Air-anion concentration detector
The utility model relates to a kind of detecting instrument, is specially the pick-up unit detecting air freshness.
Air-anion concentration detector is applicable to detect the device of contained negative ion concentration in unit volume in air.Air-anion concentration detector obtains by ion trap the size of current that in certain volume air, contained negative ion is corresponding, then the size of this electric current is detected by microgalvanometer, the size of current recorded by microgalvanometer finally by controller is converted into the number of contained negative ion in unit volume air, China introduces anion generator from the eighties, and the art technique level of present stage maintains an equal level with developed country.At present, negative aeroion pick-up unit is portable and outdoor measurement two type mainly, but the measurement range of portable unit is little, precision is not high, and the volume of outdoor measurement mechanism is too large.These problems mainly come from precision and the measurement range of micro-this module of current detecting.
As shown in Figure 1, the designed parameter in this schematic diagram comprises existing air-anion concentration detector structure principle chart:
I---corresponding electric current (A),
Net sectional area (the cm of A---gatherer
f---the flow velocity (cm/s) of air in gatherer,
Q---quantities of charge (1.6 × 10
N---air-anion concentration (ions/cm
Wherein, the net sectional area A of gatherer is the parameter set, the flow velocity v of air in gatherer
fit is the parameter obtained by fluid analysis after setting the speed of fan, we think the negative charge of a negative aeroion band unit, quantities of charge q is a physical quantity constant, namely negative aeroion with electricity, corresponding electric current I is detected by microgalvanometer and obtains.The electric charge that in unit air volume, electric charges contained amount is corresponding is obtained by the electric current recording the quantity of electric charge contained in certain volume air corresponding, thus the number of contained negative ion in air unit volume can be obtained, i.e. the concentration of negative aeroion: N=I/ (qAV
f).Emphasis is wherein microgalvanometer, be that tens femto-amperes (fA) are to tens microamperes (μ A) by obtaining the required range of current measured to the estimation of negative aeroion, make the precision of air-anion concentration detector reach 1 ion, namely the precision of micro-current detecting will reach 1fA.The problem that so will solve now is measurement range and the measuring accuracy of microgalvanometer, in existing airion concentration detects, the precision comparison measured is low, display measurement result needs manually to transfer the files, and such equipment use is not very convenient, in portable air Ion Density Measurement Instrument, due to the restriction of equipment scale, much smaller relative to outdoor measurement of the net sectional area of gatherer, wants to reach identical precision, just has higher requirement to micro-current detection module.
Utility model content
Technical purpose of the present utility model is the deficiency existed for prior art, provides a kind of scheme can improving the micro-current detection module measuring accuracy of air-anion concentration detector and measurement range.
Technical scheme disclosed in the utility model is:
Air-anion concentration detector, is provided with ion trap and microgalvanometer, it is characterized in that:
Described microgalvanometer comprises change-over switch module, zeroing module, I-V modular converter, low-pass filtering module, voltage amplification module, filtration module, A/D modular converter, control module and display module;
Described I-V modular converter, voltage amplification module, filtration module, A/D modular converter, control module connect in turn, described I-V modular converter is connected with ion trap, described low-pass filtering module, zeroing module are connected with I-V modular converter, described change-over switch module is connected with I-V modular converter and control module connects, and described display module is connected with described control module;
Described I-V modular converter is provided with a simulation amplifier and is connected in parallel on three road feedback resistances of simulation amplifier inverting input and output terminal both sides thereof, the inverting input of described simulation amplifier is connected with current signal input end to be turned, described feedback resistance separately with a Capacitance parallel connection, the connecting circuit between each feedback resistance and current signal input end to be turned is serially connected with a change-over switch separately; , in three road feedback resistances, the resistance value of the first feedback resistance, the second feedback resistance, the 3rd feedback resistance differs the order of magnitude of 1000 times successively.
Further technical scheme also comprises:
As preferably, the resistance value of three road feedback resistances can get 100G Ω, 100M Ω, 100K Ω respectively.
The in-phase input end ground connection of described simulation amplifier, the circuit connecting its inverting input and output terminal is serially connected with protective resistance.
As preferably, be connected in parallel on the ceramic condenser of the electric capacity employing temperature compensating type at feedback resistance two ends.
As preferably, described change-over switch adopts the dry-reed relay putting teflon pipe.
As preferably, described simulation amplifier can adopt any one in LMC6062A, LMC6042, INA116.
The utility model improves the measuring accuracy of microgalvanometer by circuit design and realizes measuring the automatic switchover of range, reaches the object that air-anion concentration testing result directly accurately shows, easy to use.
Accompanying drawing explanation
Fig. 1 is the structural representation of air-anion concentration detector;
Fig. 2 is the modular structure schematic diagram of microgalvanometer;
Fig. 3 is the electrical block diagram of I-V modular converter and change-over switch module in Fig. 2.
In order to illustrate the technical solution of the utility model and technical purpose, below in conjunction with drawings and the specific embodiments, the utility model is described further.
As the air ion collector be made up of collecting board and polarising sheet of Fig. 1, by the effect of fan, air is blasted in air ion collector, applying polarizing voltage to gatherer makes collecting board positively charged press the electronegative pressure of polarising sheet, thus the negative ion in air all forms one weak current to collecting board deflection on collecting board, then record the size of this electric current by microgalvanometer.Due to electric current very little, in different ecologic environments, the concentration of negative aeroion differs multiple order of magnitude, and the scope of so corresponding electric current also can differ multiple order of magnitude, therefore directly can not be recorded by common reometer, need to be measured by microgalvanometer.
As shown in Figure 2, described microgalvanometer is provided with change-over switch module 2, zeroing module 3, I-V modular converter 4 (current/voltage modular converter), low-pass filtering module 5, voltage amplification module 6, filtration module 7, A/D modular converter 8 (D/A switch module), control module 9 and display module 10.Described I-V modular converter 4, voltage amplification module 6, filtration module 7, A/D modular converter 8, control module 9 connect in turn, described I-V modular converter 4 is connected with the collecting board of ion trap, described low-pass filtering module 5, zeroing module 3 are connected with I-V modular converter 4, described change-over switch module 2 be connected with I-V modular converter 4 and control module 9 connect, described display module 10 is connected with described control module 9.
Described I-V modular converter is provided with a simulation amplifier and is connected in parallel on three road feedback resistances of simulation amplifier inverting input and output terminal both sides thereof, the inverting input of described simulation amplifier is connected with current signal input end to be turned, described feedback resistance separately with a Capacitance parallel connection, the connecting circuit between each feedback resistance and current signal input end to be turned is serially connected with a change-over switch separately.The in-phase input end ground connection of described simulation amplifier, the circuit connecting its inverting input and output terminal is serially connected with protective resistance.
In Fig. 2, current module 1 to be measured is provided by the collecting board in accompanying drawing 1, and the circuit structure design of I-V modular converter 4 and change-over switch module 2 as shown in Figure 3.
Because the electric current of required measurement may differ multiple order of magnitude, therefore I-V modular converter 4 needs multiple feedback resistance, the feedback resistance that different ranges is corresponding different, and theoretical according to Johnson Noise, the theoretical current noise of resistance is
k is Boltzmann constant, K=1.38 × 1, get generalized case T=300 degree, B=1Hz, as calculated when measuring fA level electric current, resistance at least gets 20G Ω in theory, during pA level electric current, resistance at least gets 20K Ω in theory, the first feedback resistance R1 so in accompanying drawing 3, the second feedback resistance R2, the 3rd feedback resistance R3 get 100G Ω, 100M Ω, 100K Ω respectively, correspond respectively to range 1fA ~ 1pA, 1pA ~ 1nA, 1nA ~ 1 μ A, by the voltage of the current conversion of input to mV level.
It is change-over switch group that simulation amplifier in Fig. 3 needs to select in dotted line frame, by control module 9 gating, the weak current of input is converted into the scope that voltage amplification module 6 can be amplified, and is just switched to the range of high a grade when institute's measured value exceedes setting threshold value.R11 and R12 in Fig. 3 is the protective resistance of amplifier input, output.Because amplifier has the input stray capacitance of several pF ~ tens of pF, can make the bad stability of 0P amplifier, can make delayed phase, therefore electric capacity C1, electric capacity C2, electric capacity C3 compensate for control phase, the ceramic condenser of best serviceability temperature offset-type.Here change-over switch device adopts the dry-reed relay having high insulation resistance, and puts teflon pipe.Wherein simulate the chip that amplifier needs to adopt high impedance, low bias current, low maladjustment voltage, Low Drift Temperature, can LCM6062A, LMC6042, INA116 etc. be adopted.
Amplifier itself has certain bias current, offset voltage, can have an impact to the output voltage of I-V, and zeroing module 3 can offset this impact.The power supply that the operating voltage of amplifier is used can bring partial noise into, and low-pass filtering module 5 can offset this impact.The mV step voltage that I-V modular converter exports is converted into V step voltage thus meets the requirement of A/D modular converter 8 by voltage amplification module 6.What voltage amplification module 6 exported is the noisy signal of band, and filtration module 7 carries out active power filtering process to the output signal of voltage amplification module 6, can adopt three rank Butterworth low pass wave circuit process noises.A/D modular converter 8 is connected with filtration module 7, the analog voltage signal that filtration module 7 exports is converted into the digital signal being suitable for control module process.Control module 9 is connected with display module 10 with change-over switch module 2, A/D modular converter 8, and it also can be other embedded controller that control module 9 is specifically as follows single-chip microcomputer, and controller, according to the threshold value set, adopts threshold value return difference method to switch change-over switch.Display module 10 is connected with control module 9, and the digital signal provided by control module 9 shows final air-anion concentration, LCD can be used to show display waveform, LED also can be used to show concrete numerical value.
In actual applications, need to select above-mentioned components and parts according to concrete requirement, in order to obtain better side circuit, also needing between each components and parts in such scheme to connect suitable resistance, capacitive element, not being limited with this example.
In the air-anion concentration detector device that the utility model provides, I-V modular converter needs to shield, prevent electromagnetic interference (EMI), the signal wire of the change-over circuit of I-V can adopt low noise concentric conductor, the noise of 1/10 ~ 1/100 will be alleviated compared with common wire, the importation of signal adopts the teflon terminal that hydroscopicity is little, chemical stability is good, guarantees high input impedance.During actual use, all around will get up with equipotential conductor chip shield, not produce potential difference (PD), and leakage current can be reduced to minimum.
More than show and describe ultimate principle of the present utility model, principal character and advantage of the present utility model.The technician of the industry should understand; the utility model is not restricted to the described embodiments; what describe in above-described embodiment and instructions just illustrates principle of the present utility model; under the prerequisite not departing from the utility model spirit and scope; the utility model also has various changes and modifications, and the claimed scope of the utility model is defined by appending claims, instructions and equivalent thereof.