HP 5501A Operating And Service Manual page 103

The 10781A Pulse Converter (Figure 3-7) converts the measurement and reference signals to
pulses that can be counted by an external counter. The output consists of up/down or A-Quad-
B pulses of IM-wave length value. Refer to the unit manual for additional information and
specifications.
10780A
Receiver
Laser Beam
_
~ o ~ p t i a
I
Reference Sisnal
b
Measurement Signal
UpIDovm or
Aauad-B
Pulses to
External
Equipment
10780A
Receiver
10781A
Pull9
Converter
10781A
Pull9
Converter
Figure 3-7. 70781A Pulse Converter Electronics Block Diagram
3.10 DETAILED THEORY O F OPERATION
The detailed theory of operation is subdivided a s follows:
a. 5501A Laser Transducer.
b. 10780A Receiver.
c. 10740A Coupler.
d. 10745A HP-IB Interface.
e. 10746A Binary Interface.
f. 10760A Counter.
g. 10762A Comparator.
h. 10764B Fast Pulse Converter.
i. 10761A Multiplier.
j. 10781A Pulse Converter.
k. 10763A English/Metric Pulse Output.
1.
10755A Compensation Interface.
m. 10756A Manual Compensator.
n. 5510A Opt 010 Automatic Compensator.
o. 10783A Numeric Display.
p. 5501A Power Supplies.
3.11 5501A Laser Transducer
The 5501A Laser Transducer (laser head) i s the source of the laser light for the system. The
laser head package meets the NEMA-12 standard for industrial packages. Figure 3-8 is the
laser head block diagram.
The laser tube has the advantages of very long life-time, instant-on service, and automatic
tuning. I t is a two-frequency laser source; that is, the laser beam contains two components at
slightly different frequencies, polarized at right angles to each other. The frequency split is
about 2 x 106 Hz, compared to the laser frequency of some 1014 Hz, and is produced by an
axial magnetic field which causes Zeeman splitting in the energy levels of the laser medium
(helium-neon gas).