JP4041938B2 - Electronic balance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic balance, and more particularly to an electronic balance provided with a program for automatically calculating a temperature correction coefficient for temperature compensation of a sensitivity coefficient.
[0002]
[Prior art]
In electronic balances, generally, the load on the measuring pan is transmitted to the load sensitive part, and the weight value on the measuring pan is obtained by multiplying the load detection data from the load sensitive part by the sensitivity coefficient (span coefficient). Is displayed on the display. For example, an electromagnetic force balanced type is often used as the load sensitive part. In this electromagnetic force balanced type load sensitive part, the load detection data includes a measurement error due to temperature due to the temperature coefficient of the permanent magnet. Even if other types of load sensitive units are used, the load detection data includes measurement errors due to similar temperatures.
[0003]
Therefore, in an electronic balance, a temperature sensor is usually arranged near the load-sensitive part to detect the temperature, and the sensitivity coefficient is calculated by calculating the temperature detection data and a temperature correction coefficient stored in advance. By correcting, the temperature of the measured value is compensated. This temperature correction coefficient is about 3 to 5 points including the upper and lower limits of the temperature compensation range, and any one point between them, by inserting the electronic balance into a thermostat etc. It is calculated by using load detection data of about 3 to 5 points obtained by changing the temperature and applying a constant load to the load sensitive part at each temperature. Generally, the sensitivity coefficient K is a function of the temperature T.
For example, K (T) = aT ² + bT + c (1)
The coefficients a, b and c are determined and stored in the electronic balance.
[0004]
Conventionally, an electronic balance in which the electronic balance itself has a program for calculating the above temperature correction coefficient has been put into practical use. In this type of electronic balance, as described above, it is inserted into a thermostatic chamber or the like and its temperature is changed to a plurality of temperatures, and load detection data obtained by applying a constant load at each temperature is stored. A temperature correction coefficient is automatically calculated from the detected data.
[0005]
[Problems to be solved by the invention]
By the way, in an electronic balance, there is generally a hysteresis in the change in load detection data due to temperature as described above. That is, even in the load detection data in the state where the same load is applied at the same temperature, the value when the temperature is reached by raising the temperature and when the temperature is reached by lowering the temperature is: Slightly different from each other.
[0006]
In the conventional electronic balance equipped with a program for calculating the temperature correction coefficient, the above temperature hysteresis is not taken into consideration.For example, a constant load is applied under a plurality of temperatures while increasing the temperature sequentially. A temperature correction coefficient was calculated from the obtained load detection data. Therefore, conventionally, even if the temperature correction coefficient is accurately calculated, an error will not occur if the temperature history of the electronic balance at the time of mass measurement is the same as the history at the time of calculating the temperature coefficient. In other words, an error caused by temperature hysteresis occurs, and as a result, there is a problem that the nominal accuracy of the electronic balance does not become higher than the error caused by temperature hysteresis.
[0007]
An object of the present invention, in the conventional electronic balance can be made smaller error which could not have been removed due to thermal hysteresis, to provide an electronic balance which may be a higher accuracy nominal accuracy with There is.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the electronic balance of the present invention has a sensitivity coefficient for converting load detection data from the load sensitive part into a mass value, an output of a temperature sensor that measures the temperature in the vicinity of the load sensitive part, and In addition to temperature compensation calculation means for temperature compensation by calculation using a temperature correction coefficient stored in advance, the temperature in the vicinity of the load sensitive part includes the upper and lower limits of the temperature compensation range and any one temperature in between The temperature correction coefficient is automatically calculated and stored using load detection data of three or more points obtained by changing the temperature to three or more points and applying a constant load to the load sensitive part at each temperature. in an electronic balance provided with a temperature correction coefficient calculating means for, the temperature correction coefficient calculating means, load detecting de obtained at a temperature of more than 3 points above while increasing or lowering the temperature in the vicinity of the load sensing unit The data, in a direction approaching the load detection data when taken while lowering or raising the temperature, after correction by half the temperature hysteresis difference of the load detection data in the electronic balance is set in advance, the Characterized by subjecting it to the calculation of a temperature correction coefficient.
[0009]
The present invention calculates the temperature correction coefficient for performing temperature correction of the sensitivity coefficient in consideration of the temperature hysteresis of the load detection data of the electronic balance, thereby eliminating the error that could not be compensated due to the temperature hysteresis. It is intended to reduce to about 1/2.
[0010]
That is, in the electronic balance, as shown in the graph of FIG. 3, generally, when a constant load is applied to the measuring pan while sequentially changing the temperature in the vicinity of the load sensitive portion, the load detection data is the same temperature. Even when the temperature rises and falls, the data values are different from each other and draw a hysteresis loop. In the conventional electronic balance, load detection data D ₁ , D ₂ and D ₃ are collected by applying a constant load at each temperature while raising the balance temperature from T ₁ → T ₂ → T _3. Calculate each coefficient of the above equation (1) using D ₁ , D ₂ and D ₃ , or apply a constant load in the same way while lowering the balance temperature from T ₃ → T ₂ → T _1. Detection data D ₃ , D ₂ ′ and D ₁ were collected, and the coefficients of equation (1) were calculated using the data D ₃ , D ₂ ′ and D ₁ . Accordingly, when the electronic balance is used, that is, when the balance temperature at the time of mass measurement reaches, for example, the temperature T ₂ in a history opposite to the temperature history at the time of calculating the temperature correction coefficient, the measured value is set at the temperature T ₂ . An error corresponding to the hysteresis difference Δ occurred, and eventually, the error corresponding to the hysteresis difference Δ could not be guaranteed.
[0011]
On the other hand, in the present invention, the electronic balance of the same model uses the fact that the shape of the temperature hysteresis loop of the load detection data is substantially the same. When calculating the temperature correction factor for the balance, for example, load detection data obtained by applying a constant load while raising the balance temperature is set so that the hysteresis difference is closer to the load detection data obtained when the balance temperature is lowered. Is used for calculation of the temperature correction coefficient. That is, in the example of FIG. 3, the load temperature is increased from, for example, T ₁ → T ₂ → T ₃ and a constant load is applied to collect the load detection data D ₁ , D ₂ and D _3. The load detection data D _{2 having} an influence of hysteresis is used for calculating a temperature correction coefficient after subtracting Δ / 2. As a result, regardless of the balance temperature history at the time of mass measurement, for example, the measured value at the temperature T ₂ only has an error corresponding to Δ / 2, and therefore the temperature correction coefficient is calculated without considering the conventional temperature hysteresis. The guaranteed accuracy can be halved as compared with the case of doing so.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment of the present invention. The load sensitive unit 1 is an electromagnetic force balanced type sensitive unit, for example, and outputs a signal corresponding to the load on the measurement dish 1a. The output signal from the load sensing unit 1 is digitized by the A / D converter 2a and then collected as load detection data D by the computing unit 3 every moment. The calculation unit 3 is mainly composed of a CPU 31, a ROM 32, a RAM 33, a non-volatile RAM 34, and an input / output interface 35. The input / output interface 35 gives a display 4 for displaying a measured value and various commands. An operation key 5 is connected. In addition, a temperature sensor 6 is provided in the vicinity of the load sensing unit 1, and the output of the temperature sensor 6 is also digitized by the A-D converter 2b, and thereafter is calculated as temperature detection data T every moment. 3 is taken in.
[0013]
The calculation unit 3 stores the data D in the RAM 33 each time the load detection data D is collected in accordance with the measurement program written in the RAM 32, and averages the latest predetermined number of load detection data, for example. By multiplying the average value by the sensitivity coefficient K, the mass value on the measuring pan 1 a is obtained and displayed on the display 4.
[0014]
The sensitivity coefficient K is stored in the non-volatile RAM 34 as a function K (T) of the temperature T expressed by the above-described equation (1), and the value thereof depends on the value of the temperature detection data T from the temperature sensor 6. It is corrected.
[0015]
In the ROM 32, in addition to the measurement program, each coefficient in the quadratic expression of the sensitivity coefficient K (T), that is, a temperature correction coefficient is automatically calculated and stored in the nonvolatile RAM 34. The temperature correction coefficient calculation program is started by giving a specific command from the operation key 5, for example, and is executed before shipment of the balance. Hereinafter, the temperature correction coefficient calculation program will be described in detail.
[0016]
FIG. 2 is a flowchart showing an operation procedure when the temperature correction coefficient calculation program is executed. In this example, a hysteresis difference Δ at a temperature T ₂ described later is written based on an actual measurement result of temperature hysteresis of an electronic balance of the same model . Further , this example shows an example in which the temperature coefficient is calculated by changing the balance temperature to three points of a lower limit temperature T ₁ , an upper limit temperature T ₃ and an intermediate temperature T ₂ of the temperature compensation range. When executing this program, in order to change the temperature of the entire balance to a plurality of specified temperatures, a thermostatic chamber or the like that can accommodate the electronic balance is prepared, and a weight with a constant mass such as a weight is prepared. First, an electronic balance is inserted into a thermostat or the like, the balance temperature is raised to the lower limit value T ₁ of the temperature compensation range, and a constant mass is loaded on the measurement dish 1a in that state. In the electronic balance, the load detection data in that state is sampled and averaged by a specified number, and the value is stored in the RAM 33 as the load detection data D ₁ at the temperature T ₁ when the temperature rises.
[0017]
Next, after the balance temperature is raised to the intermediate temperature T ₂ by temperature control of a thermostatic chamber or the like, a constant mass is loaded on the measurement dish 1a in that state. The electronic balance, this time only averaged specified number and constantly collect load detection data, and stores the value as the load detection data D ₂ at temperature T ₂ in the temperature rise in the RAM 33. Is raised to a further upper limit temperature T ₃ of the balance temperature by the temperature control of a thermostat or the like, also by loading a constant weight on the measuring pan 1a in this state, the load detection data D at the temperature T ₃ in the same manner as described above ₃ is stored in the RAM 33, and the measurement operation is terminated.
[0018]
If the temperature hysteresis characteristic of this electronic balance is as shown in FIG. 3, the load detection data D at temperatures T ₁ , T ₂ and T ₃ at the time of temperature rise is stored in the RAM 33 as a result of the above measurement operation. ₁ , D ₂ and D ₃ will be stored. As described above, the hysteresis difference Δ at the temperature T ₂ is written in the electronic balance. Among the collected temperature detection data, the data D _{2 at the} temperature T ₂ is corrected to D ₂ −Δ / 2. In addition, the temperature correction coefficient is used for calculation. That is, the load detection data at the temperature T ₂ is substantially equal to the load detection data D ₂ at T ₂ when the temperature is actually collected and the load detection data D ₂ ′ at T ₂ when the temperature is decreased. It is equivalent to using the average value (D ₂ + D ₂ ′) / 2, and the time required for collecting data for calculating the temperature correction coefficient is equivalent to that of a conventional electronic balance, and the error due to temperature hysteresis is about 1 / 2.
[0019]
Here, it takes a considerable amount of time to change the overall temperature of the balance using a thermostatic chamber, etc.For example, load detection data is obtained by collecting the load detection data at a certain temperature and then changing the balance temperature to the next temperature. It takes several hours to collect the temperature, but by using the fact that the temperature hysteresis loop is almost the same in the balance of the same model, the hysteresis difference is simply written in the RAM 32 of the electronic balance in advance. By collecting only the load detection data at the time of rising or falling, the error due to the temperature hysteresis can be reduced to about 1/2, compared with the case of collecting both the data at rising and falling of temperature. The data collection time can be shortened.
[0020]
Incidentally, in the above implementation mode, as the load detection data used in calculating the temperature correction coefficient, the upper limit of the temperature compensation range, the lower limit Oyohi was used data of total 3 points in between the temperature, 4 points It goes without saying that data at the above temperatures may be used.
[0021]
【The invention's effect】
As described above, according to the present invention, the temperature correction coefficient for correcting the temperature of the sensitivity coefficient of the electronic balance is calculated in consideration of the temperature hysteresis of the electronic balance. The maximum error due to hysteresis can be reduced to about ½, and the nominal accuracy of the electronic balance can be reduced to about ½.
Moreover, since the load data for calculating the temperature correction coefficient can be collected either when the temperature rises or falls, the time required for data collection is equivalent to that of a conventional electronic balance that does not consider hysteresis. The effects described above can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a flowchart showing an operation procedure when executing a correction coefficient calculation program written in a ROM 32 in the embodiment of FIG. 1;
FIG. 3 is a graph showing an example of temperature hysteresis of load detection data of an electronic balance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Load sensitive part 1a Measuring dish 2a, 2b AD converter 3 Calculation part 31 CPU
32 ROM
33 RAM
34 Nonvolatile RAM
35 I / O interface 4 Display 5 Operation key 6 Temperature sensor

Claims (1)

The sensitivity coefficient for converting the load detection data from the load sensitive part into a mass value is calculated by calculating the temperature sensor output that measures the temperature in the vicinity of the load sensitive part and the temperature correction coefficient stored in advance. Temperature compensation calculating means for compensating, and changing the temperature in the vicinity of the load-sensitive portion to three or more temperatures including the upper and lower limits of the temperature compensation range and any one temperature in between, at each temperature In an electronic balance provided with temperature correction coefficient calculation means for automatically calculating and storing the temperature correction coefficient using load detection data of three or more points obtained by applying a constant load to the load sensitive part,
The temperature correction coefficient calculating means, load detecting data when the load detection data obtained at a temperature of above three or more while increasing or lowering the temperature in the vicinity of the load sensing unit, were taken while lowering or raising the temperature The electronic balance is subjected to the calculation of the temperature correction coefficient after correcting by a half of the temperature hysteresis difference of the load detection data in the electronic balance set in advance in the direction approaching .

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