CN202998053U - Interface circuit of conductivity sensor of micro-electro-mechanical system - Google Patents
Interface circuit of conductivity sensor of micro-electro-mechanical system Download PDFInfo
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- CN202998053U CN202998053U CN 201220694281 CN201220694281U CN202998053U CN 202998053 U CN202998053 U CN 202998053U CN 201220694281 CN201220694281 CN 201220694281 CN 201220694281 U CN201220694281 U CN 201220694281U CN 202998053 U CN202998053 U CN 202998053U
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Abstract
The utility model relates to an interface circuit of a conductivity sensor of a micro-electro-mechanical system. The interface circuit comprises a current module, a signal conditioning module, a direct-current conversion module, a temperature compensation module and a data acquisition module, wherein the current module is connected with an input end of the conductivity sensor, the signal conditioning module is connected with an output end of the conductivity sensor, the direct-current conversion module is connected with the signal conditioning module, the temperature compensation module is connected with measured liquid of the conductivity sensor, the data acquisition module is connected with the direct-current conversion module and the temperature compensation module, and the data acquisition module is further connected with the current module. The interface circuit of the conductivity sensor of the micro-electro-mechanical system, provided by the utility model, is more convenient for data acquisition and processing, no sine fitting algorithm is needed and the value of the output voltage of the conductivity sensor can be completely reflected, the complexity of the algorithm is greatly reduced, the formation of the interface circuit is simplified, the complexity of the system is reduced, and the accuracy of measurement is improved.
Description
Technical field
The utility model relates to a kind of interface circuit of MEMS (micro electro mechanical system) conductivity sensor.
Background technology
Conductivity sensor is the transducer that is used to measure the concentration of the electrical conductance of the various solution such as ultra-pure water, pure water, drinking water, sewage, seawater or this whole ion of water gauge in laboratory, industrial production and field of detecting.The MEMS (micro electro mechanical system) conductivity sensor is the miniature four electrode type conductivity sensors that adopt the preparation of micro-nano process technology.Its method of measurement is to apply electric current toward two input electrodes, measures the voltage difference of two output electrodes, according to the value that applies current value and measuring voltage value and can calculate corresponding conductivity.The DC driven electric current can make electrode produce electrolysis, and works long hours to damage electrode and introduction measure error, therefore needs to adopt to exchange drive current; Because electrode size is micron level, the slight change of signal can cause huge measure error, therefore needs accurate interface circuit; Liquid electric conductivity can change along with the variation of fluid temperature, therefore need to carry out temperature-compensating.
The interface circuit of present MEMS (micro electro mechanical system) conductivity sensor is all to adopt alternating current as input drive signal basically, and alternating voltage is as output signal.Obtaining aspect calculated value, roughly be divided into two kinds of methods.A kind of method is that output voltage is carried out three parameter Sine-Fittings, thereby obtains amplitude, phase place and the direct current offset of sinusoidal voltage output.Can calculate the value of conductivity according to the amplitude of the amplitude of input current and output voltage.The defective of the method is, the Processing Algorithm of sinusoidal signal is comparatively complicated, need to increase digital signal processing module in circuit, has improved the complexity of system.Another kind method is the peak value that the employing peak detector obtains input current and output voltage, calculates the value of conductivity according to both peak values.The defective of the method is that antijamming capability is not strong, and interference signal is probably obtained by peak detector and as calculated value, thereby affects the accuracy of conductivity.
Therefore, in prior art, the interface circuit for the MEMS (micro electro mechanical system) conductivity sensor haves much room for improvement.
The utility model content
The purpose of this utility model is, for the problems referred to above, provides a kind of interface circuit of MEMS (micro electro mechanical system) conductivity sensor, reduces the complexity of system, and improves the accuracy of measuring.
For achieving the above object, the utility model by the following technical solutions:
A kind of interface circuit of MEMS (micro electro mechanical system) conductivity sensor comprises current module, signal condition module, DC conversion modules, temperature compensation module and data acquisition module;
Current module is connected with the input of conductivity sensor;
The signal condition module is connected with the output of conductivity sensor;
DC conversion modules is connected with the signal condition module;
Temperature compensation module is connected with the fluid to be measured of conductivity sensor;
Data acquisition module is connected with temperature compensation module with DC conversion modules;
Data acquisition module also is connected with current module.
Described current module comprises interconnective current source chip and switch chip.
Described current source chip is the LT3092 chip, and described switch chip is the ADG884BRMZ chip.
Described signal condition module comprises interconnective low pass filter and instrumentation amplifier.
Described DC conversion modules comprises one root mean square-DC converting circuit.
Described root mean square-DC converting circuit comprises the AD637JRZ chip.
Described temperature compensation module comprises a divider resistance and a platinum resistance thermometer sensor, of series connection successively, and described platinum resistance thermometer sensor, also is connected with the output of temperature compensation module.
Described data acquisition module comprises interconnective Collect conversion unit and data transmit-receive unit.
Described Collect conversion unit comprises AD μ C841 chip and is connected in the peripheral circuit of AD μ C841 chip exterior.
Described data transmit-receive unit comprises the MAX3232 chip and is connected in the peripheral circuit of MAX3232 chip exterior.
The interface circuit of the MEMS (micro electro mechanical system) conductivity sensor that the utility model provides, for conductivity sensor provides the interchange drive current, and use root mean square-DC converting circuit that alternating voltage output is converted to direct voltage output, calculate conductivity value according to the alternating current of input and the direct voltage of output.Compared with prior art, the interface circuit of the MEMS (micro electro mechanical system) conductivity sensor that provides of the utility model is convenient to carry out data acquisition and processing (DAP) more; Neither need to carry out the Sine-Fitting computing, can truly reflect the value of conductivity sensor output voltage again comprehensively, greatly reduce the complexity of algorithm, simplify the formation of interface circuit, in the complexity that reduces system, greatly improved the accuracy of measuring.
Description of drawings
Fig. 1 is the high-level schematic functional block diagram of the interface circuit of the utility model embodiment.
Fig. 2 is the circuit structure diagram of current module of the interface circuit of the utility model embodiment.
Fig. 3 is the circuit structure diagram of signal condition module of the interface circuit of the utility model embodiment.
Fig. 4 is the circuit structure diagram of DC conversion modules of the interface circuit of the utility model embodiment.
Fig. 5 is the circuit structure diagram of temperature compensation module of the interface circuit of the utility model embodiment.
Fig. 6 is the circuit structure diagram of data acquisition module of the interface circuit of the utility model embodiment.
Embodiment
Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.
As shown in Figure 1, the interface circuit of a kind of MEMS (micro electro mechanical system) conductivity sensor of providing of the utility model embodiment comprises current module 1, signal condition module 2, DC conversion modules 3, temperature compensation module 4 and data acquisition module 5.
Current module 1 is connected with the input of conductivity sensor, is used to conductivity sensor that current drive signal is provided;
Temperature compensation module 4 is connected with the fluid to be measured of conductivity sensor, is used for the variations in temperature of fluid to be measured is converted into the corresponding signal of telecommunication that changes;
Data acquisition module 5 is connected with temperature compensation module with DC conversion modules 3 and is connected, and is used for collecting the data of DC conversion modules 3 and temperature compensation module 4 outputs, and carries out analog-to-digital conversion;
Data acquisition module 5 also is connected with current module 1, and being used for provides clock signal to current module 1.
Particularly, the first output 11 of current module 1 and the second output 12 are connected respectively to two input electrodes of conductivity sensor, it is the AC square wave current of 0.5mA that current module 1 produces amplitude, is applied to two input electrodes of conductivity sensor as current drive signal.Data acquisition module 5 clockings send to the clock signal receiving terminal 13 of current module 1 from clock signal output terminal 53, be used for controlling the frequency of AC square wave current.The first input end 21 of signal condition module 2 and the second input 22 are connected to two output electrodes of conductivity sensor, after the differential voltage signal that signal condition module 2 is exported conductivity sensor carries out filtering and amplification, output to the ac input end 31 of DC conversion modules 3 from ac output end 23.DC conversion modules 3 is converted to d. c. voltage signal with ac voltage signal, outputs to the first Gather and input end 51 of data acquisition module 5 from dc output end 32.Simultaneously, after temperature compensation module 4 is converted into the corresponding signal of telecommunication that changes with the variations in temperature of fluid to be measured, be sent to the second Gather and input end 52 of data acquisition module 5 from temperature signal output 41.Data acquisition module 5 carries out analog-to-digital conversion to the data of collecting from DC conversion modules 3 and temperature compensation module 4, and result is uploaded to the outside host computer that connects by gathering output bus 54.
As shown in Figure 2, current module 1 in the utility model embodiment is comprised of the LT3092 current source chip of Linear Techn Inc.'s production and the ADG884BRMZ switch chip of Ya De promise semiconductor technology company production, two chip blocks interconnect, and can produce ± AC square wave current of 0.5mA.The LT3092 chip is a two ends current sources, only needs two resistors just can set the output current of 0.5mA to 200mA.The ADG884BRMZ chip is a low pressure COMS device, comprises two independently single-pole double-throw switch (SPDT)s, and this device has the ultralow conducting resistance less than 0.4 Ω.
Particularly, the driving voltage Vdd of 5V is connected respectively to the IN pin of LT3092 chip and the VDD pin of ADG884BRMZ chip.The SET pin of LT3092 chip is connected to S1A pin and the S2B pin of ADG884BRMZ chip through the first resistance R 17, the OUT pin is connected to S1A pin and the S2B pin of ADG884BRMZ chip through the second resistance R 16; The TAB pin of LT3092 chip is connected with the OUT pin.The S1B pin of ADG884BRMZ chip, S2A pin and GND pin ground connection; The IN1 pin of ADG884BRMZ chip is connected with the IN2 pin, as the clock signal receiving terminal 13 of current module 1.Under the control of same clock signal, the D1 pin of ADG884BRMZ chip and D2 pin are respectively as the first output 11 and second output 12 of current module 1, to conductivity sensor output AC square wave current.
The output current amplitude of current module 1 is to determine by the resistance of the first resistance R 17 and the second resistance R 16 is common.In the utility model embodiment, the resistance of choosing the first resistance R 17 is 20k Ω, and the resistance of the second resistance R 16 is 400 Ω.The output current amplitude of described current module 1:
As shown in Figure 3, signal condition module 2 in the utility model embodiment is comprised of interconnective low pass filter and instrumentation amplifier, wherein instrumentation amplifier is comprised of three NE5532P operational amplifiers and 7 resistance, and the multiplication factor of instrumentation amplifier is determined by the resistance of these resistance.
Particularly, the 3rd resistance R 18 of series connection and the first capacitor C 5 form a simple single order RC low pass filter mutually, and the upper bound of passband is about 100kHz frequently.The first input end 21 of signal condition module 2 is connected with an input of instrumentation amplifier by the 3rd resistance R 18, and the second input 22 is connected with another input of instrumentation amplifier, and the first capacitor C 5 is connected between two inputs of instrumentation amplifier.Three NE5532P operational amplifiers and the 4th to the tenth resistance R 9 ~ R15 form an instrumentation amplifier, and the multiplication factor of instrumentation amplifier is determined by the resistance of the 4th resistance R 9, the 5th resistance R 10, the 7th resistance R 12 and the 9th resistance R 14.Through after filtering and amplifying, output to DC conversion modules 3 from ac output end 23 from the signal of the first input end 21 of signal condition module 2 and the second input 22 inputs.
In the utility model embodiment, the resistance of described the 4th resistance R 9 is 1k Ω, and the resistance of the 5th resistance R 10 is 1k Ω, and the resistance of the 7th resistance R 12 is 500 Ω, and the resistance of the 9th resistance R 14 is 2.5k Ω.Be the multiplication factor of described instrumentation amplifier:
As shown in Figure 4, the root mean square-DC converting circuit of the DC conversion modules in the utility model embodiment 3 for setting up take the AD637JRZ chip as core.The AD637JRZ chip is a high accuracy, the single-chip root mean square direct current transducer that Ya De promise semiconductor technology company produces, and can calculate the Ture RMS of any complicated wave form, ac voltage signal can be converted to d. c. voltage signal.
Particularly, the positive source Vcc of DC conversion modules 3 and power cathode Vee are connected respectively to VS+ pin and the VS-pin of AD637JRZ chip; The BUFIN pin of AD637JRZ chip, COM pin and OFFSET pin ground connection, the CS pin is connected to positive source Vcc through the 11 resistance R 8.The ac input end 31 of DC conversion modules 3 is connected with the Vin pin of AD637JRZ chip through the second capacitor C 20, and described the second capacitor C 20 is used for the isolated DC signal; The Cav pin of AD637JRZ chip is connected with the dc output end 32 of DC conversion modules 3 through average capacitance C6, and described average capacitance C6 is used for arranging constant average time of output signal; Simultaneously, AD637JRZ chip DEN pin and RMS pin also are connected to the dc output end 32 of DC conversion modules 3.Ac voltage signal is from ac input end 31 input, after the conversion of AD637JRZ chip from dc output end 32 output dc voltage signals to data acquisition module 5.
As shown in Figure 5, the temperature compensation module 4 in the utility model embodiment comprises divider resistance R19 and the platinum resistance thermometer sensor, RTD of mutual series connection.The end of divider resistance R19 connects the operating voltage of 3.3V, and the other end connects the temperature signal output 41 of temperature compensation module 4; The end of platinum resistance thermometer sensor, RTD connects temperature signal output 41, other end ground connection.The relation of the resistance of platinum resistance thermometer sensor, RTD and fluid to be measured temperature is as follows:
R
T＝R
0[1+α
R(T-T
0)]
Wherein, R
TThe resistance of fluid to be measured temperature platinum resistance thermometer sensor, RTD when being T, R
0That the fluid to be measured temperature is T
0The time platinum resistance thermometer sensor, RTD resistance, α
RTemperature coefficient of resistance for platinum resistance thermometer sensor, RTD.According to circuit shown in Figure 5 and above-mentioned formula, dividing potential drop on platinum resistance thermometer sensor, RTD has reflected the resistance of platinum resistance thermometer sensor, RTD, the temperature that has namely reflected fluid to be measured, the voltage division signal on platinum resistance thermometer sensor, RTD reach data acquisition module 5 as output from temperature signal output 41.
As shown in Figure 6, the data acquisition module 5 in the utility model embodiment comprises and interconnects Collect conversion unit and data transmit-receive unit.Wherein, the Collect conversion unit is comprised of AD μ C841 chip and peripheral circuit thereof, the data transmit-receive unit is comprised of MAX3232 chip and peripheral circuit thereof, and the RXD pin of AD μ C841 chip is connected with the TXD pin and is connected the R1OUT pin with the MAX3232 chip and is connected with the T1IN pin.
AD μ C841 chip is a fully-integrated single-chip 12 Bit Data Acquisition Systems, adopt high-speed kernel, accurate modulus and analog conversion function and a Flash microcontroller are provided on single-chip, controller and analog to digital converter, digital to analog converter are integrated, shorten the development time, improved Systems balanth.Particularly, the first Gather and input end 51 of data acquisition module 5 and the second Gather and input end 52 are connected respectively to P1.0 pin and the P1.1 pin of AD μ C841 chip.3.3V external power supply be connected respectively to AVDD pin, CREF pin, DVDD1 pin, DVDD2 pin, EA pin and the DVDD3 pin of AD μ C841 chip, the first to the 5th shunt capacitance C14, C15, C16, C18, C19 are the shunt capacitance of external power supply; AGND pin, DGND1 pin, DGND2 pin and DGND3 pin be ground connection respectively.Described CREF pin also carries out decoupling by decoupling capacitance C17, for AD μ C841 chip provides reference power source.11.0592MHz crystal oscillator X1 be connected between XTAL1 pin and XTAL2 pin, the most basic clock signal of self using is provided for AD μ C841 chip, simultaneously, XTAL1 pin and XTAL2 pin also are connected respectively to the 6th shunt capacitance C7 and the 7th shunt capacitance C8, then ground connection.The DAC0 pin is connected to the clock signal output terminal 53 of data acquisition module 5, and the clock signal that AD μ C841 chip was processed sends to current module 1.
For realizing and the communicating by letter of host computer PC, the utility model embodiment selects the MAX3232 chip as the RS-232 data collector.Particularly, the VCC pin of MAX3232 chip is connected with the external power supply of 3.3V, GND pin ground connection; The C1+ pin is connected the 3rd capacitor C 9 and connects with the C1-pin, the C2+ pin is connected the 4th capacitor C 10 and connects with the C2-pin; The V+ pin is connected to the external power supply of 3.3V by the 5th capacitor C 11, the V-pin also is connected with the 7th capacitor C 13 by the 6th rear ground connection of capacitor C 12 between the 5th capacitor C 11 and the 6th capacitor C 12.The R1IN pin of MAX3232 chip and T1OUT pin are connected to the output bus 54 of data acquisition module 5, and the signal after analog-to-digital conversion is uploaded to host computer PC.
The interface circuit of the MEMS (micro electro mechanical system) conductivity sensor that the utility model provides, for conductivity sensor provides the interchange drive current, and use root mean square-DC converting circuit that alternating voltage output is converted to direct voltage output, calculate conductivity value according to the alternating current of input and the direct voltage of output.Compared with prior art, the interface circuit of the MEMS (micro electro mechanical system) conductivity sensor that provides of the utility model is convenient to carry out data acquisition and processing (DAP) more; Neither need to carry out the Sine-Fitting computing, can truly reflect the value of conductivity sensor output voltage again comprehensively, greatly reduce the complexity of algorithm, simplify the formation of interface circuit, in the complexity that reduces system, greatly improved the accuracy of measuring.
The above embodiment has only expressed several execution mode of the present utility model, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to the utility model the scope of the claims.Should be pointed out that for the person of ordinary skill of the art, without departing from the concept of the premise utility, can also make some distortion and improvement, these all belong to protection range of the present utility model.Therefore, the protection range of the utility model patent should be as the criterion with claims.
Claims (10)
1. the interface circuit of a MEMS (micro electro mechanical system) conductivity sensor, is characterized in that, comprises current module, signal condition module, DC conversion modules, temperature compensation module and data acquisition module;
Current module is connected with the input of conductivity sensor;
The signal condition module is connected with the output of conductivity sensor;
DC conversion modules is connected with the signal condition module;
Temperature compensation module is connected with the fluid to be measured of conductivity sensor;
Data acquisition module is connected with temperature compensation module with DC conversion modules;
Data acquisition module also is connected with current module.
2. interface circuit according to claim 1, is characterized in that, described current module comprises interconnective current source chip and switch chip.
3. interface circuit according to claim 2, is characterized in that, described current source chip is the LT3092 chip, and described switch chip is the ADG884BRMZ chip.
4. interface circuit according to claim 1, is characterized in that, described signal condition module comprises interconnective low pass filter and instrumentation amplifier.
5. interface circuit according to claim 1, is characterized in that, described DC conversion modules comprises one root mean square-DC converting circuit.
6. interface circuit according to claim 5, is characterized in that, described root mean square-DC converting circuit comprises the AD637JRZ chip.
7. interface circuit according to claim 1, is characterized in that, described temperature compensation module comprises a divider resistance and a platinum resistance thermometer sensor, of series connection successively, and described platinum resistance thermometer sensor, also is connected with the output of temperature compensation module.
8. interface circuit according to claim 1, is characterized in that, described data acquisition module comprises interconnective Collect conversion unit and data transmit-receive unit.
9. interface circuit according to claim 8, is characterized in that, described Collect conversion unit comprises AD μ C841 chip and is connected in the peripheral circuit of AD μ C841 chip exterior.
10. interface circuit according to claim 8, is characterized in that, described data transmit-receive unit comprises the MAX3232 chip and is connected in the peripheral circuit of MAX3232 chip exterior.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201220694281 CN202998053U (en) | 2012-12-14 | 2012-12-14 | Interface circuit of conductivity sensor of micro-electro-mechanical system |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201220694281 CN202998053U (en) | 2012-12-14 | 2012-12-14 | Interface circuit of conductivity sensor of micro-electro-mechanical system |
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| CN202998053U true CN202998053U (en) | 2013-06-12 |
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| CN 201220694281 Expired - Fee Related CN202998053U (en) | 2012-12-14 | 2012-12-14 | Interface circuit of conductivity sensor of micro-electro-mechanical system |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103856203A (en) * | 2014-03-19 | 2014-06-11 | 成都引众数字设备有限公司 | Signal conversion circuit |
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2012
- 2012-12-14 CN CN 201220694281 patent/CN202998053U/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103856203A (en) * | 2014-03-19 | 2014-06-11 | 成都引众数字设备有限公司 | Signal conversion circuit |
| CN103856203B (en) * | 2014-03-19 | 2017-01-18 | 成都引众数字设备有限公司 | Signal conversion circuit |
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Granted publication date: 20130612 Termination date: 20141214 |
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| EXPY | Termination of patent right or utility model |