Lakeshore Learning Materials 622 - Manual (Page 37)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Operation 3-11
3.9 DITHERING IN AUTOMATIC MODE
Dithering is a means of arriving at the magnet current by executing excursions around the final current which
decay to zero in a specified dwell (delay) time.
For example, suppose the final magnet current (MGT END) is 100 amperes, the maximum dither is 0.5%, and
the Dither Delay is 30 seconds. The operation in the Automatic Mode proceeds the same as in Paragraph 3.8
up to the time that the magnet current ramps. The current in the magnet ramps to 100 * (1 + 0.005) = 100.5
amperes, which is 0.5% above the final magnet current. When the current reaches 100.5 amperes, it dwells
for 30 seconds at that current. After the 30 seconds, the current ramps at the MGT RATE to 100 *(1 - .0025) =
99.75 amperes, that is, half of the 0.5% in the opposite direction. The 30 second dwell begins when the
current reaches 99.75 amperes. The process continues at 100 * (1 + 0.00125) = 100.125 amperes, then 100 *
(1 - 0.000625) = 99.9375 amperes, then 100 * (1 + 0.0003125) = 100.031 amperes, and finally 100 amperes.
To access the dithering feature, turn ON (up
position) switch 5 of the rear panel CAL AND ID DIP
switches. Select DELAY/DITHER from Function
Menu 3 to display the AUTOMATIC MODE DELAY
screen shown to the right.
To enable dithering, move the cursor to the last line
using the Up/Down cursor keys. Press either the
Data Entry up or down key to toggle the Dither
Feature on and off. Default is off. For our example,
the DITHER (delay) changes to 30 S from the
default 60 S. The dither of 0.5% is the default. If a
Dither of 1% were entered, the process would
produce 1% over the MGT END, then -0.5% under,
+0.25% over, -0.125% under, 0.0625% over and finally the MGT END selected.
The last line of the Automatic Mode screen shows the stage of the dithering. The screen above indicates the
first current of the dithering at 0.5% above the 100 amperes with 20 seconds left in the Dither delay. Press
either the Data Entry up or down key to skip the delay and ramp immediately to the next current in the dither.
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 G
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
< D I T H E R = 0 . 0 5 % >
O U T P U T S : *
+100.500A 1 0 . 0 0 0 A
1 0 0 . 0 0 0 A
1 . 0 0 0 A
1 . 0 0 0 A
1 0 . 0 0 0 A
< O F F >
+ 0 . 0 0 1 V
: +
: +
: +
: +
: +
: 2 0
¥ T O S K I P
A U T O M A T I C M O D E D E L A Y S :
¤ R U N U P
P E R S O F F
R A M P E N D
P E R S O N
D I T H E R
D I T H E R
D I T H E R
O U T P U T S : *
+0.000A : 6 0 S
: 6 0 S
: 6 0 S
: 6 0 S
: 6 0 S
: + 0 . 5 0 %
: < O F F > ¥
+0.000V