system, and the third valve is used to ventilate the system in order to
release pressure.
The following is a simplified explanation to illustrate the functioning
of these valves during a blood pressure simulation sequence:
1. When entering a simulation start menu all valves are open, so the
system is ventilated. Once the start menu is entered, the ventilate
valve is then closed.
2. As the blood pressure monitor increases the pressure, the pres-
sure sensor detects this activity. The stepper motor then starts to
move the piston in the cylinder in order to simulate pulses. The
length of movement is given by the number of pulses applied to
the stepper motor.
3. As the pressure rises, the pulses increase in strength up to a
maximum where it starts falling again. At a high pressure the
pulses almost disappear. This is detected by the monitor, which
then starts to release the pressure slowly while simultaneously
monitoring the pulses.
4. QA-1290’s firmware calculates the pulse strength on the basis of
the pressure measured. This makes the pulse envelope look like
the pulse envelope of a human.
5. When the monitor has found both the systolic and diastolic pres-
sures, it releases the pressure. QA-1290 senses that the meas-
urement is completed, displays or prints the simulated values,
and ventilates the system. QA-1290 is then ready for a new
simulation.
8.5 Power Supply
The Processor and QA-1290 boards are powered by the same power
supply. This supply delivers +5V and +24V to the QA-1290 board.
This board generates the additional voltages –5V, +12V, -12V and
+15V required.
The following are specifications for the ASTEC LPT65 Power Supply
used in the QA-1290:
Output Voltage Minimum load Maximum Load Peak Load
+5 V 0.7 A 7 A 10 A
+24 V 0.1 A 1.5 A 3 A
This power also has a 12V output but this is not used.
Input specifications for this power are 85 – 264 VAC, 120 –370 VDC,
47 – 440 Hz, and a maximum input RMS current at 115V.
8.6 Connector Signals
1. Stepper motor
8-6
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