Lakeshore Learning Materials 622 - Manual (Page 29)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Operation 3-3
The magnet manufacturer supplies the inductance of the magnet, maximum ramp voltage, and maximum
current ramp rate. The relationship for these parameters is given by the equation:
V
L
di
dt
max ≥
where: V
max
= rated maximum magnet ramp voltage in volts,
L = magnet inductance in henrys, and
di/dt = maximum magnet current ramp rate in amps/second.
To set the Magnet Ramp Rate for manual PSH control or no PSH control, move to the RAMP RATE line and
enter a ramp rate less than the magnet's maximum ramp rate. In manual PSH control, the MPS uses the
RAMP RATE value to ramp both the magnet current and the persistence switch current. To activate ramping,
move to the RAMP ENABLE line and toggle RAMP ON. Upon entering a new current set point, the current
ramps at the entered ramp rate.
RAMP ENABLE: <ON> or <OFF>
RAMP ENABLE ON causes current to ramp at the specified ramp rate when the current/field is changed. Turn
RAMP ENABLE OFF to force the MPS to step immediately to the new CURRENT (or FIELD) SETTING. Move
to the RAMP ENABLE line and toggle the RAMP ENABLE OFF.
3.4 NORMAL DISPLAY FOR MANUAL PSH CONTROL
To the right is the default start-up Normal Display
screen for an MPS with a PSH option card installed
and Manual Persistence Control Mode selected. To
change to Automatic Persistence Control Mode,
press the MENU key and select Automatic Mode
from Function Menu 1. For Automatic Persistence
Control Mode see Paragraph 3.5.
The Normal Display for Manual PSH Control functions the same as the Normal Display for Manual Mode with
the exception of the option below:
PERSISTENCE: <ON> or <OFF>
Persistence Mode Status. If Persistence Mode is On, the PSH heater is Off. If it is Off, the PSH heater is On.
Note: To set PSH heater current, see Chapter 6 Options And Accessories.
3.5 NORMAL DISPLAY FOR AUTOMATIC PSH CONTROL
To the right is the default startup Normal Display
screen for an MPS with a PSH option card installed
and Automatic Persistence Control selected. To
change to Manual Persistence Control Mode press
the MENU key and select MANUAL MODE. For
Manual PSH Control Mode, see Paragraph 3.4.
When using a Persistence Switch, Automatic Mode
simplifies superconducting magnet control. After the user defines initial parameters, Automatic Mode permits
the MPS to use two different ramp rates and four time delays, and to manage the Persistence Switch Heater
to change magnet current from its existing value to a new value automatically. Dithering is supported (see
Paragraph 3.9).
Use the Cursor keys to move the line indicator up or down. Change parameters using any numeric entry
mode, including the cursor.
MGT START: 0 to ±50.000 A (620), 0 to ±125.000 A (622), 0 to ±155.000 A (623), 0 to ±72.000 A (647)
Magnet Start Current. The current in the magnet in persistence prior to the automatic run. The MPS opens the
persistence switch after it reaches this current and the user-specified delay expires.
C O M P L I A N C E
R A M P R A T E
R A M P E N A B L E
P E R S I S T E N C E
: § 1 . 0 0 0 V
: § 1 . 0 0 0 A / S
: < O F F > ¥
: < O N > ¥
O U T P U T S : *
+1.999A
+ 0 . 0 0 1 V
S E T T I N G S :
¤
+ 0.1999A
A U T O M A T I C M O D E :
¤ M G T S T A R T
M G T E N D
M G T R A T E
P E R S R A T E
L A S T E N D
P E R S I S T E N C E
R U N ¥
O U T P U T S : *
+0.000A : 0 . 0 0 0 A
: 0 . 0 0 0 A
: 1 . 0 0 0 A / S
: 1 . 0 0 0 A / S
: 0 . 0 0 0 A
: < O F F >
+ 0 . 0 0 1 V
S T A N D B Y