JPH0523371B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention generates an electromagnetic force that balances the load on the pan, and determines the magnitude of the load on the pan from the current required to generate the electromagnetic force. , concerning an electromagnetic balance type balance.

<Prior art> In an electromagnetic balance type balance, a coil (hereinafter referred to as a force coil) is placed in the magnetic field to supply a current in order to generate an electromagnetic force that balances the load on the pan. The magnitude of is determined by detecting the displacement of the plate due to the load on the plate and feeding back the value. The current flowing through the force coil is digitized by an A-D converter and sent to a microcomputer to determine the measurement surface value.

However, since the A-D converter has a limited accuracy, the above configuration cannot satisfy both the accuracy and weight of a high-resolution balance.

Therefore, conventionally, two force coils were provided,
The A-D converter that feeds back the displacement detection value to one side (the first force coil) and inputs the current flowing through the force coil has two ranges, fine and coarse, as shown in the flowchart of Figure 4. The measurement program determines the weighing display value. That is, when the value of the current flowing through the first force coil exceeds the fine range of the A-D converter, switch to the coarse range, measure the approximate value of the load on the pan, and set the current corresponding to that value. second
power coil. This makes the first
The value of the current flowing through the second force coil is within the precision range of the A-D converter, so at the same time, switch to the precision range and calculate the value on the plate from the output value and the current value set in the second force coil. The load is required.

<Problems to be Solved by the Invention> According to the conventional balance described above, at the same time as changing the range of the A-D converter from coarse to fine, the second force coil is equipped with a wire of a size that approximately balances the load on the pan. A current large enough to generate an electromagnetic force is supplied all at once, causing a large instantaneous displacement of the plate and the beam that engages with the plate, and the displayed weighing value fluctuates until the vibration of the beam, etc. due to this change is attenuated. Therefore, there was a problem that the measurement time became longer. In addition, when working with liquids, powders, and granules,
Frequently switching between fine and coarse ranges is required,
There was a problem that the beam etc. vibrated each time, making it difficult to perform the work smoothly.

<Means for Solving the Problems> The present invention has been made for the purpose of solving the above problems, and its configuration will be explained based on the basic conceptual diagram shown in FIG.

Displacement of the dish is detected by the displacement detection means via the beam. An electromagnetic force generating device is engaged with the beam to generate an electromagnetic force corresponding to the load on the plate, and this electromagnetic force generating device is provided with first and second force coils placed in a magnetic field. It is being

The value detected by the displacement detection means is fed back to the first force coil, and the magnitude of the current flowing through the first force coil is determined in order to generate an electromagnetic force corresponding to this magnitude. The current value flowing through the first force coil is digitized by an A-D converter with two ranges, fine and coarse.
The determining means determines whether the value exceeds the precision range. Based on the determination result, the range switching means switches the A-D converter to the coarse range when the value exceeds the fine range, and switches to the fine range when the value falls within the fine range.

The coil current setting means sequentially additionally supplies a current corresponding to a predetermined ratio of the output of the A-D converter to the second force coil when the A-D converter is in the coarse range state. . Setting of the current value supplied to the second force coil by the coil current setting means is repeated until the value of the current flowing through the first force coil falls within the precision range of the AD converter. The measurement display value is determined from the current value supplied to the second force coil by the coil current setting means and the output value of the A-D converter in the precision range state, that is, the current value flowing through the first force coil.

<Function> When the A-D converter is in the coarse range state, current corresponding to a predetermined ratio of its output value is sequentially supplied to the second force coil; in other words, the current is supplied to the second force coil. The current is changed in steps to keep the current flowing through the first force coil within the precision range of the A-D converter, so that the A-D
When the range of the converter is changed from coarse to fine, the dish, beam, etc. do not vibrate due to the electromagnetic force generated by the second force coil.

<Example> Examples of the present invention will be described below based on the drawings.

FIG. 2 is a circuit configuration diagram of an embodiment of the present invention.

The plate 1 is connected to one end of a beam 2, and the beam 2 is rotatably supported around a fulcrum 3, and the other end is connected to an electromagnetic force generator.

The electromagnetic force generator 4 has a first force coil 5 and a second force coil 6 arranged in a static magnetic field composed of a permanent magnet, etc., and by passing current through these coils, the plate 1 It is possible to generate an electromagnetic force in a direction that eliminates the displacement of the beam 2 due to the load of the upper king.

The displacement of the beam 2 is detected by a displacement sensor 7, and the detected value is fed back to the first force coil via an amplifier 8. The magnitude of the current flowing through the first force coil is digitally converted by the A-D converter 9 and then input to the microcomputer 10 via its input/output port.

The second force coil 6 passes a rectangular wave current supplied from the pulse current generator 11, and uses its electromagnetic force to reduce the magnitude of the current flowing to the first force coil 5 in order to balance the beam 2. The magnitude of the electromagnetic force is determined by changing the square wave current pulse duty ratio. This duty ratio can be changed by a command from the microcomputer 10.

The A-D converter 9 has two ranges, fine and coarse, and these ranges are controlled by the microcomputer 1.
It is determined by operating the switch 9a in response to a command from 0.

The microcomputer 10 determines the duty ratio of the output of the pulse current generator 11 and the range of the A-D converter 9 according to a program to be described later, and also determines the output duty ratio of the pulse current generator 11 and the range of the A-D converter 9. A metering display value can be determined from the current flowing and displayed on the display 12.

FIG. 3 is a flowchart showing a measurement program written in the ROM of the microcomputer 10, and the operation of the embodiment of the present invention will be explained with reference to this diagram.

When a load is placed on plate 1, beam 2 is displaced,
As a result, a current flows through the first force coil 5 to make the displacement zero. The magnitude of the current is digitized by the A-D converter 9, but the A-D
The precision range is initially selected as the range of the converter 9. In this precision range, when the load is less than 200mg, the digital input data is averaged while the precision range is used to determine the weighing value and the display is displayed.
Display on 2.

When the load exceeds 200mg, the first
The magnitude of the current flowing through the force coil 5 is A-
The fine range of the D converter 9 is exceeded, and in this case a command is issued to the switch 9a to switch to the coarse range. At the same time, a pulsed current is supplied from the pulsed current generator 11 to the second force coil 6, and the pulse duty ratio at this time is:
A predetermined rate of the A-D converter 9 output in the coarse range state,
For example, it is set to 80%. By this, the first
The current flowing through the force coil 5 is reduced accordingly, and the magnitude of the input signal to the A-D converter 9 is also reduced, but since it is not 100%, it will not decrease to the extent that it enters the precision range at once. Therefore, after the duty ratio is changed several times, the electromagnetic force generated by the second force coil 6 reaches a size that almost balances the load, and the magnitude of the current flowing through the first force coil 5 becomes A-D conversion. This will fall within the precision range of vessel 9. After waiting for the weighing value to stabilize to some extent in this state, switch to the precision range and display the weighing value. This display value becomes a precise measurement value that is combined with the duty ratio setting value for the pulse current generator 11 and the digital data of the A-D converter 9 in the precise range state.

Since the value of the current supplied to the second force coil 6 gradually approaches the value that should be finally supplied, the vibration of the beam 2 etc. caused by supplying the current to the second force coil 6 can be prevented by the conventional method. This decreases significantly compared to the previous year. Note that stability is determined before switching to the fine range because, in a certain amount of weighing work, when the displayed value in the coarse range reaches near the target weighed amount, sample input is stopped. By detecting this through stability determination, the switching to the fine range during such work can be minimized to enable smooth work.

Note that the ratio of the current change value supplied to the second force coil 6 with respect to the output of the A-D converter 9 in the coarse range state is not limited to 80%, but may be a ratio smaller than 100% as appropriate depending on the characteristics of the balance. You can set it to a suitable value.

Further, in the above embodiment, an example was shown in which the current to the second force coil 6 is a rectangular wave current and the generated electromagnetic force is changed by changing the duty ratio. Of course, a method of changing the current stepwise may also be used.

Furthermore, in determining the current to be supplied to the second force coil 6, the magnitude of the current flowing through the first force coil 5 is compared with a predetermined reference value by a comparator, and thereby a preset quantum The converted current is transferred to the second force coil 6
In addition, the remaining portion can also be determined from the output of the A-D converter 9 in the coarse range by the above-mentioned program.

<Effects> As explained above, according to the present invention, the magnitude of the current to the second force coil 6 is not determined at once and supplied at once as in the conventional method, but is Since the current value is sequentially changed so as to approach the current value that should be supplied according to the , the work of measuring a certain amount can be carried out smoothly.

Furthermore, just before switching from the coarse range to the fine range, the balance is almost achieved and the magnitude of the input signal to the A-D converter 9 becomes very small, so there is no need to make the precision of the coarse range very high. , it is possible to prevent display errors from occurring due to sensitivity changes in the coarse range state.

[Brief explanation of the drawing]

Fig. 1 is a basic conceptual diagram of the present invention, Fig. 2 is a circuit configuration diagram of an embodiment of the present invention, Fig. 3 is a flowchart showing a measurement program written in the ROM, and Fig. 4 is a measurement of a conventional device. This is a flowchart showing a program for DESCRIPTION OF SYMBOLS 1... Dish, 2... Beam, 4... Electromagnetic force generator, 5... First force coil, 6... Second force coil, 7... Displacement sensor, 8... Amplifier.

Claims (1)

[Claims] 1. A balance that measures the magnitude of a load by generating an electromagnetic force that balances the load on a pan, which has first and second force coils for generating the electromagnetic force and two fine and coarse ranges. and an A-D converter for digitizing the value of the current flowing through the first force coil, a displacement detector for detecting the displacement of the plate due to the load, and feeding it back to the first force coil; Discrimination means for determining whether the magnitude of the input to the D converter exceeds the precision range of the converter; and range switching means for changing the range of the A-D converter based on the determination result. , coil current setting means for sequentially additionally supplying a current corresponding to a predetermined rate of the output of the A-D converter to the second force coil when the A-D converter is in the coarse range state, and a current flowing through the first force coil; When the value exceeds the fine range of the A-D converter, the A-D converter is switched to the coarse range, and the current value supplied to the second force coil is sequentially changed according to its output. , by adding electromagnetic force from this second force coil to sequentially reduce the current flowing through the first force coil to keep its magnitude within the precision range of the A-D converter, and then -D
An electronic balance characterized in that the converter is switched to a precision range and the magnitude of the load on the pan is determined from the output thereof and the current value from the coil current setting means.