User Manual

Rev. 5 75

Operation

Ramping Functions : States and Controls

to be defined and executed (up to 10 segments, each with a unique ramp

rate). The basic charging equation for a superconducting magnet is:

where V is the charging voltage (V), L is the magnet inductance (H), 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 dB/dt

is the ramp rate expressed in kG/s.

A desired ramp rate should be selected by the user and entered into the

Model 430 Programmer. A Voltage Limit should also be specified that is

greater than or equal to the voltage calculated from the equations above

plus energy absorber voltage (if installed) plus power lead voltage drop

(usually less than 2 V).

Once the ramp rate and Voltage Limit are specified, the Model 430

Programmer provides two modes of ramping: manual and automatic.

Manual ramping will ramp to the Current Limit via manual direction

control by the user. Automatic ramping will ramp to the target field/

current automatically. Automatic ramping can be thought of as a “next

point” operation, whereby the Model 430 determines the appropriate ramp

direction based on the present magnet current and the target 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 430 Programmer even though the full

precision is not displayed after entry.

3.12.1 Ramping States and Controls

The ramping state may be one of several values as described in Table 3-6.

If the

RAMP / PAUSE key is pressed while ramping, the PAUSED mode

becomes active. To begin automatic ramping, press the

RAMP / PAUSE

key to deactivate the PAUSED mode. If manual ramping is desired, use

either the

INCR. FIELD or DECR. FIELD SHIFT-key for manual control of

ramping up or ramping down, respectively.

Voltage limit and ramp rate may be specified from quickly accessible

SHIFT-key menus from the front panel keypad

. The settings for Voltage

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