Lakeshore Learning Materials 642 - Manual (Page 11)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
Introduction 1-1
CHAPTER 1
INTRODUCTION
1.0 GENERAL
This chapter provides an introduction to the Model 642 Electromagnet Power Supply. The Model 642 was designed and
manufactured in the United States of America by Lake Shore Cryotronics, Inc. The Model 642 features include the
following.
• True 4-quadrant (bipolar) 70 A, 35 V output
• 0.1 mA output setting resolution
• Linear regulation minimizes noise and ripple to 0.007% of maximum current into a 0.50
Ω load
• 1.0 mA stability per hour, 5 mA per 24 hour
• CE compliance to both the low voltage directive and the electromagnetic compatibility (EMC) directive
1.1 DESCRIPTION
The Model 642 Electromagnet Power Supply is the ideal supply for small- to medium-sized magnets used in
high-sensitivity materials research applications. The Model 642 is a practical alternative to both the larger one-size-fits-
all magnet supplies and the endless adaptations of generic power supplies. By optimizing output power, Lake Shore was
able to concentrate on the performance requirements of the most demanding magnet users. The resulting Model 642
provides high precision, low noise, safety, and convenience.
Precision in magnetic measurements is typically defined as smooth continuous operation with high setting resolution and
low drift. Achieving these goals while driving an inductive load requires unique solutions. The Model 642 delivers up to
70 A at a nominal voltage of 35 V, with the supply acting as either a source or a sink in true 4-quadrant operation. Its
current source output architecture with analog control enables both smooth operation and low drift. A careful blending of
analog and digital circuits provides high setting resolution of 0.1 mA and flexible output programming.
Lake Shore chose linear input and output power stages for the nominal 2450 W output of the Model 642. Linear
operation eliminates the radiated radio frequency (RF) noise associated with switching power supplies, allowing the
Model 642 to reduce the overall noise in its output and the noise radiated into surrounding electronics.
Safety should never be an afterthought when driving an inductive load. The Model 642 incorporates a variety of
hardware and firmware protection features to ensure the safety of the magnet and supply. For improved operator safety,
the power supply was also designed for compliance with the safety requirements of the CE mark, including both the low
voltage and the electromagnetic compatibility (EMC) directive.
Instrument users have come to rely on Lake Shore equipment for convenience and ease of use. The Model 642 includes
features such as built-in current and power limits, internal cooling-water and magnet-water control to minimize
condensation, current ramping and the capability to modulate the output current. Computer interfaces are also integrated
for automation of the magnet system. The Model 642 is truly an excellent one-box solution for controlling an
electromagnet.
Output Architecture
True 4-quadrant output capability of the Model 642 is ideal for the charge and discharge cycling of electromagnets for
both positive and negative fields. Tightly integrated analog control of the 4-quadrant output provides smooth current
change with very low overshoot on output change. The Model 642 has the ability to charge and discharge magnets up
to a 50 A per second rate into a nominal 0.5 Ω, 0.5 H load.
True 4-quadrant operation eliminates the need for external switching or operator intervention to reverse the current
polarity, significantly simplifying system operation. The transition through zero current is smooth and continuous,
allowing the user to readily control the magnetic field as polarity changes.
At static fields, output current drift is also kept low by careful attention in the analog control circuits and layout.
The high stability and low noise of the Model 642 provides a quiet and uniform magnetic field.