Closed Loop Magnet Control

Group3 Controller Module + Analog Hall Probe

Enhance stability by employing closed loop magnet control


Group3 Controllers


Communications on DeviceNet - the industrial control standard.

Communications on fiber optics - for high noise/high voltage areas.

Group3 Analog Hall Probe

Hall element, corrected for temperature and non-linearity.  Fixed probe or flexible cable.  Custom design for OEMs possible.

The Group3 controllers - the CNA and DNA - have a built-in PID algorithm, that allows them to perform local closed loop control. A controller, combined with a Group3 analog Hall probe forms a compact, inexpensive way to implement closed loop magnet control. The computer only needs to send the desired field value - the controller will drive the power supply to steadily maintain that field setting. The magnet and power supply becomes a simple "set and forget" system, relieving the control computer and the communications network of any ongoing control or supervision.

Two controller modules are offered - the CNA is part of the Group3 Control system, and communicates via fiber optic cables to a Group3 card in the computer. The DNA communicates on a DeviceNet network, the standard for industrial control.

The Group3 Hall probe produces an analog voltage as its output signal, corrected for temperature effects and non-linearities, producing a signal accurate to within 0.05%, from -1 to +1 T, over 10 to 50 deg C. Group3 can offer different field and temperature ranges, and custom probe dimensions.

Advantages of Closed Loop control - stability and repeatability

Closed loop control, with the appropriate sensor, provides much greater stability.

If the magnetic field is controlled by setting the current of the power supply, then as the magnet or supply temperature changes the current can vary - so the field will deviate from its desired setting. If you are measuring the field directly then you can hold the field constant, despite external influences.

This can have the big spin-off that you no longer need a very tightly regulated power supply, and you don't need very precise temperature stability in it either reducing the cost of the power supply considerably. Stability is of particular interest in keeping a beam on target for a long period, and is vital for big ring magnet systems.

Closed loop control will also give much better repeatability.

If you ask for a particular field, that is what you get, no matter what the temperature is, or was, and no matter what the history of the magnet. Closed loop control overcomes temperature and hysteresis effects.

In a production environment the repeatability of field can speed up switching between ion species or energies. If you ask for the same field as last time, you know the beam will be in the right place. It is almost vital if a machine wants to be able to operate on a recipe" type system,

VI Control Systems is a Factory Authorized Distributor for Group3 Control and Analog Hall Probes.

Manufactured by:

Group3 Technology Ltd.
2 Charann Place, Auckland 7
P0 Box 71 111, Rosebank, Auckland, New Zealand
Phone +64 9 828-3358 Fax +64 9 828-3357


For further information contact Neal Pederson at
VI Control Systems Ltd., 2173 Deer Trail, Los Alamos, NM 87544
Tel: (505) 662-1461, Fax: (866) 422-2931

Designed and Created by VI Control Systems Ltd.
Copyright 2005 All Rights Reserved.