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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.

Basic Operation

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.

Impedance Checking

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.

Recording Cals

(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.

Baseline Recover

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.

Led Indicators

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.

Switching Between Nicolet Amps and James Long Amps in the White Lab

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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