ADInstruments Bio Amp, Owner'S Manual

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Chapter 2 Setting Up
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with the I
2
C cable as shown in Figure 2–1. The remainder are daisy-chained
via I
2
C cables, connecting the I
2
C output of the last connected front-end to
the I
2
C input of the front-end to be added, as shown in Figure 2–2. Note that
signal degradation may occur if multiple Bio Amps share a common ground,
such as by being connected to a single subject.
Using More Than One Bio Amp
If you intend to record with more than one channel using a common ground,
such as recording from a single subject, it is recommended that you use a
Dual Bio Amp rather than two Bio Amps, and that you use an Octal Bio Amp
rather than two or more Dual Bio Amps. Some interaction can take place
between individual Bio Amps, causing up to 10 μV of induced low-frequency
signal, through slight differences in frequency between the isolated power
supplies. For multiple channel recordings, using the Dual Bio Amp instead of
two Bio Amps or the Octal Bio Amp instead of two Dual Bio Amps avoids the
problem. Using multiple Dual Bio Amps (usually three or more) causes
similar problems on the second channel of each. This should not affect most
biopotential measurements, especially if you use filters or signal averaging. It
is of little or no consequence, for instance, when recording electroretinograms
or electro-oculograms.
Using ADInstruments Programs
Front-ends are used with PowerLabs and ADInstruments applications such as
LabChart and Scope. The amplification and filtering of the Bio Amp is
combined with that of the PowerLab and the application and presented as a
PowerLab I
2
C output
Front-end I
2
C input
Front-end I
2
C
output
Figure 2–2
Connecting a front-end to
the PowerLab: a PowerLab
has only one I
2
C output,
and each front-end has one
I
2
C output and one I
2
C input