How do Sensors work?

Sensors are like detector which detects physical quantity and converts that quantity into a signal that can be read by an electronic instrument. It is a device which measures and responds to a signal. A sensor's sensitivity indicates how much the sensor's output changes when the measured quantity changes.

Sensors are a new solution for measuring currents and voltages needed for protection and monitoring in medium voltage power systems.

Certain strong trends have been present during the whole period of electrical equipment manufacturing: a continuous reduction of equipment size, a continuous improvement of equipment performance and a continuously grooving need for standardization.

Sensors are the part of our life and they are used in every day life devices we use like proximty sensor in smartphones, accelerometer sensor, motion detector etc. The use of sensors make the different devices to function smartly, more accurately and make it possible to develop Intelligent Electronic Devices(IED).

Resolution

The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made.

There are many different types of sensor, used in our everyday lives. These are now used in almost every type of applications. But there are only 2 basic types of sensor available:-

1. Active Sensor - These are the sensors which emit energy in the form of sound using ultrasound waves or light using infrared light through LEDs, into the immediate area.

• Working of Active Senor- Active sensors work by sending infrared light or ultrasound waves into the immediate area. After that sensor waits for the energy emitted to return back for further analysis. When there is no moment of an object or a person in the path of sound waves or light, the floor or walls reflects back the energy without any change in the pattern. It means the reflected wave or light will have static pattern when there is no moment. If there is a moment, sensor responds to the wave s reflected by the object and sends the signal to the installed system for further action to take place like automatic opening and closing of the door.

2. Passive Sensors - Passive sensors do not emit any energy, but instead read changes in the energy, using a predetermined baseline, in the surrounding area. These sensors are used in motion detectors more commonly used to secure businesses and residential homes than active motion sensors. Hence known as PIR(Passive Infrared Sensors) sensors.

• Working of Passive Senors- A passive infrared door sensor works on the basis of ambient temperature. It measures the temperature and emits a pulse as soon as there is a change, recognized as 1° C or about 1.8° F is equal to a person walking at 1.2 meters (4 feet) per second. Example, PIR systems are combined with a basic photo-sensor motion detector. You frequently see these at a shopping mall, near the entrance to a store. When someone walks between them, the motion detector will sometimes emit a tone. Photo sensors usually consist of a laser beam and a light sensor. When the light is interrupted by the motion of a person crossing it, the sensor notices the brief drop in the light level, and alerts the control box, which will either sound an alarm or emit that bell sound you often hear in stores.

Advantages of using Sensors:

• Short delivery times- Because of the linearity over a wide range of current and/or voltage, a minimum of order-specific actions are required and consequently the logistic process is short.

• Compactness- As sensing elements are noticeably small, they can easily be combined in one device, a combi sensor, or integrated into other equipment like switches, bushings or post insulators, resulting in more compact switchgear.

• Versatile protection and control solutions- The sensors are linear up to the highest currents and voltages with a good dynamic performance. As a result, the sensors enable high protection performance and many-sided disturbance analysis.

• Overvoltage and disturbance withstand- Voltage sensors do not need to be disconnected for voltage testing at power frequency on the switchgear. They can not cause ferroresonance and are not sensitive to ferroresonance and DC-voltages.

• Transmitted signal. The nominal value of the transmitted signal is low enough to be harmless to secondary equipment and people, even when the highest currents and voltages occur on the primary side. A broken circuit or short-circuit in the signal cable will cause no hazards or damage.

Impact and Advantages of sensors from environment point of views:

• Less use of raw materials- Sensors with small dimensions, as well as combined and integrated sensors leading to compact and uncomplicated cubicles, give savings in highly-valuable raw materials.

• Less copper inside cast resin- In Life Cycle Assessment, the use of copper does not automatically give a high environmental impact because copper can, in most cases, easily be recycled. However, casting copper into cast resin is negative because the recycling of copper is more difficult or impossible. The amount of copper in the single Rogowski coil of a current sensor is only a fraction of that used in a corresponding multi-core current transformer. The absence of iron cores makes the recycling of the primary winding possible. A voltage sensor does not contain copper windings at all!

• Small power consumption- The efficiency of a sensor is high compared with instrument transformers. In addition, there are no losses in the secondary cabling.

These savings add up with a long lifespan of the equipment and at a utility level these savings could be significant.