Service manual

Revision 2/18/05 3 - 61
Hardware Description
Patient Signal Path - VikingSelect
The Patient Signal Path functional unit is a Nicolet-
unique part of the VikingSelect. The Least Replaceable
Units (LRUs) are designed and manufactured by
VIASYS Healthcare.
Hardware Components
The signal path functional unit consists of the following
components:
• 2- or 4-Channel EP/EMG Amplifier and/or
• 8-Channel IOM Amplifier with
• Headbox ET16A and
• Headbox ET16B
EA-2 and EA-4 EP/EMG Amplifiers
The following block diagrams show the similarities and
differences between the 2-channel and 4-channel
EP/EMG amplifiers.
Each amplifier channel offers a five-pin DIN input
connector and individual electrode connectors for
accepting the patient electrodes. Each channel has an
on/off switch for turning off unused channel inputs. The
2- and 4-channel amplifiers also provide a temperature
probe input connector.
Input multiplexers, under computer control, select the
proper inputs for recording patient data, conducting an
impedance test, or running a calibration pulse.
Each Amp/Filter stage contains a differential input
amplifier and selectable gain/filter circuits. In the 2-
channel amplifier, the Amp/Filter stage is fabricated
from discrete components. In the 4-channel amplifier,
this stage is a hybrid module.
Two analog to digital converters change the filtered
analog signals to a series of digital samples. These
samples are processed by a digital signal processor
(DSP) and transferred to the host PC via an IEEE 1394
(FireWire) port. Information for synchronizing the data
with stimulus events is placed into the data stream as
well.
The digital patient data samples are also mixed and
presented via a Digital to Analog Converter (DAC) to
an audio amplifier and the EMG speaker for listening.
Control and status information from the host PC to the
amplifier are exchanged along with the data on the
single FireWire interface cable.
ADC2
ADC1
+15V
Mux
Mux
Cal/Z
Source
Temp
Ch1
Ch2
Amp/Filters
Amp/Filters
Control Logic
Mux
A
IEEE 1394
Interface
2 Channel
Audio DAC
DSP
DC-DC
Converter
Opto-Isolators
Ch1 Ou
t
Ch2 Out
I+8V
I+15V
I-15V
Isolation
Barrier
VikingSelect EA-2 EMG Amplifier Block Diagram