User`s guide

M3000A/M3046A/M3015A/M3016A Service Guide
Introduction to the Instrument 1-25
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The excitation current source feeds a small current into the right arm and left leg electrodes.
This results in a voltage drop between the right arm and left leg which is proportional to the
thorax impedance.
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The bridge subtracts an offset from the voltage between right arm and left leg. The amplifier
amplifies the remaining signal.
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The CPU performs the following functions:
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initializes the intended ASIC configurations such as gain, A/D sampling rate, and DAC
operation.
• $FTXLUHVWKHGLJLWL]HG(&*DQG5HVSVLJQDOVDigitized ECG signals are used to calcu-
late 3 ECG leads which are then passed on to the Pace Pulse detecting software, and the
wave processing and filtering software.
• 3HUIRUPV(&*ZDYHILOWHULQJThe waves are digitally filtered and scaled then passed to
the software that communicates with the system CPU.
• 3HUIRUPVSDFHSXOVHGHWHFWLRQA digital high-pass filter acts as a slope detector for the
received ECG waves. The output of the slope detector is fed into two comparators compar-
ing the signal to a positive and negative threshold. The output of the comparators indicate
the absence or presence of a pace pulse. The threshold of the comparators is moving and
adapts itself to the amount of noise present in the ECG wave. Detected pace pulses are
communicated to the wave processing and filtering software.
• &RPPXQLFDWHVZLWKWKHV\VWHP&38Communication is via a serial, bi-directional data
link. The ECG/Resp CPU sends the following data to the system CPU:
• 3 ECG waves,
• A respiration wave,
• Pace pulse data,
• INOP messages, and
• status messages.
The ECG/Resp CPU receives control messages from the system CPU.
ECG ASIC
Controller
Data
Acquisition
Pace Pulse
Detection
Wave Processing
& Filtering
System CPU
Communication
System
CPU