JPH01170814A - Electronic balance - Google Patents

Abstract

PURPOSE:To prevent the occurrence of correction error at the time of the quick change of temperature by estimating the temperature in the near future in accordance with plural past sampling temperature data by operation to correct momentary load data. CONSTITUTION:Outputs of a load sensor 1 and a temperature sensor 2 are taken into a control part 5 through a changeover switch 3 and an A/D converter 4, and the control part 5 determines a measured value and digitally displays it on a display device 6. The control part 5 is provided with a CPU 51, a ROM 52, a RAM 53, etc., and the temperature at the time of taking-in of certain load data w0 is estimated in accordance with a group of plural past temperature data stored in the RAM 53. The output supply interval of the temperature sensor 2 is made longer than that of the load sensor 1, and the estimated temperature is used to perform the temperature correcting operation of data w0. Thus, this device copes with the quick change of temperature even if the sampling interval of load data is made shorter.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to electronic balances.

<Conventional technology> In electronic balances such as electromagnetic balance types,
-i, in order to eliminate the temperature dependence of the output of the load sensor,
A temperature sensor is provided near the load sensor, and the load detection result is corrected based on the temperature detection result.

Conventionally, this correction method basically includes an analog type and a digital type.

In the analog type, the analog output of the temperature sensor is introduced into the reference voltage signal of an A-D converter that is used to digitize the output of the load sensor, and correction is performed during digital conversion.

In addition, with the digital method, the outputs of both the load sensor and temperature sensor are digitally converted and sampled, and using these data, digital calculations are performed to convert the load data to temperature based on a correction formula stored in memory. This is a data-based correction method. The temperature dependence of the output of a load sensor includes a temperature change at the zero point and a temperature change at the span. In particular, the span change often does not show linearity with temperature, and such correction is performed using an analog method. It is difficult to do so, and a digital method is effective.

By the way, in the digital type that requires decile conversion of both the output of the load sensor and the temperature sensor, conventionally,
A method of digitizing the output of a temperature sensor using an A-D converter for a load sensor has been put into practical use. In other words,
This system includes one A-D converter, and a changeover switch is provided at its analog input terminal to selectively switch and digitize the outputs of the load sensor and temperature sensor.

<Problems to be Solved by the Invention> Although the conventional method of digitizing both load and temperature analog signals using one A-D converter as described above is cost-effective, Since load data cannot be captured during digital conversion of temperature signals, the following problems arise.

In other words, if the temperature data is digitized and sampled every 6 seconds, and the load data is digitized and sampled every second at other times, the sixth
When a sudden temperature change occurs as shown in Figure Cal, the correction interval may be too long and an error of, for example, four force counts may occur immediately before the correction, as shown by the solid line in Figure Cal. .

Therefore, if the temperature data is captured and corrected more frequently, for example, by digitizing and sampling the temperature data every second (black dots in Fig. 6(a)), as shown by the broken line in Fig. 5 (bl), It becomes possible to perform corrections based on errors within 1 power count.Here, the data immediately after switching the input of the A-D converter to take in the temperature data may be affected by electrical transient fluctuations, etc. Since it is often inaccurate and cannot be used, the next decile conversion value is usually taken as data.The same applies to word load data.Therefore, the conversion speed of the A-D converter is set to 0 per sampling. Assuming .25 seconds, 0.5 seconds is required to sample the temperature data, and eventually the load data,
The temperature data for the sampling ink hull is 11↓. When the sampling interval of load data is long, digital filter processing or averaging processing is performed to stabilize the display in order to remove the effects of vibrations and disturbances, or when the sampling period is longer than the fluctuation period of the input signal. Problems arise such as the occurrence of aliases, a decrease in response or noise attenuation rate, poor display response as a balance, and low vibration resistance, making it difficult to put it to practical use.

The present invention has been made in view of these points, and is a method in which load data and temperature data are digitized and sampled using one A-D converter, and temperature correction of the load value is performed by digital calculation. The purpose of the present invention is to provide an electronic balance that does not cause correction errors even when the temperature changes, and does not impair responsiveness or vibration resistance.

Means for Solving the Problems] The configuration for achieving the above object will be explained with reference to the functional block diagram shown in FIG. Temperature sensor b disposed nearby, A-D converter C, and A-D that selectively supplies the outputs of load sensor a and temperature sensor b to the input of A-D converter C at predetermined intervals. Input switching means d and A-
In a balance equipped with a calculation means f that performs temperature correction on load data W0 and determines a weight value W to be displayed on a display e by calculation using digital conversion data of load and temperature by a D conversion device C. , the load data W is obtained from the temperature data group T1 by storing the digital temperature data of a plurality of times in the past. Temperature estimating means g is provided to estimate the temperature Tp at the time of sampling by calculation, and the supply interval of the output of the temperature sensor b to the A-D converter C by the A-D input switching means d is determined from the output of the load sensor a. The calculation means f calculates the estimated temperature T by the temperature estimation means g.
It is characterized by being configured to perform temperature correction of the load data wo using .

<Operation> Generally, the temperature change of the load sensor of an electronic balance has a relatively simple pattern. The present invention focuses on this point. In other words, the temperature in the near future can be estimated by calculation from the temperature data sampled multiple times in the past.
The purpose is to correct momentary load data based on the estimated temperature.

Therefore, as shown in Fig. 4, for example, even if the temperature data is digitized and the sampling interval is lengthened, and the load data sampling interval is made denser, the load data can be corrected by the estimated temperature. It can also handle large temperature changes.

<Example> 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.

A load sensor 1 that engages the pan 1a outputs an analog electrical signal corresponding to the load on the pan 1a. For example, in an electromagnetic force-balanced electronic balance, this output signal corresponds to a voltage conversion signal of a current flowing through a force coil of an electromagnetic force generator.

A temperature sensor 2 is disposed near the load sensor 1, and the outputs of the load sensor 1 and temperature sensor 2, which output analog signals correlated to temperature, are sent to an A-D converter 4 via a changeover switch 3, respectively. is led to the analog input terminal of the The digital output of this A-D converter 4 is taken into the control section 5.

The control unit 5 is mainly composed of a microcomputer, and includes a CPU 51 . ROM52. It is equipped with RAM53, input/output interface 54, etc., and ROM52.
Based on a program, which will be described later, written in the controller, an operation command for the selector switch 3 and a conversion command for the A-D converter 4 are outputted, and a measured value is determined using the acquired data. The measured value is digitally displayed on the display 6.

In addition to the work area, the RAM 53 stores a plurality of temperature-corrected load data W, , W2 . . . . and the latest multiple, for example, two, temperature data T +
, T2, and an area as a counter are set.

FIG. 3 is a flowchart showing the contents of the program written in the ROM 52, and the operations will be explained one by one with reference to this figure.

In this example, load data is digitized and sampled every 0.5 seconds, and temperature data is digitized and sampled every 6 seconds.

Now, each time the changeover switch 3 is set to the load sensor 1 side and the digital conversion data W0 of the load is taken in, the counter value n is increased by one count (STI, 5T2
). Also, each time load data WO is taken in, RAM5
W
Estimate the temperature T at the time of taking in Q (Sr1
).

The calculation method for estimating the temperature TP is, for example, assuming that the change in temperature is a straight line, and calculating the temperature at the time to be estimated, that is, W. Temperature TP at the time of capture is the latest two past temperature data T
This method assumes that it is on the extension of the straight line connecting I and T2. That is, as is clear from Sr2 mentioned above and 5T13 mentioned later, the value n of the counter is W from the time when the latest temperature data T is taken. Therefore, the temperature TF can be calculated from T+, Tz, n and the temperature data sampling interval (constant, 6 seconds).

Next, using this estimated temperature T, load data W is obtained using a known correction algorithm. temperature correction (Sr
4). That is, temperature-compensated load data W is calculated using a correction formula W, = f (wo, TP), which has been determined experimentally in advance. At this time, both zero drift and span drift due to temperature should be corrected.

Then, the data collected and corrected in the past in the load data storage area in the RAM 53 is shifted, Wl is stored as the latest load data (Sr5), and a plurality of data including this W1 w,, wg7w3... The measured value W is determined by averaging processing or digital filtering (5T6) and displayed on the display 6 (Sr7).

The above operation is repeated until the counter value n reaches 11. When n reaches 11, the temperature data T, T2 in the RAM 53 is shifted (Sr1, 5T9), and the changeover switch 3 is moved to the temperature sensor 2 side. 5TIO), new temperature data T is digitized, sampled, and stored (STII). Next, set the changeover switch 3 to the load sensor 1.
5T12), resets the counter value to 0, and returns to STI (ST13).

FIG. 4 is an explanatory diagram of the operation of the above embodiment of the present invention, and is a graph showing the relationship between temperature change and display error.

If there is a sudden temperature change as shown in the same figure (al),
Although the temperature data is sampled only every 6 seconds, the load data W. For every sampling of , that is, 0
．． Since the current temperature TP is estimated and corrected every 5 seconds, the display error is smaller than in the conventional case where temperature data is sampled every 1 second. Furthermore, the sampling interval of the load data is the same as the conventional sampling of temperature data every 6 seconds, and no problems occur when performing averaging processing or digital filter processing.

In addition to the method of estimating the temperature as shown in the example above, in which the temperature change is assumed to be a straight line, there is also a method of calculating the temperature using a quadratic or cubic curve pattern using three or more pieces of past temperature data. There is also a method that assumes that the temperature changes, and the optimal method may be adopted by taking into consideration the characteristics of the balance, the required accuracy, the capacity of the program ROM, the processing speed of the CPU, etc.

In addition to the above configuration, each time the temperature data T is captured, it is compared with the previously captured temperature data T2, and based on these differences, for example, the amount of temperature change per unit time is calculated. However, if the temperature data sampling interval is made longer when the amount is small, and shorter when the amount is large, the effect will be further increased.

Furthermore, in addition to the method of performing temperature compensation entirely by digital calculation as in the above-mentioned embodiment, the present invention also provides
It goes without saying that this method can be similarly applied to balances that have already been proposed in No. 159026, in which the output of the load sensor is corrected to some extent using the analog output of the temperature sensor, and then the remaining error is further corrected using digital calculations. be. FIG. 5 is a block diagram showing the main parts of the configuration. The output of the temperature sensor 2 is led to the A-D converter 4 via the changeover switch 3 as in FIG. 2, and also to the summing amplifier 11. The output voltage of the reference voltage 1ru2 is also led to the summing amplifier 11, and by adding these inputs, a voltage having a temperature change approximately equal to the temperature change of the balance output is created. This voltage is applied to A via the changeover switch 13 together with the output voltage of the reference voltage source 12.
- led to the reference voltage input terminal of the D converter 4. and,
By switching the changeover switch 13 in synchronization with the above-mentioned changeover switch 3, the output of the summing amplifier 11 is used as the reference voltage of the A-D converter 4 when sampling the output of the load sensor 1, so that digital conversion data of the load can be obtained. Before being corrected by digital calculation, rough correction is performed in advance in an analog manner. By applying the present invention to correction by digital calculation in this method, similar effects can be obtained.

<Effects of the Invention> =14- As explained above, according to the present invention, one A-D converter selectively digitizes and samples load data and temperature data, and digitally calculates the load data. For balances that perform temperature compensation, we focused on the fact that the temperature change pattern of the balance is relatively simple, and estimated the temperature at the time of load data sampling using multiple past temperature data, and calculated the load based on the estimated temperature. Since the structure is configured to perform temperature compensation, even if the temperature data sampling interval is lengthened, correction errors are less likely to occur during sudden temperature changes, and load data can be sampled more densely as the temperature data sampling ink hull is lengthened. This makes it more susceptible to aliasing and disturbance vibrations.
Moreover, problems such as loss of responsiveness do not occur.

In general, the benefits of adopting a temperature compensation method using digital calculations are that the adjustment of the zero point temperature coefficient and span temperature coefficient can be automated at the time of shipment, and the cause of failure of the trimmer, etc. required during adjustment with the analog method is reduced. In this digital method, digitizing both the load and temperature with one A-D converter contributes to further cost reduction.

Although the conventional method has such effects, it has the above-mentioned drawbacks, making it difficult to put it into practical use, but the present invention can solve these problems.

[Brief explanation of the drawing]

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, and FIG. 3 is a functional block diagram showing the configuration of the embodiment of the present invention.
A flowchart showing the contents of the program written in the OM52, and FIG. 4 is an explanatory diagram of its operation. FIG. 5 is a block diagram showing the main structure of another embodiment of the present invention. FIG. 6 is an explanatory diagram of the operation in a conventional temperature compensation method using digital calculation using one A-D converter. 1...Load sensor 2...Temperature sensor 3...Selector switch 4...A-D converter 5...Control unit 6...Display device

Claims (3)

[Claims] (1) A load sensor, a temperature sensor disposed near the load sensor, an A-D converter, and the A-D converter selectively converts the outputs of the load sensor and temperature sensor at predetermined intervals. A-D input switching means for supplying the input to the input of the
In a balance equipped with a calculation means that performs temperature correction on the load data and determines the weighing value to be displayed on the display by calculation using the digital conversion data of load and temperature by the above-mentioned A-D converter, several times in the past. Temperature estimating means is provided for storing digital temperature data of , and estimating the temperature at the time of loading data from the temperature data group by calculation. The supply interval of the sensor output is made longer than the supply interval of the load sensor output, and the calculation means is configured to perform temperature correction of the load data using the temperature estimated by the temperature estimation means.
Electronic balance. (2) The A-D input switching means has a determining means for determining the magnitude of the amount of change in the temperature data, and the A-D input switching means is configured to input the above to the A-D converter when the temperature change is small according to the result of the determination. 2. The electronic balance according to claim 1, wherein the electronic balance is configured to lengthen the supply interval of the temperature sensor output and to shorten it when the temperature sensor output is large. (3) When the output of the load sensor is input to the A-D converter, the reference voltage signal of the A-D converter is changed based on the output of the temperature sensor, so that the load data is The electronic balance according to claim 1 or 2, characterized in that the electronic balance is configured to be roughly analog-corrected in advance before the correction by the calculation means.