CN104501925A

CN104501925A - Simulation lowpass filter circuit of medicine bottling line dynamic weighing system

Info

Publication number: CN104501925A
Application number: CN201410157759.0A
Authority: CN
Inventors: 黄劼; 李俊国; 于少航; 郭锐
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2014-04-21
Filing date: 2014-04-21
Publication date: 2015-04-08
Anticipated expiration: 2034-04-21
Also published as: CN104501925B

Abstract

The invention relates to a base hardware circuit simulation lowpass filter circuit based on a medicine bottling line real-time weighing system. A system front-end acquisition channel simulation signal circuit uses two-stage amplification configuration. A MAX293 filter is disposed between two amplifiers, and is used to extract a weighing signal of medicine. After second time amplification, an analog signal is converted to a standard 5V analog signal, and finally the signal is input a 16-bit A/D converter. The MAX293 is not only the core of the analog circuit, but also the core of the whole bottom layer module. The core mission of the MAX293 is to filter forced vibration interference of a medicine bottling line. The MAX293 can select two methods to provide filtering clock frequency. One method is to directly connect a capacitor on a CLK pin, forming an RC oscillation circuit with an internal resistor, and inputting a triangular wave to the MAX293. The other method is to provide a square wave signal by an external logic device. The analog circuit provides filtering beginning and stop signals in a manner of using a single-chip microcomputer to provide square signals. A MAX4486 is selected to be used as the secondary amplifier of the analog circuit, and the interior of the MAX4486 is provided with two operational amplifiers of an operational amplifier A and an operational amplifier B, and the amplifier formed by the operational amplifier A is used as the secondary amplifier of the analog circuit.

Description

Drug product filling lines dynamic weighing system analogue low pass filtering circuit

Technical field

The present invention relates to a kind of analogue low pass filtering circuit, be specifically related to a kind of bottom hardware analogue low pass filtering circuit being applicable to drug product filling lines real-time weighing system.

Background technology

Medicine metering packing is the important step of pharmaceutical production.Whether accurate prestige and the economic benefit singly not having influence on enterprise of medicine weighing and bagging, is more related to the life security of user.Pharmaceutical industry generally adopts the artificial mode inspected by random samples afterwards to realize the control to filling amount, and this can not ensure the accuracy of every bottle of drug metering, is also an impediment to the production efficiency of medicine enterprise.At present, medicine mainly can be divided into graininess, liquid state and Powdered 3 kinds of forms, and wherein powdered drug causes the deviation of filling amount because its minimum form is very easily subject to outside disturbance on filling line.But the domestic research at powdered drug canning line dynamic weighing system is also in the starting stage, there is no a set of system that can be practical.The research and development of this technology contribute to the quality controlling powdered drug in source, to improving the production efficiency of medicine enterprise and ensureing that the health of patient is all significant.Drug product filling lines dynamic weighing system comprises 1 host computer as man-machine interface and data processing and bottom hardware system, and bottom hardware system is made up of 1 cover motherboard and 8 cover front-end modules.Highlight bottom hardware system, for gathering the voltage signal that LOAD CELLS senses, and be converted into digital signal and pass to host computer and do further digital filtering process.The voltage signal experienced due to LOAD CELLS only has several millivolts, very easily be subject to the interference of external environment condition, front-end module in bottom hardware system just need carry out simulating signal filtering process to the original signal of sensor, being mingled with the noises such as the vibration interference of high frequency interference, common mode interference and canning line in the signal to reaching filtering, extracting comparatively clean sensor signal.

Summary of the invention

The design mainly realizes the bottom hardware analogue low pass filtering circuit design of the filling on-line weighting system of medicine.In order to realize filtering object, front-end collection channel analog signal circuit adopts two-stage to amplify framework, MAX293 wave filter is placed between twice amplification, for extracting the weighing-up wave of medicine, after second time is amplified, simulating signal is just converted into standard 5V simulating signal, and last signal inputs 16 A/D converters and turns.Secondary amplifies can also be avoided useless noise being amplified to 5V and flogging a dead horse, weighing-up wave is amplified to the trigger voltage of MAX293 by first stage amplifier, secondary amplifies in order to improve signal gain and the filtering MAX293 wave of oscillation, and increases the load-carrying ability of simulating signal.Adopt this kind of design proposal to process the advantage of weighing-up wave: circuit power consumption is little, highly sensitive, and structure is simple.

The core that MAX293 is not only mimic channel is also the core of whole bottom module, and its core missions are forced vibration interference of filtering drug product filling lines.MAX293 is the oval Chebyshev filters in eight rank, has precipitous rising edge, makes its amplitude-versus-frequency curve more close to rectangle, be extremely suitable for rapid weighing; But have stronger undulate quantity in passband, and rising time is shorter, undulate quantity is larger, namely the overshoot of step response is larger, is unfavorable for reducing stabilization time.

MAX293 is optional provides filtering clock frequency in two ways, and one directly on CLK pin, connects electric capacity, forms RC oscillatory circuit with the resistance of inside, inputs triangular wave to MAX293; Another kind provides square-wave signal by external logic device.This mimic channel adopts single-chip microcomputer to provide the mode of square-wave signal to provide filtering signal all the time.

The two-stage amplifier of mimic channel selects MAX4486, and there are amplifier A and amplifier B two operational amplifiers in its inside, and the amplifier that amplifier A forms is as the two-stage amplifier of mimic channel.Signal singly will not done secondary and amplify process, the vibratory output of filtering MAX293 step response passband by the two-stage amplifier of mimic channel, and can not amplify the bias voltage be carried on analogue amplifier.

Accompanying drawing explanation

Fig. 1 is front-end collection Channel Digital Circuitry framework;

Fig. 2 is front-end collection tunnels analogy circuit framework;

Fig. 3 is analogue amplifier INA128 mimic channel figure;

Fig. 4 is RS-485 interface circuit figure.

Embodiment

Below in conjunction with drawings and Examples, the present invention is further described.

Fig. 1 is front-end collection Channel Digital Circuitry framework, and the digital circuit of front-end collection passage comprises 485 telecommunication circuits and microprocessor two parts.485 telecommunication circuits and the communication submodule of front-end collection submodule are similar, need to be connected with high speed photo coupling after 6N137 connects to be connected with single-chip microcomputer again.But micro-process of front-end collection submodule is endowed more mission, device, also will to the data mean value filtering gathered, the setting filter cutoff frequency of MAX293 and the switch of control AD converter except Control on Communication.Eight road front-end collection passages are all designed with untreated chip, being the work efficiency in order to provide passage on the one hand, effectively can intercepting crosstalk on the other hand.When the above front-end collection passage of two-way works simultaneously, single-chip microcomputer will input High frequency filter cutoff frequency to MAX293 simultaneously, if there is coupling circuit in passage and interchannel on power circuit, obscuring of signal will be there is, impact is greatly produced on the output of analogue signal circuit, the waveform that the simulating signal frequence of exposure collected is fixing.Therefore, each paths is all designed with single-chip microcomputer and insulating power supply module, realizes working alone of passage, cuts off coupling path from physical circuit.Analogue signal circuit also collects other high frequency spurious signals while gathering drug quality signal, the effect of MAX293 is the low frequency forced vibration interference of filtering canning line, in order to filtering high frequency clutter interference native system adopts the mode of 1024 groups of data mean value filtering process, experimentally the data program effectively achieves the effect of filtering spurious signal interference.

Fig. 2 is front-end collection tunnels analogy circuit framework, and front-end collection channel analog signal circuit adopts two-stage to amplify framework.There is serious hyperharmonic vibration in the output due to MAX293, if adopt the method for once amplifying, the oscillation period exported causing MAX293 is elongated and amplitude change is large, extend the Time Created of signals collecting submodule and the stability of influential system, so minimizing system reaches the stable time, front end acquisition module adopts two-stage to amplify framework.

MAX293 wave filter is placed between twice amplification, and for extracting the weighing-up wave of medicine, after second time is amplified, simulating signal is just converted into standard 5V simulating signal, and last signal inputs 16 A/D converters and turns.Secondary amplifies can also be avoided useless noise being amplified to 5V and flogging a dead horse, weighing-up wave is amplified to the trigger voltage of MAX293 by first stage amplifier, secondary amplifies in order to improve signal gain and the filtering MAX293 wave of oscillation, and increases the load-carrying ability of simulating signal.

Fig. 3 is analogue amplifier INA128 mimic channel figure, and the mimic channel output voltage of front-end module only has several millivolts, and therefore the total magnification of mimic channel is set as 990 times, and wherein the enlargement factor of first order amplifier INA128 is 330 times.In figure, C7, C8, C9, R3 and R4 form rfi filter, not only can effectively filtering outside radio frequency interference, and have intercepted amplifier and LOAD CELLS because of the existence of R3 and R4, add the overload protection ability of amplifier.INA128 has the common-mode rejection ratio being not less than 120dB, in order to not affect the common mode ability always of amplifier, C8/R3 and C9/R4 all Striking symmetry in numerical value, specification, position and wiring.Electric capacity C7 is connected across the positive-negative input end of amplifier, connect with C8 and C9 Capacitance parallel connection, C7 effectively can reduce the non-match error that C8 and C9 causes, and the capacitance of general C7 is ten times of C8 or C9, so just the non-match error of C8 and C9 can be reduced 20 times.

The filter network of C8/R3, C9/R4 and C7 composition is used for the differential mode Radio frequency interference (RFI) of filtering amp.in, the interference namely between amplifier positive-negative input end.

The filtering circuit of C8/R3 or C9/R4 composition is used for the common mode Radio frequency interference (RFI) of filtering amp.in, and namely amplifier positive input terminal or negative input end are relative to the interference on ground.

The output resistance of LOAD CELLS is about 350 Ω, according to impedance matching principle, the resistance of R3 and R4 is set as 1K Ω, the capacitance choosing C8 and C9 is 1000pF, the capacitance of C7 is 0.01 μ F, the differential mode filter cutoff frequency that can be obtained mimic channel front-end filtering network by formula is 7571.4Hz, and common mode filtering cutoff frequency is 159KHz.

The transition time of LOAD CELLS unit-step response is 10ms, and Time Created is more than 100ms.The slew rate of INA128 is 4V/ μ s, and Time Created when gain is 1000 times is 80 μ s, so INA128 can meet system requirements completely in the speed of response.

The maximum zero point drift of INA128 is ± 125 μ V, namely when positive-negative input end all ground connection time, the voltage of output terminal is ± 125 μ V.If LOAD CELLS input is too small, and when zero point drift is negative value, the output of mimic channel may be made to be negative value.Therefore need reference edge (REF) input offset voltage at INA128, compensate the zero point drift voltage that INA128 may be negative value, the voltage follower that the bias voltage circuit in native system is made up of the B amplifier of MAX4486 provides, and voltage is 1V.

Be illustrated in figure 4 RS-485 interface circuit figure, the amplifying circuit in the same way that the output signal input of MAX293 is made up of R8, R9, R10 and amplifier A, enlargement factor is three times.The bias voltage of the negative input termination INA128 of amplifier A, can avoid bias voltage also to amplify three times.Electric capacity C37 be connected across amplifier A negative input and between exporting, to can be considered and R9, R10, amplifier A form single order low-pass active filter, its filter cutoff frequency formula:.

Claims

1. the present invention relates to a kind of analogue low pass filtering circuit, be specifically related to a kind of bottom hardware analogue low pass filtering circuit being suitable for drug product filling lines real-time weighing system.

2. front-end collection channel analog signal circuit adopts two-stage to amplify framework.

3. analogue low pass filtering circuit as claimed in claim 1, is characterized in that: MAX293 wave filter is placed between twice amplification.

4. as claim 1 or analogue low pass filtering circuit according to claim 3, it is characterized in that: weighing-up wave is amplified to the trigger voltage of MAX293 by first stage amplifier, secondary amplifies in order to improve signal gain and the filtering MAX293 wave of oscillation, and increases the load-carrying ability of simulating signal.

5. analogue low pass filtering circuit as claimed in claim 1, is characterized in that: adopt single-chip microcomputer to provide the mode of square-wave signal to provide filtering clock signal.

6. analogue low pass filtering circuit as claimed in claim 1, is characterized in that: design photoelectrical coupler is for raising the voltage clock signal of single-chip microcomputer.

7. analogue low pass filtering circuit as claimed in claim 1, it is characterized in that: adopt two-stage amplifier MAX4486, the amplifier that inner amplifier A forms is as the two-stage amplifier of mimic channel.