ADInstruments POWERLAB TEACHING SERIES Owner's Manual page 52

The Bio Amp trace will not zero properly when adjusting high-pass filtering
This Bio Amp is receiving signals at a level that has saturated the input amplifier, resulting in a
large offset. This is normally due to poor contact between the electrodes and the subject.
• Check the connections for proper contact and try again.
The Bio Amp signal appears to display a constant amplitude oscillation
Frequency interference from power lines can become superimposed on the biological signal
being measured.
• You can use the internal notch filter in the Bio Amp to remove the excessive line voltage
If you are using cables and leads that were not supplied with your PowerLab, they may be
unshielded or of low quality
• Check to make sure that you are using high-quality shielded cables and high-quality
The Bio Amp signal is noisy at lower ranges
This is probably the amplified noise from the electrodes, not a fault as such. There is, in addi-
tion, noise that cannot be avoided by any amplifier (called 'thermal' or 'Johnson' noise).
• Set the low-pass filter to remove the noise. (But be careful, since important components
This could be due to an electrically noisy environment, particularly if there is some equipment
that produces a radio frequency that interacts with the Bio Amp modulator, giving a hetero-
dyne effect
• Turn off pieces of unnecessary equipment to try and isolate the cause, then either leave
• At the lowest ranges you may have to shield, shorten or even replace the Bio Amp leads,
The Bio Amp signal appears to be unusual, very weak, clipped or distorted in some way
This may be a problem of technique: the sampling rate, range or filter settings may be inappro-
priate for the signal you are recording.
• Make sure the settings are appropriate for the expected signal.
You may be using the wrong Bio Amp cable. The 3-lead Bio Amp cable used with the single Bio
Amp has a different pin arrangement and cannot be used with the Dual Bio Amp/ Stimulator
front- end.
• Use the correct, supplied 5-lead Bio Amp cable.
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frequency interference (use the checkbox in the Bio Amplifier dialog box).
leads. Only the supplied cables and leads should really be used.
of the signal could also be attenuated).
the equipment off, or, if possible, move the subject or equipment outside the area of
any interfering field.
since they will tend to act as radio receptors.
PowerLab Teaching Series - Owner's Guide