Siemens SC 7000 Service Manual page 38

Service Manual
ECG
22
Impedance respiration is sensed through the ECG electodes. Void-free
potting and internal shielding enable compact containment of high voltage
defibrillator and electrosurgery pulses. The small interconnecting cable to
the main assembly is captive at the MultiMed POD but plugs into the
MultiMed front end via a specially shielded connector.
The front end accepts physiological signals from the MultiMed POD
connector and feeds temperature, respiration, and ECG signals via RF
filters, configuration multiplexers, and pre-amplifiers to a high-speed
multiplexer driving a 16-bit analog-to-digital (A/D) converter. The data
stream is sent to the Main Processor board via an opto-isolator. Control
commands from the Processor are sent out to the front end on a similar
isolating link. Isolated DC power is also provided.
The ECG signals are conductively coupled to the isolated circuits via current-
limiting series resistors, whereas the SpO
the transducer. Temperature signals are doubly insulated at the patient by
disposable boots on the sensors. AC (40kHz) excitation currents for
respiration monotoring are dc-isolated by high-voltage ceramic capacitors.
The A/D samples the following parameters:
Table 2-4 Parameter Sampling Table
Parameter
ECG
Pace
SpO
SpO
NBP
Resp
Temp
The pace signal samples are used directly by the DSP to detect pace
pulses. All other signals are decimated and filtered using digital signal
processing to the above specifications. Additional filtering is user selectable
and invokes additional digital signal processing in the computer section of
the board. The high oversampling rate is required to minimize the
requirements (and size) of the analog anti alias filters. Superior rejection to
ESU and other types of interference is achieved with this type of design.
• Pacer pulses may be detectable by software on two lead-pairs.
• Bandwidth is set flexibly by software filters.
• Reconfigurable neutral selector can drive any electrode.
• Lead-on detection functions with even poor electrodes.
• Calibration voltages can be superimposed on patient wave-forms or
onto flat baselines.
See Figure 2-9. Composite electrocardiographic (ECG) signals generated
by the heart and by a pacemaker are filtered to reduce RF interference from
impedance respiration and electrosurgery and then injected with dc lead-off
detection currents. Over-voltage clamps protect the semiconductors from
the surges passing the sparkgaps in the MultiMed Pod and also reduce the
dc current applied to the patient due to a component fault.
Siemens Medical Systems, EM-PCS, Danvers
NOT A CONTROLLED DOCUMENT
SC 7000 and SC 9000XL Patient Monitors
signals are optically isolated at
2
# of Channels
4
2
Red 1
2
IR 1
2
1
1
2
7k9kXLTM.c2.CD_ROM.fm/04-99/kaupp
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