American Magnetics 420 Power Supply Programmer - Manual (Page 70)

52 Rev. 7
Operation
Ramping Functions
3.3 Ramping Functions
The ramping functions are used to control charging of the superconducting
load. The Model 420 allows a piecewise-linear charging profile to be
defined and executed. The basic charging equation for a superconducting
magnet is:
where V is the charging voltage (V), L is the magnet inductance (Henries),
and di/dt is the ramp rate (A/s). The relationship may also be defined in
terms of a ramp rate in kG/s by the relationship:
where C is the coil constant (or field-to-current ratio) in kG/A, and dF/dt
is the ramp rate expressed in kG/s.
A desired ramp rate should be selected by the operator and entered into
the Model 420. A voltage limit should also be specified that is greater than
or equal to the voltage calculated from the equations above (remember to
account for power lead resistance).
Once the ramp rate and voltage limit are specified, the Model 420 provides
two modes of ramping operation: manual and programmed. The manual
mode of operation will ramp to the current limit via manual direction
control by the user. The programmed mode of operation ramps to a
programmed current or field setting automatically. The programmed mode
can be thought of as a “next point” operation, whereby the Model 420
determines the appropriate ramp direction based on the present magnet
current and the programmed value.
Note
You may enter up to 10 digits beyond the decimal point within the
ramping control menus. These extra digits are maintained in the
internal memory of the Model 420 even though the full precision is
not displayed after entry.
3.3.1 Ramping States and Controls
The ramping state may be one of several values as described in Table 3-5.
If the 5$033$86( key is illuminated, the PAUSED mode is active. To
continue ramping in programmed mode, press the 5$033$86( key to
deactivate the PAUSED mode.
V L
i d
t d
---- =
V
L
C
----
F d
t d
------ =