Medrad ProVis Mark V, Service Manual

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Mark V ProVis Injection System
13 - 4
Single Button Disarm:
Pressing any button, or combination of buttons on the Injector Head,
will disarm the injector. Approximately 2-5 volts is required to disable
the Safe Relay and disarm the injector. If Forward or Reverse load are
pressed, +5 volts supplies the soft pots through D4, and follows the
same path as normal loading. If Enable is pressed, +15 volts goes
through the switch, R11, D3 and D5, and Q3 and Q5 to the PDCI. In
either case, the voltage is sensed as a disarm.
Forward/Reverse
Clamping Circuit This circuit protects the piston motor and ballscrew from high speed
collisions by clamping the load command at the slow speed value
when the piston is approximately 0.25” (0.635 cm) from forward or
reverse limits. At fast speed, approxi14 volts is applied to the
drive circuit on the PDCI. As the piston approaches front or rear limits,
the load command is clamped to +9.1 volts (slow speed).
Forward Load Clamp - U1B/Z1:
The non-inverting input of U1B is referenced at +9.0 volts by a voltage
divider consisting of R8, R9, R7, and R17. The inverting input is a
buffered plunger position voltage (U3A), while output of U1B is in pos-
itive saturation if the plunger position is below the reference. As the
piston moves forward, plunger position voltage increases. When the
reference input is reached, U1B goes to zero, making Z1 (9.1 volts
zener diode) conduct, clamping the forward load command (base of
Q3) to +9.1 volts, driving the motor at slow speed.
Reverse Load Clamp - (U2B/Z5):
The inverting input of U2B is referenced at +0.66 volts by a voltage
divider consisting of R8, R9, R7, and R17. The non-inverting input is a
buffered plunger position voltage (U3A), while output of U2B is in pos-
itive saturation if plunger position is above the reference. As the piston
moves in reverse, plunger position voltage decreases. When voltage
drops below the reference input, U2B goes to zero, making Z5 (9.1
volts zener diode) conduct; thus clamping the reverse load command
(base of Q5) to +9.1 volts, driving the motor at slow speed.
Volume Remaining
Display The Volume Remaining Display provides a 3 digit display of the
amount of contrast media remaining in the syringe. DVM IC U4 uses
the buffered plunger position from U2A to derive the Volume Remain-
ing Display (seven segment LED output). The plunger position is
inverted and offset by U2C and sent to the scale switching voltage
divider network R23, R4, R6, R14, R16, Q5, and Q6. The output of the
divider is sent to the input of U4.
PAL’s U8 and U9 buffer the LED outputs and drive the seven segment
LED’s directly (non-multiplexed). The PAL’s are also responsible for
all leading zero blanking, and displaying “200”.
U5 is a supply IC that produces the -5V supply required by U4.