Service manual
PN 4237242C
2.5-1
INSTRUMENT DESCRIPTION
DATA ACQUISITION
2
2.5 DATA ACQUISITION
The data acquisition section is responsible for the accumulation and measurement of system
data that is used to determine final system output (instrument results). The data acquisition
section includes the:
r Sensor Preamp Adapter (SPA) card
r Hgb Preamp card
r Vacuum Sensor card
r SPAD card.
Sensor Preamp Adapter (SPA) Card
The Sensor Preamp Adapter card is located in the lower chassis (Figure 2.2-2) and has three
distinct circuits:
r The Preamp circuit
r The Dc Restorer circuit
r The High-gain Stage circuit.
Signals are input from the RBC and WBC aperture sensors in the form of current pulses.
These pulses are preprocessed by the Sensor Preamp Adapter card and then passed on to the
SPAD card for further processing.
The first stage of the Sensor Preamp Adapter card is the Preamp circuit. This circuit provides
a constant current source for the aperture system, and changes in aperture resistance produce
voltage pulses. In effect, the Preamp is a current-to-voltage converter that senses changes in
the current source it provides and passes voltage pulses to the Dc Restorer circuit. An aperture
zap of ≈200 V, supplied by the Linear Power Supply card, is applied through this stage to
dynamically clean the apertures.
The Dc Restorer circuit receives these voltage pulses and provides the proper dc offset
required by the SPAD card. This circuit ensures that the voltage output will always be
positive.
The last stage of the Sensor Preamp Adapter card is a times-eight signal conditioner, which
produces a suitable signal amplitude to pass on to the SPAD card.
Input connections for the Sensor Preamp Adapter card are summarized in Table 2.5-1, output
connections are summarized in Table 2.5-2, and jumper settings are summarized in
Table 2.5-3. Figure 2.5-1 shows jumper locations and settings and the location of input and
output connectors.
Inputs
Table 2.5-1 Sensor Preamp Adapter Card Input Connections
Connector Description
J1 High voltage supply
J2 Analog power entry (from Linear Power Supply card)
J7 Diagnostics
J8 WBC APERTURE signal
J10 RBC/PLT APERTURE signal
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