The Analog Inputs; The Analog Outputs - ADInstruments POWERLAB TEACHING SERIES Owner's Manual

CAUTION:
Applying more than
±15 V to
the input can damage
the input circuits.
WARNING:
Analog outputs are
not to be used for
connection to
human subjects.
Figure 4-2
The analog output
stage, set up for a
diff erential stiimulus
30

The Analog Inputs

PowerLab input amplifiers have been designed with a considerable amount of
computer-controlled gain (up to × 2000). Thus it is possible to record a variety of signals
without any external pre-amplification. Each analog input is a separate DC amplifier with
programmable gain able to be set independently (the gain is set through the soft ware
range control). The PowerLab inputs can be set by the soft ware to be either single-
ended or diff erential. In the diff erential setting, the amplifier measures the diff erence
between the positive and negative inputs, irrespective of ground.
It is important to note that the PowerLab grounds the inputs to amplifiers not in use.
It also grounds each amplifier and measures the DC off set voltage when the gain is
changed. In this way, the soft ware corrects for any DC drift or off set in the circuits that
may develop over time or between readings.
Input impedance is one megohm. (On the 15T and /26 model PowerLabs, the impedance
between the earthing stud (ground connection) and the input connector grounds is
close to zero.

The Analog Outputs

The analog outputs provide computer-controlled variable outputs (±10 V) that can be
used with the LabChart and Scope applications either directly as a stimulator, or to
control peripheral devices. All stimulation voltage is generated by the PowerLab via the
output sockets on the front of the PowerLab (marked Output + and –), giving positive,
negative, diff erential, depending on the sockets used and the soft ware settings.
From DAC
By default, the outputs are used for complementary (diff erential) stimulation, where
Output + is positive and Output – is negative. When Output + is used, a positive stimulus
voltage (set up in LabChart or Scope) gives a positive voltage output, and a negative
voltage a negative one. When Output – is used, the voltage outputs are inverted. When
both output sockets are used, the stimulus is the diff erence between the voltages at the
positive and negative outputs: you could generate up to a 20-volt pulse, given a ±10 V
range setting.
+
GND
-
PowerLab Teaching Series - Owner's Guide
+10V
-10V
+10V
-10V