DATA PRECISION 1350 User Manual

62-5008 MODEL 1350
4.6 DISPLAY
The display is driven directly by inverted outputs of A/D Converter Z2.
Since the A/D outputs are active low the inverted signals are active high
to drive the cathode of each display segment. The display components for
the 3 digits have internal current limiting circuitry, eliminating the need for
external current-limiting resistors. Additional current limiting for the MSB
"1", and polarity sign are provided through external resistors. All returns
from the display digits are brought to digital ground through CR16 which
introduces a 0.7 volt drop in the path and further reduces the current
through the display to safe levels.
4.7 POWER SUPPLY
a. The power supply for the Model 1350 DMM converts line voltage input
into rectified and regulated dc levels of -i- 5V, - 5V, Digital Ground, and
Analog Common. Note that Analog Common, which is the return for cur
rent shunts, voltage attenuators, AC/DC converter and A/D converter, is
not at the same level as the Digital Ground, which is the return for display,
display drivers, and digital section of the A/D IC. The Analog Common is
regulated by the A/D chip and is nominally 2.8 volts less than the -i- 5V rail.
Hence the 2.2 volt difference between Analog Common and the Digital
Ground reference for the -i- 5V. Refer to the fold out reference schematic
for design details described below.
b. Transformer T2 supplies current through full wave rectifiers CR11 and
CR12 to charge C16 and provide unregulated voltage to the negative 5V
volt regulator, Z7. CR13 conducts during the half cycles when CR12 is off,
charges C1 and provides an unregulated negative voltage at its anode.
Z7 is a 5 volt negative regulator which sources digital return at 5 volts
down from the positive rail. The display and drivers operate between digi
tal ground and the positive rail. CR14 Is a shunt regulator which smooths
the negative rail, and regulates it at 6-7V below digital return, or equiva-
lently 11-12 volts below the positive rail.
c. Z1A is a reference diode regulator. It obtains power from the positive
and negative rails. Z1A operates by measuring the difference between its
attenuated output at A1 pin 7, and the attenuated reference diode voltage
at A1 pin 5, and by forcing that difference to be zero. The result is a highly
regulated voltage at Z1A pin 1, and therefore, regulated current to CR15.
The anode of CR15 is regulated at 6.4 volts down from the positive rail,
and Z1A pin 1 at 7.5 volts down from the positive rail. The 7.5 volts at Z1A
pin 1 provides a convenient highly regulated supply from which the A/D
converter Z2 is operated.
©
Copyright 1977. Data Precision Corporation. All rights reserved.
4-9

DATA PRECISION 1350 Specifications

General

Brand	DATA PRECISION
Model	1350
Category	Multimeter
Language	English