JPH0479404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic balance, and more specifically:
Related to a temperature compensation device for an electronic balance.

For example, in an electromagnetic balance type electronic balance, the pan is generally displaceable by a Roberval mechanism, etc., and the Roberval mechanism is also equipped with an electromagnetic force generator to generate a force that counteracts the load acting on the pan. It has a structure in which units are connected. Displacement of the mechanism caused by a load acting on the plate is detected by a displacement sensor, and the electromagnetic force generating unit is driven and controlled by a servo circuit using the detection signal as a feedback signal. In other words, in this servo circuit, a current that changes based on the magnitude of the displacement detection signal is supplied to the electromagnetic force generation unit so that the displacement detection result by the displacement sensor is always zero. generates an electromagnetic force that always returns the displacement to the balance position (zero point). With this configuration, when the mechanism is stationary at the balance position, the electromagnetic force generated by the electromagnetic force generating unit, in other words, the current flowing through this unit, and the The load to be measured is in a balanced state, and the magnitude of the load to be measured can be determined from the magnitude of the current. In addition to the amplifier that amplifies the power of the displacement detection signal and supplies it to the electromagnetic force generation unit, this servo circuit usually includes a PID at the front stage.
(Proportional, differential, integral) control circuits, etc. are inserted to make the system highly responsive and stable at the same time, and are designed to provide strong braking performance.

By the way, in the above-mentioned electronic balances, heat generated from electromagnetic transformers, electronic components, etc. generally causes a temperature distribution in the balance mechanism, causing expansion and contraction and changes in the elastic coefficient of the members that make up the mechanism. As a result, effects such as zero drift appear for several minutes to several tens of minutes after energization.

In order to deal with this phenomenon, conventional methods have been to reduce the amount of heat generated as much as possible, reduce the spring constant of the elastic fulcrum used to increase mechanical sensitivity, and reduce zero drift by using bimetal or temperature sensors. A rise in temperature is detected to perform mechanical balance adjustment, or, as will be described later, electrical compensation is performed using the output of a single temperature sensor installed near the electromagnetic force generator.

However, with such conventional measures, it has been impossible to completely compensate for the drift of the balance when it does not appear as a linear function with respect to the temperature rise.

In other words, in the conventional electrical compensation method using one temperature sensor, a temperature sensor is installed in the balance mechanism near an electromagnetic force generating unit with a large heat capacity, and the sensor output represents the temperature of the balance mechanism. The output signal is used to electrically compensate the weighing output of the balance. However, in this compensation method, as illustrated in Fig. 4, the output signal is Zero drift that changes in a convex manner frequently occurs.

An object of the present invention is to provide an electronic balance that can keep zero drift due to heat generation after energization extremely small even if an elastic fulcrum with a large spring constant is used in the balance mechanism.

In order to achieve this object, the electronic balance of the present invention houses the balance mechanism part except the dish part in a container made of a good thermal conductor, and in the container,
Temperature difference detection for detecting a temperature difference between a first location within the balance mechanism that is close to the heat source and a second location that is far from the heat source and where a transient temperature difference occurs after power is applied to the first location. A group of temperature sensors for detecting a temperature difference, and a temperature sensor for detecting a representative temperature for detecting the temperature in the vicinity of the electromagnetic force generating unit in the balance machine, and a temperature sensor group for detecting a temperature difference between the first and second
It is characterized by comprising a correction circuit means for correcting the drift of the weighing output of the balance using both the two variables, the temperature difference signal between the locations and the output signal of the temperature sensor for detecting the representative temperature. .

Although the temperature inside the balance mechanism is detected near the electromagnetic force generator, etc. to compensate for the drift, the cause of the convex drift in the transient state in the graph of Figure 4 is that the drift of the balance is This is due not only to expansionary thermal expansion due to the rise in temperature of the balance mechanism, but also to distortion due to temperature differences until the temperature distribution in the balance mechanism becomes steady.

Therefore, in the present invention, in addition to the conventional temperature sensor (temperature sensor for representative temperature detection) that generates an output representative of the temperature inside the balance mechanism, we have developed a temperature sensor that generates an output representative of the temperature inside the balance mechanism. A temperature sensor group for detecting temperature differences (temperature sensor group for temperature difference detection) is provided, and both the temperature rise signal from the temperature sensor for representative temperature detection and the temperature difference signal from the temperature sensor group for temperature difference detection are used. By correcting the weighing output, the above-mentioned convex drift in the transient state is removed.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention.

The dish 1 is supported by a roberbal mechanism consisting of a movable column 2, an upper parallel link 3, a lower parallel link 4, and fulcrums 6, 6 of a fixed column 5, and the movable column 2 is supported by the action of a beam 8 via an elastic link 7. connected to points,
A moving coil 10 of an electromagnetic force generating unit 9 is connected to the force point of the beam 8, and a displacement sensor 11 is provided at the tip of the beam 8.

Such a mechanical part and electromagnetic force generating unit 9
is a container 1 made of a good conductor of heat, such as an aluminum plate.
It is housed inside 2 and is cut off from the outside.

A printed circuit board 13 is provided in the space above the container 12.
There is an electronic circuit mounted on top. If this electronic circuit includes parts that generate a particularly large amount of heat, such as a power transistor or a resistor with large power consumption, a plate made of a heat insulating material such as styrene is placed on the inner surface of the container near the circuit board 13. 14
You may also paste.

Now, temperature sensors 15 and 16 are arranged near the upper parallel link 3 provided near the circuit board 13 which is the heat source, and near the lower parallel link 4 which is quite far away from the circuit board 13, respectively. ing. In addition, the magnet in the electromagnetic force generating unit 9, which is a component with a large heat capacity and is not easily affected by transient temperature distribution in the balance mechanism,
A temperature sensor 17 is arranged as in the conventional case,
The output of each of these sensors is used to compensate for zero drift due to energization of the balance, as shown below.

FIG. 2 is a block diagram showing an electric circuit of an electronic balance according to an embodiment of the present invention.

The output signal of the displacement sensor 11 is amplified by an amplifier 18, subjected to PID control, phase control, etc. by a controller 19, and then amplified by a power amplifier 20 and sent to the moving coil 10 of the electromagnetic force generation unit 9. . When a current flows through the moving coil 10, an electromagnetic force is generated in the electromagnetic force generating unit to keep the displacement of the beam 8 at zero. By detecting the coil current i in this balanced state from both ends of the resistor R, a weighing signal is obtained. This weighing signal is A
The signal is converted into a digital signal by the -D converter 21, and output to a data processing section composed of a computer or the like. The above is a known circuit configuration.

Now, the temperature sensors 15 and 16 described above are incorporated into a temperature difference detection circuit 22 using a bridge circuit or the like, and this temperature difference detection circuit 22 is connected to the temperature sensor 15.
and 16, that is, a signal corresponding to the temperature difference between the upper parallel link 3 and the lower parallel link 4. Further, the temperature rise detection circuit 23 includes the above-mentioned temperature sensor 17, and outputs a temperature signal near the magnet of the electromagnetic force generating unit 9 having a large heat capacity.

The outputs of the temperature difference detection circuit 22 and the temperature rise detection circuit 23 are output from addition points 24 and 2 provided between the amplifier 18 and the controller 19, respectively.
5, both of which are configured to compensate for the current flowing through the moving coil 10, that is, the weighing signal. In other words, the degree of influence that changes in the output difference between temperature sensors 15 and 16 and changes in the output of temperature sensor 17 have on the zero point drift of the balance is experimentally investigated in advance, and the gain is adjusted accordingly. The amplification degree of each of these circuits is adjusted so that the outputs of the temperature difference detection circuit 22 and the temperature rise detection circuit 23 are input to the above-mentioned known servo circuit via addition points 24 and 25. As a result, in this embodiment, when the servo circuit is in a balanced state, the balance mechanism is not positioned at the original balanced position.
Balance is achieved at a position shifted by an amount corresponding to the sum of the input signals from the temperature difference detection circuit 22 and the temperature rise detection circuit 23. In other words, in the servo circuit, the target value of displacement is 0 when such compensation is not performed, but by performing compensation based on this embodiment,
By the amount that the target value of displacement corresponds to the sum of the outputs of the temperature difference detection circuit 22 and the temperature rise detection circuit 23,
The appearance will change. Here, the system including the balance mechanism and servo circuit needs Electromagnetic force (current)
It is designed so that the weighing signal becomes 0 with the magnitude of , and if the above compensation is not performed,
Since the servo circuit functions to balance the balance mechanism at its original balance position even under conditions other than the ideal temperature conditions described above, zero point drift occurs as a result. In contrast, in the embodiment of the present invention, when the load is 0 and the system is in equilibrium, the balance mechanism moves from the original balance position by an amount corresponding to the amount of deviation of the temperature state at that point from the ideal temperature state. The servo circuit functions to balance at the shifted position, and as a result, the weighing signal becomes 0 in this state, that is, the zero point drift is eliminated.

FIG. 3 is a graph showing the transition of the zero point drift after the power is turned on and the transition of the output values of the temperature sensors 15 and 16 in the above embodiment of the present invention.

In addition, Figures 4 and 5 are graphs shown as comparative examples, and Figure 4 shows the case where only the temperature rise signal based on the output of the temperature sensor 17 is used, and therefore the same temperature compensation measures as conventional ones are taken. FIG. 5 is a graph showing the transition of the zero point drift when temperature compensation is not performed. Note that both FIGS. 4 and 5 are shown using the same scale as FIG. 3.

As is clear from these graphs, if the temperature inside the balance mechanism is detected near the magnet of the electromagnetic force generating unit 9 and the zero point drift is compensated for, the There is a point in time when the drift becomes large. At this point, the temperature sensor 1 of the embodiment of the present invention
This almost coincides with the point at which the difference between the output values of No. 5 and No. 16 reaches its maximum, and it can be confirmed that there is a zero point drift due to the temperature difference inside the balance mechanism. In the embodiment of the present invention, the zero point drift always shows a small value regardless of the time course after energization.

In the above embodiment, the temperature sensors 15 and 16 for detecting the temperature difference were provided near the upper and lower parallel links 3 and 4, respectively. parallel link 3 or lower parallel link 4
It may also be configured to be directly attached to the device and to take out the output via a flexible lead wire.

As explained above, according to the present invention, a first
and a second location that is far from the heat source and has a transient temperature difference with respect to the first location;
A temperature sensor for detecting a representative temperature is provided to detect the temperature near the electromagnetic force generating unit in the balance mechanism. In addition to compensation, the structure is designed to compensate for drift caused by transient changes in temperature distribution, so it eliminates convex shapes that appear several minutes or tens of minutes after energization, which could not be resolved using conventional compensation methods. It is now possible to compensate for drift.

Furthermore, by surrounding the balance mechanism with a good thermal conductor, the reproducibility of the above compensation effect can be improved.

The above effects also make it possible to reduce drift without significantly reducing the spring constant of the elastic fulcrum, and by using a high-strength spring, impact resistance and durability can be improved. It has now become possible to create highly sensitive electronic balances.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a block diagram showing its circuit configuration, FIG. 3 is a characteristic diagram showing the relationship between elapsed time after energization and zero point drift of the embodiment of the present invention, and FIG. 5 and 5 are similar characteristic diagrams according to comparative examples, respectively. 1...Plate, 2...Movable column, 3...Upper parallel link, 4...Lower parallel link, 5...Fixed column, 8...
...beam, 9...electromagnetic force generation unit, 10...
Moving coil, 11...Displacement sensor, 12...Container, 13...Printed circuit board, 14...Insulating material, 15, 16, 17...Temperature sensor, 22...
Temperature difference detection circuit, 23...Temperature rise detection circuit, 2
4, 25...additional points.

Claims (1)

[Claims] 1. The balance mechanism, excluding the pan, is housed in a container made of a good thermal conductor, and inside the container,
A temperature difference for detecting a temperature difference between a first location in the balance mechanism that is close to the heat source and a second location that is far from the heat source and where a transient temperature difference occurs after energization with respect to the first location. A detection temperature sensor group and a representative temperature detection temperature sensor for detecting the temperature in the vicinity of the electromagnetic force generating unit in the balance mechanism are provided, and the temperature difference detection temperature sensor group is used at the first and second locations. An electronic balance comprising a correction circuit means for correcting a drift in a weighing output of the balance using both of two variables: a temperature difference signal between the two temperatures and an output signal of the temperature sensor for detecting the representative temperature.