Variable Resistor

-

A variable resistor is a resistor whose value is variable.many factors can induce a variation of R according to its constitution.

The most common are the following factors:

Mechanical: Most often a variation in the length of the resistant body. These are strain gauges, Potentiometers or Rheostats.

Thermal: The temperature to which the resistance is subjected (thermistor).

We can find the Positive Temperature Coefficient resistance (the resistance increases when the Temperature increases) and the Negative Temperature Coefficient (the resistance decreases for an increase in T).

Radiation: The radiation to which the resistance is subjected. (Many models exist, each one is sensitive to a specific radiation range).

Chemical: A substance (gas, liquid, solid) brought into contact with the resistance.

Electrical: the varistor is a resistor whose value drops from a threshold voltage.

NTC Thermistors 

Thermistors or resistors with negative temperature coefficient or NTC:

They are manufactured with semiconductor oxides. The relationship between the resistance of a NTC and the temperature of the NTC resistor is approximately R = A.e ^ (B / T) where A and B are characteristic component constants.



 PTC thermistor

Positive temperature coefficient (PTC) resistors: They are characterized by a very sudden variation in their resistance at a given temperature. They can be used for:

• protection devices against overheating

• varistors or VDR resistors (Voltage Dependent Resistor):

They consist of an agglomerates of silicon carbide crystals. It is a resistor whose value depends on the value of the applied electric voltage. They come in the form of sticks or discs.


Photoresistors (LDR)

Photoresistors or LDR (Light Depending Resistors): These are cadmium sulphide-based resistors which have a small transparent window and whose value varies depending on the lighting, usually from 75 to 300 Ω for 1000 lux to some 10 MΩ in the dark.

The two best known types are LDR03 and LDR05 which differ only in their connection wires.

 

Varistors (VDR)


Varistors or VDR: These are resistors for which there is a non-linearity between the electrical resistance and the applied voltage. The relationship between current and voltage  U = f (I)  non-linear :


characteristic U = f (I)


The main applications are

• protection against overvoltage

• voltage stabilization

• expansion of the reading scale of measuring devices

 

Potentiometer


Potentiometers are widely used in electronics.There are rotary potentiometers, but also rectilinear potentiometers in which the contact moves in a straight line.

A potentiometer is a resistive element with three terminals:

• Two correspond to the ends of the resistance body,

• The last corresponds to the cursor which can move on the body of the resistance.

There are several kinds of potentiometers depending on the variation in resistance due to displacement of the contact.

If the resistance is proportional to the displacement, the potentiometer is said to be linear (type A)

But we also manufacture logarithmic variation potentiometers (type B).







Comments

Post a Comment

Popular posts from this blog

7 segments display

-
Image
The 7-segment displays are displays that allow you to view a figure or a number using luminous segments. The light sources are internal. It is almost always this type of display which is used on radio clocks when the color of the digits is green or red.  The 7-segment displays mostly emit a red or green light, but there are also some that glow in the blue. to display a number between 0 and 9, at least seven segments are needed, and these segments have been conventionally assigned the first seven letters of the alphabet: A, B, C, D, E, F and G. Common anode: Here is the principle of common anode displays: (Diagram of the inside of the box) To use its displays, you must always follow the instructions for supplying the LEDs. the (+) of the power supply on the anode and the (-) on the cathode. Just like the LEDs, you will need to add a resistor (220 ohms if the power supply is equal to 5v) to reduce the current on each segment of the display. Otherwise you risk toasting the segment...
Read more

Mosfet

-
Image
Metal-oxide semiconductor field-effect transistor (mosfet) is the second type of field-effect transistor. The mosfet gate is a channel isolated by a layer of silicon dioxide (Si02). The drain and the source are made from substrate materials. they are connected to the gate by a narrow channel. Transistor has type of metals. The first is called the mosfet at depletion and the second is called the   enhancement mosfet (E). The MOSFET transistor is different from the JFET in that the gate is isolated from the channel. Like diodes, these elements are most often made of silicon. They are used to make amplifiers. The enhancement MOSFET In the absence of a control signal at the Gate (Vgs = 0V), the Mosfet is blocked regardless of the type of channel (N or P).Conduction only begins to manifest from a threshold:+ Vth for Drain an N-channel MOS and –Vth for a P-channel MOS. N-channel   enhancement mosfet is a positive voltage applied to the input. The positive charge sticks...
Read more

LM35 Temperature Sensor

-
Image
  The LM35 temperature sensor is an analog temperature sensor .This integrated circuit has 3 pins and generates an output voltage in linear relation with the temperature expressed in degrees Celsius The LM35 sensor is able to measure temperatures ranging from (-55 ° C to + 150 ° C) in its most precise version and with the right mounting, enough to measure any temperature. The analog output of the sensor is proportional to the temperature. It suffices to measure the voltage at the output of the sensor to deduce the temperature. Each degree Celsius corresponds to a voltage of + 10mV. The LM35 does not require any external calibration or size and maintains an accuracy of (+ / -0.4 ° C) at room temperature and (+ / - 0.8 ° C) over a range of 0-100° C. The temperature measured by the sensor is given by the relation: T = Vout / 10 with: T: Temperature [° C] Vout: Output voltage [mV]   DHT22 sensor The DHT22  temperature and humidity sensor communicates with ...
Read more