Chapter 1 — Overview
7
input signals. Do not attempt to record from both the BNC and pod
connectors for an input at the same time, or the signals will compete.
Pod connectors allow the connection of ADInstruments pods —
small, low-cost units that provide alternatives to front-ends for
specific tasks, for use with precalibrated transducers and so on. The
pod connectors on the PowerLabs do not handle transducers directly
unless the transducers are so labelled (unsuitable transducers will
give a very weak signal). Transducers designed for direct connection
can be provided with power and control, since the pod connectors
provide some functions of the I
2
C output as well as alternative analog
inputs to the BNC connectors.
Analog Output
The PowerLab can generate a stimulus voltage through its analog
output sockets (marked Output), giving positive, negative, or
differential (complementary) stimuli, depending on the sockets used.
The negative output is always the opposite of positive output. This
means that if the positive output gives a +5 V signal, then the
negative output will simultaneously give a –5 V signal. The outputs
cannot be run independently. If only the positive output socket is
used, a positive stimulus voltage (set up in the software) will give a
positive voltage output, and a negative voltage a negative one. When
the negative output socket is used, the voltage outputs are inverted.
When both output sockets are used, the stimulus is the difference
between the voltages at the positive and negative outputs.
Trigger
The external trigger connector allows you to use an external signal to
synchronise recording to an external event. This input can handle
voltages of up to
±
12 V. The threshold voltage (the voltage above
which the trigger circuit activates) is 2.9 volts for the /20 series
PowerLabs. When the trigger threshold is crossed, the indicator
beside the external trigger connector will glow yellow. The external
trigger is described in more detail in Appendix A, and the software
documentation covers its practical use in normal recording.
▲
Caution
PowerLab inputs and
outputs are not electrically
isolated. Human subjects
must not be connected
directly to the PowerLab.
If such measurements are
to be made, an isolated
front-end must be used,
such as the Bio Amp.
Summary of Contents for PowerLab 2/20
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