Medrad ProVis Mark V, Service Manual

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Mark V ProVis Injection System
10 - 6
Auxiliary Monitor
U2C The AUX MONITOR circuit will shut down the PDCI if either of the fol-
lowing conditions exist: Excessive current flowing through the motor;
Actual motor speed is greater than the selected flow rate. U2C, with
diode D14 in the feedback loop, acts as a latch circuit. When either
above stated conditions occurs, output of U2C goes positive, forward
biasing D14, and feeding positive voltage to the non-inverting input
(latching U2C positive). An AUX MONITOR will: Disable pulses to the
SCR bridge through D8, D9, and D10; Disable the Safe Relay Enable
(SAFRELEN) through Q6; Activate the brake through D8 and D2;
Send a signal to U16 (PIO3) on the SCC to interrupt the CPU and ter-
minate the injection.
Excessive Motor Current:
The inverting input of U2C receives the motor current signal from
Motor Current Amplifier U1D. Normally, this input is used to decrease
the sensitivity of U2C at the beginning of an injection, thus preventing
false Aux Monitor indications caused by initial motor voltage and cur-
rent requirements at the beginning of an injection. As motor current
increases, the inverting input goes negative (eventually to the point at
which U2C output becomes positive). When this occurs, U2C will
latch, shutting down the PDCI, sending a signal to U16 (PIO3) on the
SCC (prompting the system to terminate the injection).
Excessive Motor Voltage:
The non-inverting input to U2C receives the output of Brake Compara-
tor U2D. Input to U2D is Overrate Detector U2A which senses if motor
speed is greater than the selected Flow Rate. If an overrate is
detected by U2A, U2D will send +15 volts to the non-inverting input of
U2C, making its output positive. When this occurs, U2C will latch,
shutting down the PDCI, sending a signal to U16 (PIO3) on the SCC
(prompting the system to terminate the injection).
Forward/Reverse
Loading Circuit
U3, U4B, U4C, U5D The Forward/Reverse Loading circuit develops a load profile voltage
which is summed with the output of Ramp Generator U5C, to trigger
the SCR bridge and produce a drive voltage for the plunger motor.
Plunger pressure and velocity when loading are controlled by Error
Amplifier U5D.
Forward or Reverse loading sends a voltage that ranges from +7.9-
12.9 volts (slow to fast). This voltage is sent to U4C (clamping by D20
not required), generating a negative load profile (-1.5 to -6.5) which is
inverted by Error Amplifier U5D to produce an error signal. This signal
is summed with the Ramp Generator output to trigger the SCR bridge.
Ten Volt Regulator U3 and Inverter U4B supply -10 volts to the input of
U4C. The summation of -10 volts and the load rate command voltage
at U4C, produce a 0 volt velocity command voltage in standby mode,
or when only one button is depressed on the injector head.