permittivity (electric permittivity)

Permittivity, also called electric permittivity, is a constant of proportionality that exists between electric displacement and electric field intensity. This constant is equal to approximately 8.85 x 10^-12 farad per meter (F/m) in free space (a vacuum). In other materials it can be much different, often substantially greater than the free-space value, which is symbolized e_o.

In engineering applications, permittivity is often expressed in relative, rather than in absolute, terms. If e_o represents the permittivity of free space (that is, 8.85 x 10^-12 F/m) ande represents the permittivity of the substance in question (also specified in farads per meter), then the relative permittivity, also called the dielectric constant e_r, is given by:

e_r = e / e_o
= e (1.13 x 10¹¹)

Infra-Red Thermometer

The theory of operation 

All objects above absolute zero (-273.15°C) give ou t infrared energy. This radiated energy is emitted in all directions at the speed of light.

The instrument’s lens picks up this energy and focuses it on an infrared detector. This detector gives a voltage signal proportional to the quantity of energy received and hence proportional to the temperature of the object.
English

What is the  emissivity  that mean ??

Some objects not only give out infrared energy, but also reflect it as well. Unlike matt surfaces, brilliant or highly polished surfaces tend to reflect energy. This possible reflection is represented by a factor known as the emissivity, and can vary between 0.1 for a highly reflective surface, and 1 for a black body.


((TARGET DISTANCE / MEASUREMENT FIELD DIAMETER)) 
RATIO
This ratio, also known as the field of vision, indicates the diameter of the probes’ measurement field at a given distance from the target (see figure below).

In the case of a measurement point of small dimensions, it is important to bring the probe to a short enough distance from the target, so as to avoid including other points into the field of measurement.

Definition of measurement categories

كثيرا ما نسال او نتسائل عن المعني الفني للتصنيف  ( cat IV او cat III )   كثيرا ما نواجها في المواصفات الفنية وغالبا ما ترفض مناقصات او تخرج من المنافسة لعدم مطابقتها للفئة المطلوبة 

الموضوع في غاية البساطة .. هذه الفئات ما هي الا تصنيف مراتب الحماية التي قد يتعامل معها الفني او الجهاز الكهربي المستخدم ويتم توضيحها كما يلي :-

1- Measurement category IV corresponds to measurements taken at the source of low-voltage installations. 

                Example: power feeders, counters and protection devices.

2- Measurement category III corresponds to measurements on building installations. 

             Example: distribution panel, circuit-breakers, machines or fixed industrial devices.

3- Measurement category II corresponds to measurements taken on circuits directly connected to low-voltage installations. 

        Example: power supply to electro-domestic devices and portable tools.

4- Measurement category I corresponds to measurements taken on circuits not directly connected to the network. 

Example: protected electronic circuits.

Operating principle of Circuit breaker

A circuit breaker as a switching and current interrupting consist of fixed and moving contacts, which are touching each other and carry the current under normal condition. When the circuit breaker is closed, the current carrying contacts, called the electrodes, engage each other under the pressure of a spring.

Whenever a fault occurs on any part of the power system, the trip coils of the breaker get energized and the moving contacts are pulled

The tripping circuit is a coil which can be energized and produce a magnetic field that attract an armature that can be able to handle with the mechanical system to open or close the contact of the circuit breaker

Circuit Breaker Classification

What is a circuit breaker?

A circuit breaker is an apparatus in electrical systems that have the capability to, in the shortest possible time, switch from being an ideal conductor to an ideal insulator and vice versa. Circuit breakers requires to reduce arcing ie, Sparks jump for several inches in the highly ionized ambient atmosphere

TN-S system earthing

A TN-S system, shown in fig, has the neutral of the source of energy connected with earth at one point only, at or as near as is reasonably practicable to the source, and the consumer’s earthing terminal is typically connected to the metallic sheath or armored of the distributor’s service cable into the premises.