Valhalla 2300 Operation Manual - page 75
10-2-9.
A to D Converters and Displays
The three A to D converters convert the
analog voltage, current and power signals into
digital data for display. The A to D
converters are of the dual slope integrating
type.
10-2-10. Control
Logic
This stage accepts inputs from the keyboard
and IEEE interface to control the 2300 ranges.
This stage also drives the front panel LED's.
10-2-11. Keyboard
The front panel push-buttons are scanned by
the keyboard circuitry. Key data is sent to the
control section for range and display
selection.
10-2-12. IEEE
Interface
The IEEE interface contains the circuitry
necessary to control and read the 2300 via the
IEEE-488 bus.
10-3. Detailed
Descriptions
The paragraphs that follow use the same
functional blocks as used in 10-2, but give full
detail on operation down to component level.
Throughout this section, it is assumed that the
reader has a knowledge of electronics and is
familiar with the operation of the 2300 from
the front panel.
10-3-1.
Current Amplifier
The schematic for this section may be found
on drawing number 2300-070. IC1 is a
differential four input analog multiplexer.
Pins 9 and 10 are binary control lines
selecting which pair of inputs are connected to
the outputs. The current shunts are connected
across the inputs to IC1. Pins 1 and 12 are
connected across the 1 amp shunt, pins 5 and
14 across the 10 amp shunt, and pins 2 and 15
to the 100 amp shunt. Resistive networks R5-
R6, R7-R8 are used to compensate for the
resistance tolerance of the shunts. The
outputs of IC1 are applied to the amplifier
stage composed of IC's 2 and 3 and their
associated components.
The gain of the stage is determined by the
ratio of R11 and the series combination of
R16 and R17. When different current ranges
are selected, relays K1 and K2 are energized.
Series combinations R12-R13 and R14-R15
modify the gain so that the output of IC2 is
always 5 volts RMS at full scale of the range
selected.
IC3 is connected as a unity gain follower
buffering the output of IC2 from the RMS
converter, current peak detector, and power
multiplier.
IC10 and its associated components form an
RMS-to-DC converter. Its output is a DC
voltage which is equal in value to the RMS
AC voltage input. If the RMS converter or
multiplier are operated outside of their range
of input levels, inaccurate readings may result.
To prevent this source of error, peak
comparator IC5 monitors the output of IC3. If
the peak exceeds the limits set by R33 to R36,
opto-isolator IC6 is activated, which in turn
drives the front panel mounted peak overload
LED.
10-3-2.
Voltage Amplifier
The schematic for this section may be found
on 2300-070. The voltage amplifier is
composed of IC4 and its associated
components. The measured voltage is
attenuated by resistors R21-R23 to levels
compatible with IC4. The amplifier's gain is
set by the ratio of R24 to the series resistor
combinations selected by relays K3-K5. With
all relays de-energized the gain of the stage is
unity. Series combinations R29-R30, R27-
R28, R25-R26 modify the gain so that the
output of the stage is always 5 volts RMS at
full scale of the range selected.