JPS6013223A - Electronic balance - Google Patents

Abstract

PURPOSE:To make it possible to perform highly accurate measurement all the time, by automatically performing span calibration for every specified temperature, and limiting the measured value within the range of specified errors all the time. CONSTITUTION:An input signal to an A-D converter 13 is made to be a signal from a temperature sensor 16, and the converted digital data (t) is received. When the difference between said data (t) and temperature data 10 at the time of previous span calibration is not larger than a preset temperature T, the input signal to the converter 13 is made to be a signal from a load detecting part 11, and the converted digital data W is received. The data W is converted by using a counted number K stored in a memory 14b at present. General operating processes such as subtraction of tare weight and zero-point correction are performed. The measured display value is determined and displayed on a display device 15. Thus the highly accurate measurement can be always performed.

Description

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

(b) Conventional technology High-precision electronic balances have a ratio of weighing capacity to reading limit of 1.
/1.6 million to 1/2 million (0.5 PPM). However, electronic components and other components have relatively large temperature dependencies and changes over time. For example, among the components, permanent magnets have a temperature dependence of 200 to 400
PPM / ” C, the number of changes over time is 110PP7.Therefore, even if various design measures and strict adjustments are made during manufacturing, the temperature dependence of the span can be reduced to 1 to 2PPM/7.
The limit is to keep it within 1°C, and even if the ambient temperature at the time of measurement changes by only 1°C, it will cause an error of 2 to 4 counts above the reading limit when measuring near the weighing level. Therefore, with such a high-precision electronic balance, reliable measurements can only be made in a constant temperature room where the room temperature is controlled at a constant level. There is a concern that errors may occur, and the disadvantage is that it is extremely difficult to use.

(c) Purpose The present invention has been made in view of the above, and is capable of maintaining the span of the balance at all times without error, using parts that are relatively temperature-dependent, and without making very strict adjustments. The purpose of the present invention is to provide an electronic balance that can perform highly accurate measurements without having to perform measurements in a constant temperature room or the like or without worrying about errors caused by aging.

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

The load detection unit 1 converts the loaded load into an electrical signal.

The signal is converted into mass by the mass conversion means 2 using the conversion coefficient stored in the conversion coefficient storage means 3 and displayed on the display means 4.

When the span calibration command is issued, the weight addition/removal mechanism 5
A built-in weight of a predetermined mass is placed on the load detection section 1, and the output of the load detection 1 at that time is taken into the conversion factor calculation means 6. The conversion coefficient calculation means 6 calculates a new conversion coefficient based on the output value and the mass of the weight, and replaces the value with the contents of the conversion coefficient storage means 3 to update the conversion coefficient. The span calibration command is automatically generated by the temperature change determining means 7 as follows. That is, the temperature change judgment means 7 issues a span calibration command when the detected value of the ambient temperature by the temperature detection means 8 changes by more than a preset predetermined temperature with respect to the temperature at the time of the previous span calibration. .

(Po) Example Embodiments of the present invention will be described based on the drawings.

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

The load detection unit 11 detects the load on the weighing scale 11a using the load sensor 11.
b, outputs an analog electrical signal corresponding to the load, and the signal is introduced into the A-D switch 13 via the switch 12, converted to a digital signal, and then input to the control unit 14. Ru. The control unit 14 is composed of a microcomputer, and includes a CPU 14a that executes various calculations and programs, and controls each peripheral device, and a memo IJ that has an area for storing programs to be described later, conversion coefficients, etc.
14b, and an interface circuit 14C for connecting the control unit 14 with external peripheral devices. The digital conversion input from the load detection section 11 is configured to be converted into mass by the control section 14 and displayed on the display 15 as described later.

The load detection unit 11 is provided with a temperature sensor 16 adjacent to the load sensor llb, and this temperature sensor 16 detects the temperature near the temperature sensor 16 and outputs an analog electrical signal corresponding to the temperature. do. The signal is introduced into the A-D converter 13 via the switch 12, converted into a digital signal, and then input into the control section 14.

The switch 12 switches between A and D based on a command from the control unit 14.
The input signal to the converter 13 is switched to the signal from the load detection section 11 or the signal from the temperature sensor 16 described above.

The weight addition/removal mechanism 17 includes a motor 17a that is driven based on a command from the control unit 14, an eccentric cam 17b that is rotated by the motor 17a, and a displacement about a fulcrum 170' due to the rotation of the eccentric cam 17b. The calibration weight 18 can be applied to the load sensor 11b or the load can be removed based on a command from the control unit 14.

Next, we will discuss the effect.

FIG. 3 shows a memory 14 according to an embodiment of the present invention. 2 is a flowchart showing a data processing program written in FIG.

First, a command is issued to the switch 12 to make the input signal to the A-D converter 13 the signal from the temperature sensor 16, and the digitally converted data t is taken in (ST1, S, T2). The data t is the temperature data t from the previous span calibration, which will be described later.
For Q, set temperature T (for example, 0.
When there is no difference of more than 5°C), the switch 12
- The input signal to the D converter 13 is the signal from the load detection section 11, and the digital conversion data W is taken in (ST3
．． ST4, 5T5) and convert the data W into the mass W using the conversion count K currently stored in the memory 14b.
Convert it as follows, and convert W=-w---(1) Perform general arithmetic processing such as tare subtraction and zero point correction to determine the weighing display value and display it on the display 15 ( ST6.S'
l'7, 5T8), a measurement routine like this is normally being executed.

If the temperature near the load sensor 11b changes by more than the above-mentioned temperature due to a change in the room temperature, etc., the data t from the temperature sensor 16 is read at a certain period, in this example, every time a weighing value is displayed. , the span calibration routine from ST9 onwards is executed immediately from ST3. In this routine, the detected temperature data t is stored as t□ and used as the reference temperature for the next span calibration (at the next span calibration, it becomes "temperature data tQ from the previous span calibration"), and the switch 12 inputs the output of the load sensor llb to the A-D converter 13 and collects the digital conversion data W (STIO, 5T11). If the value is not within the specified value near zero load, the weighing pan 11a
It determines that there is a sample on top of the weighing plate 11a, that is, that measurement is in progress, and issues an alarm to notify that reliable measured values cannot be obtained unless calibration is performed, prompting the user to take the sample down from the weighing pan 11a (
ST12, 5T13). If it is within the above range, the data W is stored as WQ (5T14), and the motor 17a of the weight addition/removal mechanism 17 is driven to drive the biasing cam 17.
b by a predetermined angle, and the lever 17c is moved downward to load the calibration weight 18 onto the load sensor llb (
ST1'5), after waiting for a predetermined prescribed time based on the response characteristics of the load sensor 11b and waiting for the data W to become stable, the data W is captured (ST16, 5T17). Then, the conversion count K (or S) is calculated using the data W due to the load on the calibration weight 18, the data WQ at the time of no load mentioned above, and the mass P of the calibration weight 18, as follows: K = P / (w - wo ) - --(2) (or S = (w - wo) / P - (21')), and update the conversion factor by replacing the value with the value stored up to that point (ST18) Next, the motor 17a is driven to remove the load of the calibration weight 18 on the load sensor llb by the weight addition/removal mechanism 17 (STI
9) Proceed to ST5 and return to the normal measurement routine. Note that when S shown in (2)' is used as a conversion factor, the conversion formula (11) in ST6 is changed to (1)' below.

W = W / S-41) ' Also, the no-load data WO during span calibration,
Regarding the collection of data W when the calibration weight 18 is loaded, it is desirable to specifically average a large number of digitally converted data from the load sensor llb to obtain an accurate conversion count. Note that since the temperature changes slowly, it is not necessary to check the temperature t every time the display is performed. For example, as shown in FIG. 5, after ST8, 5T20,
5T21 may be provided to check t every Q times of display.

Next, as another embodiment of the present invention, an example will be described in which, in addition to the calibration for each fixed temperature change, the calibration can also be performed for each fixed period of time. In this case, the S shown in FIG.
Just insert T3'. As a result, the calibration routine is executed when the earlier of the following conditions is reached: when the temperature changes by a predetermined temperature or more from the temperature at the previous span calibration, or when a predetermined time or more has elapsed since the previous span calibration. be done. Even if time-based calibration is performed, the process proceeds from ST3' to ST9 and the temperature at that point is t(1
Therefore, there is no need to immediately perform calibration based on temperature changes after time based calibration. In addition,
The means for measuring the elapsed time does not need to be equipped with separate hardware such as a clock function, and can be easily determined by the number of cycles of the program. For example, a step may be provided between ST7 and ST8 to count up the contents of the Lujistar each time the routine passes, and a step may be provided between ST7 and ST8 to reset the contents when the calibration routine is executed.
It may be provided at the next stage after 9.

Furthermore, it would be more complete if the calibration routine was executed unconditionally once when the power was turned on, and then the calibration was performed over temperature changes and over time.

In the above embodiment, an example was described in which the output of the temperature sensor 16 is introduced into the A-D converter 13 at a predetermined period for digitizing the output of the load sensor llb. An AD converter may be provided separately, and if a crystal oscillation temperature sensor whose oscillation frequency changes depending on the temperature is used, for example, the data can be directly input to the control unit without A-D conversion.

(Effect) As explained above, according to the present invention, span calibration is automatically executed every time a predetermined temperature change occurs, and the measured value is always kept within a certain error range, so the user can Highly reliable measurement values can be obtained, and there is no need to prepare a special room such as a constant temperature room for measurement. In addition, the temperature dependence of the span of the balance can be made 3 to 10 times rougher than in the case where the present invention is not adopted, which reduces the cost by making the components cheaper and making the opening work easier. be able to.

Furthermore, if the calibration is configured to be automatically performed every time a certain period of time passes, there is no need to worry about changes over time, which is even more effective.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention, FIG. 2 is a configuration diagram of an embodiment of the present invention, FIG. 3 is a flowchart showing the data processing program, and FIGS. 12 is a flowchart showing a main part of a data processing program according to another embodiment. 11-.-Load detection section 11a...-Weighing pan 1 l b-
--One load sensor 12・-Switcher 13・-A-D converter 14---Control unit 14 a-CPU 14
b-1-Memory 14G--Interface circuit 15--Display device 16--Temperature sensor 17--Weight addition/removal mechanism 17a--Motor 17cm
Lever 18... - Calibration weight patent applicant Shimadzu Corporation representative Patent attorney Nishi 1) Arata

Claims (1)

[Claims] (11) The output signal from the load detection unit that converts the placed load into an electrical signal is converted into mass using a stored conversion coefficient and displayed, and a span calibration command is given. In an electronic balance that can update the conversion factor by placing a built-in weight of a predetermined mass on the load detection section and using the output signal from the load detection section and the mass of the weight at that time, The apparatus includes means for detecting ambient temperature and means for determining whether the detected temperature has changed by a preset constant temperature or more with respect to the temperature at the time of the previous span calibration, and the span calibration is performed every time the constant temperature change. An electronic balance characterized in that it is configured to be able to automatically update the conversion coefficient by issuing a command. (2) It has a timekeeping means, and issues the span calibration command every time the constant temperature change and updates the previous conversion coefficient. The electronic balance according to claim 1, characterized in that the electronic balance is configured to emit the signal every predetermined period of time after span calibration. (3) The means for detecting the temperature is configured with a temperature sensor that outputs an analog signal. Claim 1, characterized in that the output signal of the temperature sensor is switched at a predetermined cycle and inputted to an A-D converter for digitizing the output signal of the load detection section. The electronic balance described in paragraph or paragraph 2.