Lakeshore Learning Materials 622 - Manual (Page 32)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Operation 3-6
3.6.1.3 Step Limit/Zero Screen
Press the Function Menu key to display Function
Menu 1. Press the STEP LIMIT/ZERO Function Key
to display the Step Limit/Zero screen to the right.
This screen combines two features: Current Step
Limit and Current Zero.
Use the Cursor keys to move the line indicator up or
down. Parameters with a ¥ icon toggle with the Data
Entry up or down key. Change all others using any numeric entry mode, including the cursor.
3.6.1.3.1 Current Step Limit
When a superconducting magnet quenches, the magnet becomes resistive. The output current forces the
MPS output to the compliance voltage setting and the output current drops rapidly. To avoid excessive
cryogen boil-off, the output current setting should be changed to 0 as quickly as possible. The output current
step limit, if exceeded, automatically resets the output to 0 A. The Step Limit function also prevents the user
from entering steps that exceed the current step limit.
STATUS: <OFF> or <ON> I STEP: + 0.010 A to + 999.99 A
Output Current Step Limit Status. Output Current Step Limit.
3.6.1.3.2 Current Zero
There may be configurations, like multiple auto-parallel MPS units, that introduce an output current offset from
zero. This small offset current may result in high energy stored in the magnet load. The output current zero
feature allows the user to zero this output current offset. The MPS stores the current zero value in non-volatile
memory. Before accessing output current zero from the MPS front panel, enter a current of zero and allow the
output current to settle to the offset value.
If the status is ON, toggle it OFF and allow current to settle, to clear the old value before entering a new value.
When the status is toggled ON, the MPS stores the output current as the current zero and displays it as the I
ZERO value.
3.6.1.4 Instrument Setup Screen
The Instrument Setup screen defines the major
operating characteristics of the Normal Display.
Press the Function Menu key to display Function
Menu 1. Press the INSTR. SETUP Function key to
display the Instrument Setup screen to the right.
Use the Cursor keys to move the line indicator up or
down. Parameters with a ¥ icon toggle with the Data
Entry up or down key. Change all others using any numeric entry mode, including the cursor.
NOTE: FLD ENABLE, B UNITS, and FIELD/A apply to superconducting magnets where there is a linear
relationship between current and field. Do not confuse this with the Model 6226 Gaussmeter Card reading.
This is a computed field directly related to the current by the constant entered on the fourth line.
FLD ENABLE: <ON> or <OFF>
Field Enable. Allows the user to change the Normal Display units from amps to field units. To change Normal
Display units, move to the Field Enable line and toggle it ON. Move to the B UNITS (Field Units) line and
toggle the units between kG or Tesla. Move the cursor to the kG/A or Tesla/A line and enter the magnet Field
to Current ratio. Usually, the ratio is on the magnet data sheet. If not, call the magnet manufacturer. The MPS
now sets and displays magnet field in the desired units. The Default is Field Enable OFF.
B UNITS: kG or tesla Define B Field Units in kilogauss (kG) or tesla. The Default is kG.
FIELD/A: kG/A or tesla/A
Magnet Field to Current ratio. Obtain this value from the magnet data sheet, or calculate it from magnet
manufacturer information. The Default is 1.000 kG/A (0.1000 tesla/A).
C U R R E N T S T E P L I M I T :
¤ S T A T U S
I S T E P
Z E R O :
S T A T U S
I Z E R O
I M O D E
O U T P U T S : *
+1.999A : < O F F >
: + 1 0 . 0 0 0 A
: < O F F >
: + 0 . 0 0 0 A
: E X T E R N A L
¥
¥
+ 0 . 0 0 1 V
I N S T R U M E N T S E T U P :
¤ F L D E N A B L E
B U N I T S
t e s l a / A
I M A X S E T
C O M P L I A N C E
O U T P U T S : *
+1.999A : < O F F >
: t e s l a ( T )
: § 0 . 1 0 0 0
: § 1 2 5 . 0 0 0 A
: § 3 0 . 0 0 0 V
¥
¥
+ 0 . 0 0 1 V