Valhalla 2300, Operation Manual

Page: 77 / 115

being over-driven (inputs voltage or current
limits are exceeded), the pulses will be
interrupted.
The pulses from IC103 continually trigger the
two sections of IC11. External timing
components R56-C13, R57-C14 set the period
of the one-shots slightly longer than the
period of the input pulses. As long as the
pulses continue, the one-shot outputs will
remain high. If the pulses stop, the one shot
output goes low which illuminates the front
panel peak overload LED's.
10-3-7. V-A-W Ranging
The schematic for this section is shown on
2300-071 sheet 1. The ranging circuits are
composed of IC's 5-8 and their associated
components. The voltage, current, and power
signals from the receivers are applied to
resistor strings R10-R16, R17-R25, and R26-
R42. Taps from the resistor strings are
selected by analog multiplexers IC5-7. The
multiplexer outputs are applied to the A to D
converter inputs for display. The voltage and
current outputs of the receivers are
approximately 5 volts full scale for all ranges.
The power output may be 0.75 volts, 2.5
volts, or 5 volts full scale depending on the
voltage and current range selected and
whether a single or three-phase display is
selected.
The A to D converters require 1VDC input for
a display of 10000. The taps on the resistor
strings attenuate receiver output voltages to
the values required for a full scale display.
10-3-8.
Power Supplies
The schematic for this section may be found
on sheet 2 of 2300-071. The chassis
referenced circuits in the 2300 (main board,
display board, and IEEE-488 board) are
powered by the earthy supplies composed of
transformers T1 and T2 and their associated
components. Each transformer has two
primary windings that are connected in series
for 240 volt operation or parallel for 120 volt
operation.
The secondary of T1 is rectified by diodes
CR1-CR4 and smoothed by capacitors C1 and
C2. IC's 1 and 2 regulate the raw DC voltage
providing regulated ±15VDC. The ±7.5VDC
rails are provided by resistive dividers R1 to
R4. The secondary of T2 is rectified by
diodes CR5 and CR6 and smoothed by C5.
IC3 regulates the raw DC providing the
+5VDC rail.
Each signal processing PCB is powered by its
own separate floating supply. All three
supplies are identical therefore only the phase
A supply will be described. The secondary of
T101 is rectified by diodes CR101-CR104
and smoothed by C101 and C102. IC's 101
and 103 regulate the raw DC voltages
providing the floating ±15VDC rails.
10-3-9. A to D Converters and Displays
The schematic for this section may be found
on 2300-072, sheets 1-3. The operation of the
voltage, current, and watts A to D converters
are the same. Only the voltage A to D
converter will be described. The A to D
converter is comprised of IC's 1, 2, and 3, and
their associated components. The A to D
clock is provided by IC4 which is common to
all A to D's and has an output of 100KHz at
pin 8.
The operating cycle of the dual-slope
integrating A to D converter is divided into
three stages whose duration is set by the
clock. During the first, or auto-zero stage, the
analog input is internally shorted to analog
ground and C3 is charged to the integrator's
output offset voltage. This is connected to the
integrator's non-inverting input which
subtracts from the analog input, cancelling the
offset.
During the second, or input-integrate
stage, the input voltage is connected
to the integrator and IC2 integrates