperature a user would want depending upon what
season of the year it is. Most thermostats either use mercury or bimetallic strips
to bend as the temperature changes. Bimetallic strips are two different metals
that break or make electrical contact within a thermostat. These two metals
expand by different amounts depending upon the material being used and
eventually causing the strip to bend. This expansion is known as average
coefficient of linear expansion. In order to find the average coefficient of linear
expansion, the formula needed to derive this is as follows:   

.  is
the change in the initial and final lengths of the metals,  is the coefficient of
linear expansion, and  is the change or difference in the final and initial
temperatures.
An air conditioner consists of the following categories: sensors, microcontrollers,
and actuators. All three of these categories go through a control loop starting
from a sensor where it reads/ interprets a signal and sends an electronic signal to
the microcontroller. Then the microcontroller reads the sensor‟s signal and
eventually converts it to the user‟s preferred setting on the controller. Finally the
actuator responds to the microcontroller signal and performs an action to activate
the sensors information.
In order to search for good sensors one needs to determine how reliable a
sensor is, whether the sensor is weather proof in case of a wire short-circuiting,
and its relative tolerance or resolution. The next step would be to search for how