Service manual

Revision 2/18/05 2 - 7
System Overview
Neurodiagnostic Instrument - Generic Block Diagram
The diagram above represents a generic NCS/EMG/EP
system. This section describes the functions of the
blocks that make up this basic system. Later these
blocks will be broken down into the specific functional
blocks that compose each VIASYS neurodiagnostic
system.
Patient Interface
Electrodes and Headbox
Electrodes connect the patient to the system. The
electrodes generally plug into some type of headbox or
amplifier module.
Electrode Select Switches
Mechanical or electronic select switches direct the
selected electrode leads to the appropriate amplifier
channels. The Endeavor CR 16-channel amplifier and
the VikingSelect ES-8 amplifier are the only amplifiers
available with electrode switching.
Impedance Measurement Circuit
An impedance measure circuit lets the user measure the
integrity of the patient-to-electrode connection. This is
necessary to check that the recording electrodes have
been applied properly.
Amplifier
The input amplifier is typically an isolated differential
amplifier with a large voltage gain. This stage amplifies
the difference in the signal applied between the positive
and negative inputs (the patient signal). The use of a
differential amplifier allows the amplifier stage to reject
unwanted environmental signals applied to both inputs,
while amplifying the patient signal. The measure of the
amplifier’s ability to reject these signals is called the
Common Mode Rejection Ratio (CMMR).
Electrical
Stimulator
Auditory
Stimulator
Stimulus
Pulse
Generator
Analog to Digital
Converter
(Digitizer)
Signal
Conditioning
LFF, HFF,
NCH, SNS
Signal
Conditioning
LFF, HFF,
NCH, SNS
MARK
CAL
STIM
Pattern Reversal
Visual Stimulator
Amp
Amp
Electrodes
to Patient
Printer
Input Select Switches
SIGNAL A/B SELECT ADJUST
Generic NCS/EMG/EP System