ELECTRICAL SAFETY DEVICES 2 Flashcards
How do fuses, circuit breakers, and interlocks protect radiography equipment?
- They protect circuits and components from damage due to higher current than design allows.
- Fuses are short lengths of wire in series in a circuit, breaking continuity if an abnormal high current occurs.
- Circuit breakers and interlocks prevent overload currents.
What is the basic function of a circuit breaker?
- To interrupt current flow to protect equipment
- Prevent the risk of fire by breaking the continuity of a circuit when an overload current or short circuit occurs.
What is the function of a fuse in radiography equipment?
- A fuse is the weakest part of the circuit, protecting components from overload by melting and breaking the circuit if excess current flows.
- Each electrical component is rated for maximum current and voltage it can withstand.
- Fuse wire is rated for maximum current it can carry before melting (e.g., 5A, 10A, 15A).
How does a circuit breaker work?
It works on the switching principle by either electromagnetism or thermal expansion, depending on the type, and is placed in series with the circuit it is protecting.
What are the two main types of circuit breakers?
- Thermal circuit breaker
- Electromagnetic circuit breaker
What is the principle of operation for a thermal circuit breaker?
- It operates based on the coefficient of linear expansion of a bimetallic strip, which bends when heated, causing a contact to open and break the circuit.
How does an electromagnetic circuit breaker prevent transient rises in current from switching off the circuit?
Movement of the metal core into the coil may be impeded by pressure of oil in a small dashpot, ensuring only a sustained rise in current will operate the trip mechanism.
How does a bimetallic strip work in a thermal circuit breaker?
When heated, the two metals with different coefficients of linear expansion bend, causing the strip to bend and open a contact, breaking the circuit.
What is the principle of operation for an electromagnetic circuit breaker?
- It relies on the magnetic effect of a current-carrying conductor.
- Excessive current causes a magnetic field that draws a moveable metal core into the coil, operating a trip mechanism to open the circuit.
What is the function of interlocks in radiography equipment?
- Interlocks break the circuit when an unsafe situation arises.
- They prevent the machine from harming its operator, a patient, or damaging itself.
- Ensure actions cannot take place until permitted by another controlling unit.
What are the key differences between a fuse and a circuit breaker?
-
Fuse:
Simple design
Small size and easy to understand
Standalone device that detects and interrupts on its own
Very small operating time
Inexpensive
Requires replacement after operation
Circuit Breaker:
Complex design
Larger size and complex working
Requires a relay system for proper working
Larger operating time compared to a fuse
Expensive
No replacement required
How do interlocks operate in radiography equipment?
- Interlocks can be electromechanical or purely electronic using circuit boards or microcomputers.
- One piece of equipment exerts pressure on a microswitch in another piece of equipment’s circuit.
- The microswitch “makes” or “breaks” the continuity of the second circuit.
What are some examples of interlock circuits in radiography equipment?
- Exposure interlock circuit
- Electrical safety interlock circuit
- Mechanical interlock circuit
- Radiation safety interlock circuit
- Initial delay circuit
- X-ray tube filament circuit
- Anode stator supply circuit
- X-ray tube overload circuit
What is the purpose of the exposure interlock circuit?
- Controls the “make” and “break” of the exposure contactor, thereby controlling the production of X-rays and the loading of the tube.
- Ensures all components are operating correctly before an exposure can take place.
