THEORY OF OPERATION
Test Signal Generation
One of the combinations of the L0 and L1 signals indicates TEST mode. In this mode, the lead select switch is off,
and a 70 bpm signal generated by U44 is sent to ECG amplifier U55D.
ECG Waveform
ECG Filter
The signal from the output of coupler U40 and then through a low-pass filter to amplifier U26B. The signal at
U26A Pin 1 is the filtered output. This signal is switched in or out by FET Q30 which is controlled by the NOTCH
signal from the digital circuitry. Potentiometer RV13 (60 Hz) and RV14 (50 Hz) is used to adjust the notch filter.
The processor senses the line freq from U18B and automatically switches in the correct notch filter.
X1000 Output
The output at U26 Pin 1 is the X1000 signal that is sent to the rear panel for use with a recorder or other equipment.
ECG Gain
The signal from U24 Pin 1 goes to ECG gain amplifier U24 Pin 7. The gain of this circuit is determined by resistors
switched into the circuit by U25. This switch is controlled by signals G1, G2, and G3 from the digital circuitry.
The gain depends on the settings made by the user. The output signal from U24 Pin 7 goes to the A/D converter in
the digital circuitry.
A/D Converter
The A/D converter is U21 along with amplifier U22A. The converter samples the analog ECG signal and generates
a series of 1,024 eight-bit numbers which can be stored in memory and then sent through the D/A converter for
ECG waveform display.
30 Model 101R/NR Service Manual
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