Instruction manual
6 World Precision Instruments
OPERATING INSTRUCTIONS
Operation of the A365 is controlled by applying an external voltage command
to the input or by manually operating the DC/Test switch. Any source such as
WPI’s DS8000, A300, A310 pulse generators or equivalent generator will be an
appropriate source of command and trigger sync pulses for oscilloscope viewing of
bioelectric responses.
Electrode connections
Connect an appropriate pair of stimulating electrodes from the experimental site to
the red and black OUTPUT terminals, respectively. Any conductive wire (including
carbon wire) may be affi xed to the terminals by either a banana plug (4 mm) or by
means of holding a bare wire on the plastic nut.
Keep the output switch in the OFF position to avoid accidental stimulation.
During the powering of any electronic circuit either up or down, the output may be
unstable due to internal oscillations or circuits powering at different times.
Turn the output switch to OFF. Turn POWER to ON. Select Biphasic Off (i.e., unipolar
current) and toggle the Polarity Select. A red indicator lamp lights over the output
electrode terminal which will be positive (usually, the negative electrode stimulates).
Toggling the AUDIO switch ON will allow the user to hear the advent of the
command pulse; normally this is left in the OFF position. Turn the % of Range knob
to zero and Range switch to 1mA. Switch the Output switch to ON. This connects
the electrodes to the current source. Arriving at an optimal stimulation current level
is usually an empirical procedure in which the user increases the current gradually
from sub-threshold values until a desired stimulus response is achieved.
Always toggle the Output switch to OFF while connecting electrodes or powering
up or down the unit. When this switch is toggled to OFF, the output terminals are
disconnected from the stimulus current source and the current source is short
circuited internally (see Electrode Exhauster) if the Electrode Exhauster is enabled.
Check the accuracy of the setting on the % of Range dial by connecting a milliamp
meter directly across the output connectors and pushing the DC/TEST switch.
The direction of current fl ow is determined by which output connector has been
designated as the anode, i.e., RED + or BLACK + on the POLARITY switch. AUDIO
monitoring of the pulses can be switched ON or OFF at the user’s option.
Microstimulation
Microstimulation is considered to be stimulation currents of less than 500 μA passing
through electrodes and tissues. Currents in excess of 1 mA have been known to
damage tungsten metal electrodes by burning the tip of the electrode. Tungsten
and other metal electrodes are made by an electro-etching process that leaves the
electrode behaving as a capacitor (AC) rather than a conductor (DC). This etching
action results in the formation of an electrolytic interface between the metal surface