VDC would be the abbreviation for Volt Direct Current which translated would volts direct current. The idea of ??this type is unidirectional current to the load. Direct current is normally produced by batteries, thermocouples, solar cells and a dynamo electric machine type. The direct current can flow in conductors such as wires, but may also flow through semiconductors, insulators ... In the image: 1 - current per pulse 2 - Direct Current (DC) 3 - Alternating Current (AC) 4 - Variable Current

These are two types of contacts widely used in electrical installations and circuits. Distinguishing the difference of these two types is very simple.

• A NO (normally open) type contact is one that does not let the current flow while the same or the device is in standby or standby mode. The most common type NO contact is eg house switches, which remain open (not closedCircuit) until the switch is pressed.
• The NC contacts (normally closed) are the opposite of the NO contact, they let the current pass while they are in standby or at rest to be actuated. An example would be a thermal protection relay of a motor, which remains closed while there is voltage.

Proximity or range sensors are used in many installations requiring an action according to the distance (D) of an object.
They are also used in robotics to control the movement according to the environment, in motorized or domotic installations, the applications can be many and very different.
There are a variety of proximity sensors, including the most common are position switches, Capacitive sensors, inductive sensors, photoelectric sensors where an emitter (E) and a receiver (R), ultrasonic sensors and magnetic sensors are required.
Each of these sensors have the same function, but each of them uses different systems for the detection, either by contact, sound, etc.
Its detection capacity varies according to the type of sensor, and can vary from millimeters to meters. We can vEr these sensors in automatic floor cleaning systems, safety barriers, rear parking sensors for cars, mobile phones, etc.

Inductive proximity sensors are used for detection of ferrous materials, are used to a large extent in companies that need control of presence or absence of ferrous materials in an object, counting or positioning.
This type of proximity sensors emit a magnetic signal to the ferric object, calculate the distance by detecting the loss of magnetic current that is absorbed by the object.
TheSensor consists of a coil inside its ferrite, a level sensor, an oscillator and the action circuit, its function is simple and similar to the capacitive sensor, the magnetic proximity sensor uses a coil to emit an electromagnetic signal to the object Metal, the oscillator is responsible for calculating the capacity to preserve its magnetic properties, by calculating energy loss andThe oscillation amplitude will calculate the distance and the trigger will generate the signal that changes to the status sensor to ON and OFF.
A: Coil
B: Active surface
C: Magnetic field
D: Indicator Led

VAC would be the abbreviation of Volt Altern Current which would be translated Volts of alternating current. The difference between VDC is that its sinusoidal oscillation achieving a more efficient energy transmission.

The alternating current is the energy that we receive in our homes, it is generated in the power plants by means of alternators.

The intensity of this type of current varies with time, and changes direction 50 times throughsecond (50hz). The generated voltage changes in the form of sine wave so it is not constant.

In the image:

1. Current by pulsations.
2. Direct current (DC).
3. Alternating current (AC).
4. Variable current.