JPS61148516A - Control device of magnetic field generating coil - Google Patents

Abstract

PURPOSE:To increase a response speed, and also to control with a high accuracy the strength of a magnetic field by correcting a current set value of a loop for controlling a current flowing to a magnetic field generating coil to a constant current, by a difference between a current detecting value and a current theoretical value. CONSTITUTION:When a sample command circuit 33 sends a sample command to a sample and hold circuit 32 by a prescribed timing, an input signal of that time point is outputted from this sample are hold circuit 32, added at a current detecting value and a current set value, and inputted to a current controller 24. That is to say, a difference between a current detecting value outputted from an insulating amplifier 22 and a current theoretical value outputted from a virtual current computing element 31 is a magnetic field error, and a magnitude of the current set value is adjusted by this magnetic field error portion in the time point when the sample command signal is been generated. In this case, when a time interval of the sample command signal outputted from the sample command circuit 33 is set to a suitable length, even a magnetic field detector 11 whose response speed is low can correct its error portion correspondingly enough.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fill control device that generates a magnetic field using a direct current.

[Prior art and its problems]

FIG. 2 is a block diagram showing a conventional example of controlling a magnetic field generating coil by magnetic field control, in which AC power from an AC power source 2 is converted to DC power by a disconnected transformer 3 and a rectifier 4, The smoothed DC power is converted into desired DC power by so-called chopper control that changes the ratio of the on-time and off-time of the transistor 60, and is applied to the coil 8. ζHere, the symbol F is a freewheeling diode.

When a direct current flows, the strength of the magnetic field generated by the paper film 8 is detected by a magnetic field detector 11, amplified by a magnetic field amplifier 12, and then compared with the setting value of a magnetic field setting device 13, and the deviation between the two is calculated. The control signal to make it zero is the magnetic field adjuster 14.
is output from. The output signal from the magnetic field adjuster 14 is sent to the pace drive circuit 15 to turn on and off the transistor 6 as appropriate, so that the strength of the magnetic field generated by the coil 8 can be maintained at the value set by the magnetic field setting device 13. can.

However, the magnetic field detector H for detecting the strength of the magnetic field
For this purpose, a Hall element or a system that utilizes the nuclear magnetic resonance phenomenon is used, but the Hall element has drift due to temperature changes, and systems that utilize the nuclear magnetic resonance phenomenon require measurement K at a constant periodic rate. Not only do they require manipulation, making them impossible to measure continuously, but they also have the drawback of slow response speed, making it difficult to control the strength of the magnetic field with high precision.

FIG. 3 is a block diagram showing a conventional example of controlling a magnetic field generating coil by current control, in which AC power from an AC power supply 2 is converted into DC power by an insulating transformer 3 and a rectifier 4, and then by a smoothing capacitor 5. The smoothing and further conversion to desired DC power through the transistor 6 and freewheel diode to excite the coil 8 are the same as in the conventional example shown in FIG. 2 described above. The conventional example shown in Fig. 3 focuses on the proportional relationship between the magnitude of the current flowing through the coil 8 and the strength of the magnetic field, and the current flowing through the coil 8 is divided into a shunt 21 and an isolation amplifier. 22, the deviation between the current setting value determined by the current setting device 23 and this detected current value is inputted to the current regulator a, and this current regulator 4
The current flowing through the coil 8 is controlled to a desired value by applying a control output signal from the coil 8 to the base of the transistor 60 via the pace drive circuit 15 to turn the transistor 6 on and off as appropriate.

Although high-speed control is possible with the conventional example shown in Figure 3, the strength of the magnetic field changes due to changes in coil dimensions due to temperature, residual magnetization of the iron core, etc. It has the disadvantage that it cannot be maintained at the desired value.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a magnetic field generating coil that has a fast response speed and can control the strength of a magnetic field with high precision.

[Key points of the invention]

This invention detects the current flowing through a magnetic field generating coil and the generated magnetic field, calculates the theoretical value of the required current from the detected magnetic field value, compares the theoretical current value with the detected current value, and calculates the difference between the two. is added to the current setting value to perform current adjustment operation, and the difference between the two currents mentioned above is updated at a predetermined time using a sample and hold circuit to improve control accuracy. This is intended to avoid interference with high-speed response.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of the present invention, and the content of the present invention will be described below with reference to this first diagram.

In Fig. 1, AC power from an AC power source 2 is converted to DC power by an isolation transformer 3 and a rectifier 4, which serve as both insulation and transformer, and ripples are removed by a smoothing capacitor 5, resulting in smooth DC power. Become. transistor 6
repeats on/off operations at high speed, and by changing the ratio of on time to off time, the current value flowing through the coil 8 is controlled along with the action of the freewheel diode.

The current flowing through the coil 8 is detected by the shunt 21 and the isolation amplifier 22, and the deviation between this detected current value and the current setting value set by the current setting device is determined by a proportional-integral calculator. The current setting signal is input to the current setting device, and the current setting device outputs a control signal that makes the input deviation zero, but this output signal passes through the pace drive circuit 16 and is seen in the transistor 60 base circuit. This transistor 6 controls the current flowing through the coil 8 to match the value set by the current setting mechanism. On the other hand, since the strength of the magnetic field generated by the coil 8 is detected by the magnetic field detector 11,
A virtual current calculator 31 calculates a theoretical current value to be passed through the coil 8 from this magnetic field detection value obtained through the magnetic field amplifier. The deviation between the theoretical current value obtained in this way and the above-mentioned detected current value is determined by the sample and hold circuit 3.
2 is input.

When the sample command circuit 33 sends a sample command to the sample hold circuit 32 at a predetermined timing, the input signal at that time is output from the sample hold circuit 32 and added to the above-mentioned current detection value and current setting value to adjust the current. It is now entered automatically. In other words, the current detection value output by the isolation amplifier 22 and the virtual current calculator 31
The difference from the theoretical current value output by is the magnetic field error, and the magnitude of the current setting value is adjusted by this magnetic field error at the time when the sample command signal is issued. Here, if the time interval of the sample command signal outputted from the sample command circuit product is set to an appropriate length, even the magnetic field detector U having a slow response speed can sufficiently respond and correct the error.

Note that the above-mentioned sample command may be issued only twice: when starting the coil 8 and when starting normal operation after completing the form-up. In other words, the sample command at the first startup is a so-called initial reset, and warm-up operation is started by performing current control with the current setting value corrected for the residual magnetization of the coil 8 as the target value. I will do it. Form-up is completed when the temperature of the coil 8 rises and becomes constant due to this warm-up operation, so the second sample command is issued at this point, and the relationship between the magnetic field strength and the current magnitude is adjusted to the planned value. Corrections are made for deviations from the range. After the current setting value is corrected in this way, the operating state is entered by constant current control.

〔Effect of the invention〕

According to this FIAK, the current setting value of the loop that controls the current flowing through the magnetic field generating coil to a constant current is corrected by the difference between the detected current value and the theoretical current value, so this magnetic field generating coil Once the warm-up is completed and the steady state is reached, constant magnetic field control is applied, so compared to the case where constant current control is performed from the beginning, the influence of changes in the coil outer shape and residual magnetization of the magnetic material around the coil is lower. etc. can be removed. The difference between the rounded current detection value and the theoretical current value for magnification correction is passed through a sample and hold circuit, and the current setting value is corrected as appropriate according to the sample command, so magnetic field detection using nuclear magnetic resonance phenomena is possible. It is possible to use a detector with a slow response speed such as a magnetic field detector, and even when detecting a magnetic field with a large drift, it is possible to ensure the stability of the magnetic field generated by the operating coil, and the accuracy determined by these magnetic field detectors can be ensured. . Furthermore, since direct current can be detected at high speed, a high response speed can be ensured even against power supply voltage fluctuations and various disturbances.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
The figure is a block diagram showing a conventional example of controlling a magnetic field generating coil by magnetic field control, and Figure 3 is a block diagram showing a conventional example of controlling a magnetic field generating coil by current control. 2... AC power supply, 3... Isolation transformer, 4... Rectifier, 5'° smoothing capacitor, 6... Transistor,
F...7 Lee wheel diode, 8...Coil,
11... Magnetic field detector, 12... Magnetic field amplifier, 13.
...Magnetic field setting device, 14...Magnetic field regulator, 15...Base drive circuit, 21...Shunt, vane...Isolation amplifier, Shame...Current setting device, 夙...Current adjustment Vessel, 31...
・Virtual current calculator, 32...sample hold circuit,
33...Sample command circuit. Figure 2 Figure 8

Claims (1)

[Claims] 1) A coil that generates a magnetic field by passing a direct current, including a current detector that detects the direct current flowing through the coil and a magnetic field detector that detects the strength of the magnetic field generated by the coil. a current regulator, which inputs the deviation between the current setting value determined by the current setting device and the current detection value detected by the current detector and outputs a control signal to make the DC current flowing through the coil match the current setting value; , a virtual current calculator that calculates a theoretical DC current value corresponding to the strength of the magnetic field obtained by the magnetic field detector, and a theoretical current value outputted by the virtual current calculator and a detected current value from the current detector. and a sample hold circuit that inputs the difference between the sample command signals from the sample command circuit and outputs the difference input signal so as to be added to or subtracted from the current setting value when the sample command signal from the sample command circuit is given. Generator coil control device. 2) In the control device according to claim 1, the sample command circuit is a sample command circuit that provides a sample command signal to the sample hold circuit at the time of starting the coil and at the completion of warm-up. Control device for magnetic field generating coil.