Theory of Operation—
DM 5010
measurement to any other
assigned
instrument on the
GPIB
bus.
The
DM 5010’s GPIB circuitry adheres to IEEE Stan
dard 488-1978 and will
be described later in this section.
Block Description
The following block description uses the Block
Diagram
in Section 10 at the rear of this manual. Each major block of
circuitry
is assigned a name according to its primary
func
tion.
The diamond numbers within a block represent the dia
gram^)
on
which
the complete circuit may be found. Only
the
basic interconnections between the
individual blocks are
shown.
As previously mentioned, the circuitry
of the DM 5010 is
divided into
two distinct sections, depending on how the
devices within
each
section receive their power. The block
diagram indicates the division between the Grounded
Sec
tion
and the isolated Section.
The
power for the circuitry in the Grounded Section is
derived
from the Grounded Power Supplies. These supplies
are
powered
from the TM 5000-Series power module and
regulated to meet
the requirements of
the DM 5010.
The power required for the circuitry in the Isolated Sec
tion is tranferred from the power module to the Isolated
Power
Supplies through
a transformer. The Transformer
Drive circuitry
switches the power-module current through
the transformer at a
frequency synchronized to the analog-
to-digital
conversion process to
minimize the noise error
caused by power supply ripple
in the Isolated Section.
Power
is transferred to the Isolated Power Supplies,
and
the
Isolated Regulators stage
regulates the power to the
levels
required by
the rest of the Isolated Section.
The Input Switch stage allows analog signals
from either
the
front panel or the rear
interface input to be
selected for
measurement.
The
selected input is applied to either the DCV Signal
Conditioner,
RMS, or
Ohms Converter circuits where the
applied
input
is
translated into a representative de voltage.
The
Range Control circuitry provides the gain and attenu
ation
switching
necessary to accommodate the
various
ranges of the RMS, DCV Signal Conditioner, and Ohms
circuits.
Depending on the mode of operation, the
de output from
either the
Input switch, RMS Converter, or Ohms Converter
is applied to the DCV
Signal
Conditioner as determined by
the Function Switch.
The Attenuator and DCV Signal Condi
tioner provide attenuation or
gain factors
and scale the input
signal
to
fall within
the A/D converters input range.
The A/D
converter
uses
a charge
balancing
conversion technique to
convert the applied analog de input to a corresponding digi
tal
equivalent.
As
the
conversion takes place, the A/D converter gener
ates a count direction
control signal defining
the input condi
tions. As this signal is generated, it
is transferred via an
opto-isolator to the Grounded Section and is
used to main
tain control of the on-going conversion.
The remaining opto
isolators transfer
control
information from the Grounded
Section
to
the Isolated Section
to
set
up the range
switching
and to
control the A/D conversion process.
The
microprocessor is the control center for all
activity in
the instrument.
It is a time-dependent device and most func
tional
blocks are synchronized to it, either directly or indi
rectly, shortly
after power-up. The Timing Logic, together
with
the
Control
Logic,
develops the proper time-dependent
logic signals for
the A/D
conversion circuitry on
both sides
of
the opto-isolators. The Timing Logic also drives the
Transformer
Drive
circuitry at a rate that makes the A/D
conversion most immune to power supply noise.
The Data circuitry consists of a
counter that keeps track
of
clock pulses under the direction of the count-direction
control
signal generated during
an A/D conversion. The sig
nal
originates in the A/D Converter in the
Isolated Section
and
is
passed through the opto-isolators and the Control
Logic to the
Data counter where it controls the count direc
tion of
an up/down
counter. From there, this binary-coded
counter data is transferrerd
one bit at a time onto the data
bus
via
the block labeled
Miscellaneous Buffer. This sequen
tial
data string, representing the conditions at the instru
ments inputs,
is read by the Microprocessor. Then the
processor
performs
the
manipulations necessary to bring
it
to the
desired format for display or
transfer over the GPIB.
With
the exception of some front-panel circuitry and a
battery circuit,
the remainder of the circuitry in the instru
ment is
directly connected to the microprocessor’s address
or data busses.
The Address
Decode and Logic circuits
decode certain
addresses or
groups of addresses output from the proces
sor
on its
address bus. When output by the processor, they
enable
specific blocks
of
circuitry to communicate with
the
processor.
There are
many discrete enabling
lines involved
with
the
Address Decode;
they are shown on the Block Dia
gram
as being returned back onto the address
bus. These
enable lines
may be thought of as an extension of the
ad
dress
bus.
Due to the multiplicity of devices requiring micro
ADD
JAN
1982
4-3
Summary of Contents for DM 5010
Page 14: ...DM 5010 2994 00 DM 5010 Programmable Digital Multimeter xii ADD JUL 1986...
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