Instruction manual

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2 Acquisition 14
mains. The end result of using the 50Hz Low Pass filters is the creation of a quieter, more
readable ECG. In general, the application of a low pass filter “quiets” the baseline and improves
the signal to noise ratio of the recording.
On the other hand, High Pass filters PASS frequencies HIGHer than the set frequency. These
filters can remove low frequency interference, such as baseline drift or a standing offset voltage,
so that the user sees a more stable baseline.
High Pass, Low Pass and Band Pass filters can also be applied to each channel from the
Filter function available from the Add Function button on the Channel Bar of each channel.
These filters are not “Hardware” filters; they are executed in software and work on all ADC units
running DataTrax2. Unlike hardware filters, software filters can be applied AFTER the data is
recorded. These filters also work in real time and can be applied to data as it is being recorded.
Averaging In addition to filtering, the DataTrax2 software can apply another quieting technique to data
recorded at speeds less than 200 samples per second. In the section on temporal resolution, it
was demonstrated that fast events require fast sampling speeds. What happens if slow events
are recorded at fast sampling speeds? More information is collected than is needed to
accurately display the signal. What should be done with the extra data? At sampling speeds of
100 samples per second or less, the DataTrax2 program operates on the “extra data” using a
technique similar to the oversampling employed by CD players to reduce noise. The amount of
oversampling that occurs is determined by the sample speed that you set. The end result is that
small signals recorded at slow speed will appear less noisy than small signals recorded at high
speed.
Outboard
Conditioning
WPI Data Acquisition Systems with built-in amplifiers and filters, can be controlled by the
DataTrax2 software.These amplifiers and filters should be adequate for most applications. In
cases where additional or custom signal conditioning is required, outboard devices can be used
to condition the signal before it is presented to the WPI Data Acquisition System. WPI makes a
full range of amplifiers for this purpose, but any amplifier with an analog output can be used.
This allows other amplifiers, like those from Thornton
or Grass, or special purpose devices, like
those made by Warner Instruments
, Axon instruments, or World Precision Instruments, to be
used with WPI Data Acquisition Systems. Outputs from these and other devices can be
connected to the available BNC inputs on the front panel of WPI Data Acquisition Systems.
Outputs of external devices can also be connected to the DIN 8 inputs with an adapter cable
available from WPI.
Chart Mode
Once the signal source is connected to the WPI unit and the signal conditioners are
configured, data recording can begin. The most basic controls required are the ones that turn
the recording on and off. DataTrax2 has three ways to Start a recording and two ways to Stop it.
Starting