PowerLab Teaching Series - Owner’s Guide
33
The Isolated Stimulator Output
The Isolated Stimulator output provides a so ware-controlled, isolated, constant-
current pulse stimulator that can be used for any general purpose stimulation.
The output stage consists of a high-voltage, constant-current source that can produce
pulses of variable duration and amplitude under full so ware control. The current source
can deliver pulses up to 20 mA at 100 V maximum compliance levels; its amplitude is
controlled by optically isolated digital control signals from the non-isolated section.
The output to the subject is through high-isolation optical couplers.
So ware and hardware safety features limit the energy delivered by the pulses to within
international safety standards. The pulse duration of the stimulator can be set from 50
μs to 200 μs, and the pulse frequency can be adjusted between 1 pulse per minute and
20 pulses per second.
The Isolated Stimulator Pulse indicator is an LED that is used to indicate the current
status of the Stimulator. It will flash green forevery stimulus pulse, and may seem to
glow green constantly at higher stimulus frequencies. The OOC (out-of-compliance)
indicator is a yellow LED. When lit, it indicates that the output is overloaded or out of
compliance (compliance is the ability to supply voltage to meet the required current).
This means that the impedance of the tissue being stimulated is too high, or there is
a poor electrical connection (possibly due to electrode drying), and that the Isolated
Stimulator can no longer supply constant current stimulation. If this should happen, try
reducing the output current amplitude, and check all connections.
Out of Compliance
Constant current source
Transformer
driver
Isolation amplifier
Stimulator
Power
Supply
Current setting DAC
Stimulator
pulse
safety
Stimulate
Stimulate
control
INDICATORS
Stimulate Output
Stimulus Isolator
switch
Figure 4-6
Block diagram of the
Isolated Stimulator
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