JPS61107118A - Electronic balance - Google Patents

Abstract

PURPOSE:To extremely reduce the change in capacity after span calibration with the elapse of time, by correcting span coefficient by using an elapsed time and a timewise change ratio after the span coefficient was calculated. CONSTITUTION:The load data W from a load detection part 1, the temp. data (t) from a temp. sensor 3 and the output T of a timer 7 are collected and the mass D corresponding to the load on a scale 1a is calculated according to formula (wherein K is the span coefficient stored in non-volatile RAM2c, ALPHAK is the span change ratio stored in non-volatile RAM2c and alpha is temp. coefficient). In this formula, the span coefficient K having to multiply the load data W is corrected by the product of the span change ratio ALPHAk and the output T of the timer 7. By the correction by the terms K, T, a display value comes to one more nearer to real mass.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to electronic balances.

(B) Prior Art Generally, electronic balances generate an electrical signal corresponding to the load on the pan in a load detection section, convert the electrical signal into mass, and display the result. Therefore, compared to purely mechanical balances, there are inevitably more elements that change over time. Maintaining performance is difficult. Therefore, the coefficient (span coefficient) for converting the output of the load detection unit to mass is calculated using a calibration weight etc. whose mass is known.
It is common practice to periodically perform so-called span calibration to maintain performance.

By the way, highly stable parts are generally expensive, and in order to eliminate relatively large performance changes that tend to occur in the initial stages before shipping, they are heated to a higher temperature than under normal use during the manufacturing stage. Aging is also being carried out, but both of these are factors that increase the cost.

Furthermore, in the case of φ electronic balances that require extremely high precision, even if the most stable parts available are used, sufficiently stable performance cannot be obtained between span calibrations and the next span calibration. The current situation is that this is not the case.

(C) Objective An object of the present invention is to provide an electronic balance at a low cost that exhibits very little change in performance over time after span calibration.

(d) Configuration The configuration of the present invention will be explained based on the functional block diagram shown in FIG.

The load detection section outputs an electric signal corresponding to the load on the plate.

The output is converted into mass by a correction/calculation means, which will be described later, and displayed on the display section.

When a fire pan calibration command is issued, a span coefficient ' is calculated by a span coefficient calculation means from the output of a load detection section on which a calibration weight or the like of known mass is mounted, as a span coefficient for converting the output into mass. At the same time, the span change rate calculation/storage means calculates the difference between the span coefficient ′ calculated this time and the span coefficient calculated during the previous span calibration stored in the span coefficient storage means, and the difference is measured by the timer. Using the elapsed time from the previous span calibration to the current span calibration, the temporal change rate of the span coefficient, that is, the span change rate is calculated and stored. At the end of span calibration, the contents of the span coefficient storage means are updated to the span coefficient calculated this time (to K-').

During normal measurement, the output of the load detection section is converted into mass by the above-mentioned correction/calculation means. At this time, the span coefficient by which the output should be multiplied is determined by converting the content K of the span coefficient storage means into the mass. The contents of the change rate calculation storage means,
A value corrected using the elapsed time since the latest span calibration by the timer is used.

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

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

The load detection section 1 outputs an electric signal corresponding to the load placed on the plate la, and the digital conversion data is input to the control section 2. The control unit 2 is composed of a microcomputer, and includes a CPU 2a that executes various calculations and programs and controls each peripheral device, a ROM 2b in which programs described below are written, and stores span coefficients and span change rates calculated by the CPU 2a. A nonvolatile RAM 2c with an area, a RAM 2d with an area for storing digital conversion data from the load detection section 1 and various calculation results by the CPU 2a, and an interface circuit 2e for connection with external equipment. They are connected to each other by pass lines.

The load detection section 1 is provided with a temperature sensor 3, and the temperature sensor 3 is configured so that its digital conversion data is also taken into the control section 1. The control unit 1 further includes a calibration switch 4 for issuing a calibration command and executing a span calibration routine of a program to be described later. Tare switch for giving a tare erase command 5. A display 6 for displaying measured values based on instructions from the CPU 2d, and a timer 7 that is reset based on instructions from the CPU 2a are connected. Note that the timer 7 has a built-in power supply that remains ON regardless of whether the power supply of the electronic balance is 0N10FF.

Moreover, the above-mentioned nonvolatile RAM2C is C-MO3RAM
is back-amplified with a battery, or an EE-FROM is used.

Next, before describing the operation, changes in span in general electronic balances will be explained. FIG. 3 is a graph showing an example of the span change rate when an electromagnetic force balance type load detection section is used. In other words, T1 is the time when manufacturing is completed.
To explain this simply, an electromagnetic balance type balance generates an electromagnetic force commensurate with the load by using the attractive or repulsive force of a coil inserted in a magnetic field and a permanent magnet. In order to measure the load on the plate by this,
Changes in the magnetic field result in changes in span. For this reason, in order to stabilize the magnetic field during manufacturing, a magnetic field in the opposite direction is normally applied temporarily to demagnetize the permanent magnet. This initially causes the magnetic field to gradually recover and increase as a reaction to the demagnetization, resulting in the same force being generated with less current and a decrease in the span of the balance. This is T.

This corresponds to the period from ~T3. Once this phenomenon is complete, it will begin to demagnetize naturally over time, thus T4~Ts
The span increases as shown in the period .

Now, the output of the load detecting section 1 indicating the change in span over time as described above is converted into mass by the operation of the embodiment of the present invention as described below.

FIG. 4 is a flowchart showing the program written in the ROM 2b.

In a normal measurement routine, the load data W from the load detection section 1, the temperature data t from the temperature sensor 3, and the output T of the timer 7 are collected, and the mass weight corresponding to the load on the pan is calculated using the following equation (11). Calculate (STI, 5T2).

D-W・((K+Δ−T)・(1+α1))
...-(l) Here, K is the span coefficient stored in the nonvolatile RAM 2c, Δ is the same (span change rate stored in the nonvolatile RAM 2c), and α is the temperature coefficient.

Equation (1) differs from the conventional mass calculation equation in that the span coefficient K by which the load data W is to be multiplied is corrected by the product of the span change rate Δ and the timer output T. By correcting this Δ with the −T term, the displayed value becomes a value closer to the true mass, the details of which will be described later.

The weight calculated by formula (1) is subjected to tare calculation and displayed on the display 6 as the weighing display value Ds (Sr
3.5T4). The tare amount F is determined by operating the tare subtraction switch 5 when the tare load is placed on the plate la, and by setting the weight at that time to F (Sr5.5T6). Note that F is stored in a tare memory set in the RAM 2d.

When the calibration switch 4 is operated, a span calibration routine starting from ST8 is executed (Sr7). In other words, first plate l
Load data W1 when nothing is placed on pan 1a, so-called zero load, is taken (Sr1), and then, for example, when a calibration weight of known mass is placed on pan 1a in accordance with a predetermined message on display 6. (Sr9) Based on the increase in the load data or the re-operation of the calibration switch 4, the load data W2 at that time is taken in (STIO). Using Wl, w2, the known mass of the weight, and temperature data t, the span coefficient ' is calculated by the following equation (2), which is a known method (STII).

Also, using the span coefficient calculated this time, the span coefficient K of the previous rotation on the hour stored in the non-volatile RAMZC, and the elapsed time T from the previous rotation on the hour, which is the output of the timer 7, The temporal change rate of the span coefficient, that is, the span change rate Δ′ is calculated by the following equation (3) (ST
I2).

The span coefficient ' and the span change rate Δ' calculated in this way are stored in the nonvolatile RAM 2-c in place of the span coefficient and the span change rate ΔK at the hour of the previous rotation ( ST13). At the same time, timer 7 is reset and new timing starts from this point (ST14).
).

When the span calibration routine described above is completed, the process returns to the measurement routine described above, and the correction term -T for Δ in equation (1) has the following meaning. That is, in FIG. 3, for example, assume that the current calibration is performed at time T7, and the previous calibration is performed at time T6.

For measurements immediately after T7, non-volatile RAM2C
Even if the conventional mass calculation is performed using the span coefficient K in , there is no change in the span, so the correct mass is obtained as 0.

However, as shown in the figure, the span changes with the elapsed time T, so when a considerable amount of time has elapsed from T-7, it is not possible to obtain the correct mass by converting using only the span coefficient. Δ corresponds to the slope of the graph showing the span from T6 to T7, and is approximated to the slope of the graph showing the span from T7 to T days. Therefore, by adding the product of the elapsed time T and Δ from T7 at the time of measurement to the span coefficient K calculated at T7, it is possible to obtain a span coefficient closer to the true value at that measurement time. By using the span coefficient corrected in this way (-T for K + Δ), the obtained mass is a value closer to the true mass, which is corrected for the amount of span change corresponding to the elapsed time after span calibration. Become.

In the above-described embodiment of the present invention, assuming that the manufacturing completion time is To, span calibration is performed at, for example, To and T1, and the product is shipped with ΔK stored. Even after delivery to the user, K and ΔK are updated every time the span is calibrated, so in response to span changes as shown in Figure 3,
You can always get a more correct mass.

In the above embodiment, the elapsed time T is measured by the timer 7.
An example was shown in which the calibration was performed and reset each time the calibration was executed.
A clock may be used instead of the timer 7. In this case, the elapsed time T is the difference between the previous span calibration time and the current calibration time.
, and no reset is necessary.

In addition to performing temperature correction using software as in the above embodiment, it is also possible to perform temperature correction on the output of the load detection section 1 using hardware. In this case, the output of the temperature sensor 3 is sent to the temperature correction circuit. Along with the introduction, RO, M2
From equations (1) and (2) of program b, (1+
αt) term is removed.

Furthermore, the start of span calibration can be applied to automated balances without relying on the operation of the calibration switch 4. In this case, a calibration weight is built-in and a mechanism for adding and removing it is provided, and a calibration command is automatically generated from the control unit 2 at fixed time intervals (days), or the span changes as shown in Fig. 3. Corresponding to this pattern, it can be configured to occur at short intervals initially and gradually at longer intervals as time passes. Further, if the determined span change rate ΔK is large, the interval until the next calibration can be shortened, and if ΔK is small, the interval can be lengthened. Furthermore, the interval until the next span calibration is changed according to the difference between the span change rates Δ and Δ′ between the previous and current span changes, so as to match the span change pattern of electronic balances that should be used. This is desirable.

Furthermore, the span change rate may be assumed to be 0 at the time of factory shipment, and the span change rate may be calculated by span calibration after delivery to the user.

Additionally, when giving a span calibration command manually using a calibration switch, etc., if the calibration interval is too short, the calculated value of the span change rate may contain a large error due to an error in the reproducibility of the balance. It is desirable to calculate and update the span change rate only when the calibration interval is, for example, one week or more, or one month or more, and only update the span coefficient during other calibrations.

Furthermore, in order to prevent span changes due to differences in the gravitational acceleration of the installation location from being calculated in Δ as changes over time, a mode is set to prohibit updating of Δ after changing the installation location. It is desirable to be able to update ΔK after calibrating twice or more.

(f) Effects: As explained above, according to the present invention, changes in span over time are automatically corrected, so not only does aging become unnecessary as in the past, but the components are also inexpensive. It is possible to provide high-performance electronic balances using Furthermore, since the span change rate is calculated and updated each time span calibration is performed or at an appropriate time during span calibration, it is also applicable to balances with complex span changes. For example, it is possible to stabilize the performance of an electromagnetically balanced balance using a magnet that is difficult to stabilize by demagnetizing, such as a rare earth magnet.

Furthermore, since no hardware adjustment such as volume operation is required, there is no possibility of human error occurring during adjustment.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention, FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a graph showing an example of span change of an electromagnetic balance type balance, and FIG.
The figure is a flowchart showing a program written in the ROM 2b according to the embodiment of the present invention.

Claims (2)

[Claims] (1) In a balance configured to convert the output of the load detection unit that generates an electric signal corresponding to the load on the pan into mass and display it as a measured value, the output of the load detection unit when a calibration command is issued , a means for calculating a span coefficient for the above conversion, a means for storing the span coefficient, a means for measuring the elapsed time after the calculation of the span coefficient, and a means for calculating the span coefficient previously calculated when calculating the span coefficient. means for calculating and storing the temporal change rate of the span coefficient from the difference between An electronic balance characterized by comprising means for correcting using the elapsed time since the calculation and the above-mentioned rate of change over time. (2) It has a built-in calibration weight for calculating the span coefficient and a mechanism for adding and subtracting the calibration weight to the load detection section, and the calibration command is generated based on a program preset in the balance. 2. The electronic balance according to claim 1, wherein said electronic balance is configured to automatically calculate said span coefficient and said rate of change over time.