Filament Circuits - Varian B-100 Manual De Instrucciones

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2. For a tube rated at 150 kVp, do two additional series of exposures at 140 kVp and 150 kVp. Exposures are to be
spaced approximately 20 seconds apart.
3. For a mammography tube rated to 49 kVp max. follow the above procedure but make exposures at 20, kVp, 35 kVp,
and 49 kVp.
4. If disturbances occur, repeat exposures at the kVp until they stop before raising to the next step. Make sure focal
spot rating is not being exceeded by consulting the focal spot rating chart prior to exposures.
1.8

FILAMENT CIRCUITS

A. Of the two types of filament circuits, the most commonly used is shown in Figure 1-1. The two filaments are connected
together at one end and to the focusing cup, thus forming a common lead. This lead and two more, one from each end of
the two filaments, are connected to the filament supply transformers through the three-conductor high voltage cable permitting
independent control of each filament.
B. The second circuit, Figure 1-2, is used for grid control of filament emission which permits pulsing the anode current of the
X-ray tube. Here the filaments are completely insulated from the focusing cup and connected to the filament supply
transformers through conductors in a four-wire high voltage cable. A negative 1,000 to 3,700 VDC grid voltage is
impressed between the focusing cup and the filaments for the purpose of controlling the tube current. A means of
cancelling this grid voltage is also provided (noted as a pulse generator in Figure 1-2). When the grid voltage is made
sufficiently negative with respect to the filaments, the tube current is cut off and no X-rays are produced.
1–6
X-RAY
PRODUCTS
FIGURE 1-1
X-RAY TUBE ASSEMBLY AND
INSTALLATION MANUAL