22
PowerLab Owner’s Guide
Each analog input is fitted with a fixed 20 kHz low-pass filter. The
unfiltered signal has an effective bandwidth of 45 kHz (within the
Nyquist frequency when sampling at 100,000 samples per second).
PowerLab Accuracy
The PowerLab was calibrated at the factory to an accuracy of better
than 0.1%. Some ‘zero drift’ or ‘gain drift’ can occur with time. This
can affect the accuracy of measurements, especially at the highest
input gains. The unit can be recalibrated, but in most circumstances
this is not necessary in its lifetime. There are several reasons for this.
DC drift compensation
. Each time that recording is started manually
or by triggering or the gain is changed (that is, very often in most
cases), the input to the amplifier is grounded and any DC due to the
amplifier’s drift with temperature and age is measured. The
measured voltage is removed from the readings for that input
through software correction, in a process transparent to the user.
Calibration facilities
. It is recommended and sound practice to
calibrate a measuring system from the transducer to the output. After
applying two known values to a transducer (say at 20% and 80% of
full scale) and recording the signal, you can use the units conversion
feature of ADInstruments software to convert and display transducer
readings in the appropriate units. This will compensate for any minor
inaccuracies in amplifier gain and transducer calibration.
The External Trigger
The external trigger input (marked ‘Trigger’ on the front panel)
provides a digital input for synchronising sampling to external
devices. It allows either a voltage level or a contact closure to trigger
recording. Note that for either mode the trigger signal must be
present for at least 5
µ
s to register as an event. When a trigger event
occurs, the trigger indicator light will glow yellow.
When set up through software to use a voltage level, the external
trigger input is off for input voltages between –12 V and the external
trigger level, and on between that and +12 V. The input will be
overloaded if the voltage is outside the range –12 V to +12 V. The
external trigger level, above which a trigger event is registered, is
Summary of Contents for PowerLab 2/20
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