1. Common Faults Which Occur in: - Coggle Diagram
1. Common Faults Which Occur in:
The most common problems to occur with fixed resistors are a change in resistance or a complete failure. A complete failure occurs when the resistor overheats and burns out. When the resistor interior is burned out, it produces an open circuit.
Burned out resistors are often caused by the failure of some other component in a circuit causing an excess of current. A cold solder joint can also cause an open circuit.
The internal composition of resistors make an internal short-circuit nearly impossible. However short circuits can occur on printed circuit boards or at the connections of resistors.
The failure in capacitors can manifest itself as slow degradation in performance or complete failure of the capacitor
The degradation in performance results in:
Gradual fall in insulation resistance or rise in leakage current
Increase in dissipation factor (rise in series resistance or dielectric losses
In case of a complete failure of the capacitor, the capacitor will have either:
Open circuit due to end connection failure; or
Short circuit due to dielectric breakdown
The failure in capacitors could
be due to the following reasons:
Mechanical shocks and vibration
Poor assembly technique
Subjecting the capacitor to voltage beyond its stated capability
Manufacturing imperfection: ---
Impurities in electrolytic
Mechanical damage to the end spray of metalized capacitors resulting in overheating and open circuit
Potentiometers exhibit a higher failure rate than fixed resistors. This is because they not only jointly have moving parts but also depend for their operation on a good and reliable electrical contact between a wiper and the resistance track
Usually manifests itself in the open circuit either between the wiper to track or track and the end connections. This can be caused by:
Corrosion of metal parts by moisture
Swelling and distortion of plastic part (track moldings) by moisture or high temperature
Partial failure of a potentiometer results either in rise in wiper contact resistance giving higher electrical noise or an intermittent contact. This is caused by particles of dust, abrasive matter or grease trapped between the wiper and track
A bad potentiometer due to contact problem will give sufficient indications like noise in an audio circuit, irregular behavior of the controlled parameter, etc.
The heat from excessive current through a winding can cause the wire to burn out, or a break can occur where the wire had been nicked or scraped. An ohmmeter connected across the terminals of an open winding will show infinite resistance
Occasionally the insulation on the winding may melt because of overheating, causing the turns to short to each other. The inductor then has a resistance close to zero ohms. Again, an ohmmeter can detect this fault once the inductor is removed from the circuit
Partially shorted winding
Sometimes overheating or physical damage causes just a few adjacent turns to short together. Such partial shorts reduce the resistance of the inductor somewhat, but the difference may be difficult to detect with an ohmmeter
A more accurate test can be done with an LC meter, which measures the inductance and capacitance of a component directly
LDRs are made of cadmium sulphide
They contain very few free electrons when kept in complete darkness and therefore exhibit very high resistance
When subject to light, electrons are liberated and the material becomes more conducting
When the light is switched off, the electrons are again recaptured and the material becomes less conducting or insulator
in the dark and at low light levels, the resistance of an LDR is high and little current can flow through it
in bright light, the resistance of an LDR is low and more current can flow through it
The most common failure mode of a thermistor is an open circuit
The cause of such failures are usually due to mechanical separation between the resistor element and the lead material, caused by handling damage, excessive heat, thermal mismatch, etc.