These two-terminal components have a nominal value of resistance constant (determined by the manufacturer) and a linear behavior. This component is known worldwide, serves to limit the current passing through it, with the equation that everyone knows, I = V / R. I will not clarify much because I already know I = current R = V = intention Resita.
Variable Resistance
These elements can vary its value in limits. To this was added a third terminal connected to a movable contact that can slide over the resistive element to provide variations in the value of resistance. The third terminal may have an angular displacement (rotary) or longitudinal (sliding). In his role at the circuit this resistance is called: Potentiometers: applied in circuits where the resistance change is made by the user from the outside (controls audio, video, etc.).
Trimmers or adjustable resistance, differ from previous ones in that the adjustment is final on the track where they are applied. Access is limited to technical staff (Gain, polarization, etc.)..
Rheostats: they are variable resistors in one of its end terminals is electrically bypassed. Both as a trimmer potentiometer, leaving one of its terminal ends to the air, its behavior is that of a rheostat, but these are designed to withstand high currents.
Features:
mechanical Tour: the displacement limit stop cursor points (endpoints).
Electrical Travel: is the offset you provide changes in the value of resistance. Often coincides with the mechanical travel.
nominal resistance (R n): expected value of variable resistance between the limits of the electrical circuit.
residual resistance to track (r f ) resistance between the upper limit of the electrical path of the cursor and contact B.
residual resistance from start of track (r d) resistance value between the lower limit of the electrical circuit and the contact.
total resistance (R t ): fixed resistance between the terminals A or A 'and B, regardless of the connection of the cursor and including tolerance. Although for practical purposes is considered equal to the nominal value (R t = R n).
contact resistance (r c) shows the cursor resistance between the external connection terminal and internal contact point (usually neglected, as d r r f).
nominal operating temperature (T n) is the temperature which defines the nominal dissipation.
Max Operating Temperature (T max): maximum temperature at which the resistance can be used.
Rated (P n): maximum power that can remove the device in continuous and nominal operating temperature.
maximum operating voltage (V max): maximum voltage (or AC RMS) that can be applied to the resistance between the end terminals for continuous duty at rated operating temperature .
Resolution: minimum amount of resistance that can be obtained between the cursor and end the move (or rotate) the cursor. Usually expressed in% in voltage, resistance, or angular resolution.
These resistors are characterized by ohmic value, which varies non-linear, depending on various physical quantities such as temperature , voltage, light, magnetic fields, etc. .. So these resistances are considered as sensors.
Among the most common are:
-thermistor or NTC and PTC resistors. In these, the resistance is a function of temperature.
-VDR Varistors or resistance. They resistance is a function of stress.
-Photoresistors or LDR resistance. The latter resistance is a function of light.
THERMISTOR
These resistors whose ohmic value changes with temperature, in addition to the features typical resistance linear fixed and nominal rated power, tolerance, etc.., which are similar to the thermistors, we note other:
Nominal strength: in these parts this parameter is set to an ambient temperature of 25 º C:
Self heating: this phenomenon causes changes in the value of the resistance to passing an electric current through it. Just keep in mind that also can be caused by a variation in temperature.
Thermal dissipation factor: the power to raise its temperature by 1 º C. Within we point out two groups thermistors: NTC and PTC.
VARISTOR
These devices (also called VDR) experience a decrease in its resistance with increasing the voltage applied at its ends . Unlike what happens with the NTC and PTC variation is an instant.
The most important applications of this component are in: surge protection, voltage regulation and transient suppression.
Photoresistors
These resistors, also known as LDR, is characterized by its resistance decreased with increasing light falling on them.
The main applications of these components, lighting controls, control circuit relays in alarm, etc. .. (This I use for the alarm)
is medium long but is quite comprehensive.
