4. The pressure transducer on the main CPU board then detects any oscillations from the cuff during deflation
and converts them to digital code for the CPU to determine the systolic, diastolic and pulse rate readings.
5. Rapid, complete cuff deflation occurs after all readings have been recorded. The mechanical safety
pressure switch automatically deflates the system if the pressure exceeds approximately 400 mmHg while
the cuff is being inflated.
NOTE
: Refer to Section 10 for schematics related to the functions described in this section.
6.3
Main PCB
The main Control Printed Circuit Board (PCB) of the Press-mate has many functions. Some of its circuits
include:
Main and Sub CPUs
Cuff Pressure and Oscillation Inputs
Pump and Deflation Valve Controls
Front Panel Interface
Printer Control
Power Supply Control
RS232 Interface
The heart of the Main PCB is an eight-bit CPU (U12). The Main CPU controls the system according to the
written program for the system, found on EPROM (Electrically Programmable Read-Only Memory) U13. Clock
signals used for the timing of the Main CPU are provided by Crystal X1. The Main CPU works in conjunction
with two, four-bit Sub CPUs. The first Sub CPU (U14) controls the Pump, Bleed Valve, and Dump Valve. The
Sub CPU uses the pressure and the cuff oscillations from the pressure input circuit to control the rate of deflation
of the pressure in the cuff circuit. The second Sub CPU (U15) controls the printer, while collecting information
about battery power from the Battery Low/Empty Comparator Circuit (consisting mainly of OP3).
Cuff pressure is applied to the pressure transducer (PSI). This pressure creates a differential voltage imbalance
across the arms of the transducer impedance bridge. This differential voltage is then amplified, filtered, and
separated into a pressure signal, an adult oscillation signal, and a neonatal oscillation signal This separation is
completed through the use of the CIC1 chip. The reason the signal is separated is because of the need to
amplify the neonatal oscillation signal to a higher degree than the adult oscillation signal. The MUX chip (U13)
then combines the pressure signal with either the adult oscillation signal or the neonatal oscillation signal upon the
direction of the Main CPU. The combined signal (pressure signal with oscillations signal) is then sent to the 12-
bit Analog-to Digital Converter (U30). U30 then translates this signal into a digital format for its transmission to
U12 and U14. The Main CPU (U12) with the use of COLIN's proprietary algorithms, determines systolic,
mean, diastolic, and pulse rate values. Once the Main CPU has determined these values, this information is then
loaded in the RAM (U10) for switching by the I/O controller (U23) display board via connector (CN1).
Safety circuits like those found in U24, U17, and U3 watch for cuff over pressure as well as excessive cuff
inflation/deflation duration conditions.
6-3