Mercury swivel commutator
Encyclopedia
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 ring
s 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.
OEM machinery manufacturers are discovering the benefits of using a mercury swivel commutator in their designs. For example packaging machines use some type of commutator or slip ring as a connection to the moving parts that are heated to seal the packages closed after they are filled. It is critical that the temperature sensing circuit be reliable and accurate. Unfortunately, using a slip ring assembly or standard electrical slip ring may cause problems due to electrical noise and degradation of signal produced by the rubbing contacts of the slip rings. Many OEM machinery manufacturers have switched to using mercury swivel commutators for reliable and accurate temperature control. It is also desirable to pass the power and the temperature signal through the same rotating electrical connector in order to minimize the number of connector parts that must be built into the machine. Multiple channel mercury swivel commutators are used for this purpose.
Commutator (electric)
A commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...
typically used in electrophysiological experiments
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
on head free or moving animals. Electrical recordings from stationary, head-fixed animals can be done with electrodes attached to a stereotaxic
Neurosurgery
Neurosurgery is the medical specialty concerned with the prevention, diagnosis, treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spine, spinal cord, peripheral nerves, and extra-cranial cerebrovascular system.-In the United States:In...
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 ring
Slip ring
A slip ring is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, are commonly found in electric motors, electrical generators for AC...
s 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
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
— a conducting fluid — reduces commutator noise and friction, enabling commutator use for small weaker animals.
OEM machinery manufacturers are discovering the benefits of using a mercury swivel commutator in their designs. For example packaging machines use some type of commutator or slip ring as a connection to the moving parts that are heated to seal the packages closed after they are filled. It is critical that the temperature sensing circuit be reliable and accurate. Unfortunately, using a slip ring assembly or standard electrical slip ring may cause problems due to electrical noise and degradation of signal produced by the rubbing contacts of the slip rings. Many OEM machinery manufacturers have switched to using mercury swivel commutators for reliable and accurate temperature control. It is also desirable to pass the power and the temperature signal through the same rotating electrical connector in order to minimize the number of connector parts that must be built into the machine. Multiple channel mercury swivel commutators are used for this purpose.
See also
- NeuroscienceNeuroscienceNeuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
- NeurophysiologyNeurophysiologyNeurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
- Single-unit recordingSingle-unit recordingIn neurophysiology and neurology, single-unit recording is the use of an electrode to record the electrophysiological activity from a single neuron.-History:...
- Mercury switchMercury switchA mercury switch is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switch's physical position or alignment relative to the direction of the "pull" of earth's gravity, or other inertia.Mercury switches...