Lake Shore 648 User Manual - page 12
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1:
Introduction
Model 648 Electromagnet Power Supply
1.2 Output
Architecture
The low electrical noise design of the Model 648 makes it the ideal power supply for
use with large electromagnets in high precision laboratory settings, ensuring greater
resolution and finer detail in data taken during highly sensitive measurements. Since
low noise is critical to measurement systems, the Model 648 implements both a lin-
ear design and bipolar architecture. Linear magnet power supplies have several
advantages over switch mode power supplies, primarily smooth field generation that
is nearly free from offending electromagnetic signatures. The bipolar, 4-quadrant
operation required to safely operate an inductive load provides clean transitions
through zero without discontinuities.
1.3 Output
Programming
The Model 648 output current is programmed internally via the keypad or the com-
puter interface, externally by analog programming input, or by the sum of the exter-
nal and internal settings. External programming via analog input signal provides
analog resolution. The Model 648 generates extremely smooth and continuous
ramps —the digitally generated constant current ramp rate is variable between
0.1 mA/s and 50.000 A/s. To ensure a smooth ramp rate, the power supply updates
the high-resolution DAC 12.3 times per second.
1.4 Output
Reading
The Model 648 provides high-resolution output current readings that reflect the
actual current in the magnet, and have a resolution of 1 mA. The output voltage read-
ing reports the voltage at the output terminals with a resolution of 1 mV. All output
readings can be prominently displayed on the front panel and read over the computer
interface.
1.5 Protection
The Model 648 provides built-in protection against short circuit, open circuit, line
loss, low line voltage, high line voltage, output over voltage, output over current, over
temperature, and abrupt change of the external programming input. A proprietary
circuit limits the power dissipated in the water-cooled cold plate should low resis-
tance and high line conditions exist. The Model 648 protects itself if operated into
resistances outside of nominal limits. By limiting current output, it will safely operate
into a shorted load, and operate safely into high resistance loads by limiting voltage
output. The Model 648 is also protected against power loss under full operation and
nominal magnet load. Both low and high power line conditions are reported on the
front panel display.
1.6 Interfaces
The Model 648 includes both parallel IEEE-488 and universal serial bus (USB) com-
puter interfaces that provide access to operating data, stored parameters, and
remote control of all front panel operating functions. The USB interface emulates an
RS-232C serial port at a fixed 57,600 baud rate, but with the physical connections of
a USB. This allows you to download firmware upgrades, ensuring your supply is using
the most current firmware version with no need for any physical changes. The Model
648 also provides two analog monitors for output current and voltage.
1.7 Display and
Keypad
The Model 648 has a large screen displaying output current and output voltage read-
ings simultaneously. Five front panel LEDs provide quick verification of instrument
status, including ramping, compliance, fault, power limit, and computer interface
mode. Error conditions are indicated on the main display along with an audible
beeper. The most common functions of the power supply are accessed using a single
button press.
1.8 3-Year
Warranty and
Technical Support
The Model 648 is supported by a 3-year standard warranty, our confirmation of qual-
ity and commitment for the long term. Our physicists understand your applications
and measurements and provide support throughout your decision making process
and beyond the sale.