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CHAPTER 4:
Operation
Model 648 Electromagnet Power Supply
4.9 Ramp
Segments
The magnetic field produced by electromagnets is not linear with the current setting.
The best way to compensate for this is to use closed loop field control, but if absolute
accuracy is not necessary, then some of this nonlinearity can be corrected by the use
of the ramp segments feature.
The ramp segments feature can be used to increase the current ramp rate as the mag-
net saturates in an attempt to maintain the same field ramp rate. This feature can
change the output current ramp rate based on the output current setting. As the out-
put setting ramps through the segment boundary, the new ramp rate will be used,
although it will still be limited by the maximum ramp rate setting. Refer to
section 4.12.2 to set the maximum ramp rate. To enable ramp segments, press
Ramp
Segments
. The first ramp segments setup screen appears as a prompt for the ramp
segments mode.
Menu Navigation:
Ramp Segments
Q
(
Enable, Disable
)
Default: Enabled
Interface Command:
RSEG
4.9.1 Setting Up the
Ramp Segments Table
To use the ramp segment feature, Ramp Segment mode must be enabled (section 4.9)
and the ramp segment table must be set up to specify which ramp rate to use for each
current setting. The table should be set up in order of increasing current. A current
entry of 0 A indicates the end of the table, and the instrument will not search any
higher in the table.
If the Ramp Segments mode is enabled, the next ramp segments screen that appears
is for entering or editing the ramp segments table. All five of the ramp segments are
shown on the display at the same time. The segments should be entered in order of
increasing current. An entry of 0 A will indicate the end of the table and the instru-
ment will not search beyond that segment. For example:
Ramp Segment
Current
Ramp Rate
1:
10.000 A
0.5000 A/s
2:
15.000 A
0.6000 A/s
3:
20.000 A
0.7000 A/s
4:
30.000 A
0.8000 A/s
5:
40.000 A
1.0000 A/s
1. When you enter the ramp segments table, the “1” is highlighted. Press
Enter
to
move the cursor to the current column.
2. Using number entry, enter the upper current setting for that ramp segment in
amperes.
3. When you have finished entering the desired current, press
Enter
to accept the
new selection and advance to the ramp rate column.
4. Use number entry to enter the applicable ramp rate in A/s.
5. Press
Enter
to advance to the next segment.
Similarly enter or edit all ramp segments. When complete, press
Escape
while the
segment number field is highlighted to exit the ramp segment edit screen and return
to the normal display. When output current is called for using the
Output Setting
key,
the output will ramp to the desired current using the ramp segment set points.
4.10 Pause Output
The
Pause Output
key will pause the output current ramp within 2 s after the key is
pressed. While the output current ramp is paused, the ramping LED will blink. Press
Pause Output
again to continue ramping. Press
Enter
while the ramp is paused to set
the current at the paused setting and exit the Pause Ramp mode.
