Eog; Effort Belt - Respironics Alice PDx Service & Technical Reference Manual

EOG

Refer to Alice PDx Analog Board Schematic sheets 7 and 8, located
in the Schematics section beginning on page 53.
Alice PDx contains three EMG signal conditioners which function identically to the EEG signal conditioners,
but, are designed to different parameters. All EMG signal conditioners are designed to the following
parameters:
•
Input voltage range: 300 uVp-p
•
Input coupling type: AC
•
Input impedance: 2 Megohm single-ended, 4 Megohm differential
•
Bandwidth: 10 Hz to 100 Hz (-3 dB)
•
Output voltage range: 0 to 3 VDC
•
Quiescent output voltage: 1.5 VDC
•
Total gain: 10,000
E B
FFORT ELT
Refer to Alice PDx Analog Board Schematic sheets 9 and 10
located in the Schematics section beginning on page 53.
The operation of effort belt #1 is identical to that of #2, therefore, only the operation of belt #1 will be explained
here.
An elastic belt which has wire woven through it is wrapped around the patient's abdominal or thoracic area. As
the patient breathes, the diameter of the patient's abdomen or thorax changes, causing a change in the belt
diameter. Any change in the belt diameter causes a change in the belt's inductance. The belt inductance, in
concert with C75 and C85 form a resonant circuit which controls the frequency of a Pierce oscillator formed
with U19. As the belt inductance changes, so does the frequency of oscillation. The nominal frequency of
oscillation of Belt #1 is approximately 100 KHz while Belt #2 is 170 KHz. These nominal frequencies can vary
over a wide range, depending on the inductance of the effort belt.
The nominal belt inductance is approximately 42 uH. This test was performed on a few belts that were
available at the time of test and may not be indicative of inductance values to be expected in other belt
samples.
The output of oscillator U19 is fed into U20, an LM555CM timer chip operating as a oneshot multivibrator. In
this mode, every falling edge of the signal from U19 causes U20 to output a positive pulse of a fixed duration of
approximately 1.4 usec. U20 will change the rate at which it is triggered, due to changes in U19 frequency. This
change of trigger rate, when taken with a constant duration pulse output by U20 each time it is triggered,
means the duty cycle of U20's output changes in response to changes in U19's oscillation frequency. U20's
output pulses are low pass filtered in a network formed by R165, R166, R167, C103, C104 and C105. After
filtering, a DC voltage is obtained which is proportional to the frequency of oscillation of U19. Since U19's
frequency of oscillation is controlled by the inductance of the effort belt, we now have derived a voltage whose
value is dependent upon the inductance of the effort belt.
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Alice PDx Service & Technical Reference Manual
1054417, V . 01
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