Mallinckrodt NELLCOR NPB-4000, Service Manual

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Section 11: Isolated Front End Functions -- Theory of Operation
11-2
Figure 11-2: Isolated Front End Block Diagram
The NPB-4000/C Front End module is a part of the Main Board. It provides an
isolation barrier between a patient’s body and electrical potentials on the rest of
the board as well as some high voltage protection of the isolation barrier itself.
11.2 OVERVIEW
The NPB-4000/C Front End Module consists of eight major blocks: interface
circuit, ECG, respiration, temperature, controls, power supply, isolation, and
A/D converter on the non-isolated side. It also carries an SpO
2
module which
uses Front End for isolation and power supply.
•
The ECG channel has 3-lead capability and a gain of 285. It provides two
levels of low frequency noise filtering, T-wave filtering, R-wave detection,
pacer detection capability and baseline reset.
•
The temperature channel provides measurements over the range of
15 to 45
ø
C using YS400 series probes.
•
The respiration channel incorporates the standard impedance pneumography
method of injecting 100 kHz current of 42 micro Amps into a patient
through the RA and LA leads and measuring voltage modulated by
respiration on the same leads. Respiration can be measured in the range of
200 to 2000 ohms of a body impedance with the maximum modulation of 10
ohms.