MM0474
e. The self-balancing bridge and the reference generator supplied as a
unit have the same serial numbers. These may be found engraved upon the back
panels. In addition, this number is engraved on each of the printed circuit
boards used in the instruments.
f. Specification for the NBS Type II Bridge are found in Table 1A and 1B.
3.
LOCATION AND FUNCTIONS.
a. The NBS Type II Power Measuring System is a standards laboratory
in terms of substituted DC power. The instrument is not direct reading; the
power must be calculated, generally using data obtained from an external
precision voltmeter, but usually at reduced accuracy. The system is intended
for use with non-temperature compensated bolometer mounts.
These may have
either a coaxial or waveguide input and contain a thermistor or a barretter as
the bolometer element. The frequency and power range covered depends upon the
bolometer mount used.
In general the power level will not exceed 10
milliwatts. The unit may also be used as a precision power stabilizer. The
following paragraphs contain the information necessary to operate the unit.
b. Rear Panel Controls: (Figure 2).
(1) THROUGH (3)
Q407, Q715, Q714.
These are the reference designations of the
transistors fastened to the other side of the panel. The rear panel is used as
a heat sink for these semiconductors.
(4) CONNECTING CABLE.
A 20 conductor cable and connectors supplying
power and other necessary connections to the reference generator unit from the
bridge unit. The connectors are removed by turning the knurled actuating screw
in the center of the connector until the connector is free.
(5), (6)
Q111 +15 V, Q111 -15 V.
These are the locations of the two
identical pass elements for the two P100 power supply boards.
(7) LINE FUSE.
This is a 1/4 amp slow-blow fuse.
(8) POWER CORD INPUT.
The line cord supplied with the instrument should
be used.
(9) CIRCUIT COMMON.
This terminal is connected to the front panel
terminal 4.
The bridge and reference generator circuits may be disconnected
from the power line ground by removing the link connecting this point with
terminal 10.
101
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