Closed Loop Magnet 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° C. Group3 can offer different field and temperature ranges, and custom probe dimensions.

Group3 Controller Module

The testing of 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 Loop Controller in the computer. The DNA communicates on a DeviceNet network, the standard for industrial control.

Group3 Controller Module + Analog Hall Probe

Enhance stability by employing Closed Loop Magnet Control

 

CNA
Communications on DeviceNet – the industrial control standard

 

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

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.

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 overcomes temperature and hysteresis effects,

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 will also give much better repeatability.

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.

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