MAGNET POWER SUPPLY SYSTEM 9100
22
DANFYSIK A/S - DENMARK.
3.2.6 Current setting
The output current may be set immediately as a potentiometer “SET CURRENT” or first preset
and thereafter accepted with the Enter ” ” button “SET CURRENT”.
Setting the output current choose the “SET CURRENT” menu, position the cursor above the
digit to alter and adjust the digit with the “” or “” button.
When the output current is within a predefined limit of the set value the "READY" LED will
turn ON.
It is also possible to set the output current to a predefined value, either using the storage
registers (STO, RCL in the MEM menu), to maximum current (=100% ) or to zero (=0%).
The maximum allowed set value can be limited through the LIMITS menu. This separates for
the positive and the negative set values. That is, if it is not possible to adjust the current above
a certain value, then check the limits.
The storage and the limit registers are saved within the M-Panel and can therefore not be used
in remote control. When using multidrop configuration e.g. all power supplies will share the
same limit.
3.2.7 Polarity reversal
If a polarity reversal switch is installed, a sign will be shown in front of the set value. (+ is
NOT reversed).
A polarity reversal procedure can be initiated either through the “POL” menu or simply by
putting the cursor above the sign in the “SET CURRENT” menu and changing the sign with
either the “” or “” button.
Please be aware that the system 9100 power supply is designed to work mainly in the first and
third quadrant, i.e. either positive output voltage and current or negative output voltage and
current. Working in the second or fourth quadrant is limited to the safe operating area of the
polarity switch transistors. The safe operating area of these transistors can be seen in the
picture on the next page. The Vds voltage on the horizontal axis is the drain to source voltage
of the transistors and is equal to the output voltage in the second and fourth quadrant. The Id
on the vertical axis is the drain current of the transistors. There are two transistors in parallel so
the actual allowed output current is equal to twice the drain current indicated on the graph.
The graph should be interpreted as follows:
If the output voltage of the 9100 during ramping down the current in an inductive load
becomes negative, say -10V, the current in one transistor must not exceed approx. 35 A i.e. the
output current must not exceed 70A.
The curves used in this example are the solid lines which should be used for DC operation.
The ramp time of the system 9100 bipolar version has been factory set to 3 sec., i.e. ramping
down from 150A to 0 takes 3 seconds, and from 0 to -150A also 3 seconds. Other ramp times
can be set by the user, see software manual for detailed description, but this must only be done
if the safe operating area is not exceeded. A lower ramp time i.e. ramping the current down
faster in an inductive load gives a higher negative voltage on the output (second quadrant
operation) and therefore the output current must be smaller so that the safe operating area is not
exceeded.
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