Service manual

Revision 2/18/05 2 - 9
System Overview
Auditory Stimulator
The Auditory Stimulator provides a click or a tone
stimulus. The system user controls the stimulus rate,
duration, intensity level and polarity. The three types of
click polarity are:
• Rarefaction - the earphone diaphragm moves away
from the ear.
• Condensation - the diaphragm moves toward the ear.
• Alternating - the diaphragm will deliver a rarefaction
stimulus and condensation stimulus every other
stimulus.
The variable tone parameters are frequency and
envelope shape. The envelope variables are rise/fall
time and plateau time.
The Auditory Stimulator also provides noise masking.
When stimulus levels higher than 95dB are delivered to
the patient, the stimulus can travel by bone conduction
to the non-test (contralateral) ear. Noise masking
applied to the non-test ear prevents it from contributing
to the evoked response.
Visual Stimulators
Pattern reversal and flash are the two types of visual
stimulators. The VIASYS model 2015 Visual
Stimulator presents a reversing checkerboard pattern to
the patient. This stimulus produces a short duration
evoked response that is better defined than with flash
stimuli.
Flash stimulators, such as the LED Goggles or a photic
strobe light, produce a longer duration response that is
less well-defined than a checkerboard stimuli.
Stimulus Pulse Generator
This block produces the signal that fires the stimulators.
The stimulus pulse from this block goes to each type of
stimulator and results in:
• A click or tone to the ear
• A flash or checkerboard pattern reversal on the visual
stimulator
• An electrical pulse delivered to the surface of the skin
The system user sets the stimulus pulse rate and
duration to values appropriate for each type of test.
The Stimulus Generator block also produces an internal
calibration pulse. The calibration pulse goes to the input
select switches. The calibration pulse permits you to
conduct an integrity check of the blocks that process the
patient signal.
Analog-to-Digital Converter
The Analog-to-Digital Converter changes the incoming
analog signal to a series of digital values that represent
the data. This device runs continuously during data
acquisition, sending a constant stream of digital values
to system memory. The A/D converter produces a 16-bit
digital value.
At the output of the A/D converter, 16 bits are added to
the digitized data to create a 32-bit data stream. The
additional 16 bits are designated marker bits. Markers
identify significant events associated with the data
stream, such as the occurrence of a stimulus pulse or the
press of the foot switch.
The mark provides a way for the computer to locate and
extract the important segments from the data stream.
Computer Platform
The computer platform runs the VIASYS applications
that manage patient demographics, set up
amplifier/stimulator parameters, and process the
incoming patient data.
The Endeavor CR and VikingQuest can be configured
around a desktop or laptop computer with the following
minimum specifications:
• Pentium, 3.2GHz CPU or better
• 512MB RAM minimum
• 80GB or higher IDE hard drive
• 1024 x 768 pixel graphics or better
• Two or more USB ports
• CD or DVD Writer
The VikingSelect requires a desktop computer to
accommodate a PCI firewire interface card.