Electronic balance

Abstract

We provide an electronic balance that enables high-resolution measurements. [Solution] The electronic balance 100 comprises a weighing pan 5 on which an object to be weighed is placed, a load sensor 10 for detecting the load, a control calculation unit 60 for calculating the mass of the object to be weighed from the load detection signal of the load sensor 10, and first and second A / D converters 42, 44. The first and second A / D converters 42, 44 are switchable, and the second A / D converter 44 has a mass corresponding to the least significant bit that is smaller than that of the first A / D converter 42. The load sensor 10 is mechanically balanced when a load from a first mass, which is within the input range of the first A / D converter 42, is applied to it, and the second A / D converter 44 is configured to weigh the object to be weighed using the second A / D converter 44, with the state in which a load from a second mass M2, which is set based on the input range of the first mass and the second A / D converter 44, is applied to the load sensor 10 as a reference value.

Description

Technical Field

[0001] The present disclosure relates to an electronic balance.

Background Art

[0002] Conventionally, an electronic balance includes a weighing pan on which an object to be weighed is placed, a load sensor that detects a load applied to the weighing pan by the object to be weighed and converts it into an electrical signal, an A / D converter that performs analog / digital conversion on the load detection signal from the load sensor, and a control arithmetic unit that calculates the mass of the object to be weighed based on the digitized load detection signal. Patent Document 1 discloses an electromagnetic force balance type electronic balance having such a configuration.

[0003] The A / D converter is usually selected to have a suitable input range and resolution according to the required resolution of the electronic balance itself. The A / D converter has the characteristics that the accuracy and linearity decrease in the full-scale region of the input range. Furthermore, the load sensor also has the characteristic that it becomes more stable as it approaches the balance point (the point where it balances without flowing current through the coil), but the stability deteriorates as the load applied increases.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in mass measurement, the mass of the object being measured is often large, but the mass to be measured is small. For example, this can occur when it is necessary to accurately dispense a very small amount of sample into a relatively large container such as a crucible, when measuring the amount of gas or moisture adsorbed or desorbed onto an adsorbent, or when measuring materials (oxide films, metal films, nitride films, etc.) coated on a semiconductor substrate. In such cases, the mass of the object to be measured may be on the order of μg for an object weighing 100-200g. The electronic balance in Patent Document 1 requires an A / D converter with an input range (absolute value) of 0-200g and a mass corresponding to the least significant bit of 1 μg for this measurement. In other words, the required resolution is 1 in 200 million (1 μg / 200g). Such a high-resolution A / D converter is technically difficult to produce, and even if possible, it would be extremely expensive.

[0006] Furthermore, even when using such an A / D converter, if the object being weighed is close to 200g, the system will use the area near the full scale of the input range, leading to problems of reduced accuracy and nonlinearity. Additionally, because the load sensor is far from its balance point, the weighed value varies, resulting in low accuracy. On the other hand, electronic balances that can achieve such high-resolution weighing without using such a high-resolution A / D converter were previously unknown.

[0007] This invention was proposed in view of the above circumstances and aims to provide an electronic balance that enables high-resolution measurements. [Means for solving the problem]

[0008] To achieve the above objective, an electronic balance according to one aspect of the technology of this disclosure has the following configuration.

[0009] 1. The weighing device comprises a weighing pan on which an object to be weighed is placed, a load sensor for detecting the load applied to the weighing pan, a control calculation unit for calculating the mass of the object to be weighed from the load detection signal of the load sensor, and an A / D conversion unit for converting the load detection signal from analog to digital and inputting it to the control calculation unit. The A / D conversion unit is equipped with a switchable first A / D converter and a second A / D converter. The second A / D converter has a mass corresponding to the least significant bit that is smaller than that of the first A / D converter. The load sensor is configured to be mechanically balanced when a load of a first mass, which is within the input range of the first A / D converter, is applied to the load sensor. The weighing device is configured to use the second A / D converter to weigh the object to be weighed, with the state in which a load of a second mass, set based on the first mass and the input range of the second A / D converter, is applied as a reference value.

[0010] 2. In the embodiment of 1 above, it is preferable that the device further includes a built-in weight addition / removal mechanism for placing and lowering the built-in weight onto the load sensor, and that the second mass is the built-in weight.

[0011] 3. In the embodiments described in 1 and 2 above, it is also preferable that the first mass and the second mass are equal.

[0012] 4. In the embodiments described in 1 to 3 above, it is also preferable that the first mass is the mass corresponding to the upper limit of the input range of the first A / D converter.

[0013] 5. In the embodiments described in 1 to 4 above, it is also preferable that the control calculation unit operates the first A / D converter without applying a load to the load sensor and determines that there is no load, applies a load from the second mass to the load sensor, switches the A / D conversion unit to the second A / D converter and sets the detected value as the reference value, applies a load from the object to be measured instead of the second mass to the load sensor, detects the mass difference between the second mass and the object to be measured using the second A / D converter, and calculates the mass of the object to be measured by adding the second mass to the mass difference between the second mass and the object to be measured. [Effects of the Invention]

[0014] According to the electronic balance described above, it is possible to provide an electronic balance capable of high-resolution measurement. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram showing the configuration of an electronic balance according to an embodiment. [Figure 2] (A) and (B) are diagrams illustrating the configuration of the electronic balance. [Figure 3] (A) to (C) are diagrams illustrating the measurement mechanism of the electronic balance. [Figure 4] (A) to (C) are diagrams illustrating the measurement mechanism of the electronic balance. [Figure 5] This is a flowchart explaining the operation of the electronic balance. [Figure 6] This is a diagram showing the configuration of an electronic balance according to one modified example of the same embodiment. [Figure 7] (A) and (B) are diagrams illustrating the configuration of the electronic balance. [Figure 8] This is a flowchart explaining the operation of the electronic balance. [Modes for carrying out the invention]

[0016] Preferred embodiments of the technology of this disclosure will be described below with reference to the drawings. The embodiments illustrated below are provided to facilitate understanding of the technology of this disclosure and are not intended to limit the invention as defined in the claims. The invention as defined in the claims can be modified or improved from the following embodiments without departing from the spirit thereof. In each drawing, the same reference numerals are used for components that are the same as those in the embodiments and modifications, and detailed descriptions are omitted as appropriate.

[0017] 1. Configuration of the electronic balance 100 FIG. 1 is a configuration diagram of an electronic scale 100 according to an embodiment, showing a schematic diagram of a mechanical configuration and a block diagram of an electrical configuration together. The electronic scale 100 applies the technology of the present disclosure to an electromagnetic force balance type electronic scale.

[0018] The electronic scale 100 generally includes a weighing pan 5, a load sensor 10, an A / D conversion unit 40, a control arithmetic unit 60, a storage unit 65, and a display unit 70.

[0019] In the illustrated example, the load sensor 10 has a mechanism unit 20 and a sensor unit 30. The mechanism unit 20 is a Roberval mechanism. The mechanism unit 20 includes a columnar floating frame 21 that receives a load, a fixing unit 22 fixed to a housing (not shown) of the electronic scale 100, etc., an upper sub-bar 23 and a lower sub-bar 24 that connect between the floating frame 21 and the fixing unit 22 via a hinge element 25.

[0020] The first end 28a of the beam 28 is connected to the floating frame 21 by a suspension band 26. The beam 28 is also connected to an extension 22a of the fixing unit 22 via a suspension band 27, and is supported rotatably in the direction of arrow B with the connection portion with the suspension band 27 as a fulcrum F. The load sensor 10 is designed to be mechanically balanced in a state where a load due to a first mass M1 described later acts. Details of this configuration will be described later. The first mass M1 is known and is, for example, a reference weight 82 (FIG. 2).

[0021] The weighing pan 5 is a pan on which an object to be weighed is placed, and is supported on the upper surface of the floating frame 21. When a load acts on the weighing pan 5, the floating frame 21 moves in the direction of gravity as shown by arrow A, transmits the load to the beam 28, and causes the beam 28 to rotate and displace around the fulcrum F as shown by arrow B.

[0022] The sensor unit 30 includes a displacement sensor 32 positioned opposite the second end 28b of the beam 28, an electromagnetic unit 34 installed on the fixed unit 22, a feedback circuit 36 ​​connected to the displacement sensor 32 and the electromagnetic unit 34, and an I / V (power / voltage) conversion circuit 38 connected to the feedback circuit 36 ​​and the A / D conversion unit 40.

[0023] The displacement sensor 32 detects the amount of displacement of the second end 28b of the beam 28. As the displacement sensor 32, known types such as optical displacement sensors, capacitive displacement sensors, and differential transformer displacement sensors can be used. In the illustrated example, the displacement sensor 32 is attached to the fixed part 22. However, it only needs to be positioned to detect the displacement of the beam 28, and may be attached to the second end 28b of the beam 28.

[0024] The electromagnetic unit 34 comprises a permanent magnet 34b and a force coil 34c, which are positioned within the yoke 34a. The force coil 34c is fixed to the second end 28b side of the beam 28, but is configured to be movable relative to the static magnetic field formed by the permanent magnet 34b. As a result, when current flows through the force coil 22c, the beam 28 maintains an equilibrium state against the load acting on the weighing pan (floating frame).

[0025] The feedback circuit 36 ​​controls the current flowing through the force coil 34c so that the displacement detected by the displacement sensor 32 becomes zero. Therefore, the current value flowing through the force coil 34c is proportional to the magnitude of the load acting on the weighing pan 5. The feedback circuit 36 ​​may be a single-drive type that allows current to flow in one direction, or a bipolar drive type that allows current to flow in both positive and negative directions. The force coil 34c outputs the current value to the I / V conversion circuit 38. The I / V conversion circuit 38 converts the current value into a voltage signal and outputs it to the A / D conversion unit 40 as a load detection signal.

[0026] The A / D conversion unit 40 converts the load detection signal from the load sensor 10 from analog to digital and outputs it to the control calculation unit 60. The A / D conversion unit 40 is equipped with a first A / D converter 42 and a second A / D converter 44 that can be switched between. In the figure, "A / D converter" is indicated as "ADC". The input range of the second A / D converter 44 is configured to be narrower than that of the first A / D converter 42.

[0027] Furthermore, the resolution of the second A / D converter 44 is configured to be equivalent to or higher than that of the first A / D converter 42; that is, the least significant bit (the smallest voltage change that can be identified) of the second A / D converter 44 is smaller than the least significant bit of the first A / D converter 42. As the first and second A / D converters 42 and 44, known A / D converters combining sampling circuits, quantization circuits, clock circuits, amplification circuits, etc., can be used. In addition, depending on the drive method of the feedback circuit 36, a corresponding input format is used.

[0028] The control calculation unit 60 is composed of at least one electronic circuit. A preferred example is a microcontroller in which a CPU (Central Processing Unit) and memory (ROM (Read Only Memory) and RAM (Random Access Memory)) are implemented on an integrated circuit. Alternatively, at least a portion of the control calculation unit 60 may be configured using other processors such as a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), or a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array).

[0029] The control calculation unit 60 calculates the mass of the object to be weighed, S, placed on the weighing pan 5, based on the load detection signal input from the A / D conversion unit 40. The control calculation unit 60 also uses the state in which the second mass M2 is placed on the weighing pan 5 (i.e., the state in which a load based on the second mass M2 is applied to the load sensor 10) as a reference value, switches the A / D conversion unit 40 to the second A / D converter 44, and weighs the object to be weighed S on the weighing pan 5 instead of the second mass M2, thereby measuring the mass difference between the second mass M2 and the object to be weighed S. Then, by adding the mass difference between the second mass M2 and the object to be weighed S to the known second mass M2, the mass of the object to be weighed S is calculated with the resolution of the second A / D converter 44 (least significant bit is 1 μg). Detailed operation of the measurement method will be described later.

[0030] The storage unit 65 is a non-temporary computer-readable storage medium such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory. The storage unit 65 stores a measurement program for the control calculation unit 60 to execute the operation of the measurement method described below. The storage unit 65 also stores the first mass M1.

[0031] The display unit 70 is, for example, a liquid crystal display. It displays the measured value and instructions and information for the user for measurement.

[0032] 2. Measurement Mechanism The mechanism by which the electronic balance 100 enables high-resolution weighing will be explained below with reference to Figures 2(A), 2(B), 3(A)-3(C), 4(A), and 4(B). Figure 2(A) is a diagram illustrating the design of the electronic balance 100 and shows it in the OFF state. Figure 2(B) is a diagram illustrating the electronic balance 100 in the OFF state. Furthermore, Figure 3(A) shows the electronic balance 100 with the power ON and no load on the weighing pan 5, Figure 3(B) shows the electronic balance 100 with the power ON and a second mass M2 placed on the weighing pan 5 (load sensor 10), and Figure 3(C) shows the electronic balance 100 with the power ON and the object to be weighed S placed on the weighing pan 5. Note that the load sensor 10 of the electronic balance 100 is shown in a simplified form in each figure.

[0033] For ease of understanding, we will explain an example using a first A / D converter 42 with an input range of 0 to 200 g and a resolution of 1 / 2,000,000 (the mass corresponding to the least significant bit is 100 μg), and a second A / D converter 44 with an input range of 0 to 2 g and a resolution of 1 / 2,000,000 (the mass corresponding to the least significant bit is 1 μg). Furthermore, we will explain an example in which the first mass M1 is a reference weight 82 of 200.000000 g (hereinafter, the reference weight will simply be referred to as 200 g), and the second mass M2 is also a reference weight 84 of 200 g, and weigh an object S of approximately 200 g (for example, 198 g).

[0034] In conventional electronic balances, the load sensor is typically designed to be mechanically balanced (at the balance point) when no current is flowing through the force coil (i.e., when the power is off) and the load sensor is unloaded. Theoretically, this mechanical balance means that the beam is balanced when no current is flowing through the force coil. However, in practice, it is difficult to achieve perfect balance due to the weight of the load sensor itself and static forces from surrounding components, so it may be necessary to flow an initial current through the force coil to compensate for the tilt. In this specification, balances configured so that the beam is balanced by such an initial current when the power is turned on are also treated as being mechanically balanced when the power is off.

[0035] On the other hand, the electronic balance 100 is designed to be mechanically balanced when the power is OFF and the reference weight 82 is placed on the weighing pan 5 (a load based on the first mass M1 is applied to the load sensor 10), as shown in Figure 2(A). In this case, "mechanically balanced" also includes the fact that the beam 28 is balanced when an initial current is passed through the force coil 34c. Therefore, in this specification, "designed to be mechanically balanced" is not limited to designing to be theoretically mechanically balanced, but also includes designing to be mechanically balanced within the range compensated by the initial current.

[0036] Here, the first mass M1 and the second mass M2 are masses corresponding to load detection signals that fall within the input range of the first A / D converter 42. The initial current is configured such that the corresponding load detection signal falls within the input range of the second A / D converter 44. In other words, the system is mechanically balanced so that the load detection signal corresponding to the initial current falls within the input range of the second A / D converter 44.

[0037] Incidentally, in the normal power-off state, as shown in Figure 2(B), the first mass M1 is not placed on the weighing pan 5. Therefore, an upward force F1 equivalent to the load of the first mass M1 acts on the weighing pan 5, causing the beam 28 to tilt downwards at its second end 28b.

[0038] The following describes the case where the feedback circuit 36 ​​is a single-drive system. The initial current values ​​are assumed to be 0.20mA, 20mA for 200g, and 0.4mA for 2g. When the power is turned ON, as shown in Figure 3(A), the force coil 34c supplies a current to generate an upward force F2 to balance the upward force F1, thereby electrically balancing the beam 28. That is, the feedback circuit 36 ​​adjusts the current in the force coil 34c to generate an upward force of 20mA. At this time, the load detection signal is outside the input range of the second A / D converter 44, but within the input range of the first A / D converter 42.

[0039] Next, when the second mass M2 is placed on the load sensor 10, a downward force L1 acts on the weighing pan 5. This downward force L1 is equivalent to the upward force F1. Therefore, as shown in Figure 3(B), the upward force F1 acting on the weighing pan 5 is almost canceled out by the downward load L1 due to the second mass M2, resulting in a balance point. Consequently, the upward force F2 required to balance the beam 28 becomes small, and the current flowing through the force coil 34c becomes the initial current of 0.2mA. Therefore, the corresponding voltage signal falls within the input range of the second A / D converter 44. In this state, by switching the A / D converter 40 to the second A / D converter 44, the second mass M2 can be weighed with the resolution of the second A / D converter 44 (least significant bit is 1μg). This value is used as the reference value.

[0040] Here, when the object to be weighed S is placed on the weighing pan 5 and the second mass M2 is lowered from the weighing pan 5, as shown in Figure 3(C), the upward force F1 acting on the weighing pan 5 is offset by the downward load L2 from the object to be weighed S, instead of the downward load L1 from the second mass M2. In the above example, the difference in mass between the second mass M2 and the object to be weighed S is 2g, so the current that generates the upward force F2 to balance force F1 is 0.4mA. If the load detection signal corresponding to this current value is within the input range of the second A / D converter 44, the difference in mass between the second mass M2 and the object to be weighed S can be detected with the resolution of the second A / D converter 44 (least significant bit is 1μg).

[0041] Therefore, using the value in the state shown in Figure 3(B) as the reference value, the measured value in the state shown in Figure 3(C) (the mass difference between the second mass M2 and the object S being measured) can be determined, and by adding the known second mass M2 to this, the mass of the object S being measured can be calculated. The reference value and the mass difference between the second mass M2 and the object S being measured can be detected with the resolution of the second A / D converter 44 (1 / 2,000,000 of 2g, with the least significant bit being 1μg), as long as they are within the input range of the second A / D converter 44. Therefore, it is possible to measure the mass of the object S being measured with a resolution of 1 / 200,000,000,000 (with the least significant bit being 1μg) across the entire electronic balance 100.

[0042] This mechanism will be explained again using Figures 4(A) to 4(C). Figures 4(A) and 4(B) show the relationship between the mass of the object being weighed by the electronic balance 100 and the current flowing through the force coil. Figure 4(A) shows the case where the feedback circuit 36 ​​is a single-drive system, and Figure 4(B) shows the case where it is a bipolar drive system. Figure 4(C) shows the relationship between the mass of the object being weighed and the current flowing through the force coil 34c in a conventional electronic balance, and shows the case where it is a single-drive system. Note that a positive current is a current that generates a downward force on the beam, and a negative current is a current that generates an upward force. The input range of each A / D converter is indicated by a double-headed arrow in the figures.

[0043] In conventional electronic balances, as shown in Figure 4(C), the current value is 0 when the mass of the object being weighed is 0 (no load), and the current value increases in proportion to the mass. Furthermore, weighing is possible within the range R corresponding to the input range of the A / D converter, as indicated by the double arrow, at the resolution of the A / D converter.

[0044] On the other hand, as shown in Figure 4(A), the electronic balance 100 is configured such that the current value is 0 when the mass of the object to be weighed is equal to the first mass M1. As the mass decreases, the negative current value increases, and when the mass is 0, it is configured to be the upper limit of the input range of the first A / D converter 42. Therefore, weighing is possible with the resolution of the first A / D converter 42 when the mass is in the range R1 from 0 to the first mass M1. Also, weighing is possible with the resolution of the second A / D converter 44 when the mass is in the range R2 between (first mass M1 - mass m corresponding to the upper limit of the second A / D converter 44) and the first mass M1. However, the weighed value for a mass of 0 is outside the input range of the second A / D converter 44. Therefore, by using a second mass M2 within this range R as a reference value, the mass difference between the second mass M2 and the object S being measured is determined, and by adding this to the known second mass M2, it is possible to determine the mass of the object S being measured with the resolution of the second A / D converter 44.

[0045] Furthermore, even when the feedback circuit 36 ​​is a bipolar drive type and the first and second A / D converters 42 and 44 correspond to the input methods, it is similarly possible to determine the mass of the object to be weighed S with the resolution of the second A / D converter 44. In this case, as shown in Figure 4(B), the measurable range R2 with the resolution of the second A / D converter 42 is in the range of (first mass M1 ± mass m corresponding to the upper limit of the second A / D converter 44).

[0046] 3. Operation of the electronic balance 100 in the measurement method Figure 5 is a flowchart illustrating the operation of the electronic balance 100 in a measurement method using the electronic balance 100. Here, we refer to an example in which an object S weighed weighing approximately 200g is measured using a first A / D converter 42 with an input range of 0 to 200g and a resolution of 1 / 2,000,000 (least significant bit of 100μg), a second A / D converter 44 with an input range of 0 to 2g and a resolution of 1 / 2,000,000 (least significant bit of 1μg), and reference weights 82 and 84 with a mass of 200g each as the first mass M1 and second mass M2.

[0047] In step S01, the power to the electronic balance 100 is turned ON and operation begins. In step S02, the control calculation unit 60 operates the first A / D converter 42. Specifically, if the first A / D converter 42 is selected, that state is maintained, and if the second A / D converter 44 is selected, it switches to the first A / D converter 42.

[0048] Next, in step S03, the control calculation unit 60 determines that the current state is one in which no load is applied to the weighing pan 5.

[0049] Next, in step S04, the user places the second mass M2 on the weighing pan 5. To enable the user to perform this action, the control calculation unit 60 may be configured to instruct the user to place the second mass M2. In this case, the instruction may be given, for example, by display on the display unit 70 or by voice from the voice output unit, which is not shown in Figure 1. Once the second mass M2 is placed on the weighing pan 5, the state shown in Figure 3(B) is reached.

[0050] Next, in step S05, the control calculation unit 60 determines whether the load detection signal has entered the input range of the second A / D converter 44. If the load detection signal is within the input range of the second A / D converter 44 (Yes), in step S06, the control calculation unit 60 switches the A / D conversion unit 40 to the second A / D converter 44. Once the load detection signal stabilizes, in step S07, this detected value is set as the reference value (zero point). If the result in step S05 is No, the determination in step S05 is repeated, and if it does not become Yes a predetermined number of times, it terminates as an error.

[0051] Next, in step S08, the control calculation unit 60 switches the A / D conversion unit 40 from the second A / D converter 44 to the first A / D converter 42.

[0052] Next, in step S09, the user removes the second mass M2 from the weighing pan 5, and in step S10, places the object to be weighed S on the weighing pan 5. The control calculation unit 60 may be configured to give instructions to the user in order to perform these actions. The manner of the instructions is the same as that described in step S04.

[0053] Next, in step S11, the control calculation unit 60 determines whether the load detection signal has entered the input range of the second A / D converter 44. If it has entered the input range (Yes), the process proceeds to step S12, and the A / D conversion unit 40 is switched to the second A / D converter 44. In the determination in step S11, if the result is No a predetermined number of times, the process may be terminated as an error because the object to be measured S is outside the measurement range.

[0054] Next, in step S13, the control calculation unit 60 takes the difference between the second mass M2 and the object to be measured as the measured value, and calculates the measured mass of the object to be measured S from the measured value and the mass value of the second mass M2. The calculated measured mass is then displayed on the display unit 70.

[0055] Next, in step S14, the user removes the object to be weighed S from the weighing pan 5. For this purpose, the control calculation unit 60 may display an instruction to the user on the display unit 70 to remove the object to be weighed S. When the object to be weighed S is removed from the weighing pan 5, the load acting on the load sensor 10 decreases by the amount of the object to be weighed S (198g), and the detection signal exceeds the input range of the second A / D converter 44.

[0056] Therefore, in step S15, the control calculation unit 60 determines whether the detection signal has moved outside the input range of the second A / D converter 44. If it has moved outside the input range (Yes), the process proceeds to step S16, where the A / D conversion unit 40 is switched to the first A / D converter 42.

[0057] Then, if the control calculation unit 60 does not turn off the power in step S17, the process returns to step S03.

[0058] 4. Action and Effects Thus, with the electronic balance 100, it is possible to weigh the object to be weighed with the resolution of the second A / D converter 44 (the least significant bit is 1 μg). There is no need to use an expensive, high-resolution A / D converter.

[0059] As a result, it becomes possible to weigh relatively large masses (e.g., 100-200g) with high resolution (resolution of 1 part in 20 billion), which was difficult with conventional electronic balances. For example, it becomes possible to determine the amount of a substance on the order of μg adsorbed or coated onto 100-200g of material (adsorbent, semiconductor substrate, etc.) from the difference in mass before and after adsorption or coating.

[0060] Such high-resolution weighing is possible for objects S whose mass falls within the input range of the second A / D converter 44, from the first mass M1. Objects S exceeding this range will not fall within the input range of the second A / D converter 44 in step S12. Therefore, depending on the application, it is preferable to use first and second masses M1 and M2, and first and second A / D converters 42 and 44 such that the object S falls within this range.

[0061] In the example above, the case where the first mass M1 and the second mass M2 are equal was described as a preferred example. This is because, in the electronic balance 100, the state in which the load from the first mass M1 is applied to the load sensor 10 becomes the balance point, and the mass of the object to be weighed can be calculated using the detected value near the balance point where the load sensor 10 is most stable.

[0062] However, perfect equality is not required; the second mass M2 may be different from the first mass M1, as long as it is within the input range of the second A / D converter 44. Within this range, the second mass M2 can be measured with the resolution of the second A / D converter 42. In this case as well, the mass of the object being measured S can be calculated using the detected value near the balance point.

[0063] In the example above, the first mass M1 is equal to the upper limit (full scale) of the input range of the first A / D converter 42. While this is not strictly necessary, setting the first mass M1 to the upper limit of the input range of the first A / D converter 42 maximizes the mass ratio corresponding to the least significant bit and thus maximizes the effect of improving resolution, which is advantageous.

[0064] Note that the first mass M1 and the second mass M2 do not necessarily have to be reference weights; any object with a known mass will suffice.

[0065] 5. Variations This embodiment may be modified as follows. Figure 6 is a configuration diagram of an electronic balance 100A according to one modified example of this embodiment, corresponding to Figure 1. Figure 7(A) is a diagram illustrating the design of the electronic balance 100A and shows the power-off state. Figure 7(B) is a diagram illustrating the power-off state of the electronic balance 100A. The electronic balance 100A has generally the same configuration as the electronic balance 100, but differs in that it includes a built-in weight addition / removal mechanism 50 in addition to the configuration of the electronic balance 100. Furthermore, for this reason, the floating frame 21A of the load sensor 10A differs in that it includes a built-in weight receiving part 29 in addition to the floating frame 21.

[0066] The internal weight addition / removal mechanism 50 comprises an internal weight 52 and a drive mechanism 54. The internal weight 52 is a calibration weight with a known mass. The mass of the internal weight 52 is stored in the memory or storage unit 65 of the control calculation unit 60A. The drive mechanism 54, although not shown in the figures, comprises, for example, a motor and a cam mechanism, and is configured to move the internal weight 52 in the direction of arrow C, and to place the internal weight 52 on and off the internal weight receiving part 29 provided on the floating frame 21. The internal weight addition / removal mechanism 50 is not limited to this, and known configurations such as those disclosed in Japanese Patent Application Publication No. 2008-32610 can be applied.

[0067] As shown in Figure 7(A), the electronic balance 100A is designed to be mechanically balanced when the power is OFF and the internal weight 52 is placed on the load sensor 10A (a load based on the internal weight 52 is applied to the load sensor 10A). Therefore, the internal weight 52 functions as the first mass M1. However, this is not mandatory, and a reference weight with the same mass as the internal weight 52 may be used. Also, when using a reference weight, it is not mandatory that it has the same mass as the internal weight 52; it is sufficient if the mass is within the range of the input range of the second A / D converter 44, relative to the mass of the internal weight 52.

[0068] In the normal power-off state, as shown in Figure 7(B), the internal weight 52 is not placed on the weighing pan 5. Therefore, an upward force F1 equivalent to the load of the internal weight 52 acts on the weighing pan 5, causing the beam 28 to tilt downward at its second end 28b. This is the same as in the electronic balance 100.

[0069] Furthermore, the electronic balance 100A differs in that it is equipped with a control calculation unit 60A instead of the control calculation unit 60. The control calculation unit 60A has the same mechanical configuration as the control calculation unit 60.

[0070] The control calculation unit 60A calculates the mass of the object to be weighed S placed on the weighing pan 5 based on the load detection signal input from the A / D conversion unit 40. The control calculation unit 60A also controls the built-in weight addition / removal mechanism 50 to place the built-in weight 52 on and off the load sensor 10A. The control calculation unit 60A sets the value measured using the second A / D converter 44, when the built-in weight 52 is placed on the load sensor 10A, as a reference value. When the object to be weighed S is placed on the weighing pan 5, the control calculation unit 60A switches the A / D conversion unit 40 to the first A / D converter 42 to remove the built-in weight 52 from the load sensor 10A, and then switches the A / D conversion unit 40 back to the second A / D converter 44 to calculate the built-in weight and the weighed value. The measured mass of the object to be weighed S is then calculated from the weighed value and the mass value of the built-in weight 52 stored in memory.

[0071] The measurement mechanism of the electronic balance 100A is the same as that of the electronic balance 100, except that the built-in weight 52 functions as the second mass M2 of the electronic balance 100A, and the loading and unloading of the second mass M2 is performed automatically by the built-in weight addition / removal mechanism 50. Therefore, a detailed explanation is omitted.

[0072] Figure 8 is a flowchart illustrating the operation of the electronic balance 100A in a measurement method using the electronic balance 100A. Steps S21 to S23 are the same as steps S01 to S03. Then, in step S24, instead of the user loading or unloading the second mass, the control calculation unit 60A controls the built-in weight loading / unloading mechanism 50 to load the built-in weight 52.

[0073] Next, in steps S25 to S27, the measured value of the built-in weight 52 using the second A / D converter 44 is set as a reference value, similar to steps S05 to S07. Then, in step S28, when the user places the object to be weighed S on the weighing pan 5, in step S29, the control calculation unit 60A determines whether the detection signal is outside the input range of the second A / D converter 44. If it is outside the range (Yes), the process proceeds to step S30, where the A / D conversion unit 40 is switched to the first A / D converter 42. Then, in step S31, the control calculation unit 60A controls the built-in weight addition / removal mechanism 50 to remove the built-in weight 52 from the load sensor 10.

[0074] Subsequently, steps S32 to S38 perform the same processing as in steps S11 to S17. Each step corresponds to the other.

[0075] Thus, in the electronic balance 100A, the user does not need to place or remove the reference weight 84, as a built-in calibration weight, configured to be placed and removed automatically, is used as the second mass M2. Therefore, in addition to the effects of the electronic balance 100, the electronic balance 100A further reduces the user's burden of placing and removing the reference weight 84 during measurement and managing the reference weight 84. [Explanation of Symbols]

[0076] 5:Measuring pan 10,10A: Load sensor 40: A / D conversion unit 42: First A / D converter 44: Second A / D converter 50: Built-in weight adjustment mechanism 52: Built-in weight 60: Control calculation unit 100, 100A: Electronic balance M1: First mass M2: Second mass

Claims

1. A weighing pan on which the object to be weighed is placed, A load sensor for detecting the load applied to the weighing pan, A control calculation unit that calculates the mass of the object to be measured from the load detection signal of the load sensor, The system includes an A / D conversion unit that converts the load detection signal from analog to digital and inputs it to the control calculation unit, The A / D conversion unit is equipped with a first A / D converter and a second A / D converter that can be switched between, wherein the second A / D converter has a smaller mass corresponding to the least significant bit than the first A / D converter. The load sensor is configured such that it is mechanically balanced by the action of a load from a first mass that is within the input range of the first A / D converter, but when the power is OFF, no load is acting on the load sensor. The system is configured to weigh the object to be weighed using the second A / D converter, with the state in which a load due to a second mass, which is set based on the first mass and the input range of the second A / D converter, is applied to the load sensor as a reference value. An electronic balance characterized in that the second mass is within the range of the input range of the second A / D converter, derived from the first mass.

2. The system further includes a built-in weight addition / removal mechanism for placing and lowering the built-in weight onto the load sensor, The electronic balance according to claim 1, characterized in that the second mass is the built-in weight.

3. The electronic balance according to claim 1, characterized in that the first mass and the second mass are equal.

4. The electronic balance according to claim 1 or 2, characterized in that the first mass is the mass corresponding to the upper limit of the input range of the first A / D converter.

5. The control calculation unit is Without applying a load to the load sensor, the first A / D converter is operated to determine that there is no load. The load sensor is subjected to a load from the second mass, the A / D conversion unit is switched to the second A / D converter, and the detected value is set as the reference value. The load sensor is subjected to the load of the object being measured instead of the second mass, and the second A / D converter is used to detect the mass difference between the second mass and the object being measured. The electronic balance according to claim 1 or 2, characterized in that the mass of the object to be weighed is calculated by adding the second mass to the difference in mass between the second mass and the object to be weighed.

Images