Lake Shore 625, Руководство пользователя

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Lake Shore Model 625 Superconducting MPS User’s Manual
4-10 Operation
4.13 FIELD CONSTANT
In a superconducting magnet, magnetic field is directly proportional to the current in the magnet. Because of this
relationship, the Model 625 is able to display a calculated field based on a user entered field constant in units of T/A or
kG/A. This value is usually supplied by the magnet manufacturer. In order to display the field reading, the display must
be setup to display in field. Refer to Paragraph 4.4.1 to setup the display mode. Note that the field reading is not an
actual measurement of the magnetic field but an approximation calculated by multiplying the measured output current by
the field constant. To actually measure the magnetic field, an external gaussmeter must be used.
4.13.1 Field Constant Units
The field constant can be entered in either units of T/A or kG/A. This choice not only changes the way the field constant
is entered, but it also chooses the units of the calculated field as well as the output setting units.
To set the field constant press Field Constant . The first field constant screen appears as a prompt for the field constant
units.
Field Constant
Select With °®
Field Constant Units: T/A
Use the
s
or
t
key to select the field constant units, either T/A or kG/A. Press Enter to accept the new selection and
continue to the next setting screen. Press Escape to cancel the new selection and return to the normal display.
4.13.2 Field Constant Value
The field constant value can be entered in units of T/A or kG/A depending on what was chosen in the previous step. The
field constant value will be used to calculate the magnetic field.
To enter a value for the field constant, continue from the field constant units screen or press Field Constant then Enter
until the following display setup screen appears as a prompt for the field constant value.
Field Constant
Enter a Value For
Field Constant: 0.1000 T/A
Use the data entry keys to enter the field constant value between 0.00100 and 1.00000 T/A or 0.0100 and 10.0000 kG/A.
Press
Enter to accept the new value. Press Escape to restart the setting sequence and enter a different value. Press
Escape again to leave the setting sequence.
4.14 PERSISTENT SWITCH HEATER OUTPUT
Some superconducting magnets are constructed with a persistent switch. A persistent switch is a length of
superconducting wire that shorts across the terminals of the magnet. This length of wire can be heated to drive it into a
resistive state so that a voltage can be applied across the magnet terminals and the magnet can be charged or discharged.
When the heater is shut off, this section of wire will cool and become superconducting again and the magnet will be in
persistent mode. At this time, the power supply can be ramped to zero current and even removed from the system while
the magnet holds its charge. The magnet will continue to hold its charge indefinitely unless the cryogen is allowed to boil
off to the point where there is insufficient cooling to keep the magnet in its superconducting state.