Common definitions and explanations of the Sensor and Relay on the electrical system

Relay is a switch that is controlled by the current. Relay has a low-voltage coil is wound on a core. There is an iron armature core when it is pulled towards the current flowing through the coil. Armature is mounted on a spring-loaded task. When the armature is attracted to, contact with the track will change the position of the contacts are normally closed to normally open contacts.

 
A relay of this type can be activated in about 10 ms. Most of modern relay is placed in a package that is fully sealed. Most of them have the kind of SPDT contacts (sliding switch), but there are also several versions of DPDT (double-pole, double throw or double-pole, two-way). Relays that can connect the larger currents up to 10 A at a voltage of 250 V AC. The maximum DC voltage for switching is always much lower, often only half, of the maximum voltage to AC. There are also miniature relays.

Sometimes we have to use a transistor circuit for controlling a high power device. Such devices may require a larger current or voltage that is higher than what is handled by a power transistor. Or maybe have to switch the AC current, which is a matter beyond the capability of the transistor. In situations of this kind requires the user to use the relay.

 
The sensor used is a thermistor. This component controls a FET switch circuit, which in turn serves as a switch to a relay circuit. Cognac - relay contacts to control a space heater powered by electricity from the source.

 

 

As is the case in almost all series of switches, the first stage of this circuit is a voltage divider. A variable resistor used to set the temperature values ​​are used as the trigger point. There is no resistor between voltage divider with FET gate terminal.

 
When the temperature falls, R2 will increase resistance, resulting voltage at the wiper VR1 increased. Q1 becomes active when this voltage exceeds the threshold voltage. Current flows through Q1 and the relay coil (RL). D1 serves as a protective diode. Serves as a relay switch that connect and disconnect the electricity of a chain of separate power, used his contacts are normally open. When current flows through the coil of the relay, the relay contacts are normally open to close. Heating circuit will be connected to the power circuit and the heater will turn on. Heater will light up the room temperature reaches a predetermined value.

Light emitting diode, the which is more known as LEDs, Produce light when current flows through it. Led initially only made ​​in red, but now the color of orange, yellow, green, blue, and white are also available on the market. There are also infrared LEDs That Produce.  

Requires about 20 mA LED current to emit light with maximum brightness, although the currents as small as 5 mA was still Able to Produce visible light. LED forward voltage drop an average of 1.5 V, so the supply voltage of 2 V can turn most of the LEDs with maximum brightness. With higher voltage levels, LED forward voltage can be burned if given more than 2 V, and crucial limiting resistor connected in series to the flow of a LED.