flowing per second in a circuit. In a simple series circuit, the current flowing through all
points in the circuit is the same. Since the ammeter is used to measure all the current
flowing in a circuit, it must be connected in series in that circuit--that is, directly into the
d. In most equipment, the milliamperage meter can be converted to a ballistic or
milliampere-second (mAs) meter. The conversion is accomplished by eddy current
damping of the moving coil. By setting up eddy currents (counter EMF) in the moving
coil, we can cause it to assume a high degree of inertia which causes the pointer or
indicating needle to deflect slowly so that it registers a value equivalent to the
milliampere-seconds (mAs). The ordinary moving-coil milliammeter does not have
sufficient time to register the true mA at 1/2-second or less intervals. For very rapid
exposures where high milliamperage is being used, the mAs meter gives a far more
accurate reading than the milliammeter. At exposure times of greater than 1 second,
the ordinary milliammeter will give an accurate reading.
a. For the production of x-rays, extremely high voltage is required. A
transformer can be used to increase or decrease voltage with little loss of energy.
Using the principle of mutual induction, the transformer transfers electrical energy from
one circuit to another via an electromagnetic field.
b. In its simplest form, the transformer consists of a primary coil placed close to
a secondary coil. The two coils are completely insulated from, and they lie parallel to,
each other. This type of transformer is an air core transformer (figure 2-16). The
primary coil (input side) is the one into which AC is introduced; the secondary coil
(output side) is the one in which AC is developed by mutual induction. When AC flows
in the primary winding (coil), it sets up an alternating magnetic field that expands about
the coil and collapses each time the current changes direction. An alternating
expanding and contracting magnetic field sweeps back and forth through the secondary
winding inducing an EMF in the secondary coil.
Figure 2-16. A simple air core transformer.