JP2518131B2 - Electronic balance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic balance, and more particularly to a high precision balance having a small reading limit.

[0002]

2. Description of the Related Art Generally, in an electronic balance, a load on a measuring pan is transmitted to an electromagnetic force generating mechanism through a balance beam, and the electromagnetic force generating mechanism counteracts the load and balances the beam. Generate force. This electromagnetic force is generated by passing a current through a coil placed in a magnetic field. The magnitude of the coil current is measured, and the load on the measuring pan is calculated from the measured data.

[0003]

Among the electronic balances as described above, in a balance with a small reading limit called a micro or semi-micro balance, the balance beam keeps a constant state (stationary or close to it) for a long time. When performing the measurement after
Specifically, the phenomenon that the measured value becomes unstable at the first time or at the first time to several times after the start of measurement often occurs. For this reason, after making a standby state without performing measurement for a long time in the energized state, a dummy measurement must be performed once or several times, and the actual measurement must be performed after confirming that the measured value is stable. There is an annoyance.

The present invention has been made in view of such circumstances, and it is possible to display a highly reliable measured value from the first measurement even in the measurement after the standby state is continued for a long time in the energized state. The purpose is to provide an electronic balance that can do this.

[0005]

The structure for achieving the above object will be described with reference to the basic conceptual diagram shown in FIG. 1. The electronic balance of the present invention can be applied to the load to be measured on the measuring pan a. An electromagnetic force generating mechanism c that generates an electromagnetic force that counterbalances the balance beam b and a measuring value determining means d that calculates the load to be measured based on the measurement data of the current flowing in the electromagnetic force generating mechanism c coil. In the balance, the measuring pan a
Sensor f for detecting the open / closed state of the door of the weighing chamber e surrounding the
And a determination means g for determining whether or not the balance is in a standby state based on the output of the sensor f, and a time point when a preset time has elapsed in the standby state based on the determination result, or A beam displacement imparting means h for forcibly displacing the beam b is provided at any one of the time points when the temperature in the vicinity of the electromagnetic force generating mechanism c changes, or at both time points. Characterized by

As a method for forcibly displacing the beam b, for example, a predetermined current is forcibly applied to the coil of the electromagnetic force generating mechanism, or there is a balance having a built-in calibration weight and its addition / removal mechanism. For example, a method of loading the built-in weight can be adopted.

[0007]

The reason why the measured value becomes unstable in the initial measurement after the standby state is continued for a long time in the balance having a small reading limit is as follows.

In this type of balance, a current is normally passed through the coil of the electromagnetic force generating mechanism to generate a certain amount of electromagnetic force to balance the balance beam even when there is no load. In such a state, if the beam remains stationary or close to it, the temperature distribution of the air inside the balance becomes biased due to the heat generated by the coil current.
As a result, temperature unevenness occurs in the components of the balance. When the sample to be measured is placed on the measuring dish in such a state, the balance beam sways to move the air inside the balance, and the temperature distribution of the air or the components of the balance changes. The measured value becomes unstable until the temperature distribution becomes steady.

The present invention grasps this fact and forcibly displaces the balance beam to stir the air inside the balance every time a certain period of time elapses or a constant temperature change occurs during the standby, and the balance is in the standby state. It is intended to mitigate the uneven temperature of each part of.

That is, the door of the weighing chamber e is opened and closed when loading and unloading the sample to be measured on the measuring dish a, and it is possible to determine whether the balance is in use or in standby depending on the opening and closing operation. It is possible. In the state that it is determined to be waiting,
When the balance beam b is forcibly displaced after a lapse of a certain period of time or whenever a certain temperature change occurs, the air inside the balance is stirred, and the temperature distribution state of the air inside the balance or its components is stable. It is possible to prevent a transient unstable phenomenon of the measured value at the beginning of measurement after waiting for a long time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a diagram showing a schematic configuration diagram of a balance mechanism portion and a block diagram of a circuit portion of the present invention together.

The measuring dish 1 is a movable column 21 of the Roberval mechanism 2.
The movable beam 21 is supported by the balance beam 3
One end of is attached. The balance beam 3 is supported by an elastic fulcrum 31, and the movable coil 41 of the electromagnetic force generating mechanism 4 is attached to the other end.

The displacement of the beam 3 is detected by a displacement sensor (not shown).
The PID control circuit 5 receives the detection result. The PID control circuit 5 controls the current flowing through the movable coil 41 of the electromagnetic force generation mechanism 4 so that the inclination of the beam 3 becomes zero.

The current flowing through the movable coil 41 is converted into a voltage signal by a resistor or the like, converted into digital data by the AD converter 6, and sampled by the microcomputer 7. The microcomputer 7 calculates the load on the measuring dish 1 using the sampling data, determines the measured value, and displays it on the display 8.

The measuring dish 1 is arranged in the weighing chamber 9, and the door 91 has a sensor 1 for detecting the open / closed state.
0 is provided. The output of this sensor 10 is taken into the microcomputer 7 via the input / output interface 11. On the basis of the output of the sensor 10, the microcomputer 7 determines whether or not the balance is in a standby state, as will be described later.

A balance case 13 for accommodating the mechanical portion
Inside, a temperature sensor 14 is arranged close to the electromagnetic force generation mechanism 4, and the output of the temperature sensor 14 is digitized by an A / D converter 15 and incorporated in the microcomputer 7.

FIG. 3 is a flowchart showing a part of the program written in the ROM of the microcomputer 7 which is relevant to the present invention, and the operation of the embodiment of the present invention will be described below with reference to this figure. Note that this routine is repeated at regular intervals during execution of a normal measurement routine, for example.

Based on the output of the sensor 10 for detecting the opening / closing state of the door 91 of the weighing chamber 9, for example, when the opening / closing operation is not performed for a certain period of time, it is determined that the balance is in the standby state and the temperature at that time is determined. At the same time that the output of the sensor 14 is stored as T ₁ , the timer t is started.

In that state, the output data T of the temperature sensor 14
Each time ₂ samples, the data T ₂ is compared with the temperature data T ₁ described above. Then, each time the difference reaches a preset temperature difference ΔT, and each time the time measured by the timer t reaches a preset time t ₀ , the electromagnetic force generation mechanism 4 of the electromagnetic force generation mechanism 4 is controlled via the PID control circuit 5. A predetermined current is supplied to the movable coil 41. When this current is supplied, the temperature data T ₂ at that time is supplied.
Is stored as temperature data T ₁ and the timer t
Is reset.

By supplying this current, the electromagnetic force generating mechanism 4
Generates a certain electromagnetic force, disturbs the balance of the beam 3, and causes the beam 3 to swing. As a result, the air in the case 13 accommodating the balance mechanism section is agitated.

In the standby state of the balance, the beam inside the balance case 13 is agitated by displacing the beam 3 at regular time intervals or at constant temperature differences.
The unevenness of the temperature distribution of the air in the air conditioner 3, and consequently the unevenness of the temperature distribution of each component such as the elastic fulcrum 31 in the balance mechanism is reduced. In other words, even if the balance is in the standby state, it is as if the balance is being used.

As a result, even if the sample to be measured is placed on the measuring dish 1 as it is after the stand-by state is continued for a long time, the measured value does not become unstable as in the conventional case, and it is stable from the first measurement. It will be what you did.

In the above embodiment, the balance beam 3 is used.
A current was passed through the movable coil 41 of the electromagnetic force generation mechanism 4 in order to give a forced displacement to the balance. Instead, in the case of a balance having a calibration weight and its addition / removal mechanism built-in, the built-in calibration Use a weight to balance beam 3 or Roberval mechanism 2
By loading the movable column 21 of the balance beam 3
May be forcibly displaced.

Further, as the timing for forcibly displacing the beam 3, in the above-mentioned embodiment, both the elapse of a certain time in the standby state and the generation of a certain temperature difference are combined. Even if either timing of the temperature difference is used, substantially the same operational effect can be achieved.

Further, the timing for forcibly displacing the beam 3 can be set to the time when an instruction is given by, for example, switch operation in addition to the passage of time and / or the temperature difference as described above. It is possible to forcibly stir the air in the case depending on the intention of the user.

Furthermore, the output of the temperature sensor 14 is a predetermined temperature detection output to the A / D converter 6 for digitizing the current data without using the dedicated A / D converter 15. It is needless to say that the moving coil 41 may be configured so as to be digitized by conducting it through a switch that operates at intervals, and the current to be passed through the movable coil 41 may be a direct current or a pulsed current. Modifications such as changing the generated electromagnetic force by changing the duty are possible.

[0027]

As described above, according to the present invention,
Based on the open / closed state of the weighing chamber door, it is determined whether or not the balance is in the standby state, and based on the determination result, the balance is returned every time a certain time elapses and / or a predetermined temperature difference occurs in the standby state. Since the beam is forcibly displaced to stir the air in the balance case, the temperature unevenness of the air surrounding the balance mechanism is always removed even during standby, and each component that constitutes the balance mechanism is in standby. Regardless, the temperature distribution will be the same as during use, and a stable measured value can always be obtained from the first measurement even after the standby state has continued for a long time.

Further, forcibly displacing the balance beam and agitating the air in the case during standby has the effect of stabilizing the zero point drift after the start of measurement. That is, normally, the zero point drift is caused by a temperature change, and when the temperature change is gradual, an average value of the zero points before and after the measurement can be adopted as the zero point.
However, when the beam starts to move after waiting for a long time, the zero point drift due to the change in the atmosphere due to the movement overlaps, and the correct measured value cannot be obtained by simply taking the average value of the zero points before and after the measurement. According to the present invention, if the beam is forcibly displaced at a predetermined timing during standby, such a problem is solved, and in this respect also
From the second time, the reliability of the measured value will be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram showing the configuration of the present invention.

FIG. 2 is a diagram showing both a schematic configuration diagram of a balance mechanism portion and a block diagram of a circuit diagram according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a main part of a program written in a ROM of the microcomputer 7.

[Explanation of symbols]

 1 Measuring dish 3 Balance beam 31 Elastic fulcrum 4 Electromagnetic force generating mechanism 41 Moving coil 5 PID control circuit 7 Microcomputer 9 Weighing chamber 91 Door 10 Door open / close detection sensor 13 Balance case 14 Temperature sensor

Claims (1)

(57) [Claims] 1. An electromagnetic force generating mechanism for generating an electromagnetic force for balancing a balance beam against a measured load on a measuring dish, and a measured object based on measurement data of a current flowing through a coil of the electromagnetic force generating mechanism. In a balance equipped with a weighing value determining means for calculating the load, a sensor that detects the open / closed state of the door of the weighing chamber that surrounds the measuring pan and whether or not the balance is in the standby state based on the output of the sensor Based on the result of the determination and the determination result, in the standby state, a preset time has elapsed, or the temperature near the electromagnetic force generation mechanism has a preset temperature change. An electronic balance comprising beam displacement imparting means for forcibly displacing the beam at any time point or at both time points.