Noise is defined as "unwanted signal". It is likely to be a problem at lower recording range settings, when you are trying to measure very small signals. Random noise, such as thermal noise, is inherent in all electronic circuits, including those of the PowerLab data acquisition unit, and generally must be filtered to minimize it. For biological signals, differential inputs are preferred, and can reduce common-mode noise due to ground looping. Ground loops occur where multiple connected pieces of recording equipment are connected to mains power ground. PowerLab single-ended inputs are quasi-differential, and automatically neutralize up to a fraction of a volt of ground loop noise, the most that normally appears.
Other important causes of noise are stray electromagnetic and electrostatic fields, and include interference (often at the mains frequency of 50 Hz or 60 Hz) from unshielded power lines, switching equipment, fluorescent lights, transformers, computers, network cables, etc.. This interference can interact significantly with a recorded signal. Reasonable care in the arrangement and shielding of equipment and cables will reduce such interference. Below is a list of steps to use when trying to identify and remove noise from a given signal:
- Use LabChart's Spectrum Feature to determine the frequency components of noise. This information can sometimes help discover the source of the noise.
- A Notch or Mains filter removes most components of noise seen from the mains power system. Use the Mains filter when recording an ECG.
- When making extracellular or intracellular recordings, the noise can be reduced by using a Faraday Cage and grounding the equipment to the cage.
- The Smoothing Channel Calculation can be used to remove unwanted 'random' noise or high frequency components from a waveform.
- In LabChart, adjustment of the Range setting within the Input Amplifier settings can reduce noise resulting from poor digital resolution. If a signal is very small in relation to the chosen range, its resolution will be compromised. In extreme cases, the recorded waveform may appear stepped rather than smooth.
If you require further technical assistance with this or any other issue, please contact ADInstruments Technical Support.