Mercury swivel commutator
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A mercury swivel commutator is an electrical commutator typically used in electrophysiological experiments on head free or moving animals. Electrical recordings from stationary, head-fixed animals can be done with electrodes attached to a stereotaxic rig. The wires leading from the electrode can be connected to the amplifier and recording setup using regular wires, since no twisting occurs. Freely moving animals may turn through several revolutions in one direction. While recording from freely moving animals, therefore, an electrical commutator is needed to prevent twisting of the wires that go from the electrode (moving and rotating with the head) to the amplifier/recorder (fixed to the ground).
Traditional electrical commutators use slip rings for coupling. Slip rings however inject commutator noise into the connection. This is because as the contact points slide over the surface of the slip-rings they make microscopic bumps. The resultant variation in resistance and inductance causes electrical noise in the circuit. To reduce the electrical noise the contact points need to be pressed against the slip rings with greater force. This leads to great resistance and a higher rate of wear.
Replacing the slip rings with pools of mercury - a conducting fluid - reduces commutator noise and friction, enabling commutator use for small weaker animals.
[edit] References
- An inexpensive, enclosed pool mercury commutator suitable for use with small animals Ryan LJ, Hall FL, Young SJ. [1]
