Powerlab Accuracy; The External Trigger - ADInstruments PowerLab/4SP Owner's Manual

Each input produces either a filtered or an unfiltered signal. Each
input is fitted with a software-selectable low-pass filter (a fourth-
order anti-aliasing filter), which can be set at a range of frequencies
from 20 kHz down to 1 kHz. The unfiltered signal has an effective
bandwidth of 45 kHz (within the Nyquist frequency when sampling
at 100,000 samples per second).

PowerLab Accuracy

Your 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 applications 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 provides a digital input for synchronising
sampling to external devices. The external trigger input represents
1 TTL (transistor–transistor logic) load. The 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 is 2.9 V ±
0.25V; once on, the trigger turns off at 1.8 V ± 0.25V, giving a
hysteresis voltage of 1.1 V. When the external trigger input is on, the
indicator beside it is on.
Appendix A — Technical Aspects 33