Model 625
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Model 625 Superconducting Magnet Power Supply Features 60 A/5 V, bipolar, true 4-quadrant output Instruments 127 Model 625 Superconducting Magnet Power Supply 0.1 mA output setting resolution Linear regulation minimizes noise Ripple ≤ 0.007% of maximum current (into a 1 mΩ load) 1 mA per hour stability Parallel operation to ±120 A compliant to both the low voltage directive and the electromagnetic compatibility (EMC) directive, which includes the radiated emissions requirements Introduction The Model 625 superconducting magnet power supply is the ideal supply for small to medium sized superconducting magnets used in high sensitivity materials research applications. The Model 625 is a practical alternative to both the larger, one size fits all, superconducting magnet supplies and the endless adaptations of generic power supplies. By limiting output power, Lake Shore was able to concentrate on the performance requirements of the most demanding magnet users. The resulting Model 625 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 a challenging load, such as a superconducting magnet, requires a unique solution. The Model 625 delivers up to 60 A at a nominal compliance voltage of 5 V, with the supply acting as either a source or a sink in true 4quadrant 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. www.lakeshore.com Lake Shore Cryotronics, Inc. (614) 891-2244 Lake Shore chose linear input and output power stages for the moderate 300 W output of the Model 625. Linear operation eliminates the radiated radio frequency (RF) noise associated with switching power supplies, allowing the Model 625 to reduce the overall noise in its output and the noise radiated into surrounding electronics. Safety should never be an afterthought when combining stored energy and liquid cryogens in a superconducting magnet system. The Model 625 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 CE mark safety requirements, including both the low voltage directive and the electromagnetic compatibility (EMC) directive. Instrument users have come to rely on Lake Shore for convenience and ease of use. The Model 625 includes the features necessary to conveniently manage a superconducting magnet, such as a persistent switch heater output, calculated field reading, current ramping, and quench detection. Computer interfaces are also integrated for automation of the magnet system. The Model 625 is truly an excellent one-box solution for controlling a superconducting magnet. fax: (614) 818-1600 e-mail: info@lakeshore.com

128 Instruments Model 625 Superconducting Magnet Power Supply Current Change Using Internal Programming Output Architecture True 4-quadrant output capability of the Model 625 is ideal for the charge and discharge cycling of superconducting magnets 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 625 has the ability to charge and discharge magnets up to a 5 V rate. True 4-quadrant operation eliminates the need for external switching or operator intervention to...

Model 625 Superconducting Magnet Power Supply Instruments 129 Output Programming The Model 625 output current is programmed internally via the keypad or the computer interface, externally by the analog programming input, or by the sum of the external and internal settings. For the more popular internal programming, the Model 625 incorporates a proprietary digital-to-analog converter (DAC) that is monotonic over the entire output range and provides a resolution of 0.1 mA. The remote inhibit input allows an external device to immediately set the output current to zero in case of a failure....

Model 625 Superconducting Magnet Power Supply The Model 625 incorporates a large 8-line by 40-character vacuum fluorescent display. Output current, calculated field in tesla or gauss, output voltage, and remote voltage sense readings can be displayed simultaneously. Five LEDs on the front panel provide quick verification of instrument status, including ramping, compliance, fault, PSH status, and computer interface mode. Error conditions are indicated on the main display along with an audible beeper. Extended error descriptions are available The keypad is arranged logically to separate the...

Model 625 Superconducting Magnet Power Supply Readings Output current Resolution 0.1 mA Accuracy ±1 mA ±0.05% of reading Update rate 2.5 readings/s display, 10 readings/s interface Compensation Compensated for lead resistance and 25 Ω source resistance Output voltage (at supply terminals) Resolution 100 µV Accuracy ±1 mV ±0.05% of reading Update rate 2.5 readings/s display, 5 readings/s interface Remote voltage (at magnet leads) Resolution 100 µV Accuracy ±1 mV ±0.05% of reading Update rate 1.25 readings/s Input resistance >50 kΩ Connector Shared 15-pin D-sub Persistent Switch Heater Output...