4.4.1 Fault LED
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4.4.1 Fault LED
The fault LED lights when an error condition is encountered. It may also be accompa-
nied by an alarm depending on the fault (TABLE 6-2 and TABLE 6-3 defines hardware
and operational errors).
4.4.2 Compliance LED
The compliance LED lights when the maximum output voltage is reached. This can
happen when attempting to rapidly ramp a magnet with higher than usual voltage
required to overcome the magnet’s inductance. The LED will go out when the condi-
tion clears.
4.4.3 Power Limit LED
The Model 648 has a hardware power limit to protect the internal power MOSFETs. If
the power supply is driving a load which has a resistance lower than the supply’s
rated minimum, the power required may be higher than the devices can safely han-
dle. If this happens, the power in the devices is prevented from exceeding the safe
limit and the power limit LED will light to alert the operator to the condition. The LED
will go out when the condition clears.
4.4.4 Ramping LED
The ramping LED lights when the internal control circuitry is changing the output
current. When the ramp is completed and the current is at the desired point, the LED
goes out. The LED does not light when the output current is being controlled by an
external source.
4.4.5 Remote LED
The remote LEDlights when the remote key has been pressed to accept remote com-
puter programming input, or upon receiving the first command over the IEEE bus.
When the LED is lit, the main keypad is locked out. Pressing the
Local
key will return
the unit to the local mode and reestablish keypad functions.
4.5 Keypad
Definition
The Model 648 has 20 keys separated into three groups on the instrument front
panel. The sixteen keys in the center of the grouping combines instrument setup and
data entry. The keys to the left control the output current and ramping. The keys to
the right assist with menu navigation. See FIGURE 4-4 for key locations. Refer to
TABLE 4-3 for keypad descriptions.
Model 648 keypad and LED layout
FIGURE 4-4
