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Processor Circuit Boards Theory of Operation
1 - 12 0070-10-0691 Accutorr Plus Service Manual
1.3.3 Nellcor
®
Nell-3 Interface Board Theory of Operation
The Nellcor
®
Nell-3 interface circuit board (0670-00-0740) establishes bilateral
communication and control of the Nellcor
®
Nell-3 oximeter circuit board. The circuit
board consists of a power supply section that converts the system +5 VDC into the logic
and analog supplies required by the oximeter, and optically isolated logic control for the
processing circuits of the oximeter. A 5V to 10V DC/DC converter (T1) and two voltage
regulators (U4 and U5) generate the required digital (+5VD) and analog (+5VA) voltages.
Regulator U4 also provides optocoupler U1 and protection array U6 with power. The logic
control section, consisting of U1, U2 and U3, provide the buffer and isolation from the
main CPU circuit to the Nellcor
®
Nell-3 oximeter section.
1.3.4 Masimo SET
®
Technology
Masimo SET
®
Technology combines advances in fundamental sensor technology, digital
signal processing, an easily portable platform, and a low noise hardware platform
incorporating multiple wavelengths applicable to many physiological parameters. Masimo
SET
®
Technology is composed of three components: (1) new signal processing apparatus,
(2) a new method for in vivo measurement, and (3) new sensor technologies. The main
benefit of Masimo
®
technology is the effective cancellation of unpredictable “in-band
noise” (noise that is in the same frequency, phase, and/or amplitude space as the desired
signal). Conventional fixed filters, whether analog or digital form, have been designed to
pass certain frequencies while rejecting others.
For example, a bandpass filter with a lower cut-off frequency of 1Hz and an upper cut-off
frequency of 10Hz will pass all frequencies between 1Hz and 10Hz and reject frequencies
below 1Hz and above 10Hz. Therefore, any “noise” that has a frequency outside the pass
band is rejected and not considered (i.e., 120Hz due to room light and 60Hz noise from
electrical lines).
However, if noise exists between the pass band of 1Hz and 10Hz, it will enter the system
with the desired signal and corrupt the measurement (i.e., patient motion at 2Hz). Fixed
filters will always have this limitation. Masimo
®
has overcome these problems by
developing a novel technique to accurately determine the noise reference (patents issued
and pending); thus, making adaptive filters work in real-time even when applied to
medical monitoring of widely variable and unpredictable patients. With this new
technique, Masimo
®
is able to solve the perennial problem of motion artifact in pulse
oximetry. Further technical information is available from Masimo
®
on the Internet at
www.masimo.com.
1.3.5 Masimo
®
Interface Board Theory of Operation
The Accutorr Plus Masimo
®
interface board (P/N: 0670-00-0716) provides an isolated
data and power interface between the Accutorr Plus and the Masimo
®
MS-3 Pulse
Oximetry module. The patient isolation requirement for the Masimo
®
section is
1500VAC, less than or equal to 1mA leakage current, from input connectors J1 and J4-all
terminals to J2-all terminals.
To Purchase, Visit Avobus.com or call 1-800-674-3655
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