Philips 50 T Series, Руководство по обслуживанию

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Receiver Functional Blocks
Chapter 9 - Theory of Operation
• Encode the marker signal into the Toco signal
If more than two consecutive frames are disturbed (wrong CRC checksum) or
no synchonisation is possible due to not matching serial numbers of the
transmitter and the receiver, the output signals are switched off and the range/
transmission INOP LED on the frontpanel is switched on.
Toco D/A Converter
This module converts the digital Toco value (12 bits) into an analog voltage
(the fetal monitors can only accept analog input signals for all parameters). It
is built up with a pulse width modulator followed by a 3Hz lowpass.
The marker is also encoded with the Toco output signal. If a marker pressed
bit is received, the Toco signal will make a deflection over the complete range
for 1 second if a fetal monitor with an old telemetry interface is connected. If
a new interface is detected, the marker will be output as a digital mode output
only.
EEPROM
The EEPROM keeps the following settings:
• Serial Number
• Nurse Call volume control
These values all can be set via the Service/Production interface, or in the case
of the nurse call volume control, by pressing the nurse call acknowledge
button if no nurse call is active.
Service Interface
This is a RS232 type serial interface used for servicing and production test
and settings, to read back internal values or to store serial numbers and other
settings in the EEPROM.
Power Supply
This module delivers all the necessary supply voltages. It has an input selector
for 110V or 230V mains input. It outputs the following voltages:
+21V RF Preamplifier
+12V Analog circuitries and the M1402A Receiver Module
-12V Analog circuitries and the M1402A Receiver Module
+5V Digital circuitries and the M1402A Receiver Module
Oscillator
The oscillator produces a CMOS clock signal for the digital circuitries. It is
running at 16.256 MHz. This frequency is divided by 2; the resulting 8.128
MHz frequency is used as a clock signal for the microcontroller.