Single Channel EEG Test System | User Manual
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2.5.2 Main parameters
Amplitude:
Can be set in either mV or µV, changing one will
automatically change the other to match. The waveform
amplitude from -2 mV to +2 mV at a 0.001mV (1 µV)
resolution. For all waveforms the amplitude represents the
peak to peak value. For example, for a 1mV sine wave the
actual waveform varies b0.5mV and -0.5mV. This
correlates with testing requirements in standards.
Frequency:
Set in either Hz. Continuous waveform (Sine, Triangle and
Square), can up to 500 Hz, for pulse waveforms (rectangle,
triangle), the frequency can also be referred to as the pulse
repetition rate. For some pulse settings the frequency is
limited to prevent overlapping pulses (limit to 5 Hz).
Pulse Width:
Apply to rectangle, triangle and exponential pulse
waveforms only. For the rectangle, pulse width is defined as
the time between crossing the 50% point in rising and falling
edges of the pulse
2
. For triangle pulses, the setting matches
the base of the triangle pulse. For exponential pulse, the set
pulse width is time constant. Pulse width can be set to down
to 2ms
3
.
2.5.3 DC offset setting
This function allows the operator to switch in a dc offset. In the
default condition (not variable), only +150mV, 0 or -150mV can
be set. In this mode, the dc offset is sourced from an internal
“super capacitor” which at least
3 minutes of accurate and
stable 150mVdc offset to be placed in series with the main
waveform, without impacting the quality of that main
waveform. The capacitor is charged while not in use (i.e. when
the setting is zero).
In the variable mode, the dc offset is provided by a second
channel. It is limited to 1000mV.
2
To minimise ringing due to EEG notch filters, rectangle pulses have a rise time of 1ms. This means
that a 20ms rectangle pulse will actually have a 21ms base and a 19ms at the top of the pulse. This
definition ensures that the pulse integral matches the setting, e.g. a 3mV 100ms pulse will have an
integral of 300µVs.
3
Note the sampling rate is limited to 0.2ms. Therefore, a 2ms pulse will have limited time resolution.