4.12.2 Maximum Current Ramp Rate
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4.16 External
Current
Programming
The output current of the Model 648 can be set internally, externally, or by the sum of
the external and internal settings.
D
Internal:
(default) the current is controlled internally by entering a setting from
the front panel using
Output Setting
. Refer to section 4.7 to set the
output current.
D
External:
when the external program mode is set to external, the front panel set-
ting is fixed at 0 A and the output current is set using an external voltage where
10 V = 135 A.
D
Sum:
when the external program mode is set Sum, the internal and external set-
tings are summed together to set the output current.
When using the External or Sum modes, care must be taken to insure that the output cur-
rent does not exceed the maximum current for the magnet. The software maximum set-
ting limits cannot limit the output current or ramp rate that is set when using the
External or Sum modes. Failure to comply may result in damage to the magnet.
A -3 dB, 40 Hz, two-pole, low-pass filter limits the bandwidth of the external current pro-
gramming input. The bandwidth of the output is also limited by the compliance voltage
and the inductance of the magnet.
Menu Navigation:
External Program
Q
(
Internal, External, Sum
)
Interface Command:
ER
To avoid discontinuities in the output current, the external current programming
mode cannot be changed if the programming voltage or the front panel current set-
ting is not zero. If the external current program mode is going to be kept from chang-
ing, an error box will pop up explaining why the new setting is being ignored.
4.17 Locking the
Keypad
The keypad lock feature prevents accidental changes to parameter values. When the
keypad is locked, parameter values may be viewed but not changed from the front
panel. The Model 648 has two keypad lock modes.
D
Lock All mode:
locks out changes to all parameters.
D
Lock Limits mode:
locks out changes to all of the parameters except Output Setting,
Ramp Rate, Zero Output and Pause Ramp. This allows the power supply to be
operated without allowing any changes to the power supply setup.
A 3-digit code must be used to lock and unlock the keypad. The factory default code is
123, and it can only be changed using a computer interface. If the instrument param-
eters are reset to default values (section 4.19), the code is reset to the factory default.
The instrument parameters cannot be reset to default values from the front panel
when the keypad is locked. If you attempt to change a parameter while the keypad is
locked you will receive this message: Change not allowed while keypad is locked.
The computer interface has a remote operation mode that could be mistaken for a locked
keypad. If the front panel remote LED is lit, press Local to change to local control of the
instrument.
Once the keypad lock mode has been selected, the keypad lock code must be entered
to accept the change. Use the data entry keys to enter the 3-digit lock code (default
123). An asterisk will appear on the display for each number entered. If the code
entered matches the lock code, the display will show “Change Accepted” and the key-
pad lock mode will be updated. If the code entered does not match the lock code, the
display will show “Invalid Lock Code” and the keypad lock mode will not change.
Menu Navigation:
ENTER
(Press and hold for 3 s)
Q
(
Unlock, Lock All, Lock Limits
)
Q
Keypad lock code
Default: Unlock
Interface Command:
LOCK
