Siemens SC 7000 Service Manual page 48

Service Manual
12.2.2 Cardiac Output
12.2.3 EEPROM Storage
12.2.4 LCD and Push Buttons
12.2.5 Current Limiting the Voltage
Reference
13Remote Comm
Subsystem
Hardware
13.1 Connection
Characteristics
32
A multiplexer selects one of the two temperatures or one of the two
calibration points and connects the voltage to the input of a fixed gain
amplifier. The two calibration points are used to correct gain and offset
errors in the amplifier circuits.
An offset is added to center the signal within the dynamic range of the A/D
converter. The signal is then further multiplexed with two power supply
voltage monitors and Cardiac Output. A fixed gain of two is finally applied
to match the signal range to the full scale range of the A/D converter.
Cardiac output operates in much the same way as temperature. The
thermistor signals are filtered and clamped then multiplexed to the input of
a fixed gain amplifier. Two calibration voltages are also multiplexed in to
correct amplifier offset and gain errors.
Next, an offset is added to the signal to center it to the dynamic range of the
A/D converter. The amplified signal is then multiplexed with temperature,
then through a fixed gain of two and finally to the A/D converter.
Two EEPROM's are used for non-volatile information storage. One
EEPROM is used for reading and writing data that changes during the
operation of the POD, such as pressure offsets, the other stores more
permanent information such as POD serial number and is therefore write
protected. A state machine inside the logic gate array supports
communications between the Host and the two EEPROM's. A mechanism
is provided which allows service personnel to disable the write protection of
the otherwise write protected EEPROM.
A total of 16 LCD characters are provided for use as pressure labels. Each
pressure channel is allocated 4 LCD characters. The Logic Gate Array
supports communication of controll between the Host and the LCD's.
Up to three push buttons are provided for user interface. There is one for
pressure zero, one for Cardiac Output Start and one spare. The interface
of the buttons to the Host is handled by the gate array.
In the event a defective pressure sensor presents a short circuit to the
excitation voltage source, the voltage source goes into current limit during
the bad transducer's time slot.
The main processor sees the Remote Bus interface to the CPS or IDS
Network as a slave device with a dedicated address space. The responding
devices, however, are in the CPS/IDS. Status bits indicate when the remote
device is connected and powered up, and signal validity on the
communication link. If a proper connect is established, a periodic poll is
sent to the CPS/IDS to up-date the interrupt status to the monitor every 8
microseconds.
Two mechanisms are used to verify physical attachment to a docking station.
• First, a hardwired signal between the monitor and CPS or IDS is
activated when a cable connection is achieved. This signal is valid
even if the CPS or IDS is powered off.
• Second, an opto-isolator is activated when a powered CPS or IDS is
attached to the monitor. A current loop is established by current
flowing thru the receive lines, opto-isolator and transmit lines.
A time filter is applied to both functions, such that the function must be valid
for a minimum of 100ms before activating. Deactivation is immediate.
Siemens Medical Systems, EM-PCS, Danvers
NOT A CONTROLLED DOCUMENT
SC 7000 and SC 9000XL Patient Monitors
ASK-T898-03-7600
7k9kXLTM.c2.CD_ROM.fm/04-99/kaupp