The AMI Model 420 Digital Programmer is a sophisticated power supply
controller which allows an operator to manage a superconducting magnet system with
unprecedented accuracy and ease of use. The Model 420 is the heart of a modern
superconducting magnet system; when it is used in conjunction with a four-quadrant power
supply, it provides for a degree of flexibility and accuracy previously unavailable in an
economical commercial product.
The Model 420 is managed by a microcomputer-based controller which
controls all analog data conversion, display/keypad functions, communications I/O, analog
programming signals for the external power supply, and all control law computations. The
Model 420 also incorporates digital signal processing (DSP) functions that provide for
accurate control, low drift, and flexibility for a wide range of applications.
The Model 420 Programmer utilizes 20-bit converters to translate signals
between the analog and digital domains. Precision instrumentation techniques and
potentiometer-free designs are employed throughout the instrument to ensure accurate
signal translation for a wide range of conditions. All pause and hold functions are performed in the digital domain which
provides for excellent stability and low drift (<0.01%) of the programmed magnetic
field.
The Model 420 Programmer was designed so as to simplify the interface
where possible. All functions were analyzed and subsequently programmed so that the most
commonly used functions are accessible via the least number of keystrokes. The menus are
also presented in a logical fashion so that the operation of the Model 420 is intuitive to
the user.
The provision of a velocity-sensitive rotary encoder on the front panel
also allows the operator to fine-adjust many of the operating parameters of the magnet
system. Operating current can be controlled to 15-digit resolution
(double-precision floating point used for internal storage).
The Model 420 Programmer is engineered to be compatible with many magnet
power supplies. From simple single-quadrant supplies, to more elaborate four-quadrant
units, the Model 420 is user-configurable such that the operational paradigm complies with
a specific power supply system.
The Model 420 Programmer is available in five standard
configurations: ± 10 A, ± 100 A, ± 200 A, ± 300 A. Configurations of 300 A and below use internal current-measuring shunts.
The ± 10 A configuration is designed for applications that
require high-resolution magnet current and ramping controls for applications
such as ADR.
The Model 420 Programmer provides an RS-232 (or optional RS-422) serial
port and a GPIB port (IEEE 488.2 compliant) as standard features. In
contrast to other magnet power supply system designs, an expensive and complex
additional
analog-to-digital conversion system is not required to collect data via a host computer.
Most settings can be controlled via the remote interfaces and the front panel can be
remotely locked to prevent accidental operation. The Model 420 also provides trigger
functions for data collection and/or logging during operation.
LabVIEW-compatible drivers are included with the Model 420 and provide an
integrated environment for magnet system monitoring and control (see image below). The
collection includes GPIB drivers and integrated panel examples for the Model 420 Digital
Power Supply Programmer, Model 135 Liquid Helium Level Monitor, and the Neocera Model
LTC-21 Temperature Controller.
The Model 420 Programmer is designed to allow the operator to program the system from the front panel, or remotely, with current and voltage limit parameters which will not be exceeded during operation of the system. Once set, should an operator inadvertently attempt to operate beyond the specified limits, the programmer will not accept the parameter and audibly beep. An appropriate error message is available via the remote interface. The Model 420 Programmer also automatically limits the charge rate of the magnet to the specified voltage limit.
Level Instrumentation
