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amps - using the James Long Bioelectric Amplifiers (ERP manuals)
This document provides instructions for using the James Long
Bioelectric Amplifiers in the Kutas Lab. Much of
the information here
was gleaned from the James Long
Company "OPERATION and SPECIFICATIONS"
manual that was provided
with the amps - for more detailed information
about the amps see that
manual (it should be kept near the amps somewhere).
A James Long amp is powered by a single 12V rechargeable battery.
Each amp
has two batteries so at all times there can be one battery in
use and
another battery waiting fully charged as the spare. An experimenter
is responsible for logging his use of the battery, changing the
battery
when needed, and placing the depleted battery on the charger.
Longest battery life is obtained when the battery is changed BEFORE
its
power runs out. Typical battery run time is about 40 hours,
but even an
unused battery runs down over time so a good policy
is to change the battery
every 10 subjects or every 2 months, whichever
is sooner. Somewhere near
the battery charger should be a log sheet
that indicates the date of the
last battery change and how many
subjects have been run on the current
battery. An experimenter
should inspect this log before running each subject,
change
the battery when it is time, and remember to log on the sheet
each subject and each battery change.
To change the battery: TURN THE AMP OFF (be sure to turn off the
amp
rather than the impedance meter on the headbox); remove the
discharged
battery;
connect the charged battery; then turn the amp ON. Data collection
can begin immediately. RECHARGE DEPLETED BATTERIES IMMEDIATELY -
failure
to do so may permanently damage battery cells.
To recharge a battery connect it to the charger. A depleted battery takes
up to 16 hours to fully charge - when the charge lamp
turns from red to
green the battery is in float mode and ready for use.
The battery can be
left connected to the charger to maintain a float-charge
until it is ready
for use.
Chargers can be plugged into the AC power and left; there is no
need to
plug and unplug these devices.
Prior to powering-up the amp, always set the MODE switch
to CALIBRATE.
Switching to NORMAL should occur only after all inputs are
either
connected up or switched to GND on the headbox.
Ensure the HEADBOX CAL-TEST CABLE is completely removed from the
headbox
during data collection; this cable should only be attached
when recording
calibration pulses.
On the headbox, plug electrodes to be referenced to the REF electrode
into the red (+) jacks and switch these channels to REF, which connects
the black (-) jack to the headbox REF bus and ultimately to the REF
source
point via a loose-lead reference electrode connected directly
into the
REF jack.
For electrodes to be referenced to each other, plug the electrode
pair
into the red (+) and black (-) jacks and switch the channel to OPEN.
In the OPEN position the black (-) jack is not connected to the REF
bus
and both the red (+) and black (-) jacks are available for an
electrode
pair. Switch open/unused channels to GND to prevent them
from "glitching"
other channels. In the GND position the (+/-)
inputs are both tied to ISO-GND.
The REF electrode should be an exact-material copy of the signal
electrodes
to minimize data blocking and FAIL mode problems.
In all cases the headbox
ISO-GND must be connected to the subject
for proper amp operation, but
unlike the REF electrode the ISO-GND
electrode material is not critical.
To check the integrity of the electrode connections see
IMPEDANCE CHECKING.
To acquire data set the MODE switch to NORMAL; when not recording
data
set it to CALIBRATE. This will speed up baseline re-zero when
resuming
data collection.
If massive input-opens occur (i.e. loss of the REF lead),
turn the amp OFF
and rectify the problem. A
30 second power down with a temporary move
of the
HPF settings to the highest setting will speed up recovery when
powering back up.
To record calibration pulses (usually done after the subject
data are
collected) see RECORDING CALS.
When data collection is complete turn the amps OFF. The amps should
remain
off when not in use.
An impedance meter is integrated in the headbox for
checking
the contact integrity of the electrodes - the target is to ensure
that the impedance of each electrode is below 5 kilo-ohms.
The meter circuitry
is such that it
tests an electrode as compared to all other electrodes
in parallel,
so for reasonable accuracy A MINIMUM OF SIX CHANNELS INCLUDING
THE
REFERENCE AND ISO GROUND SHOULD BE ACTIVE.
To check electrode impedances switch ALL channels to GND,
switch the
impedance meter on, then check each electrode as follows:
The reference (REF) electrode: press and hold the REF push button.
The ground (ISO-GND) electrode: press and hold the GND push button.
A referenced electrode: switch its channel to REF, ensure all
other channels
are switched to GND, then using the small plastic pick
press and hold
the recessed Z-TEST push button for the channel.
Electrode pairs (i.e. both input jacks of a channel are used):
switch the
channel to OPEN, ensure all other channels are
switched to GND, then using
the small plastic pick press and hold
the recessed Z-TEST push button for
the channel.
Remember to restore the channel switches on the headbox to their
appropriate
settings (REF for referenced electrodes, OPEN for
electrode pairs, and
GND for unused channels) after impedance checking.
Always turn the impedance
meter OFF when not in use to prevent data
contamination.
(NOTE: for the time being ignore this section, cals are
currently being
recorded differently than is described here.)
There is no need for a cal box with the James Long amps.
Each amp contains
circuitry for generating an externally
triggered 10 uV 200 ms calibration
pulse that can be directed into
all channels of the headbox via the temporary
attachment of a
specially built cable.
To record cals:
1. set the amp MODE switch to NORMAL
2. set the amp CALIBRATOR switch to 10uV-200ms
3. set the amp toggle switch to REMOTE/MANUAL
4. connect the HEADBOX CAL-TEST CABLE to the headbox: the A
and B connectors attach to their respective ports on the
left side of the headbox, and the plug attaches to the
CALIBRATION SOURCE jack on the front panel of the headbox.
5. set ALL the headbox channel switches to REF
6. present your calibration stimuli (via the STIMPRES program)
and ensure the dig program is recording the cal pulses.
When finished recording cals, completely remove the HEADBOX CAL-TEST
CABLE.
To facilitate baseline zeroing always power up the amp
with the MODE
switch set to CALIBRATE; only switch to NORMAL after the
inputs are
connected up and any unused channels are set to GND.
If baseline zero is lost due to some input disturbance, press the
BASELINE
RECOVER button on the amp for a ~3 second recovery period.
This button
can be pressed multiple times or held down if necessary
to recover from
excesive or ongoing input distrubances.
An experimenter should check the LED indicators on the amps
each
time he is in the subject chamber since these are his only opportunities
to see them. The "LED MONITORS" section of the James Long "OPERATION and
SPECIFICATION" manual has a complete description of each indicator;
here
are indicators that can signal a problem during a run:
ELECTRODE MONITOR: A modulated (variable brightness) LED for each
channel
indicates a poor electrode connection (the brighter the LED
the poorer
the connection) or a lead-off. In normal operation all
these LEDs will
be off. If one of these LED lights,
move the related headbox switch to
GND to prevent corruption of the
other channels until the electrode connection
is repaired.
If all are on, the REF electrode is suspect. Note the REF
electrode
should be an exact-material copy of the signal electrodes to
minimize
blocking problems. The ISO-GND electrode must also be connected
for
proper operation however its material is not critical.
Press TEST
to check these LEDs.
ELECTRODE STATUS: Indicates when the intensity of one of the ELECTRODE
MONITOR LEDs has reached the data output blocking level - a situation
requiring
repair of the electrode connection.
LOW-BATTERY: The battery is nearly depleted. When this LED lights there
is
enough power for 30 to 60 minutes more of data collection. If you are
certain you can complete your subject and collect cals within 30
minutes
of this LED having lit then do so and change the battery when
you are
done; otherwise you must pause data collection, shut down the
dig program,
change the battery (see BATTERIES), then restart
the dig program and continue
collecting data in a second set of raw and
log files.
FAIL: Indicates the amp has shut itself down from low battery,
multiple
input overloads or opens, or internal electronic failure.
To reset a FAIL
turn the power off, wait 20 seconds, then turn the
power on again. The
POWER indicator should come on. If the amp
goes "dead", ensure that the
battery is charged, the fuses are OK
(on back panel of amp), and all inputs
are connected up.
The fuses are two 1/2 amp FAST-BLOW - DO NOT USE SLOW-BLOW
fuses.
If no problems are found, discontinue use and submit for repair.
The James Long amps in the white lab are set up such that either they
or the older Nicolet amps can be used to collect data. The Nicolet
amps
will remain in the white lab until all experiments using them are
complete;
any new experiments being started in the white lab should
use the James
Long amps.
How do you tell which amps are currently connected to the A/D card?
Look
behind the computer rack at the A/D card cable,
which is a gray 3 ft double
ribbon cable coming out of the
back of the dig computer. If the A/D cable
is attached to a card
hanging from four black connectors the Nicolet amps
are connected;
if the A/D cable is attached to a card sticking out of
a cardboard
box the James Long amps are connected.
Use of either set of amps requires a) connecting the subject’s
electrode
cap to the appropriate set of amp headboxes inside the
subject chamber,
and b) connecting the appropriate set of amps
to the dig computer’s A/D
card. The former is done after seating
the prepared subject in the chamber
and should be relatively obvious;
the latter is done well before the subject
arrives and should be
done as follows.
To switch amps (note the first three steps are CRITICAL
to the well being
of the equipment, failure to power down before
swapping cables can result
in nicely toasted electronics):
1. TURN OFF the dig computer via the push button switch on the
front panel.
2. TURN OFF the two Nicolet amps (next to the dig computer)
via the push button power switches on the front panels, lower
right. These switches may be somewhat hidden under note paper.
3. TURN OFF the two James Long amps (on a cart inside the subject
chamber) via the toggle switches on the front panels, lower right.
Be sure to turn off the amps which are the larger boxes beneath,
and not the impedance meter on the headboxes which are the smaller
boxes on top of the cart. Turning off the amps also turns off
the headboxes.
4. Step behind the computer rack, taking care to avoid disturbing
(i.e. unknowingly disconnecting) any of the multitude of cables.
The entire rack is on wheels, it may help to temporarily pull it
out a bit to provide more room in back to maneuver. Disconnect
the end of the A/D cable (described above) that is farthest from
the dig machine and reconnect it to the desired amps - connect it
to the card hanging from the four black connectors for the Nicolets;
or connect it to the card sticking out of the cardboard box for
the James Longs. Take care when connecting to the Nicolet card -
after the connection is complete the card should remain hanging
such that there is nothing in contact with the conductors on the
base of the card.
5. Step into the subject chamber and connect the BNC-terminated
stimpres calibration trigger cable to the appropriate calibration
device - the blue and white cal box when using the Nicolet amps,
or the James Long calibration trigger cable when using the James
Long amps.
6. Turn on the dig computer.
7. Turn on the desired amps.
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