Lecture 4

Question 1

1. How is electrical supply for a fixed x-ray unit obtained?
2. For protection against overload, what is incorporated into the switch system for mobile/fixed units and portable units?
3. Highly rated units are required to give what type of exposures (heavy or light)?

Answer 1

1. By connecting it to the output of a mains isolator.
2. Mobile/Fixed units: electromagnetic circuit breaker; Portable Unit: cartridge fuse or thermal circuit breaker
3. Heavy

Question 2

1. Under high exposure conditions, why is protection against overload needed for the voltage generator?
2. Give 3 benefits of an electromagnetic circuit breaker.

Answer 2

1. Because the voltage generator will draw very high currents
2. Quick and easy reset mechanism; precise method of setting up; quicker response to heavy overload

Question 3

1. What is the function of the electromagnetic circuit breaker?
2. The electrical supply for the unit passes through the box from the _____ to the _____.

Answer 3

1. It allows the radiographer to safely turn on/off the x-ray unit; as well as acts as a circuit breaker should an overload occur.
2. mains isolator; control unit

Question 4

1. The conductors supplying the unit are connected through ___ switches (how many?) which are closed. The switches are kept closed by what?
2. What does the solenoid control?
3. Why is the “holding” contact essential to the operation of the unit?

Answer 4

1. 2; solenoid
2. the on & off buttons
3. It allows the operator to remove pressure from the “on” switch without causing the unit to turn itself off.

Question 5

When the operator pushes the “on” button the solenoid is ______. When the operator pushes the “off” button, it causes the solenoid to ______.

Answer 5

energized; cease

Question 6

The operation circuit is usually protected by what type of fuse?

Answer 6

Low value fuse (5A)

Question 7

How do compensating devices operate to ensure a stable output?

Answer 7

They compare the incoming voltage to a predetermined (nominate) voltage; then adjusts the output voltage (whether up or down) to make it equal to the predetermined (nominate) voltage.

Question 8

1. What is the purpose of the line resistance compensation unit?
2. What are the 2 types of line resistance compensators.

Answer 8

1. To bring the total line resistance value at the input point to a point specified by the manufacturer
2. Simple for the permanently fixed unit; more elaborate one for the mobile unit

Question 9

For the permanently fixed unit, a simple variable resistor is connected in ____ (parallel or series) with the _____ unit.

Answer 9

Series; x-ray unit

Question 10

Give 3 functions of the auto-transformer.

Answer 10

1. Compensation for changes in the main voltage
2. Provision of a kVp meter
3. Provision of voltage for tube filament current