JPH0544610B2 - - Google Patents

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to an electromagnetic balance type balance.

(b) Prior art In an electromagnetic balance type balance, a force coil is movably provided in a static magnetic field created by a permanent magnet and is engaged with a weighing pan to generate an electromagnetic force that balances the load on the weighing pan. The current flowing through the force coil is controlled to generate , and the load value on the weighing pan is detected from the current value. In such balances, permanent magnets generally have a temperature coefficient of -200 to -400 x 10 ^-6 /℃ in relation to the strength of the magnetic field they create, so in order to eliminate the temperature dependence of the detected load value, It is necessary to detect the temperature of the permanent magnet with a temperature sensor and correct the conversion rate of the current value to the load value based on the temperature. If the accuracy of the balance is about 1/20,000, then the temperature correction accuracy of about 0.1°C is sufficient, so there is no major problem. But 20
In the case of a balance with an accuracy of 1/20,000 to 1/2 million, it is necessary to perform temperature correction with an accuracy of 0.01°C to 0.001°C, but the force coil placed in a static magnetic field has a A current is flowing, and the force coil generates a small amount of heat, which heats the pole piece of the magnetostatic circuit, which is then transmitted to the yoke via the permanent magnet, and then to other components. Ru. Here, the material for permanent magnets has poor thermal conductivity (for example, 1/5 of iron) compared to other constituent materials such as yokes, so permanent magnets have a large temperature gradient of, for example, 0.1°C/cm. This value is extremely large in terms of the accuracy of temperature correction described above, and it has been extremely difficult to perform temperature correction with the desired accuracy.

(c) Purpose An object of the present invention is to reduce the temperature gradient in the permanent magnet described above, accurately correct the temperature dependence of the detected load value, and thereby obtain a highly accurate electromagnetic force balance balance.

(D) Structure The present invention is characterized in that a pole piece is joined to one of both end faces perpendicular to the magnetization direction of the permanent magnet, and an inner bottom face of a cylindrical yoke with a bottom is joined to the other end face, and the above-mentioned pole piece A cylindrical static magnetic field is formed by the outer circumferential surface and the inner circumferential surface of the yoke, and a temperature sensor is provided approximately at the center of the permanent magnet, and its output is measured according to the temperature change caused by the temperature change of the permanent magnet. In addition to correcting changes in the strength of the static magnetic field, the outer circumferential surface connecting the above-mentioned both end surfaces of the permanent magnet is covered with a material other than ferromagnetic material and with a material having good thermal conductivity.

(e) Examples Examples of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

A pole piece 2 is bonded to one of both end surfaces of the permanent magnet 1 perpendicular to the magnetization direction, and the other is bonded to the inner bottom surface of a bottomed cylindrical yoke 3, forming a magnetostatic circuit. A force coil 4 is wound so that a current flows in a direction perpendicular to the direction of the magnetic field within a cylindrical static magnetic field created between the outer periphery of the pole piece 2 and the upper inner periphery of the yoke 3 in the static magnetic circuit. is provided, and this force coil 4 is
It is movable in the vertical direction and is supported by a winding frame 5 on which a load on a weighing pan (not shown) acts. The displacement of the winding frame 5 due to the load is detected by a displacement sensor 6, and the detection signal is supplied to a power amplifier 9 via a preamplifier 7 and a PID controller 8, and a direct current corresponding to the magnitude of the displacement is sent to the force coil. 4 to generate an electromagnetic force that causes the displacement of the winding frame 5 to be zero. At this time, the current flowing through the force coil 4 is converted into voltage by a resistor 10, then digitized by an A-D converter 11, converted into a load value by an arithmetic circuit 12, and displayed on a display 13. It is configured to be Note that the correction coil 20 is for eliminating the influence of the magnetic field generated by the force coil 4 on the static magnetic field.

A temperature sensor 14 is provided at the center of the permanent magnet 1, and its output is introduced into a temperature measurement amplifier 15. The temperature measurement amplifier 15 changes the reference voltage supplied to the A-D converter 11 according to the temperature of the permanent magnet 1 detected by the temperature sensor 14, and detects the load by changing the strength of the magnetic field caused by the temperature change of the permanent magnet 1. It is configured to correct the error. In addition, the outer peripheral surface of the permanent magnet 1 connecting both end surfaces joined to the pole piece 2 and the yoke is made of a material other than a ferromagnetic material such as copper, copper alloy, aluminum, or aluminum alloy, and has a high thermal conductivity. A heat transfer ring 16 made of a material with good properties is fitted therein.

According to the above-described embodiment of the present invention, the amount of heat generated by the current in the force coil 4 is transmitted from the pole piece 2 to the bottom of the yoke 3 mainly through the heat transfer ring 16. Thermal resistance is reduced to a fraction of that of the conventional one without the heat transfer ring 16, and the temperature rise and temperature gradient of the permanent magnet 1 are greatly reduced. Therefore, the temperature correction accuracy of the load detection value by the temperature sensor 14 and the temperature measurement amplifier 15 is greatly improved compared to the conventional technology.

Note that the thickness of the heat transfer ring 16 described above is approximately 1 to 1.
It has been found that a thickness of about 5 mm is sufficient.

In addition, as shown in FIG. 2, which shows the configuration of main parts of another embodiment of the present invention, the permanent magnet 1' is cylindrical, and the inner circumferential surface connecting both end surfaces joined to the pole piece 2 and the yoke 3 is also , heat transfer ring 1 fitted on the outer peripheral surface
When a second heat transfer ring 16' similar to 6 is inserted,
The effect will be further improved.

In addition, in the above embodiment, the case where the current flowing through the force coil is a direct current is described, but a positive and negative pulsed current is passed through the force coil 4 to generate an electromagnetic force, which is balanced against the load, and the average current value is determined as the load value. It can also be applied to balances that convert to In this case, the heat transfer ring 16
In addition to the effect of reducing the temperature gradient as described above, the change in magnetic flux of the static magnetic field due to the alternating magnetic field generated by passing a pulsed current through the force coil 4 causes the alternating magnetic field to be short-circuited by the electric heating ring 16. As a result of suppressing the demagnetizing effect, the stability of the magnetic field over time also improves. Figure 3 is a graph showing the difference in the demagnetization effect depending on the presence or absence of a heat transfer ring.When using a 1000Hz pulse current, the demagnetization effect is suppressed to about 1/3.

(F) Effect As explained above, according to the present invention, the heat generated by the force coil is mainly caused by the heat transfer ring formed of a material other than a ferromagnetic material and having good thermal conductivity. Since the temperature rise and temperature gradient inside the permanent magnet are small, the temperature correction by the temperature sensor becomes highly accurate, and the electromagnetic force has an accuracy of 1/200,000 to 1/2 million. A balanced balance can be easily obtained, and since the temperature of the permanent magnet is brought to a stable state immediately after energization by the heat transfer ring, warming-up time can also be shortened.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of main parts of another embodiment of the present invention, and Fig. 3 is demagnetization by a heat transfer ring when the current flowing through the force coil is a pulse current. FIG. 3 is a diagram illustrating the effect on the action. 1... Permanent magnet, 2... Pole piece, 3...
Yoke, 4... Force coil, 5... Winding frame, 6
... Displacement sensor, 8 ... PID controller, 9 ... Power amplifier, 11 ... A-D converter, 12 ... Arithmetic unit, 14 ... Temperature sensor, 15 ... Temperature measurement amplifier, 16, 16' ...Heat transfer ring.

Claims (1)

[Claims] 1. The electromagnetic force is generated by balancing the force due to the load placed on the weighing pan and the electromagnetic force generated by passing a current through a force coil placed in a static magnetic field created by a permanent magnet. In a balance that detects the load from the current required to carry out the load, a pole piece is bonded to one of both end surfaces perpendicular to the magnetization direction of the permanent magnet, and the inner bottom surface of a cylindrical yoke with a bottom is bonded to the other. The cylindrical static magnetic field is formed by the outer circumferential surface and the inner circumferential surface of the yoke, and a temperature sensor is provided approximately at the center of the permanent magnet, and the output thereof is caused by temperature changes of the permanent magnet. In addition to correcting changes in the strength of the static magnetic field, the outer circumferential surface connecting the both end surfaces of the permanent magnet is
An electromagnetic balance balance characterized by being covered with a material other than ferromagnetic material and having good thermal conductivity. 2. An electromagnetic force balance balance according to claim 1, characterized in that the current flowing through the force coil is a pulsed current, and the balance is configured to convert the average current value of the pulsed current into a load value. . 3. The permanent magnet is formed into a cylindrical shape along its magnetization direction, and the inner peripheral surface connecting the pole piece and both end surfaces joined to the yoke is also made of a material other than ferromagnetic material and has a high thermal conductivity. An electromagnetic force balance balance according to claim 1 or 2, characterized in that the balance is covered with a good material. 4. The method according to claim 1, 2, or 3, wherein the material other than the ferromagnetic material and having good thermal conductivity is copper or a copper-based alloy. Electromagnetic balance balance. 5. The method according to claim 1, 2, or 3, wherein the material other than the ferromagnetic material and having good thermal conductivity is aluminum or an aluminum-based alloy. Electromagnetic balance balance.