Background technology
Traditional electronic weighing device is divided into piezoelectric forces sensing weighing device and resistance-strain type weighing device; Piezoelectric force transducer is mainly used in dynamic weighing, and it utilizes the purpose that the measurement of alternation electric charge is reached ergometry or weight; This weighing device requires the change in charge rate to surpass certain frequency, and this has just limited piezoelectric force transducer can't realize the Static Contact force measurement.When existing piezoelectric force transducer is weighed under being used to static environment or quasi-static environments, generally directly do not utilize piezoelectric principle to realize yet, but utilize other characteristic, such as surface wave frequency or crystal oscillator frequency etc., and these weighing device complex structures, cost are higher, and be not easy to carry.
The resistance-strain type electronic weighing device, because its sensor bulk is big, the support circuit power consumption is many, own wt is bigger again, is not easy to carry.
U.S. Pat 6812413 discloses a kind of piezoelectric type weighing device, its basic structure is that the matrix upper support a cantilever design, load table places on the cantilever design, hollows out in the middle of the cantilever design two piezoelectric ceramic pieces are housed, and the space is arranged in the middle of two piezoelectric ceramic pieces.When load table is added with load, the front end piezoelectric ceramic piece is stressed to be moved, thereby causes two changes of voids between the piezoelectric ceramic piece, makes system frequency change, and catch this variation by the metering circuit that oscillator, frequency mixer are formed, just can record the weight of load.But, this weight-measuring device complex structure, production cost is higher.
Therefore, prior art awaits improving and development.
Summary of the invention
Problem to be solved by this invention is to provide a kind of metering circuit and device thereof of piezoelectricity induction type electronic weighing, realizes weigh problem down, and the contour structures of this electronic weighing device is little in order to solve static environment, and is cheap for manufacturing cost, is easy to carry.
In order to solve the problems of the technologies described above, technical scheme of the present invention is as follows:
The invention provides a kind of piezoelectricity induction type electronic weighing device, wherein, on described metering circuit, be provided with piezoelectric sensor, be used under the situation of the effect of being under pressure, exporting induced charge; Reach the charge integration amplifying circuit, be used to reduce the electric leakage speed of described induced charge; Described charge integration amplifying circuit is connected with described piezoelectric sensor, is used to receive the induced charge of described piezoelectric sensor output, and described induced charge is carried out exporting simulating signal to described analog to digital converter after the processing and amplifying; Described piezoelectric sensor is a piezoceramic transducer, and according to the time response of described piezoceramic transducer, and the time constant of described induced charge is arranged on 10
5More than.
Described metering circuit, wherein, described charge integration amplifying circuit comprises an operational amplifier, electric capacity (C) and resistance (R), two signal input parts of described operational amplifier are connected with the two ends of described piezoelectric sensor respectively, are used for the described induced charge that receives is carried out processing and amplifying; Described electric capacity (C) parallel connection is at the signal input part and the signal output part thereof of described operational amplifier; One end of described resistance (R) is serially connected in another signal input part of described operational amplifier, the other end ground connection of described resistance (R).
Described metering circuit, wherein, described electric capacity (C) is polystyrene electric capacity, its appearance value is 0.1 microfarad; The resistance of described resistance (R) is at least 10
13Ohm; The input impedance of described operational amplifier is 5 * 10
12Ohm.
Described metering circuit wherein, also is provided with single-chip microcomputer on described metering circuit, this single-chip microcomputer comprises time constant match unit, be used for time constant is carried out least square fitting, and output match signal; And arithmetic element, be connected with described time constant match unit, be used for after receiving the match signal, this match signal being compensated calculation process, and the output result.
The present invention also provides a kind of piezoelectricity induction type electronic weighing device, wherein, described electronic weighing device comprises a metering circuit, on described metering circuit, be provided with piezoelectric sensor, two signal input parts in the described metering circuit are connected with the two ends of described piezoelectric sensor respectively, are used for exporting induced charge under the situation of the effect of being under pressure; Reach the charge integration amplifying circuit, be used to reduce the electric leakage speed of described induced charge; Described charge integration amplifying circuit is connected with described piezoelectric sensor, is used to receive the induced charge of described piezoelectric sensor output, and described induced charge is carried out exporting simulating signal to described analog to digital converter after the processing and amplifying; Described piezoelectric sensor is a piezoceramic transducer, and according to the time response of described piezoceramic transducer, and the time constant of described induced charge is arranged on 10
5More than.
Described piezoelectricity induction type electronic weighing device, wherein, described charge integration amplifying circuit comprises an operational amplifier, electric capacity (C) and resistance (R), two signal input parts of described operational amplifier are connected with the two ends of described piezoelectric sensor respectively, are used for the described induced charge that receives is carried out processing and amplifying; Described electric capacity (C) parallel connection is at the signal input part and the signal output part thereof of described operational amplifier; One end of described resistance (R) is serially connected in another signal input part of described operational amplifier, the other end ground connection of described resistance (R).
Described piezoelectricity induction type electronic weighing device, wherein, described electric capacity (C) is polystyrene electric capacity, its appearance value is 0.1 microfarad; The resistance of described resistance (R) is at least 10
13Ohm; The input impedance of described operational amplifier is 5 * 10
12Ohm.
Described piezoelectricity induction type electronic weighing device wherein, also is provided with single-chip microcomputer on described metering circuit, this single-chip microcomputer comprises time constant match unit, be used for time constant is carried out least square fitting, and output match signal; And arithmetic element, be connected with described time constant match unit, be used for after receiving the match signal, this match signal being compensated calculation process, and the output result.
Described piezoelectricity induction type electronic weighing device, wherein, this electronic weighing device also comprises an objective table, be arranged on the described piezoelectric sensor, and with described piezoelectric sensor between adopt the contact dismounting to be connected.
Piezoelectricity induction type electronic weighing device provided by the invention, by a charge integration amplifying circuit is set on its metering circuit, reduces electric charge electric leakage speed, thereby realize the weighing measurement under the static environment, and need not additionally to increase components and parts, further reduced manufacturing cost; Simultaneously, this weighing device volume is little, is easy to carry.
Embodiment
Below in conjunction with accompanying drawing, preferred embodiment of the present invention is described in further detail.
As shown in Figure 1, the invention provides a kind of metering circuit of piezoelectricity induction type electronic weighing, described metering circuit is provided with piezoelectric sensor 110, charge integration amplifying circuit 120, analog to digital converter 130, single-chip microcomputer 140, power supply 150, crystal oscillator 160 and display screen 170, and described single-chip microcomputer 140 is connected with described power supply 150, crystal oscillator 160, display screen 170 and analog to digital converter 130 respectively, and described piezoelectric sensor 110 is connected with described analog to digital converter 130; Wherein, described power supply 150 provides power supply for whole metering circuit, and is controlled by gauge tap, and this power supply is 5 volts of direct supplys; Described crystal oscillator 160 provides clock signal for single-chip microcomputer 140.
Described piezoelectric sensor 110 is a piezoceramic transducer, and the contour structures of this piezoelectric sensor 110 is rounded, and diameter is less than 12mm, and thickness is subjected to heavy back to produce deformation, and will changes its impedance less than 3mm, and driving voltage changes, and produces induced charge.Because this induced charge amount is very little, can not measure with general instrument, because the input impedance of general measurement instrument is smaller, the electric charge on the piezoelectric patches can be transfused to resistance during by metering circuit and leak rapidly and introduce measuring error.Therefore, described induced charge will be transported to and carry out processing and amplifying in the charge integration amplifying circuit 120.
Described charge integration amplifying circuit 120 is in order to the high time constant, the low-leakage current that improve induced charge and avoid time drift etc.This charge integration amplifying circuit 120 is made up of operational amplifier 121, capacitor C 122 and resistance R 123, on the signal input part and signal output part that are attempted by described operational amplifier 121 of described capacitor C 122, one end of described resistance R 123 is serially connected in another signal input part of described operational amplifier 121, other end ground connection, and operational amplifier 121, capacitor C 122 and resistance R 123 constitute a time constant integrating circuit.
In view of the time response of piezoceramic transducer can be expressed from the next:
E(t)=F*D*e
(-t/RC) (1)
Wherein: E is the voltage of piezoceramic transducer output; T is the time; F is the power under pressure of carrying; The product of D piezoelectricity conversion coefficient and electric charge amplification coefficient; RC is that metering circuit discharges and recharges time constant.
By formula (1) as can be seen, time constant is big more, and the speed of system's generation electric leakage is just slow more.As seen, when metering circuit equivalent time constant during greater than certain value, electric charge leaks the measurement effect influence of system and little, and the operational amplifier of selecting for use in the present embodiment 121 adopts the NJU7009 types, and its input impedance is 5*10
12Ohm, by the serial connection of resistance R 123, the input impedance of operational amplifier 121 reaches 10
14Ohm; And electric capacity 122 capacitances are 100 nanofarads, much smaller than the electric capacity of piezoceramic transducer, so circuit equivalent electric capacity is 100 nanofarads, therefore, can obtain 10 in theory
7The time constant of second, as shown in Figure 2, by drawing the curve of measuring-signal along with the Measuring Time drift, time constant is to the influence of measure of system performance as can be seen, and horizontal ordinate express time, unit are second, ordinate is represented the maintenance degree of signal, is represented by number percent.
In the accompanying drawing 2, curve 1 express time constant is 100 metering circuit signal attenuation figure, and as can be seen, measuring-signal is difficult to accurately finish measuring process along with the time decays fast; Curve 2 express time constants are 10
4Metering circuit signal attenuation figure, the horizontal ordinate scope at 1800 seconds, its curve approximation is linear, signal attenuation is not obvious; And curve 3 express time constants are 10
5Metering circuit signal attenuation figure, do not see relaxation phenomenon in the drawings substantially.Therefore, when the metering circuit time constant more than or equal to 10
5The time, in 1800 seconds scope, can obtain more stable measuring-signal, this measuring-signal can satisfy under the static environment check weighing force measurement needs.Like this, induced charge is exported a simulating signal to described analog to digital converter 130 after charge integration amplifying circuit 120 processing and amplifying.
Described analog to digital converter 130 becomes digital signal with the analog signal conversion that receives, and export this digital signal to described single-chip microcomputer 140, carry out the match computing by the time constant in 140 pairs of digital signals that receive of this single-chip microcomputer, calculate suffered bearing capacity on the described voltage induced sensor 110.
Wherein, described single-chip microcomputer 140 comprises time constant match unit and arithmetic element, and the single-chip microcomputer 140 in the present embodiment adopts the ATMEG8 type.Described time constant match unit is used for the time constant of digital signal is carried out match, and output match signal is to described arithmetic element, be connected with described time constant match unit, be used for after receiving the match signal, this match signal being carried out calculation process, and the output result.Described time constant match unit adopts least square fitting to try to achieve time constant, such as, to produce induced charge and release gradually after loading on the bearing capacity removal on the piezoelectric sensor 110,, try to achieve the time constant of metering circuit by the signal attenuation curve that measures; When after adding bearing capacity on the piezoelectric sensor 110, obtain a new measuring-signal curve, and according to as shown in Figure 2 t-E (t) data result and formula (1), counter pushing away obtains F, according to the measuring accuracy demand,, and start the curve fitting algorithm of deriving then by time constant by described arithmetic element, measured value is compensated, according to the curve that obtains after compensation bearing capacity again.For example, the sampling interval at 10 seconds, the signal attenuation amplitude surpasses 5%, and this moment, measuring accuracy did not just reach 5% demand, according to the time constant that obtains actual measurement profile was compensated, and 10 seconds wayside signaling attenuation amplitudes can be decreased to 1% even lower.Subsequently, described single-chip microcomputer 140 will calculate the bearing capacity that obtains and export demonstration on the display screen 170 to, and shown numerical value is the bearing capacity that is born on the piezoelectric sensor 110 on this display screen 170.
The present invention also provides a kind of piezoelectricity induction type electronic weighing device that uses above-mentioned metering circuit, as shown in Figure 3, comprises shell cavity 310, objective table 320, pressure transfer 330, brace table 340 and metering circuit 350; Described shell cavity 310 is a square structure, thickness is about 12mm, and on the upper surface of described shell cavity 310, offer a loading hole 311 that is used to install described objective table 320, be used to install the display aperture 312 of the display screen on the metering circuit shown in being arranged at, and be used to install the switch hole 313 of power switch button, as shown in Figure 4.
Described brace table 340 is arranged in the described shell cavity 310, and place described loading hole 310 under, and the upper surface of described brace table 340 is provided with the piezoelectric sensor of metering circuit 350 parts, this piezoelectric sensor is connected with other parts in the metering circuit 350 by lead, such as, the charge integration amplifying circuit is used to produce induced charge.
Upper surface at described piezoelectric sensor 110 is provided with pressure transfer 330, and this pressure transfer 330 is to make by having certain flexible material, when device is weighed, in order to form a quasi-static environments.Upper surface in described pressure transfer 330 is provided with objective table 320, is used to hold object to be weighed.According to the needs of the object of weighing, described objective table 320 can be made tabular, plate-like, and adopts between objective table 320 and the pressure transfer 330 and removably connect, and is convenient to change difform objective table.
The power control switch button that is used for control survey circuit 350 is provided with described switch hole 313, comprises and releasing the button and cut-off button, as shown in Figure 4.
In sum, piezoelectricity induction type electronic weighing device provided by the invention is by being provided with a charge integration amplifying circuit on its metering circuit, reduce electric charge electric leakage speed, thereby the weighing measurement under the realization static environment, and need not additionally to increase components and parts, further reduced manufacturing cost; Simultaneously, this weighing device volume is little, is easy to carry.
Should be understood that, for those of ordinary skills, can be improved according to the above description or conversion, and all these improvement and conversion all should belong to the protection domain of claims of the present invention.