Medrad ProVis Mark V, Руководство по обслуживанию

Страница: 56 / 143

Injector Head
13 - 3
The non-inverting inputs of U2A and U2D are referenced at +7 volts
by voltage dividers R1, R4, and R3. The outputs are positive, and do
not effect normal loading. When both load buttons are pressed
(assuming Enable is also pressed), both inverting inputs (of U2A and
U2D) will have a greater positive value than the reference voltage
(+9.1 volts minimum), causing outputs to go to zero. This makes Z2
and Z6 (5.1 volt zener diodes) conduct, clamping the load voltage
sent to the PDCI (junctions of Z2/Q3 and Z6/Q5) at +5.1 volts. This
low amplitude is not sufficient to drive the piston motor, and will there-
fore disarm the injector.
Timed Enable Button:
Timed Enable is designed to allow the operator to move the plunger
piston forward or reverse by using the Forward/Reverse softpots only
after the ENABLE button is depressed. In a no load condition, the
Enable input is at +5V. Zener diode Z1 keeps the Enable LED off until
the ENABLE button is pressed.
When the ENABLE button is pressed, the Enable input (J71, pin 8)
goes to +15V at the junction of Z1 and C3. This input provides two
functions. First, the Enable LED Indicator receives positive voltage
through Z1 and R8, causing it to illuminate. Second, +15V is applied
to the junction of C3 and RN1/RN2, producing a positive pulse. The
positive pulse is applied to the inverting input of U2A pin 6, switching
the output to negative. This negative output is applied to the trigger
input of U1 pin 2, producing a positive pulse for U2B. Pulse duration is
approximately 5 seconds. This pulse, applied to U2B pin 4, causes
the output of U2B to switch negative. Q1 conducts and 15V
to hold the Enable line input positive. The action continues throughout
the duration of the pulse.
When the FWD or REV button button is pressed, +8V to +14V is
applied to the inverting input of U2D through RN1/D1 (FWD) or RN1/
D2 (REV). R1 and C6 provide a 100 mS delay when the load button is
pressed. When a U2D inverting input votage is greater than +5.5V, the
output of U2D will switch the output negative. This negative voltage
discharges capacitor C5, and prevents U1 from resetting.
NOTE : If the load button is released, the Timed Enable circuit
will remain active for approximately 5 seconds. One
button loading is still available during this time.
If FWD or REV is pressed prior to, or simultaneously with, the
ENABLE button, the Timed Enable circuit is disabled, and the injector
head will function without the Timed Enable feature. This occurs when
the inverting input to U2C (pin 10) goes more positive than the non-
inverting input (pin 11 referenced at +1.9V). The output of U2C
switches to negative, grounding the inverting input to U2A. If the
ENABLE switch is pressed, the pulse developed by C3 and RN1/RN2
is grounded, and the Timed Enable circuit is not activated.