natus Grass S88X Troubleshooting guide

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Web site: www.natus.com Manual Part Number M643H05
Release D
S88X
Dual Output Square pulSe StimulatOr
Grass ®
USER &
SERVICE MANUAL

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DBA Excel-Tech Ltd. (XLTEK)
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Canada
phone: [phone]
fax: [phone]
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Printed in the United States of America

imPortaNt
This manual is subject to periodic review, update, and revision. Customers are
cautioned to verify that the manual’s information applies to the software and
hardware present in the equipment.
This product performs as described in this manual, and in accompanying labels
and/or inserts, when assembled, operated, maintained, and repaired in accordance
with the instructions provided.
This product must be cleaned and checked periodically. Do not use a defective
product. Parts that are broken, missing, worn, or contaminated should be replaced
immediately. If repair or replacement becomes necessary, call or write to request
service advice from Grass.
This product must not be altered without the prior written approval of Grass. The
user of this product shall have the sole responsibility for any malfunction that
results from improper use, faulty maintenance, improper repair, unauthorized
service, or alteration by anyone other than Grass.
The safety, reliability, and performance of this device can only be assured under
the following conditions:
• If the device has been used according to the accompanying
operating instructions.
• If changes or repairs have been carried out by Grass.
• If it is used in buildings having ground equalization wiring that complies
with relevant UL, CSA, IEC or other local standards and regulations.
iNteNded use
The S88X Stimulator is a general purpose, electrical stimulator for nerve
and muscle that has a wide range of parameters to satisfy a wide range of
research applications.
FOR USE BY QUALIFIED PERSONS ONLY. NOT INTENDED FOR THERAPEUTIC
PURPOSES.

WarNiNgs
READ THIS BEFORE OPERATING S88X
The available voltage and current from this Stimulator may, under some
conditions, be sufficient to be lethal or cause burns, particularly with
high duration and/or high voltage settings.
It is the responsibility of the investigator/user, to determine for any given
application, the maximum safe levels of stimulation, and assure that such
stimulation levels will not be exceeded. In many applications, the mechanisms of
safe stimulation are not completely understood.
Parameters that affect safe stimulation levels are:
• Pulse Repetition Rate
• Pulse Duration
• Pulse Duty Cycle
• Voltage and/or Current Intensity
• Biphasic vs Monophasic Operation
• Total Time Exposure
• Electrode Impedance, Geometry, Area and Material
The S88X OUTPUT is NOT ISOLATED. Do not use on humans.
CONSULT GRASS IF YOU HAVE ANY CONCERNS ABOUT SAFE APPLICATION,
PARTICULARLY WHEN USED WITH OTHER EQUIPMENT.
NATUS MEDICAL INCORPORATED WAIVES THE RESPONSIBILITY
WHATSOEVER FOR ANY INJURIES INCURRED TO THE OPERATOR OF THIS
INSTRUMENT, OR TO ANY ANIMAL OR HUMAN SUBJECT AS A RESULT OF THE
IMPROPER USE AND/OR ABUSE OF THIS STIMULATOR.

S88X Dual Output Square Pulse Stimulator vii
Table of Contents
1. sPecificatioNs & symbols glossary ................................................. 1-11
SpecificationS......................................................................................1-11
GloSSaryofSymbolS..........................................................................1-12
2. iNtroductioN ................................................................................. 2-13
Safetyinformation.............................................................................2-13
   CAUTION...................................................................................2-13
   WARNING..................................................................................2-13
  electromaGneticcompatibilityinformation..........................................2-14
3. geNeral coNsideratioNs ................................................................. 3-15
  applicationS&capabilitieS..................................................................3-15
  accuracy&Waveform.......................................................................3-18
  linevoltaGerequirementS..................................................................3-19
Dutycycle........................................................................................3-19
  mountinG&inStallation....................................................................3-20
4. descriPtioN of circuits ................................................................... 4-21
General.............................................................................................4-21
  poWerSupply.....................................................................................4-21
  outputcircuit...................................................................................4-22
  S1&S2outputamplituDe.................................................................4-22

viii  Table of Contents
5. exPlaNatioN of coNtrols ................................................................ 5-25
  explanationofcontrolS.....................................................................5-25
  poWer...............................................................................................5-25
Setup&enter/accept.........................................................................5-25
  trainrate&Duration.......................................................................5-26
  S1/S2timinGparameterranGeS..........................................................5-26
TRAINRATe...................................................................................5-26
TRAINDURATION.............................................................................5-26
   S1/S2RATe...................................................................................5-26
   S1/S2DelAy.................................................................................5-26
   S1/S2DURATION............................................................................5-26
  S1&S2controlS..............................................................................5-27
FUNCTION......................................................................................5-27
   S1&S2PUlSeS.............................................................................5-27
SINGlePUlSeS................................................................................5-28
OUTPUTON/OFF............................................................................5-28
StimuluStiminGcontrolS....................................................................5-28
  outputamplituDe..............................................................................5-29
Syncout(SynchronouSoutputS)........................................................5-29
Syncin(SynchronouSinputS)..............................................................5-30
  monitorS...........................................................................................5-31
   S1/S2leDMONITORS....................................................................5-31
OUTPUTON/OFFleDMONITORS......................................................5-31
OUTPUTMONITOR..........................................................................5-31
  uSbinterface....................................................................................5-31
DutycyclelimitationS........................................................................5-32
6. comPuter coNtrol ......................................................................... 6-33
 computercontrol...................................................................................6-33
7. oPeratioN ..................................................................................... 7-35
 Setup.......................................................................................................7-35
Dutycyclelimit................................................................................7-35
  chooSeStimuluSiSolationunitS..........................................................7-36
  loaDSetup&SaveSetup.....................................................................7-37
SeTTINGUPTheS88XPARAMeTeRS....................................................7-37
SAvINGTheS88XSeTUP..................................................................7-37
   lOADINGASeTOFS88XSAveDPARAMeTeRS......................................7-37
  trainparameterSfunctionS................................................................7-38
   S1&S2TRAINDelAy....................................................................7-38
TRAINSyNClOCATION.....................................................................7-39
TyPeOFTRAINPARAMeTeRS..............................................................7-39

S88X Dual Output Square Pulse Stimulator ix
 baSicoperatinGmoDeS.............................................................................7-40
SinGlepulSeS.....................................................................................7-40
  repetitivepulSeS(S1orS2).................................................................7-41
SinGletrainS(S1orS2).....................................................................7-41
  repeatinGtrainS(rt)S1orS2...........................................................7-42
  S1SpecialmoDeS...............................................................................7-43
SyNCTOS1DelAy.........................................................................7-43
SyNCTOTRAINDURATION................................................................7-43
  S2SpecialmoDeS...............................................................................7-44
SyNCWIThS1(SS).........................................................................7-44
POSTS1TRAIN(PT).......................................................................7-45
SyNCTRAINTOS1(ST)...................................................................7-45
SINGleARRhyThMIC(SA)...............................................................7-46
SyNCTOS2DelAy.........................................................................7-47
TWINPUlSeMODe..........................................................................7-47
BIPhASICPUlSeMODe.....................................................................7-47
MONOPhASICPUlSeMODe...............................................................7-48
8. artifact, stimulus isolatioN & coNstaNt curreNt ............................. 8-49
StimuluSartifact...............................................................................8-49
SourceS&reDuctionofStimuluSartifactS..........................................8-50
StimuluSiSolation..............................................................................8-51
StimuluScurrentmonitorinG..............................................................8-53
9. troubleshootiNg & maiNteNaNce ..................................................... 9-55
General.............................................................................................9-55
  reSetcircuitry...................................................................................9-55
  troubleShootinGtipS..........................................................................9-55
  fielDSoftWareupGraDe......................................................................9-56
a. aPPeNdix ...................................................................................... a-57
  conStantvoltaGevS.conStantcurrentSourceS
  forpulSeStimulation........................................................................ a-57
b. aPPeNdix ...................................................................................... b-59
  S88xtiminGDiaGramS...................................................................... b-59

x  Table of Contents

S88XDualOutputSquarePulseStimulator1-11
1Specifications & Symbols Glossary
Specifications
Train Rate (S1 and S2) ������ 1/100 sec to 99 TPS
Train Duration �������������� 1 msec to 99 sec
Rate (S1 and S2) ������������ 1/100 sec to 1000 PPS
Pulse Delay (S1 and S2) ���� 10 µsec to 99 sec
Pulse Duration (S1 and S2) � 10 µsec to 99 sec
Synchronous Outputs (TTL) � S1, S2, S1 Delay, S2 Delay, Train;
Front panel BNC connectors, 50 ohm,
10 µsec pulses,
can source/sink 20 mA peak
Synchronous Inputs (TTL) ��� Train Duration, S1 Delay, S2 Delay;
Front panel BNC connectors,
4.75 kohm pullup to 5 volts
Stimulus Output ������������ 250 mV to 24 volts (monophasic)
250 mV to ±12 VDC (biphasic)
Peak Output Current ������� 1 A
Output Protection ���������� Yes, current limited
Output Impedance ��������� <2 ohms
Maximum Power Out ������� 24 W peak
AC Power ������������������ 115/230 volts, 50/60 Hz, 100 watts
maximum
Physical Size ��������������� 19” W x 5.25” H x 12.5” D
(48.3 cm x 13.4 cm x 31.8 cm)
Weight ��������������������� 10 lbs. (4.5 kg)
Regulatory ����������������� Safety: EN 61010-1:2001, UL 61010A-1,
CSA C22.2 No. 1010.1-92
EMC: FCC Part 15, Subpart B, Class B,
EN 61326:1998 Class B
(All specifications subject to change without notice.)

1-12Chapter 1Specications
Glossary of symbols
Warnings & Cautions

S88X Dual Output Square Pulse Stimulator2-13
2Introduction
Safety Information
CAUTION
Misuse of this product may constitute a safety hazard. Please
review the following.
WARNING
The S88X output is not isolated. Do not use on humans.
1. For use by qualified persons only.
2. Removal of the S88X Stimulator cover may expose you to lethal
voltages and other hazards. Observe labels and caution notices.
3. Never drop or push objects into the stimulator through cabinet slots,
as it is possible to come in contact with hazardous voltages or cause
damage.
4. If the cabinet is damaged, a shock hazard may exist. Unplug the
stimulator and have it checked by a qualified person or contact Grass.
5. Never expose the stimulator to rain or moisture as this can be a
potential cause of fire or shock hazard. If the S88X is exposed to
moisture, unplug it and have it checked by a qualified person.

2-14Chapter 2 Introduction
6. The S88X cabinet has slots for ventilation purposes to prevent
component overheating.
a. Never cover the slots with cloth or any other material.
b. Avoid placing the S88X over radiators or heat registers.
c. Never place the stimulator in an enclosure unless proper
ventilation is provided and all other related precautions taken.
7. Operate the S88X only on the power sources as printed on the panel.
Damage may result from incorrect voltage.
8. The voltage/current output of this general purpose stimulator can be
lethal or cause tissue damage if not used properly by persons trained
in the application intended for this instrument.
9. Note the output of this general purpose stimulator is referenced
to ground, i.e., one terminal of the output is ground. Also all sync
inputs and outputs are also referenced to ground. To obtain stimulus
potentials isolated from ground choose the appropriate Grass
isolation unit.
10. If this stimulator is to be used with an isolation output, use the
proper Grass isolation unit accessory. Contact Grass for application
information in writing.
11. Determination of the safe levels of the stimulation for each
application is the responsibility of the investigator in charge.
12. The investigator in charge is responsible for assuring safe stimulation
levels will not be exceeded.
ElEctromaGnEtic compatibility information
The included ferrite EMI suppression cores are
required for compliance with EN61326. These should
be attached to each output cable by opening the split
core, then snapping it together over the cable so that
the cable runs through the ferrite core. These should be
placed near the output connector on the S88X.
Figure 2-1: Ferrite EMI Suppression Core

S88X Dual Output Square Pulse Stimulator3-15
3General Considerations
Applications & Capabilities
The S88X is a dual output general purpose electrical stimulator for
nerve and muscle stimulation procedures. Following in the tradition of
Grass quality and reliability, the S88X is the next generation of the Grass
stimulator line.
New Features Include:
• Digital controls — precise timing accuracy
• Bright display simplifies setup
• Independent or synchronous channel operation
• Monophasic and biphasic modes
• Dual train output
• High current output facilitates field stimulation
• New companion isolation units
• Software replacement
The built-in versatility of the S88X Stimulator makes it suitable for
unlimited stimulation protocols. The S88X has four parameter control of
the two independent outputs. In addition to single, repetitive, twin pulses,
biphasic pulses, monophasic pulses, pairs of unlike pulses, trains of pulses,
and post train pulses, continuous or trains of pulses are available at one
output with continuous or discontinuous operation at the other output.
The two outputs can be connected to the same preparation site providing
the outputs are isolated from ground using the SIU-C, SIU-V, SIU-BI or the
PSIU6X Stimulus Isolation Units. The S88X also includes the capability to
introduce an arrhythmic pulse within a cycle of pulses, especially useful for
research by cardiophysiologists studying atrial and ventricular fibrillation.

3-16Chapter 3 Applications & Capabilities
The S88X makes use of current technology in it’s design. A DAC (Digital
Analog Converter) is used to generate the output pulses, and a FPGA (Field
Programmable Gate Array) to reduce the size.
Software can be updated via the USB interface connector located on the
rear chassis. See chapter7explanationofcontrolS for instructions.
The S88X is a general purpose stimulator and not intended for human
stimulation procedures. The S88X is not designed for electroshock therapy,
for the creation of localized brain lesions or for electroanesthesia.
The design includes Fail-Safe shutdown circuitry which limits the output
current and prevents component damage in response to overload or
accidental short circuiting of either output.
The S88X can provide three types of pulses;
monophasic, biphasic, and twin.
See Figure 3-1a, b, and c. As shown in Figure 3-1b,
the biphasic mode provides equal and opposite
amplitude phases. This mode is especially suited
to applications where relatively long-term
stimulation of implanted electrodes is anticipated
and minimization of ion transfer from metal
electrodes to tissue is desired.
All modes and timing parameters are displayed
on the Vacuum Fluorescent Display. In general,
the following steps are used to set parameters.
1. Select S1 or S2 FUNCTION, then use the
TIMING thumbwheel dial to select the function.
2. Select appropriate PULSES and use the TIMING thumbwheel dial to
select the pulse type.
3. Select the TIMING RATE, DELAY, and DURATION values and the TRAIN RATE
and DURATION values using the TIMING left and right arrow keys and
the thumbwheel dial.
4. Adjust the desired output voltage using the OUTPUT AMPLITUDE left and
right arrow keys and the thumbwheel dial.
Note: To increase or decrease the rate, delay, duration or output
amplitude use the left and right arrow touch-pad controls to select
the digit to be changed. The number that is flashing is the number
that is selected. Then use the thumbwheel control to increase or
decrease that number.
Figure 3-1a:
Monophasic Waveform
Figure 3-1b:
True Biphasic Waveform
Figure 3-1c:
TWin Waveform

S88X Dual Output Square Pulse Stimulator3-17
The display is divided vertically. The left side displays the selected channel,
S1 or S2, function, type of pulses; monophasic, biphasic, or twin, and the
output amplitude (volts). The right side of the display is used for displaying
the Delay, Duration, Rate, Train Rate and Train Duration. The graphical
symbols accompanying the timing values indicate how the values apply
to the waveforms. The right side of the display is also used for any error
messages.
Several stimulus isolation units are available for use with the S88X:
Model SIU-V Isolated constant voltage
Model SIU-C Isolated constant current
Model SIU-BI Isolated biphasic constant current
Model PSIU6X Isolated battery-operated constant current
Selection of the isolation unit is made in the SETUP screen. (SETUP > CHOOSE
STIMULUS ISOLATION UNITS)
Non-isolated stimuli can be delivered from the S88X directly. To facilitate
connecting the S1 and S2 outputs in this mode, two special cables,
CAB-21891 are provided with orders that do not include stimulus
isolation units.
Figure 3-2: Vacuum Florescent Display
00.00005 S 00.00100 S
0001.00 PPS
N.A. N.A.
STIMULATOR #1
FUNCTION = RP
PULSES = MO
VOUT =
010.00 V

3-18Chapter 3 Applications & Capabilities
accuracy & WavEform
All timing parameters are crystal
controlled and are accurate to within
±0.00005%. This feature provides
repeatability for the most demanding
applications.
Both the rise and fall times of the
S88X output pulses are approximately
4 microseconds. Calibration of the
duration is based on the average
width of the pulse. Figure 3-3
illustrates the pulse waveform at a
duration of 10 microseconds.
Because of this high accuracy, it is seldom necessary to monitor the
stimulus. However, when complex pulse patterns are produced and until all
basic modes of operation of the S88X are understood clearly, monitoring
the output with an oscilloscope is advised. Figure 3-4 shows typical pulse
waveforms obtainable with the S88X.
Figure 3-3: Pulse Waveform
Figure 3-4: Typical Stimulus Waveforms
10 sec
150 Volts
S1
Single Stimulus
S1
Continuous Stimuli
S1
Trains of Stimuli
S2
S1
S1
S1S2
S2
Trains
with
Post
Train
Stimulus
S1
S2
Trains S1 - Continuous S2
S1
S2
Pre-train Stimulus followed
by Delayed Train
S2
S1
Same Train Rate - Different Train
Duration and Pulses in each Train
S2
S1
Trains with Mid
Train Stimulus
S2
S1
Same Train Duration and
Rate - Different Number of
Pulses in each Train
S2
S1
S1
S1
S1
S2
S2
Pairs
of
Stimuli
S2

S88X Dual Output Square Pulse Stimulator3-19
linE voltaGE rEquirEmEnts
The S88X has an IEC320 Power inlet for a standard 3-wire AC cable. The
unit accepts 115 to 230 volts, 50/60 Hz. The maximum power is 100 watts.
The S88X power inlet accepts a standard 3-wire AC Power cord. The input is
115-220 volts, 50/60 Hz and 100 watts. Fusing is in the S88X power supply.
Duty cyclE
Duty cycle is defined as the ratio of the time that the stimulus is on to the
total period or interval. Since the time from the start of one pulse to the
start of the next pulse in seconds is the reciprocal of the frequency or PPS
(T=1/F), the DELAY and DURATION controls should not be set greater than
T=1/2F which is equivalent to 50% duty cycle. 100% duty cycle occurs when
a circuit is on continuously, as with DC.
Note: If TWIN or BIPHASIC PULSES are selected, the duty cycle is calculated as
twice the pulse time divided by the period multiplied by 100.
The S88X duty cycle limit can be set in the SETUP function. The default
value is set to 50%. Values from 0 to 99% are selectable. The S88X display
will flash and limit the value when the selected duty cycle is exceeded
while making a selection with the OUTPUT ON/OFF on. During setup, with the
OUTPUT ON/OFF in the off position, a duty cycle message will display if the
duty cycle is exceeded. In these messages, the DCWL value is a percentage
and is the Duty Cycle Warning Level. When the output is initially turned
on, all parameters will be checked against the duty cycle limit. If the limit
is exceeded, a message will be displayed. The output will not be turned on
until the output is below the duty cycle limit.
Example #1:
50% duty cycle occurs if there is on-off symmetry, as with a
symmetrical square wave, where the on time (or pulse duration) is
equal to the off time (or time between pulses) for one cycle. See
Figure 3-5.
Figure 3-5: 50% Duty Cycle
“off” time
T = 1/F
“on” time

3-20Chapter 3 Applications & Capabilities
The 50% duty cycle can never be exceeded if the DELAY and DURATION
controls are set for less than 500 µs. If the DELAY circuit is not being
used, always set the DELAY controls for less than 500 µs.
Most triggered circuits, such as those in the S88X, cannot be driven
satisfactorily over 90% of their duty cycle. Although the stimulator will not
be harmed if the duty cycle is exceeded, the stimulator calibration may be
affected if operated above a 50% duty cycle.
The train duration should not exceed 50% of the TRAIN RATE settings.
mountinG & installation
The S88X is housed in a compact cabinet 9” W x 5.25” H x 12.5” D
(48.3 cm x 13.4 cm x 31.8 cm) and can simply be placed on a laboratory
table. An optional Model S88XBT adjustable bench-top stand to mount
one stimulator is also available. The S88X can also be rackmounted in a
standard 19” equipment rack with the optional Model S88XRK rackmount
brackets. When rackmounting, be sure to provide adequate spacing
around the S88X for ventilation. Do not cover the ventilation holes in the
S88X cabinet.