Medrad ProVis Mark V, Руководство по обслуживанию

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Mark V ProVis Injection System
10 - 4
Trigger Comparator,
SCR Controller
U5B, Q8 Trigger Comparator U5B uses the summed Error, or load profile, sig-
nal and ramp wave-form to determine at what point in the sine-wave
the SCR bridge is fired. In standby, input to U5B is a negative voltage
(-2 to 0 volt integration from U5C), thus output of U2D is negative sat-
uration, and Q8 is off.
During injection, or when forward or reverse loading, the DC signal
raises the ramp wave-form input to U5B above zero volts, causing
output of U5B to enter positive saturation, making Q8 conduct. Q8
provides a ground path for +26 volts (through R27, R28, and Q8),
which creates a positive to negative transition on the primary of pulse
transformer T1. The pulse transformer is connected, to invert the
polarity of the secondary, creating a negative to positive pulse to fire
the SCR bridge. The duration of the pulse is determined by C4, R28,
and the primary of T1.
Full Error Trigger
Q9 The Full Error Trigger will fire the SCR bridge if a large, instantaneous
Error signal does not allow U5B to trigger the SCR bridge. In order for
Trigger Comparator U5B and the SCR Controller to fire the SCR
bridge, input to U5B must be allowed to go below zero. If the Error sig-
nal is too large, input of U5B stays above zero, consequently, output is
held in positive saturation. When this occurs, positive pulses from
Zero Crossing Detector U4D will make Q9 conduct. This transition
momentarily resets SCR Controller Q8, to enable the next positive
output from U5B to fire the SCR bridge. Pulses will continue to reset
the SCR controller until the Error signal drops to a value which allows
U5B to take over.
Transistor Q9 is used to ground trigger pulses (remove base voltage
to Q8) if a SYSTEM OVERRIDE (D8 and D9), AUX MONITOR (D10
and D9), or overrate injection (D11 and D9) occurs.
Delinearizing
Network The circuit comprised of R75, R87, R88, R107-110, D26, D27 and
C10, increases drive circuitry sensitivity to small error signals, and
decreases sensitivity to larger error signals.
Power Output Stage AC power from the power transformer is applied to SCR bridge Z1.
The output of the bridge, controlled by gate pulses from the SCR con-
troller, is filtered by C3 (on DRCI). The SCR bridge is protected by an
internal MOV across the AC input. SCR Bridge output is spike pro-
tected by MOV Z2, while direction of motor rotation is controlled by
Reverse Relay K2. Motor current is sampled for the pressure circuits
and the Overcurrent Shutdown circuit by Sampling Resistor R4 on the
DRCI.
Pressure Signal Filter
U1C U1C is a non-inverting, low-pass filter that eliminates 50 and 60 Hz
oscillations from the Motor Current signal.