Multichannel Systems MPA2I Manual - Manual (Page 8)

2-Channel Miniature Preamplifier Manual
4
3 Setting Up and Connecting the MPA
3.1 General Setup Recommendations
In the following, you find general recommendations for the installation.
Important: It is important that the complete setup refers to a single common ground. The reference
input has always to be connected. It is recommended to use a reference electrode. However, if you
are not using a reference electrode, connect the reference input to ground (GND). Otherwise, noise
picked up by the reference input will be subtracted from the recording signals. This will either lead
to signal loss or to a very high noise level.
Ground the animal with a ground electrode of large surface area, for example, a liquid gel
adhesive electrode, that is connected to the ground of the setup, for example, a large metal table
or a Faraday cage, to avoid pickup of noise from the environment. The ground electrode is best
positioned in an electrically inactive region, not near muscle, nor heart, for example, at the belly.
Connect the GND input or the metal case of the miniature preamplifier to the common ground of
the setup. The GND input is internally connected to the metal case.
Connect the reference electrode to the reference input of the miniature preamplifier. Generally, a
reference electrode is inserted into non-active tissue of the experimental model. The reference electrode
should be identical to the recording electrode so that both electrodes see the same background noise.
This is necessary because despite the grounding, the animal’s body often has not exactly a potential of
zero, due to the electrode impedance, for example. The background noise is then subtracted from the
recording signal, increasing the signal to noise ratio. Please note that this may not work if the complete
setup is not properly grounded.
Connect the recording electrodes to the recording channels of the miniature preamplifier. You can
either use single electrodes or multitrodes with the miniature preamplifier. MCS provides adapters for
standard probes.
Connect all unused recording channels to the GND input or to the reference electrode, if ground
and reference are short circuited to avoid noise pickup. As the total amplifier gain generally lies in the
range of 1000, even very small noise signals may generate high noise signals.