Smiths Graseby 3200, Техническое и сервисное руководство

Страница: 47 / 117

Smiths Medical International Ltd.
3200 Service Manual Issue 5 (August 2004)
4 — 4
The seven opto-sensors are split into three groups (see Figure 4.6 ) and these three groups are
multiplexed onto three lines into the microprocessor.
The three groups are used as follows:
• One group is used by the size sensor board.
• The second group monitors whether the pump's plunger clamp is open or closed,
whether the slotted disc used in the occlusion sensing system is rotating and whether
the nearly empty flag has entered the opto-sensing slot.
• The third group has only one member, which is used to signify whether a pressure
sensing disc has been inserted into the pump.
Q3 activates the size sensor LEDs, Q1 activates the status sensors LEDs and Q18 activates
the disc detector LED. The three transistors are activated independently and should not be
active at the same time.
R4, R5, R8, R9, R81 and R82 are current limiting resistors.
On the detection side of the opto-detectors, R77, R78 and R79 are pull up resistors. R6A, B,
C, D, R7A and R7B are current limiting resistors. Zener diodes D1, D2 and D3 are used for
electrostatic discharge protection.
When a photo transistor detects the LED associated with it, the line OPTO_0,1 or 2, will be
pulled low. This signal is then input to the microprocessor via SENSE3, 4, or 5.
R1, R2, and C1 make up the low battery voltage sensing circuit. R1 and R2 act as a
potential divider enabling the voltage between them to be input to the A-to-D converter of
the main processor.
The pressure sensing interface circuit (see Figure 4.7 ) consists of an instrumentation amplifier
with an adjustable offset. The Tee filters L3 and L4 along with C3, C4, R17 and R18 are for
electrostatic discharge protection.
IC1A, B and C with associated components R12 to R16, R19, R20, C5 and C6 make up the
instrumentation amplifier.
IC1D is a voltage follower and allows the processor to detect a signal on one of the inputs to
the instrumentation amplifier. R11 is a pull up resistor for op-amp IC1A.
OFFSET_TRIM (see Figure 4.7 ) is a PWM output signal from the processor and this signal is
attenuated by the potential divider R21 and R22. C42 smooths the PWM output to a DC
level. This DC signal is applied to the relevant stage of the instrumentation amplifier, so that
when the pressure sensor is being calibrated the zero mmHg calibration point will be
equivalent to 0.5 V, and this voltage appears at the PRESSURE output.
This PWM signal will remain constant until the transducer is next calibrated.
Each time the pressure sensing disc is inserted, or the pump is switched on, an auto zero is
carried out. This allows the zero pressure voltage to differ by up to ± 0.5 V of the calibrated
zero point.
If the voltage is outside these limits the pump will issue a warning and must be re-calibrated.
So the voltage on the PRESSURE output line will normally be between 0 and 1.0 V, and
exactly 0.5 V immediately after a calibration routine.
IC1D is a voltage follower and allows the processor to detect a signal on one of the inputs to
the instrumentation amplifier.
Sensors
interface
Sensors interface