|
|
Docs: SA Amplifiers
Each battery should last for 26 hours of recording time, but this will decrease as the batteries age.
A battery should be recharged when:
It has been used for 20 hours or more
Its voltage drops below 6.0V
The battery low LED is lit
A full recharge requires 8-10 hours.
A battery may be left on the charger indefinitely. Do not, however, leave a battery connected to the charger unless the charger is plugged in to an active electrical outlet. This may destroy the charger and/or battery.
One battery should be connected to the charger and one to the amplifier at all times.
Each channel of the amplifier has an active pin (marked "+") and a reference pin ("-") on the headbox.
The active pin is connected to the amplifier input and also to a pin on the electrode cap (DB25) inputs. If an electrode is connected to the active pin while an electrode cap is connected to the corresponding DB25 connector, the signals from the cap and the individual electrode will be combined. This is fine if, for example, a quick insert electrode is being used, because this creates two parallel connections from a single electrode to a single input. However, care must be taken when connecting an electrode to an amplifier channel that is normally used for a different electrode cap site.
Each channel has a 3-position switch that determines the reference source for that channel. In the "REF" position, the "common" reference will be used; specifically, the headbox "REF" pin jack and pin 25 from all 3 electrode cap DB25 connectors are tied together and used as the reference. In the "OPEN" position, the reference pin jack for the specific channel will be used as the reference. In the "GND" position, the active and reference for that channel will both be connected to ground.
The ground signal can be connected either directly through the electrode cap cables (pin 9 of the first DB25 connector) or indirectly through the ground pin jack on the headbox. These two sources are tied together inside the headbox.
Any channels that aren't being used should be set to "GND". Otherwise, those channels will enter the "fail" state and draw substantial power from the amplifier. If enough channels are left open, degradation of performance may occur in the other channels.
Each channel has an impedance (Z TEST) switch, which causes its active and reference signals to be routed to the impedance meter pin jacks on the headbox. To test a channel's impedance, simply connect an impedance meter to these pin jacks and press the switch for the to-be-tested channel.
To test the impedance of the ground electrode, connect one impedance meter lead to the ground jack on the headbox and the other lead to the reference jack of any channel that is switched to "REF". The measured value will reflect the impedance between the ground and reference electrodes.
The electrode cap inputs on the headbox are male DB25 connectors, which are the wrong gender for our caps. To use an electrode cap, a double-female gender changer must be used.
Pin assignment for the VER headbox (64 channels) is available here.
There are several indicator LEDs on the main unit's front panel. Each channel has a "fail" LED; these light when there is a bad connection or open circuit (i.e., high impedance). The output of a channel will be garbage if its fail LED is lit, so do not collect data if one or more of these are lit.
There is a system-wide "fail" LED that lights when the whole system goes into a fail state. This usually occurs when several individual channels are disconnected, causing the amplifier to draw too much power from the battery. To clear this fail state, fix the problem that caused the fail state (e.g., switch the open channels to "GND") and turn the amplifier off and back on.
The gain and filter settings for channels 1-60 are controlled by a single set of rotary switches. Channels 61-64 have their own switches.
The amplifier has 3 built-in calibration sources, two continuous sine waves and a triggerable square wave. These signals are available on female mini phone jacks on the amplifier front panel and on the headbox.
To connect the calibration signals to the amplifier inputs at the headbox, use the adapter with 1 male mini phone plug and 3 female DB25 connectors. Plug the phone plug into the jack for the desired calibration source and the DB25 connectors into the amplifier inputs. For best results, plug in all 3 DB25 connectors even if only a subset of channels will be used.
To connect the calibration signals to the amplifier inputs at the main amplifier unit, use the adapter with 1 male mini phone plug and 6 female DB25 connectors. Plug the phone plug into the jack for the desired calibration source and the DB25 connectors into the connectors where the headbox is normally attached. For best results, plug in all 6 DB25 connectors even if only a subset of channels will be used.
During calibration, all 64 channels must be set to "Ref" on the headbox. If one or more are set to "Gnd", the calibration signal will be shorted to ground, degrading the signal.
The square wave calibrator can be triggered by the stimulus presentation system. This is accomplished by setting the calibrator switch to "External/Off" and connecting the trigger pulse from the SPI box (BNC connector marked "ALL") to the BNC connector on the DB25 interface box.
The calibration signals run from the amplifier to the headbox through the same cables that bring the EEG signals to the amplifier. To avoid contaminating the EEG with cal pulse artifacts, turn off the sine wave calibration signals and disconnect the trigger pulses while collecting EEG data.
1) At the beginning of each recording session:
Use the voltmeter to check the battery
voltage (using the + and - "Battery Monitor" pins on the amplifier front panel).
If the reading is below 6.0V, swap batteries.
Make sure that the calibration trigger pulse cable is disconnected.
Position all headbox switches at GND.
It is best to leave the amplifier turned off until the
subject is connected.
2) Connect the subject to the headbox:
Plug the electrode cap into the headbox.
Plug the individual electrodes into
the appropriate pin jacks on the headbox (e.g., mastoid and EOG electrodes).
Switch all channels being used to
REF for common reference or OPEN for bipolar. Turn on the amplifier and make sure
that no fail LEDs are lit. 3) Re-check all impedances:
Plug the impedance meter into the Z TEST pin jacks.
Press the Z TEST button for each channel to
check the impedance for that channel.
Check the ground impedance by connecting the impedance meter
to the ground pin jack and to the - input of a channel that is
set to REF.
4) Disconnecting the subject:
To disconnect the subject for a break in the middle of the
session, simply turn the amplifiers off and disconnect the
cap and individual electrodes from the headbox. The switches
can be left on. Reconnect the subject before turning the
amplifier back on. Check fail LEDs before recording.
To disconnect the subject at the end of the session,
first turn all headbox switches to GND. Then disconnect
the cap and individual electrodes from the headbox.
5) To record calibration pulses:
Plug the grey calibration adapter
cable into the square wave source on the headbox, and attach the DB25
connectors (labeled "A", "B", "C", and so on)
to the correct headbox inputs. Turn all channel switches (ALL
of them) to REF (including any not being recorded). Turn the amp on and switch the square
calibration signal to "External". Make sure all needed channels
are online (not FAILED).
Now start the necessary programs...
Start Presentation on the
stimulus computer. Load the calibration scenario file.
Start Acquisition. Set the
condition to "0". Always record calibration
in condition 0!!
Run the calibration scenario. You
should observe:
An event code "1"
appearing on the event code display:
The external event led on the
amplifier blinking
Tiny cal pulse traces on the
eeg traces in the digitizer display
Transfer data to Linux when scenario finishes...
Once the cal.log and cal.raw files
have been collected, transfer them to Linux for verification. Verify that all cal events are in
the cal.log file (using logfile). Also check that they were recorded
in Condition 0. Use rawfile to check the cal.raw
data. You should see square wave pulses oriented "up", of 100msec
duration, with an SOA of 500msec. 5) Final cleanup:
Turn off amplifier.
Make sure that all headbox switches are set to GND.
Write down number of hours of battery use, or swap batteries
if use exceeds 20 hours.