SM0486
A connecting rod.
(2) The moving element assembly is mounted in the body structure so that
the two rod-connected coils are centered in the annular air gaps of the two
permanent magnets. The two flexures serve to position the coils and to constrain
the reciprocating movement of the element assembly.
b. Electric Panel Assembly.
The electric panel assembly is
equipped to
provide the following:
An alternating electric current to the driver coil.
Amplification of the signal from the generator coil.
Control of the amplitude of vibration produced at the exciter table.
Amplification of the electric signal received from the vibration pickup
under test.
A means of comparing the signal voltages of the vibration pickup and the
signal generator.
c. Operating Theory.
Figure 5 will help you to understand the operating
principle of the calibrator.
(1) Locate the AC input on the circuit, you can see that the 115-volt input
power is applied to a transformer containing two secondary coils.
The first
secondary reduces the input voltage to 3.5 volts AC, which is used to energize the
driver coil of the calibrator's moving element.
The remaining secondary coil
raises the input voltage to 125 volts. Leads from this secondary are wired into a
selenium rectifier and voltage-doubler circuit which produces 250 volts B+ supply
for the amplifier circuit.
(2) The operation of the PC1-A exciter mechanism and its signal generator
is based upon fundamental principles of electromagnetic theory.
Alternating
current, at 3.5 volts, is passed through the driver coil of the moving element from
the transformer.
This current creates an alternating magnetic field around the
driver coil.
Because the driver coil is located in the air gap of a strong
permanent magnet, an interplay of magnetic forces takes place whenever the driver
coil is energized.
The alternating characteristic of the flux field around the
coil, reacting against the permanent magnet field, imparts a reciprocating movement
to the driver coil so that it moves in and out of the permanent magnet air gap
within the limits imposed by available voltage.
116
Previous Page
