Chapter 2
Setting Up
29
You can stop the signal scrolling by clicking the Pause button at the
bottom left (Macintosh) or top right (Windows) of the data display
area. On the Macintosh this changes to the Scroll button. Click the
Scroll button to start scrolling again.
Shift and stretch the vertical Amplitude axis, by clicking and dragging
it in various ways, to make the best use of the available display area. It
functions the same as the Amplitude axis of the Chart window,
controls are identical and any change is applied to the Chart Window.
On a Macintosh,
Show Range Axis
in the Scale pop-up menu displays
the range axis at the right of the display area, and the Compression
buttons adjust the horizontal axis of the data display area.
Setting the Range
The
Range
pop-up menu lets you select the input range or sensitivity
of the channel (combined range of the PowerLab and Bridge Amp).
Changing the range in the Bridge Amp dialog is equivalent to
changing it in the Chart window. The default setting is 5 V and the
ranges go down to 200 μV in 14 steps.
Filtering
The filtering options provided are appropriate to the type of
transducers used with the Bridge Amp, and the signals usually
measured, which tend to be of lower frequency. Low-pass filters allow
you to remove high-frequency components, such as noise, from an
input signal. The Mains filter allows you to remove interference at the
mains frequency (typically 50 or 60 Hz).
Low-Pass Filtering
. The
Low Pass
pop-up menu provides a choice of
filters to remove high-frequency components from the signal. They
are: 1, 2, 10, 20, 100, and 200 Hz, and 1 kHz. (The highest frequency
you can actually record is limited by the transducer you use: such
information should be in the documentation supplied with it.)
Mains Filter (/20, /25 and /30 series PowerLabs only)
. The
Mains filter
checkbox allows you to filter out interference at the mains frequency
(typically 50 or 60 Hz). Note that in general it is better to prevent
interference at its source than to filter it. The mains filter is an adaptive
filter which tracks the input signal over approximately 1 second. It
analyzes the signal and creates a template of any interference due to
the mains frequency (see Appendix C). Subtraction of the template
from the incoming signal cancels most of the interference.
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