20
PowerLab Owner’s Guide
achieved with an external relay contact, a manual push-button, or a
microswitch. The trigger input is not electrically isolated when set up
for contact closure.
A single 16-bit DAC (digital-to-analog converter) is used to provide
an analog output or stimulation capability through the analog
outputs of the PowerLab (marked ‘Output’ on the front panel). The
DAC can produce constant DC voltage levels or waveforms under
software control. Stimulation frequency is completely independent of
the analog input sampling rate. The output of the DAC is fed through
a programmable attenuation network to produce different output
ranges. The signal is then split into a positive and negative output
through buffer amplifiers. The outputs are capable of driving up to
12 mA into a load.
The PowerLab is also fitted with an I
2
C front-end expansion port.
This is a 9-pin port that allows ADInstruments front-ends to be
attached to the system. It provides both power and communications
to allow software control of the attached hardware.
The PowerLab uses an IEC601-1(medically) compliant switching
power supply. This provides a universal input that handles all
common international voltage supplies and frequencies without the
need to change voltage ranges. This power supply is also internally
protected in the case of a problem. It is important to note that the
PowerLab has a limited amount of power available for external
devices. Because of these power limitations, you should not use the
PowerLab as a power source for external devices other than those
produced by ADInstruments.
The Analog Inputs
PowerLab input amplifiers have been designed with a considerable
amount of computer-controlled gain (up to
×
5000). 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 software
range control: the less the range, the more the gain). Inputs 1 and 2 of
the PowerLab 2/20 and PowerLab 4/20 can be set by the software to
be either single-ended — positive or negative — or differential. In the
differential setting, the amplifier measures the difference between the
positive and negative inputs of a pod connector, irrespective of
▲
Caution
Applying more than
±
15 V
to the input can damage
the channel input circuits.
▲
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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