Electronic analytical balance and circuit device for electronic analytical balance

Abstract

The present disclosure provides an electronic analytical balance and a circuit device for the electronic analytical balance. The electronic analytical balance includes a balance mechanism, an electromagnetic coil drive circuit, a width-modulated pulse signal circuit module, and a metering circuit. The electromagnetic coil drive circuit includes: a PID controller and a transistor switch, wherein the input end of the PID controller is connected to the photoelectric detection circuit, and the output end of the PID controller is connected to the base of the transistor switch. The collector of the transistor switch is connected to a voltage source VCC, the emitter of the transistor switch is connected to the first end of the coil of the electromagnetic balance sensor, and a current is applied to the first end of the coil, and the second end of the coil is connected to a floating potential node A. The width-modulated pulse signal circuit module is connected to the floating potential node A, and is used to generate a width-modulated pulse signal corresponding to the current applied to the first end of the coil. And the metering circuit is connected to the width-modulated pulse signal circuit module, and is used to determine the mass of the load on the weighing pan according to the width-modulated pulse signal.

Description

Technical Field

[0001] The present disclosure relates to the field of measurement technology, and in particular to an electronic analytical balance and a circuit device for the electronic analytical balance. Background Art

[0002] The electronic analytical balance is a high-precision mass measuring instrument used in scientific research, industry and defense. It uses the principle of electromagnetic torque and gravity torque balance to measure the mass of an object. Figure 1 A schematic diagram of an existing electronic analytical balance is shown. Figure 1 As shown, the electronic analytical balance includes a balance mechanism 910 , a width-adjusted pulse signal circuit 920 , an electromagnetic coil driving circuit 930 , and a measuring circuit 940 .

[0003] The balance mechanism 910 includes a weighing pan 911, an electromagnetic balance sensor 912 connected to the weighing pan 911, a light-emitting tube 914, photosensitive tubes 915a and 915b, and a photoelectric conversion circuit 917. The crossbeam 913 of the electromagnetic balance sensor 912 is connected with a light shielding sheet 918, so that the light shielding sheet 918 is arranged between the light-emitting tube 914 and the photosensitive tubes 915a and 915b, and can be used to block the light emitted by the light-emitting tube 914. In addition, the photosensitive tubes 915a and 915b and the photoelectric conversion circuit 917 together constitute a photoelectric detection circuit.

[0004] The width modulated pulse signal circuit 920 includes a PID controller 921 connected to the photoelectric conversion circuit 917, a sawtooth wave generator 922, and a comparator 923. The output end of the PID controller 921 and the output end of the sawtooth wave generator 922 are respectively connected to the input end of the comparator 923. Thus, the comparator 923 outputs a width modulated pulse signal related to the output voltage of the PID controller 921.

[0005] The electromagnetic coil driving circuit 930 includes a transistor 931 and a constant current source 932. The base of the transistor 931 is connected to the output end of the comparator 923, and receives the width modulation pulse signal output by the comparator 923. The emitter of the transistor 931 is connected to one end of the coil 916 of the electromagnetic balance sensor 912, and the collector of the transistor 931 and the constant current source 932 are connected to the other end of the coil 916. Thus, the on and off of the transistor 931 can be controlled by the width modulation pulse signal, and the constant current source 932 can be controlled to transmit current to the coil 916.

[0006] The measuring circuit 940 includes a counter 941 and a microprocessor 942 connected to the counter 941 . The counter 941 counts according to the width of the width-modulated pulse signal, and the microprocessor 942 calculates the mass of the load on the weighing pan 911 according to the count value of the counter 941 .

[0007] Specifically, when a load is placed on the weighing pan 911, the light shielding sheet 918 moves upward. Thus, the photosensitive tubes 915a and 915b receive the light from the light-emitting tube 914 and generate a changing current signal, which is converted into a differential signal by the photoelectric conversion circuit 917 and then input into the PID controller 921. The PID controller 921 performs PID adjustment on the differential signal output by the photoelectric conversion circuit 917 and outputs a corresponding voltage signal. After the voltage signal is compared with the sawtooth wave signal generated by the sawtooth wave generator 922, the comparator 923 generates a corresponding width-modulated pulse signal. The width-modulated pulse signal controls the on-off of the transistor 931, so that when the transistor 931 is turned off, the constant current source 932 outputs current to the coil 916, and when the transistor 931 is turned on, the constant current source 932 stops outputting current to the coil 916. Thus, the magnitude of the average current output to the coil 916 is controlled by the width-modulated pulse signal.

[0008] Thus, the energized coil 916 generates a vertical downward electromagnetic force under the action of the air gap magnetic field of the permanent magnet magnetic circuit, causing the shading plate 918 to move downward. At the same time, the integral link of the PID controller 921 causes the voltage output by the PID921 controller to continuously increase, so that a wider width-modulated pulse signal drives a larger current to be output to the coil 916, thereby continuously driving the shading plate 918 to move downward. When the shading plate 918 completely blocks the light-emitting tube 914 and the photosensitive tubes 915a and 915b, the differential signal generated by the photoelectric conversion circuit 917 is zero, so that the voltage output by the PID controller 921 no longer changes, and at this time, the pulse width of the width-modulated pulse signal no longer changes, and the current output to the coil 916 no longer changes, and the balance mechanism 910 reaches a balanced state.

[0009] The counter 941 counts according to the width modulated pulse signal to determine a count value corresponding to the pulse width of the width modulated pulse signal, and the microprocessor 942 determines the mass of the load on the weighing pan 911 according to the count value.

[0010] However, the existing electronic analytical balance has the following problems: from the mechanical characteristics of the electromagnetic balance sensor 912, since the current output to the coil 916 is sometimes turned on and sometimes turned off by the width-modulated pulse signal, the electromagnetic force constantly attracts and disconnects the balance beam 913, and the electromagnetic balance sensor 912 is stimulated by the step signal at the moment when the current of the coil 916 is turned on and off. Although the time is extremely short and the displacement is only micron-level, the electrical signal noise generated after the motion displacement is amplified by the photoelectric conversion circuit 917 for detecting the balance of the balance is relatively large, which affects the current measurement accuracy and has a great impact on the accuracy and repeatability in engineering.

[0011] There is no effective solution to the technical problem in the prior art that the electromagnetic balance sensor of the electronic analytical balance is excited by the step signal when the current is turned on and off, resulting in large detection signal noise, thereby affecting the accuracy and repeatability of the electronic analytical balance. Summary of the invention

[0012] The present disclosure provides an electronic analytical balance and a circuit device for the electronic analytical balance, so as to at least solve the technical problem in the prior art that the electromagnetic balance sensor of the electronic analytical balance is stimulated by a step signal when the current is turned on and off, resulting in a large noise in the generated detection signal, thereby affecting the accuracy and repeatability of the electronic analytical balance.

[0013] According to one aspect of the present disclosure, an electronic analytical balance is provided, including a balance mechanism, an electromagnetic coil drive circuit, a width-modulated pulse signal circuit module, and a metering circuit. The balance mechanism includes: a weighing pan; an electromagnetic balance sensor connected to the weighing pan; and a photoelectric detection circuit for detecting the balance state of the electromagnetic balance sensor. The electromagnetic coil drive circuit includes: a PID controller and a transistor switch, wherein the input end of the PID controller is connected to the photoelectric detection circuit, and the output end of the PID controller is connected to the base of the transistor switch. The collector of the transistor switch is connected to a voltage source VCC, the emitter of the transistor switch is connected to the first end of the coil of the electromagnetic balance sensor, and a current is applied to the first end of the coil, and the second end of the coil is connected to a floating potential node A. The width-modulated pulse signal circuit module is connected to the floating potential node A, and is used to generate a width-modulated pulse signal corresponding to the current applied to the first end of the coil. And the metering circuit is connected to the width-modulated pulse signal circuit module, and is used to determine the mass of the load on the weighing pan according to the width-modulated pulse signal.

[0014] According to another aspect of the present disclosure, a circuit device for an electronic analytical balance is provided, comprising an electromagnetic coil drive circuit, a width-modulated pulse signal circuit module, and a metering circuit. The electronic analytical balance comprises a balance mechanism, which comprises: a weighing pan; an electromagnetic balance sensor connected to the weighing pan; and a photoelectric detection circuit for detecting the balance state of the electromagnetic balance sensor. The electromagnetic coil drive circuit comprises: a PID controller and a transistor switch, wherein the input end of the PID controller is connected to the photoelectric detection circuit, and the output end of the PID controller is connected to the base of the transistor switch. The collector of the transistor switch is connected to a voltage source VCC, the emitter of the transistor switch is connected to the first end of the coil of the electromagnetic balance sensor, and a current is applied to the first end of the coil, and the second end of the coil is connected to a floating potential node A. The width-modulated pulse signal circuit module is connected to the floating potential node A, and is used to generate a width-modulated pulse signal corresponding to the current applied to the first end of the coil. And the metering circuit is connected to the width-modulated pulse signal circuit module, and is used to determine the mass of the load on the weighing pan according to the width-modulated pulse signal.

[0015] In summary, the technical solution disclosed in the present invention no longer outputs current to the coil of the electromagnetic balance sensor by controlling the current source through a width-modulated pulse signal, but uses the output voltage of the PID controller to control the current output by the power supply to the coil. Since the voltage output by the PID controller is a gradually increasing voltage signal, once the transistor switch is turned on, it will not be disconnected before the electromagnetic balance sensor reaches balance. When entering the steady state, the coil current is a steady current, so that the power supply VCC can continuously transmit current to the coil of the electromagnetic balance sensor, and will not cause the electromagnetic balance sensor to be excited by the step signal. In addition, the present invention adopts a pulse width modulation current circuit with a double closed-loop control to decouple the PID controller and the current measurement hybrid circuit in the traditional measurement method, reduce the difficulty of PID controller parameter setting, avoid solving the transmission equation of the mechanical sensor and the balance detection system, and improve the control circuit response speed and current measurement accuracy. Without nonlinear correction of the measured data, the standard deviation of the original measurement data of the 31g range electronic analytical balance is 2e-5g, reaching a million-division accuracy, which is far better than the original electronic analytical balance with the same circuit and sensor. Thus, the technical problem in the prior art that the electromagnetic balance sensor of the electronic analytical balance is stimulated by the step signal when the current is turned on and off, resulting in large detection signal noise, thereby affecting the accuracy and repeatability of the electronic analytical balance is solved.

[0016] Based on the following detailed description of the specific embodiments of the present disclosure in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Hereinafter, some specific embodiments of the present disclosure will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0018] Figure 1 It is a schematic diagram of the structure of an electronic analytical balance according to the prior art;

[0019] Figure 2 is a schematic structural diagram of an electronic analytical balance according to the present disclosure;

[0020] Figure 3 is a schematic diagram of a circuit arrangement of an electronic analytical balance according to the present disclosure;

[0021] Figure 4A The electronic analytical balance according to the present disclosure is shown, when the load of the tray is 0g, 10g, 20g and 30g respectively. Figure 3 Schematic diagram of the floating potential at point A changing with time;

[0022] Figure 4B The electronic analytical balance according to the present disclosure is shown, and the load of the tray is divided into 0g, 10g, 20g and 30g. Figure 3 A schematic diagram showing the voltage across the first resistor 123 changing with time;

[0023] Figure 4C The electronic analytical balance according to the present disclosure is shown, and the load of the tray is divided into 0g, 10g, 20g and 30g. Figure 3 A schematic diagram showing the change of the level at point B over time; and

[0024] Figure 4D The electronic analytical balance of the present disclosure is shown, and the load of the tray 111 is divided into 0g, 10g, 20g and 30g. Figure 3 Schematic diagram of the charging and discharging current of the storage capacitor 131 changing with time. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0026] In order to enable those skilled in the art to better understand the scheme of the present disclosure, the technical scheme in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present disclosure.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so as to describe the embodiments of the present disclosure described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] It should be noted that the "connection" described in the present disclosure includes both direct connection and indirect connection through circuit elements such as resistors. For example, the connection between A and B includes both direct connection between A and B and connection between A and B through a resistor.

[0030] According to a first aspect of the present disclosure, an electronic analytical balance is provided. Figure 2 is a schematic diagram of an electronic analytical balance according to the present disclosure. Figure 2As shown, the present disclosure provides an electronic analytical balance. The electronic analytical balance includes a balance mechanism 110, an electromagnetic coil drive circuit 120, a width-modulated pulse signal circuit module 210, and a metering circuit 150. The balance mechanism 110 includes: a weighing pan 111; an electromagnetic balance sensor 112 connected to the weighing pan 111; and a photoelectric detection circuit for detecting the balance state of the electromagnetic balance sensor 112. And wherein, the electromagnetic coil drive circuit 120 includes: a PID controller 121 and a transistor switch 122. The input end of the PID controller 121 is connected to the photoelectric detection circuit, and the output end of the PID controller 121 is connected to the base of the transistor switch 122. The collector of the transistor switch 122 is connected to the voltage source VCC, the emitter of the transistor switch 122 is connected to the first end of the coil 116 of the electromagnetic balance sensor 112, and a current is applied to the first end of the coil 116, and the second end of the coil 116 is connected to the floating potential node A. The width modulated pulse signal circuit module 210 is connected to the floating potential node A for generating a width modulated pulse signal corresponding to the current applied to the first end of the coil 116, and the metering circuit 150 is connected to the width modulated pulse signal circuit module 210 for determining the mass of the load on the weighing pan 111 based on the width modulated pulse signal.

[0031] Specifically, see Figure 2 As shown, the balance mechanism 110 includes a weighing pan 111, an electromagnetic balance sensor 112 connected to the weighing pan 111, a light-emitting tube 114, photosensitive tubes 115a and 115b, and a photoelectric conversion circuit 117. Among them, the crossbeam 113 of the electromagnetic balance sensor 112 is connected to a light shielding sheet 118, so that the light shielding sheet 118 is arranged between the light-emitting tube 114 and the photosensitive tubes 115a and 115b, and can be used to block the light emitted by the light-emitting tube 114. In addition, the light-emitting tube 114, the photosensitive tubes 115a and 115b, and the photoelectric conversion circuit 117 together constitute a photoelectric detection circuit for detecting the balance state of the electromagnetic balance sensor 112. And, further reference is made to Figure 2 As shown, the emitter of the transistor switch 122 can be connected to the first end of the coil 116 of the electromagnetic balance sensor 112 through the first resistor 123, for example. Figure 3 As shown, the coil 116 is regarded as a resistor r x and inductor L x series connection.

[0032] Thus, when no load is placed on the weighing pan 111, the output of the photoelectric detection circuit is zero, and thus the output of the PID controller 121 is also zero. At this time, the transistor switch 122 is disconnected, and the current i flowing through the coil 116 is also zero. Thus, the electromagnetic force generated by the coil 116 is zero.

[0033] After a load is added to the weighing pan 111 , the PID controller 121 receives the signal from the photoelectric detection circuit and outputs a corresponding voltage, so that the transistor switch 122 is turned on, and the power supply VCC supplies power so that the current i is applied to the coil 116 .

[0034] The current i applied to the coil 116 is calculated as follows:

[0035]

[0036] Among them, V CE is the voltage between the collector and emitter of transistor switch 122, V CC is the voltage of power supply VCC, V A is the voltage of the floating potential node A, R is the resistance value of the first resistor 123, r x is the resistance value of coil 116. And, V CE The PID controller 121 is affected by the output voltage of the PID controller 121, so that the PID controller 121 can change V CE The magnitude of the current i is adjusted, and thus the magnitude of the electromagnetic force generated by the coil 116 is adjusted until a balance is achieved with the mass of the load.

[0037] In addition, the width modulated pulse signal circuit module 210 is connected to the floating potential node A, thereby generating a width modulated pulse signal corresponding to the current i. Thus, the metering circuit 150 can determine the magnitude of the current i according to the width modulated pulse signal, and further determine the magnitude of the electromagnetic force generated by the coil 116, thereby determining the mass of the load on the weighing pan 111.

[0038] As described in the prior art, from the mechanical characteristics of the electromagnetic balance sensor of the existing electronic analytical balance, since the current output to the coil is sometimes turned on and sometimes turned off by the width-modulated pulse signal, the electromagnetic force constantly attracts and disconnects the balance beam, and the electromagnetic balance sensor is stimulated by the step signal at the moment when the current of the coil is turned on and off. Although the time is extremely short and the displacement is only micron-level, the electrical signal noise generated after the motion displacement is amplified by the photoelectric conversion circuit that detects the balance of the balance is relatively large, affecting the current measurement accuracy, and has a great impact on accuracy and repeatability in engineering.

[0039] In view of this, the technical solution disclosed in the present invention no longer outputs current to the coil 116 of the electromagnetic balance sensor 112 by controlling the current source through a pulse width modulation signal, but uses the output voltage of the PID controller 121 to control the current output by the power supply to the coil. Since the voltage output by the PID controller 121 is a gradually increasing voltage signal, when entering a steady state, the voltage output by the PID controller 121 is basically stable, and the transistor switch 122 and the electromagnetic balance sensor 112 enter a steady state. Thus, the power supply VCC can continuously transmit current to the coil 116 of the electromagnetic balance sensor 112, and will not cause the electromagnetic balance sensor to be excited by the step signal. In addition, the present invention adopts a pulse width modulation current circuit with dual closed-loop control, decoupling the PID controller and the current measurement hybrid circuit in the traditional measurement method, reducing the difficulty of PID controller parameter setting, avoiding solving the transmission equation of the mechanical sensor and the balance detection system, and improving the control circuit response speed and current measurement accuracy. Without nonlinear correction of the measured data, the standard deviation of the original measured data of the 31g range electronic analytical balance is 2e-5g, reaching the million-division level of accuracy, which is much better than the original electronic analytical balance with the same circuit and sensor. Thus, the technical problem in the prior art that the electromagnetic balance sensor of the electronic analytical balance is excited by the step signal when the current is turned on and off, resulting in a large noise in the generated detection signal, thereby affecting the accuracy and repeatability of the electronic analytical balance is solved.

[0040] In addition, as an example, the PID control circuit 121 may use an operational amplifier LT1097, the transistor switch 122 may use an NPN transistor BC817, the resistance value of the first resistor 123 may be 300Ω, and the resistance value of the coil 116 may be 0. x can be 49Ω, inductor L x It can be 8.5mH.

[0041] Optionally, refer to Figure 2 As shown, the width modulated pulse signal circuit module 210 includes: a charge and discharge circuit 130, a controllable current source 160 and a width modulated pulse signal circuit 140. The charge and discharge circuit 130 and the controllable current source 160 are respectively connected to the floating potential node A, so that the charge and discharge circuit 130 performs charge and discharge based on the coil 116 and the controllable current source 160. The width modulated pulse signal circuit 140 is connected to the charge and discharge circuit 130 to generate a width modulated pulse signal corresponding to the voltage output by the charge and discharge circuit 130. The controllable current source 160 is also connected to the width modulated pulse signal circuit 140 to control the charge and discharge circuit 130 to perform charge and discharge based on the width modulated pulse signal generated by the width modulated pulse signal circuit 140.

[0042] Thus, when the electromagnetic balance sensor 112 transmits current through the power supply VCC and reaches balance, the coil 116 provides a steady-state current, so that when the controllable current source 160 is turned off, the charge and discharge circuit 130 is charged through the floating potential node A. Therefore, the voltage output by the charge and discharge circuit 130 decreases or increases with the charge and discharge, and then the width modulation pulse signal circuit 140 generates a corresponding width modulation pulse signal according to the voltage output by the charge and discharge circuit 130. And after the controllable current source 160 receives the width modulation pulse signal, it turns on or off the current source according to the width modulation pulse signal, thereby controlling the charge and discharge circuit 130 to discharge based on the width modulation pulse signal. For example, the controllable current source 160 turns on the current source when the width modulation pulse signal is at a high level, and the charge and discharge circuit 130 discharges at this time; the controllable current source 160 turns off the current source when the width modulation pulse signal is at a low level, and the charge and discharge circuit 130 charges at this time.

[0043] When the average current of the charge and discharge circuit 130 is greater than the average current of the discharge, the voltage of the charge and discharge circuit 130 decreases, so that the width modulation pulse signal circuit 140 generates a corresponding width modulation pulse signal with a wider duty cycle. As a result, the average current of the charge and discharge circuit 130 discharges increases until the average current of the charge and discharge circuit 130 discharges and the average current of the charge reaches a balance, at which time the duty cycle of the width modulation pulse signal generated by the width modulation pulse signal circuit 140 also reaches stability.

[0044] Therefore, the measuring circuit 150 can determine the magnitude of the charging current of the coil 116 according to the width modulation pulse signal with a stable duty cycle generated by the width modulation pulse signal circuit 140, and further determine the magnitude of the electromagnetic force generated by the coil 116, thereby determining the mass of the load on the weighing pan 111.

[0045] Optionally, refer to Figure 3 As shown, the charge and discharge circuit 130 includes: an operational amplifier 132 and an energy storage capacitor 131. The first end of the energy storage capacitor 131 is connected to the floating potential node A, and the second end is connected to the width modulation pulse signal circuit 140; and the reverse input end of the operational amplifier 132 is connected to the floating potential node A, the forward input end is grounded, and the output end is connected to the second end of the energy storage capacitor 131. Therefore, the charge and discharge circuit of the present invention can adopt an operational amplifier integration circuit, and the energy storage capacitor 131 can be charged or discharged through the floating potential node A, thereby achieving the effect of the charge and discharge circuit. And because the potential of the energy storage capacitor 131 changes during the charging process, the current in the charging process presents a nonlinear characteristic. The present invention adopts an operational amplifier 132, which can keep the current constant during the charging and discharging process.

[0046] In addition, preferably, the inverting input terminal of the operational amplifier 132 is connected to a filter capacitor 133. The operational amplifier 132 may be OPA277, the capacitance value of the energy storage capacitor 131 may be 4.7uF, and the capacitance value of the filter capacitor 133 may be 10uF. And preferably, the energy storage capacitor 131 may be a polyethylene or polypropylene film capacitor with low leakage current.

[0047] Optionally, refer to Figure 3 As shown, the width modulated pulse signal circuit 140 includes: a comparator 141 and a sawtooth wave generator 142. The positive input terminal of the comparator 141 is connected to the output terminal of the charge and discharge circuit 130, the reverse input terminal of the comparator 141 is connected to the sawtooth wave generator 142, and the output terminal of the comparator 141 is connected to the controllable current source 160. Therefore, the comparator 141 compares the voltage at the output terminal of the charge and discharge circuit 130 with the sawtooth wave generator 142 to generate a width modulated pulse signal corresponding to the voltage at the output terminal of the charge and discharge circuit 130, and sends it to the controllable current source 160.

[0048] In addition, further, the positive input terminal of the comparator 141 is connected to the charge and discharge circuit 130 through a low-pass filter. Figure 3 As shown, the low-pass filter includes a resistor 143 and a capacitor 144. The first end of the resistor 143 (i.e., the input end of the low-pass filter) is connected to the output end of the charge-discharge circuit 130, and the second end is connected to the capacitor 144. The first end of the capacitor 144 is connected to the resistor 143, and the second end is grounded. The positive input end of the comparator 141 is connected to the second end of the resistor 143 and the first end of the capacitor 144 (i.e., the output end of the low-pass filter).

[0049] Specifically, the comparator 141 may be a LM393 high-speed comparator, the resistance value of the resistor 143 may be 82KΩ, and the capacitance value of the capacitor 144 may be 1uF.

[0050] Optionally, refer to Figure 3 As shown, the controllable current source 160 includes: a switch circuit 161 and a constant current source 162. Among them, the control end of the switch circuit 161 is connected to the width modulation pulse signal circuit 140, and the output end is connected to the constant current source 162, so that the constant current source 162 is turned on or off based on the width modulation pulse signal generated by the width modulation pulse signal circuit 140. For example, the switch circuit 161 turns on the constant current source 162 when the width modulation pulse signal is at a high level, and turns off the constant current source 162 when the width modulation pulse signal is at a low level. Therefore, the opening and closing of the constant current source can be controlled according to the width modulation pulse signal, thereby controlling the charging and discharging of the charge and discharge circuit 130.

[0051] Therefore, the measuring circuit 150 calculates the current of the electromagnetic coil as τ*I according to the duty cycle τ of the width modulated pulse signal and the current I output by the constant current source, and multiplies the current by the calibration coefficient k of the electronic balance to obtain the mass of the load k*τ*I.

[0052] also Figure 4A A schematic diagram showing the variation of the floating potential at point A with time when the loads of the tray 111 are 0 g, 10 g, 20 g and 30 g respectively, according to the electronic analytical balance of the present disclosure. Figure 4B The electronic analytical balance according to the present disclosure is shown, and the load of the tray 111 is divided into 0g, 10g, 20g and 30g. Figure 3 Schematic diagram of the voltage across the first resistor 123 changing with time. Figure 4C The electronic analytical balance according to the present disclosure is shown, and the load of the tray 111 is divided into 0g, 10g, 20g and 30g. Figure 3 Schematic diagram of the change of the level of point B in the figure over time. Figure 4D The electronic analytical balance of the present disclosure is shown, and the schematic diagram of the charging and discharging current of the storage capacitor 131 changes with time when the load of the tray 111 is 0g, 10g, 20g and 30g, wherein the positive current indicates the discharging current, and the negative current indicates the charging current. Figure 4A to Figure 4D In the figure, the unit of the horizontal axis is the sampling interval. In the technical solution disclosed in the present invention, the sampling interval is 16.67us.

[0053] In addition, the following table shows the standard deviation value of the electronic analytical balance of the present disclosure after multiple sample tests:

[0054] Standard deviation value (sample size 1000)

[0055]

[0056] According to a second aspect of the present disclosure, a circuit device for an electronic analytical balance is provided. Figure 2As shown, the circuit device includes an electromagnetic coil drive circuit 120, a width-modulated pulse signal circuit module 210, and a metering circuit 150. The electronic analytical balance includes a balance mechanism 110, and the balance mechanism 110 includes: a weighing pan 111; an electromagnetic balance sensor 112 connected to the weighing pan 111; and a photoelectric detection circuit for detecting the balance state of the electromagnetic balance sensor 112. The electromagnetic coil drive circuit 120 includes: a PID controller 121 and a transistor switch 122, wherein the input end of the PID controller 121 is connected to the photoelectric detection circuit, and the output end of the PID controller 121 is connected to the base of the transistor switch 122, the collector of the transistor switch 122 is connected to the voltage source VCC, the emitter of the transistor switch 122 is connected to the first end of the coil 116 of the electromagnetic balance sensor 112, and a current is applied to the first end of the coil 116, and the second end of the coil 116 is connected to the floating potential node A. The width-modulated pulse signal circuit module 210 is connected to the floating potential node A, and is used to generate a width-modulated pulse signal corresponding to the current applied to the first end of the coil 116. Furthermore, the measuring circuit 150 is connected to the width-modulated pulse signal circuit module 210 to determine the mass of the load on the weighing pan 111 according to the width-modulated pulse signal.

[0057] Optionally, the width modulated pulse signal circuit module 210 includes: a charge and discharge circuit 130, a controllable current source 160 and a width modulated pulse signal circuit 140. The charge and discharge circuit 130 and the controllable current source 160 are respectively connected to the floating potential node A, so that when the controllable current source 160 is turned off, the coil 116 charges the charge and discharge circuit 130 through the floating potential node A, and when the controllable current source 160 is turned on, the coil 116 discharges from the charge and discharge circuit 130 through the floating potential node A; the width modulated pulse signal circuit 140 is connected to the charge and discharge circuit 130 to generate a width modulated pulse signal corresponding to the voltage output by the charge and discharge circuit 130; and the controllable current source 160 is also connected to the width modulated pulse signal circuit 140 to discharge the charge and discharge circuit 130 based on the width modulated pulse signal generated by the width modulated pulse signal circuit 140.

[0058] Optionally, the charge and discharge circuit 130 includes: an operational amplifier 132 and an energy storage capacitor 131. The first end of the energy storage capacitor 131 is connected to the floating potential node A, and the second end is connected to the pulse width modulation signal circuit 140; and the reverse input end of the operational amplifier 132 is connected to the floating potential node A, the forward input end is grounded, and the output end is connected to the second end of the energy storage capacitor 131.

[0059] Optionally, the inverting input terminal of the operational amplifier 132 is also grounded via a filter capacitor 133 .

[0060] Optionally, the pulse width modulation signal circuit 140 includes: a comparator 141 and a sawtooth wave generator 142. The positive input terminal of the comparator 141 is connected to the output terminal of the charge and discharge circuit 130, the reverse input terminal of the comparator 141 is connected to the sawtooth wave generator 142, and the output terminal of the comparator 141 is connected to the controllable current source 160.

[0061] Optionally, the positive input terminal of the comparator 141 is connected to the output terminal of the charge and discharge circuit 130 through a low-pass filter.

[0062] Optionally, the controllable current source 160 includes: a switching circuit 161 and a constant current source 162, wherein the control end of the switching circuit 161 is connected to the width modulation pulse signal circuit 140, and the output end is connected to the constant current source 162, so that the constant current source 162 is turned on or off based on the width modulation pulse signal generated by the width modulation pulse signal circuit 140.

[0063] For more information about the circuit device, please refer to the content described in the first aspect of this embodiment.

[0064] In summary, the technical solution disclosed in the present invention no longer outputs current to the coil of the electromagnetic balance sensor by controlling the current source through a width-modulated pulse signal, but uses the output voltage of the PID controller to control the current output by the power supply to the coil. Since the voltage output by the PID controller is a gradually increasing voltage signal, once the transistor switch is turned on, it will not be disconnected before the electromagnetic balance sensor reaches balance. Thus, the power supply VCC can continuously transmit current to the coil of the electromagnetic balance sensor, and will not cause the electromagnetic balance sensor to be excited by the step signal. In addition, the present invention adopts a pulse width modulation current circuit with double closed-loop control, decouples the PID controller and the current measurement hybrid circuit in the traditional measurement method, reduces the difficulty of PID controller parameter setting, avoids solving the transmission equation of the mechanical sensor and the balance detection system, and improves the control circuit response speed and current measurement accuracy. Without nonlinear correction of the measured data, the standard deviation of the original measurement data of the electronic analytical balance with a range of 31g is 2e-5g, reaching a million-division accuracy, which is far better than the original electronic analytical balance with the same circuit and sensor. Thus, the technical problem in the prior art that the electromagnetic balance sensor of the electronic analytical balance is stimulated by the step signal when the current is turned on and off, resulting in large detection signal noise, thereby affecting the accuracy and repeatability of the electronic analytical balance is solved.

[0065] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present disclosure. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0066] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0067] In the description of the present disclosure, it is necessary to understand that the orientation or positional relationship indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present disclosure; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0068] The above is only a preferred specific implementation of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present disclosure should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. An electronic analytical balance, comprising a balance mechanism (110), an electromagnetic coil drive circuit (120), a width-modulated pulse signal circuit module (210) and a metering circuit (150), wherein the balance mechanism (110) comprises: A weighing pan (111); an electromagnetic balance sensor (112) connected to the weighing pan (111); and a photoelectric detection circuit for detecting the balance state of an electromagnetic balance sensor (112), characterized in that: The electromagnetic coil drive circuit (120) comprises: a PID controller (121) and a transistor switch (122), wherein the input end of the PID controller (121) is connected to the photoelectric detection circuit, and the output end of the PID controller (121) is connected to the base of the transistor switch (122), the collector of the transistor switch (122) is connected to a voltage source (VCC), the emitter of the transistor switch (122) is connected to the first end of the coil (116) of the electromagnetic balance sensor (112), a current is applied to the first end of the coil (116), and the second end of the coil (116) is connected to a floating potential node (A), The width modulated pulse signal circuit module (210) is connected to the floating potential node (A) and is used to generate a width modulated pulse signal corresponding to the current applied to the first end of the coil (116), and The metering circuit (150) is connected to the width-modulated pulse signal circuit module (210) and is used to determine the mass of the load on the weighing pan (111) according to the width-modulated pulse signal.

2. The electronic analytical balance according to claim 1, characterized in that: The width-modulated pulse signal circuit module (210) comprises: a charge-discharge circuit (130), a controllable current source (160) and a width-modulated pulse signal circuit (140), wherein The charge and discharge circuit (130) and the controllable current source (160) are respectively connected to the floating potential node (A), so that the charge and discharge circuit (130) performs charge and discharge based on the coil (116) and the controllable current source (160); The width modulated pulse signal circuit (140) is connected to the charge and discharge circuit (130) to generate a width modulated pulse signal corresponding to the voltage output by the charge and discharge circuit (130); and The controllable current source (160) is also connected to the width modulated pulse signal circuit (140), and controls the charge and discharge circuit (130) to perform charge and discharge based on the width modulated pulse signal generated by the width modulated pulse signal circuit (140).

3. The electronic analytical balance according to claim 2, characterized in that: The charging and discharging circuit (130) comprises: an operational amplifier (132) and an energy storage capacitor (131), wherein The first end of the energy storage capacitor (131) is connected to the floating potential node (A), and the second end is connected to the width modulation pulse signal circuit (140); and The operational amplifier (132) has a reverse input terminal connected to the floating potential node (A), a forward input terminal connected to ground, and an output terminal connected to the second terminal of the energy storage capacitor (131).

4. The electronic analytical balance according to claim 3, characterized in that: The inverting input terminal of the operational amplifier (132) is also grounded via a filter capacitor (133).

5. The electronic analytical balance according to claim 2, characterized in that: The width-modulated pulse signal circuit (140) comprises: a comparator (141) and a sawtooth wave generator (142), wherein The positive input end of the comparator (141) is connected to the charge and discharge circuit (130), the negative input end of the comparator (141) is connected to the sawtooth wave generator (142), and the output end of the comparator (141) is connected to the controllable current source (160).

6. The electronic analytical balance according to claim 5, characterized in that: The width-modulated pulse signal circuit (140) further comprises a low-pass filter, wherein an input end of the low-pass filter is connected to the charge-discharge circuit (130), and an output end of the low-pass filter is connected to a positive input end of the comparator (141).

7. The electronic analytical balance according to claim 2, characterized in that: The controllable current source (160) comprises: a switch circuit (161) and a constant current source (162), wherein The control end of the switch circuit (161) is connected to the width-modulated pulse signal circuit (140), and the output end is connected to the constant current source (162), so that the constant current source (162) is turned on or off based on the width-modulated pulse signal generated by the width-modulated pulse signal circuit (140).

8. A circuit device for an electronic analytical balance, comprising an electromagnetic coil drive circuit (120), a width-modulated pulse signal circuit module (210), and a metering circuit (150), wherein the electronic analytical balance comprises a balance mechanism (110), and the balance mechanism (110) comprises: A weighing pan (111); an electromagnetic balance sensor (112) connected to the weighing pan (111); and a photoelectric detection circuit for detecting the balance state of an electromagnetic balance sensor (112), characterized in that: The electromagnetic coil drive circuit (120) comprises: a PID controller (121) and a transistor switch (122), wherein the input end of the PID controller (121) is connected to the photoelectric detection circuit, and the output end of the PID controller (121) is connected to the base of the transistor switch (122), the collector of the transistor switch (122) is connected to a voltage source (VCC), the emitter of the transistor switch (122) is connected to the first end of the coil (116) of the electromagnetic balance sensor (112), a current is applied to the first end of the coil (116), and the second end of the coil (116) is connected to a floating potential node (A), The width modulated pulse signal circuit module (210) is connected to the floating potential node (A) and is used to generate a width modulated pulse signal corresponding to the current applied to the first end of the coil (116), and The metering circuit (150) is connected to the width-modulated pulse signal circuit module (210) and is used to determine the mass of the load on the weighing pan (111) according to the width-modulated pulse signal.

9. The circuit arrangement according to claim 8, characterized in that The width-modulated pulse signal circuit module (210) comprises: a charge-discharge circuit (130), a controllable current source (160) and a width-modulated pulse signal circuit (140), wherein The charge-discharge circuit (130) and the controllable current source (160) are respectively connected to the floating potential node (A), so that the coil (116) charges the charge-discharge circuit (130) through the floating potential node (A), and the controllable current source (160) discharges the charge-discharge circuit (130) through the floating potential node (A); The width modulated pulse signal circuit (140) is connected to the charge and discharge circuit (130) to generate a width modulated pulse signal corresponding to the voltage output by the charge and discharge circuit (130); and The controllable current source (160) is also connected to the width modulated pulse signal circuit (140) and discharges the charge and discharge circuit (130) based on the width modulated pulse signal generated by the width modulated pulse signal circuit (140).

10. The circuit arrangement according to claim 9, characterized in that The charging and discharging circuit (130) comprises: an operational amplifier (132) and an energy storage capacitor (131), wherein The first end of the energy storage capacitor (131) is connected to the floating potential node (A), and the second end is connected to the width modulation pulse signal circuit (140); and The operational amplifier (132) has a reverse input terminal connected to the floating potential node (A), a forward input terminal connected to ground, an output terminal connected to the second terminal of the energy storage capacitor (131), and wherein The width-modulated pulse signal circuit (140) comprises: a comparator (141) and a sawtooth wave generator (142), wherein The positive input terminal of the comparator (141) is connected to the charge and discharge circuit (130), the negative input terminal of the comparator (141) is connected to the sawtooth wave generator (142), and the output terminal of the comparator (141) is connected to the controllable current source (160), and wherein The controllable current source (160) comprises: a switch circuit (161) and a constant current source (162), wherein The control end of the switch circuit (161) is connected to the width-modulated pulse signal circuit (140), and the output end is connected to the constant current source (162), so that the constant current source (162) is turned on or off based on the width-modulated pulse signal generated by the width-modulated pulse signal circuit (140).

Images