Theory of Operation
732B Circuit Description
4
4-5
Model 734A Functional Description 4-3.
Model 734A consists of four 732B DC Standards installed in a Model 734A-7001
Instrument Enclosure. The 734A-7001 enclosure contains four internal IEC-type ac line
cord connectors and one rear panel IEC-type ac line cord connector. When you slide a
732B or 732B-7001 into one of the instrument bays in the chassis, it automatically
connects to the ac power bus. The 734A-7001 Instrument Enclosure provides an ac line
power bus only. There is no fuse in the 734A-7001. All fusing and line voltage selection
is done in the installed 732Bs and 732B-7001s.
Model 732B-7001 External Battery/Power Supply 4-4.
Model 732B-7001 is a companion battery and charger for use with the 732B when the
there is a requirement for more than 72 hours of portable (battery) operation. The 732B-
7001 contains the same battery charger assembly (A5) and gelled-electrolyte sealed lead-
acid battery as the 732B. Theory in this section pertaining to the 732B DC Standard’s
battery charger also applies to Model 732B-7001.
On the 732B-7001, there are no front panel binding posts, and there is no IN CAL
indicator. On the rear panel, there is no CAL RESET hole, and the connector labeled
MONITOR/EXT BAT IN on the 732B is labeled BAT OUT. For rear panel BAT OUT
connector pinout, refer to Figure 3-8 in Section 3.
732B Circuit Description 4-5.
Circuits in the 732B are described to the component level in the rest of Section 2 in the
following order:
1. 10V Reference Circuit
2. A4 Oven Assembly
3. A5 Power Supplies and Battery Charger
4. A1 Front Panel Assembly
10V Reference Circuit 4-6.
Refer to Figure 4-2, the block diagram of the 10V reference circuit. Components that
make up the 10V reference circuit are located on the following four assemblies:
• Reference Hybrid (HR1)
• Oven (A4)
• Flex Circuit (A2)
• BCD Switch (A3)
The Reference Amplifier situated on the HR1 hybrid is the most critical part in the 732B
because it forms the basis for the 732B’s exceptional stability specification. It consists of
an NPN transistor in series with a zener diode. When biased properly, the combination
has a very low temperature coefficient.
The reference voltage that the Reference Amplifier generates can vary from 6.5V to 7V
from device to device. The 10V output will drift in response to the Reference Amplifier
voltage drift by the same amount when expressed in ppm. For example, if the Reference
Amplifier has a linear drift rate of 0.1 ppm per month, then its effect on the output will
be to cause the 10V output to drift 0.1 ppm per month. The Reference Amplifier is
located on the Reference Hybrid (HR1) and is identified by the reference designator U4.
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