Chapter 6 - X-Ray Circuit and Tube Heat Management

Question 1

X-Ray Circuit

Answer 1

the x-ray circuit is divided into three sections or subcircuits: the low-voltage circuit, the filament circuit, and the high-voltage circuit.

Question 2

Low-Voltage Circuit

Answer 2

It is the subcircuit between the alternating current (AC) power supply (1) and the primary (input) side of the high-voltage (step-up) transformer (7). With the exception of the step-up transformer, all of the devices in this subcircuit are actually located within the control console. The control console is the unit where the operator sets all of the exposure techniques, such as kilovolts peak (kVp), milliamperes (mA), and exposure time. They include the (1) AC Power Source, main switch (2), autotransformer (3), kVp selectors (4), exposure switch (5), and exposure timer (6), Primary for step-up transformer (7), Contacts for autotransformer (9)

Question 3

Filament Circuit

Answer 3

This circuit is divided into two parts by the step-down transformer (11 and 12). The primary purpose of the filament circuit is to supply a low current to heat the x-ray tube filament for thermionic emission of electrons. The filament circuit is activated any time the operator adjusts the mA on the generator. The primary side of this circuit begins and ends with the contacts on the autotransformer (9). Current in this circuit flows from the autotransformer, through the mA selector (10) and the primary side of the step-down transformer (11), and back to the autotransformer. The secondary side begins and ends with the secondary side of the step-down transformer (12) conducting current through the x-ray tube filament (13). The step-down transformer reduces the voltage on the secondary side, providing an appropriate current to heat the filament.

Question 4

High-Voltage Circuit

Answer 4

This circuit begins and ends with the secondary side of the step-up transformer (8). It includes the x-ray tube (14), Milliammeter (18) and Rectifier (15). This is a dangerous circuit because of the very high voltage. The high-voltage cables going to the x-ray tube age very thick because of their high insulation requirement (Fig. 6.4).
The primary purpose of the high-voltage circuit is to supply the x-ray tube with voltage high enough to create x-rays.

Question 5

heat units (HU)

Answer 5

Single phase:
HU = mA X Time X kVp

Three phase:
HU = mA X Time X kVp X 1.35

High frequency:
HU = mA X Time X kVp X 1.40

Question 6

Extending X-Ray Tube Life

Answer 6

*Warm up the anode according to the manufacturer’s instructions.
*Do not hold down the rotor switch for long periods of time.
*Use low mA settings whenever possible.
*Use the low-speed rotor whenever possible.
*Do not make repeated exposures near the tube limits.
*Do not use a tube when you can hear the rotor bearings (call a service engineer).