SENSORSSENSORS

Question:Question:Which technological system can help us to save energy?

I-Twilight sensorTwilight sensor

-Firstly, what is a twilight sensor?

A twilight sensor is also called a twilight switch. It is an electrical control device which is activated by the ambient light.

When it's dark the light sensor is activated.

-Secondly, wwhat is its purpose? The twilight sensor is generally used outdoors

because it is activated at night. It allows to activate a public lighting or neon sign, for example, once darkness sets in.

-Thirdly, what is a photoresistor?

The twilight sensor is composed of photoresistors. This component provides information on the rate of Lux. Lux is the measuring unit for luminance. It provides information used to enable or disable lighting.

-Fourthly, what can we compare the twilight sensor with (What can be replaced by a twilight sensor)?

The twilight sensor can be compared with a timer.

Twilight sensor

II-Sound sensorSound sensor movie

- The sound sensor functions like the human ear.

- Indeed, with only two receivers, the brain is able to differentiate sounds and noises of our environment and to locate the position of the emission and its intensity.

- It is these physical spects that the sound sensor collects thanks to a microcomputer and transforms into analog signals analog (to define the presence of people in the room, for example)

- Our sound sensor will collect a range of frequencies going from 20 Hz to 20 KHz, (between the infrasound (20 Hz) and the ultrasounds (20 KHz)) but other sensors can collect other ranges of frequency. That depends on their use.

- Last thing to know: For our assembly we will use a microphone with "electrets" which is based on the "electric piézo effect".

- A piezoelectric material produces electric charges when it is subjected to a constraint (a pushing or pulling force, for example)

- In our sensor this pressure is the acoustic pressure of air waves.

Sound sensor

III-THE MOTION SENSOR

-A motion sensor is an electrical control device that responds to movements of physical objects in its surrounding.-The activation threshold is usually adjustable. The device acts on electrical appliances such as lights, for example.-The sensors are used for automatic controls such as: control of the interior and exterior lighting,management of ventilation for rooms of intermittent occupancy such as conference rooms, for example, and for regulation of heating and cooling.

Motion sensor with mask Motion sensor without mask

-Motion detectors capture the movement of the human body by measuring the infrared radiation (heat) emitted by the human body.

-They measure the infrared radiation emitted by hot surfaces.

-They provide an indication about the place’s occupation: absence or presence. They do not know the kind of occupancy of a room or number of occupants.

-Specifically, the infrared motion detectors have a number of sensitive facets. Their radius of action is thus divided into several parts. Thus the passage of a body (and therefore heat) from one facet to another facet is interpreted as movement.

-The sensitivity of a detector depends on the number of sensitive segments.

IV-Result

Saving energy with motion sensorsAs part of our experience we took all the school toilets. We took several characteristics during 240 days/year: - 34 fluorescents tubes type lamps (40W) -Price of kWh: 0.1211 € - 12 Motion Sensors to 30 € the unityResult: Operation time: 1000h/yearAnnual consumption: 1360 kWh / yearSaving: 60 € / yearReturn time: 6 years

Saving with a twilight sensor:

For the second experiment we use the twilight sensor for the outdoor lighting of the school.

We took the following characteristics:

30 Halogen Bulbs (300W)

Consumption is 503 kWh unities ?????

A twilight sensor costs 100€.

In summer the sun sets later than in winter, therefore the twilight sensor activates the outdoor lighting at a better time.

Without the sensor, lightings are on from 16h to 19h:

Turn on 480h/year 241 440 kWh / year.

Thanks to the sensor, the lighting will be activated later in February. After April the lighting will be deactivated because the days are longer.

Turn on 260h/year 130780 kW/year

Therefore saving 110 660 kWh / year