CN103235273A - Five-point three-dimensional magnetic field measurement device based on board stretching pyromagnetic effect - Google Patents
Five-point three-dimensional magnetic field measurement device based on board stretching pyromagnetic effect Download PDFInfo
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Abstract
The invention discloses a five-point three-dimensional magnetic field measurement device based on board stretching pyromagnetic effect. The five-point three-dimensional magnetic field measurement device comprises a microcontroller, five magnetic sensors, a multiplexer, an analog to digital converter, a hysteresis effect cancellation circuit and a serial communication circuit. The magnetic sensors are symmetrically arranged on five points on the front face of a PCB (printed circuit board). Each magnetic sensor is provided with three signal output channels used for inputting magnetic induction signals of the three directions of x, y and z. The magnetic sensors are connected with an input port of the microcontroller through the multiplexer and the analog to digital converter. An output port of the hysteresis effect cancellation circuit is connected with pulse polarization circuits in the magnetic sensors. The microcontroller is connected with an upper computer through the serial communication circuit. By the five point three-dimensional magnetic field measurement device, a plurality of sensors capable of outputting three-dimensional magnetic field signals are used with the multiplexer and the analog to digital converter to allow for multi-point three-dimensional magnetic field measurement; and the five-point three-dimensional magnetic field measurement device is simple in structure, easy to control and construct and high in accuracy.
Description
Technical field
The present invention relates to a kind of three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect.
Background technology
Studies show that, when defective superpolymer stretches with certain speed, can around breach, produce certain temperature rise, the magnetic field of the certain intensity of association simultaneously.Relation between the temperature rise that produces during for further this magnetic field of research and stretching, need be when controlling draw speed automatically, temperature rise and magnetic induction density to test specimen carry out synchro measure, and preserve all measurement data with time synchronizing method: pulling force, displacement, magnetic induction density, temperature (view data), with research and determine relation between them.
Publication number is the patent of CN101261245A, its name is called defective rheid pyromagnetic collection and test macro (application number is 200810031098), a kind of magnetic field detection scheme has been proposed, be based on Hall sensor array and gather magnetic field data, the greatest problem that this scheme exists is complex structure, need the structure sensor array, and need complicated feed circuit and control circuit be the sensor service; This sensor can only be measured the magnetic field data of a direction in addition, can't detect three-dimensional magnetic induction data, so limitation is big.
Therefore, be necessary to design a kind of brand-new magnetic field measuring device.
Summary of the invention
Technical matters to be solved by this invention provides a kind of three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect, should adopt a plurality of sensors with three-dimensional magnetic field signal output based on three-dimensional magnetic field, 5 positions measurement mechanism of sheet material stretching thermic magnetic effect, and realization multiple spot position, three-dimensional magnetic field are detected under the cooperation of MUX and analog to digital converter, simple in structure, be easy to control, easy to implement.
The technical solution of invention is as follows:
A kind of three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect comprises single-chip microcomputer, Magnetic Sensor, MUX, analog to digital converter, hysteresis effect elimination circuit and serial communication circuit;
Described Magnetic Sensor is 5, is symmetricly set on 5 some positions in PCB front, and 4 Si Jiaochu that are arranged on pcb board wherein, another is arranged on the central authorities of pcb board; Each Magnetic Sensor has 3 signal output channels, exports the magnetic induction signal of X, Y, three directions of Z respectively;
Magnetic Sensor is connected with the input interface of single-chip microcomputer with analog to digital converter by MUX successively; The channel selecting termination single machine output end of MUX;
Two input ends of hysteresis effect elimination circuit connect reset terminal and the set end (set8 and reset8) of single-chip microcomputer respectively; Reset terminal and set end are the IO port of single-chip microcomputer; The output terminal of hysteresis effect elimination circuit links to each other with the impulse polarization circuit in the Magnetic Sensor;
Single-chip microcomputer is connected with host computer by described serial communication circuit.
Described Magnetic Sensor adopts the HMC2003 chip, described MUX comprises 3 multi-way switchs: i.e. first multi-way switch, second multi-way switch and the 3rd multi-way switch, and analog multichannel switch adopts the 74HC4051 chip with 8 road signal input channels and 1 signal output channels; Analog to digital converter adopts the ADS7825 chip of sixteen bit; The ADS7825 chip has four input end of analog signal;
The X signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of first multi-way switch respectively;
The Y-signal output channel of 5 Magnetic Sensors is joined with 5 signal input channels of second multi-way switch respectively;
The Z signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of the 3rd multi-way switch respectively;
3 signal output channels of 3 multi-way switchs join with 3 input end of analog signal of analog to digital converter respectively;
Three number word selecting sides of 3 multi-way switchs are corresponding in parallel.
Hysteresis effect elimination circuit is the pulse-generating circuit based on power MOSFET tube, and power MOSFET tube adopts the IRF7106 chip;
Join by the impulse polarization circuit in first electric capacity (C83) and the Magnetic Sensor behind the 5-8 pin short circuit of IRF7106 chip;
1 pin of IRF7106 chip and 3 pin are ground connection and direct supply anode VCC1 respectively;
2 pin (G1) of IRF7106 chip connect described reset terminal (reset8);
Another IO port of single-chip microcomputer is as set end (set8), and set end (set8) connects the base stage of the triode (Q18) of NPN type by first resistance (R81); The emitter grounding of triode (Q18), the collector of triode (Q18) meets VCC1 by second resistance (R82); The collector of triode (Q18) also connects 4 pin (G2 end) of IRF7106 chip by second electric capacity (C81); Be connected to the 3rd resistance (R83) between 4 pin of IRF7106 chip and the VCC1; Be connected to the 3rd electric capacity (C82) between VCC1 and the ground.
Serial communication circuit adopts private communication device MAX232, and single-chip microcomputer adopts the STC89C54RD chip.
Beneficial effect:
Three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect of the present invention, 5 three-dimensional Magnetic Sensors (HMC2003 chip) that employing is distributed in place, difference position detect field signal, and adopt based on the multi-channel analog multi-way switch of 74HC4051 chip and realize the data switching, adopt analog to digital converter to become digital signal to output in the single-chip microcomputer analog signal conversion again, finish the collection of three-dimensional magnetic field, multiple spot position data.
Wherein, adopt multi-way switch can effectively simplify circuit design, and take full advantage of the port of single-chip microcomputer, and control is convenient, once can gather one group of three-dimensional magnetic field data of a Magnetic Sensor output synchronously.
In addition, the present invention has also designed hysteresis effect and has eliminated circuit to eliminate magnetic hysteresis, to improve the magnetic field detection precision.
In sum, the present invention adopts a plurality of sensors with three-dimensional magnetic field signal output, and realization multiple spot position, three-dimensional magnetic field are detected under the cooperation of MUX and analog to digital converter, simple in structure, be easy to control, easy to implement, and after adopting hysteresis effect to eliminate circuit, can further improve the Device Testing precision.
Description of drawings
Fig. 1 is the general principles block diagram of three-dimensional magnetic field, 5 positions measurement mechanism;
Fig. 2 is that five Magnetic Sensors are arranged in the position view on the pcb board;
Fig. 3 is the multichannel selection of three-dimensional magnetic field, 5 positions measurement mechanism and the schematic diagram of analog to digital conversion circuit;
Fig. 4 is the multi-channel sampling process flow diagram;
Fig. 5 is constant-current source circuit figure;
Fig. 6 is set/reset pulse synoptic diagram;
Fig. 7 is set/reset pulsing circuit schematic diagram.
Fig. 8 be bias current band peripheral circuit (one of);
Fig. 9 is bias current band peripheral circuit (two);
Figure 10 is the experimental result interface of curve of containing each detection limit of experimental system.
Figure 11 is the thermic magnetic induction density-time history on test specimen surface under the 20mm/min speed.
Embodiment
Below with reference to the drawings and specific embodiments the present invention is described in further details:
Embodiment 1:
Shown in Fig. 1-9, a kind of three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect comprises single-chip microcomputer, Magnetic Sensor, MUX, analog to digital converter, hysteresis effect elimination circuit and serial communication circuit;
Described Magnetic Sensor is 5, is symmetricly set on 5 some positions in PCB front, and 4 Si Jiaochu that are arranged on pcb board wherein, another is arranged on the central authorities of pcb board; Each Magnetic Sensor has 3 signal output channels, exports the magnetic induction signal of X, Y, three directions of Z respectively;
Magnetic Sensor is connected with the input interface of single-chip microcomputer with analog to digital converter by MUX successively; The channel selecting termination single machine output end of MUX;
Two input ends of hysteresis effect elimination circuit connect reset terminal and the set end (set8 and reset8) of single-chip microcomputer respectively; Reset terminal and set end are the IO port of single-chip microcomputer; The output terminal of hysteresis effect elimination circuit links to each other with the impulse polarization circuit in the Magnetic Sensor;
Single-chip microcomputer is connected with host computer by described serial communication circuit.
Described Magnetic Sensor adopts the HMC2003 chip, described MUX comprises 3 multi-way switchs: i.e. first multi-way switch, second multi-way switch and the 3rd multi-way switch, and analog multichannel switch adopts the 74HC4051 chip with 8 road signal input channels and 1 signal output channels; Analog to digital converter adopts the ADS7825 chip of sixteen bit; The ADS7825 chip has four input end of analog signal;
The X signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of first multi-way switch respectively;
The Y-signal output channel of 5 Magnetic Sensors is joined with 5 signal input channels of second multi-way switch respectively;
The Z signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of the 3rd multi-way switch respectively;
3 signal output channels of 3 multi-way switchs join with 3 input end of analog signal of analog to digital converter respectively;
The three number word selecting sides (being A, B, C) of 3 multi-way switchs corresponding [namely the A of 3 multi-way switchs end is in parallel, and the B end of 3 multi-way switchs is in parallel, and the C end of 3 multi-way switchs is in parallel] in parallel.
74HC4051 is 8 tunnels analogy MUX/demultplexers, has 3 number word selecting sides (S0 to S2 also is A, B, C end), 1 low effective Enable Pin (E), 8 independent I/O ends (Y0 to Y7) and 1 public I/O end (Z).When E is low, one of them of 8 switches will be chosen (low resistance state) by S0 to S2.When E was high, all switches all entered high-impedance state, directly ignored S0 to S2.
Hysteresis effect elimination circuit is the pulse-generating circuit based on power MOSFET tube, and power MOSFET tube adopts the IRF7106 chip;
Join by the impulse polarization circuit in first electric capacity (C83) and the Magnetic Sensor behind the 5-8 pin short circuit of IRF7106 chip;
1 pin of IRF7106 chip and 3 pin are ground connection and direct supply anode VCC1 respectively;
2 pin (G1) of IRF7106 chip connect described reset terminal (reset8);
Another IO port of single-chip microcomputer is as set end (set8), and set end (set8) connects the base stage of the triode (Q18) of NPN type by first resistance (R81); The emitter grounding of triode (Q18), the collector of triode (Q18) meets VCC1 by second resistance (R82); The collector of triode (Q18) also connects 4 pin (G2 end) of IRF7106 chip by second electric capacity (C81); Be connected to the 3rd resistance (R83) between 4 pin of IRF7106 chip and the VCC1; Be connected to the 3rd electric capacity (C82) between VCC1 and the ground.VCC1＝20V
Serial communication circuit adopts private communication device MAX232, and single-chip microcomputer adopts the STC89C54RD chip.
A kind of three-dimensional magnetic field, 5 positions measuring method based on sheet material stretching thermic magnetic effect arranges 5 Magnetic Sensors that can export three-dimensional magnetic induction signal respectively in 5 some positions of surveyed area; 15 road signals of Magnetic Sensor output are after MUX is selected, and the three-dimensional magnetic induction signal of a Magnetic Sensor of output in each sampling period forms digital signal by analog to digital converter again and sends in the single-chip microcomputer; Be uploaded to host computer after by single-chip microcomputer all data of gathering being handled at last, finish the measurement of three-dimensional magnetic field.
In described measuring process, single-chip microcomputer is eliminated circuit by hysteresis effect and is produced forward and reverse polarization pulse and export to Magnetic Sensor, and Magnetic Sensor is magnetized in the magnetic-field measurement process to eliminate; Measuring process is:
Step 1: the magnetic-field measurement to 5 some positions is finished in circulation successively;
The magnetic-field measurement of each some position comprises the magnetic field of measurement of x, y and z direction successively;
Step 2: when the three-dimensional magnetic field of 5 some positions measure all finish after, just finished the measurement of frame data, and returned step 1 and circulate next time;
The unidirectional magnetic-field measurement process of Magnetic Sensor at each place, some position is:
Before the A/D conversion beginning, single-chip microcomputer asserts signal SET of output earlier makes sensor obtain the forward polarization, then start analog to digital converter and carry out the A/D conversion, in order to prevent that random disturbance from causing the A/D transformed error, adopt 100 sampled values AVG1 that averages, then reset signal RESET of single-chip microcomputer output makes Magnetic Sensor obtain reverse polarization, start analog to digital converter 100 sampled values of reentrying then, and trying to achieve mean value AVG2, mean value AVG1 and the AVG2 with twice acquisition obtains a numerical value as this unidirectional magnetic-field measurement value through numerical evaluation VOUT=(AVG1+AVG2)/2 then;
Described and folk prescription to referring to x, y or z direction.
Embodiment 1:
Three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect is laminated by five point sensors measurement plate and multi-channel data acquisition plate two parts, five point sensors are measured the plate sensor and are arranged as shown in Figure 2, and adopting this arrangement is to determine according to the PVC sheet material position that maximum thermic magnetic field produces in drawing process.Namely five three-dimension sensors are arranged in the magnetic field intensity maximum most possibly appears in polymer plate in drawing process position; 5 three-dimension sensor electricity theory diagrams as shown in Figure 1.
53 D weak magnetic field sensor groups that HMC2003 among the figure (1-5) is made up of 5 HMC2003, this is the core cell of whole sensor, its arrangement mode is as shown in Figure 2; MUX is made up of three 74HC4051 analog multichannel switches, the X of 5 HMC2003 of three 74HC4051 analog multichannel switch difference gatings, Y, the three-dimensional output signal of Z enters three input end IN0 of analog to digital converter, IN1, IN2, the selection control end A of three 74HC4051 analog multichannel switches, B, C is in parallel, and it selects control to be carried out by single-chip microcomputer, and single-chip microcomputer adopts the STC89C54RD+ 8-bit microcontroller, change A, B, the state of C, can realize any one sensors X, Y switches in the time of the Z signal, i.e. each sensors X, Y, the Z output signal is to arrive analog to digital converter simultaneously, and analog to digital converter is ADS7825 sixteen bit A/D converter, and four input end IN0 are arranged, IN1, IN2, as long as IN3 is four passages of timesharing gating, just can realize the conversion of input analog amount, native system is selected IN0 for use, IN1, and three input ends of IN2 are respectively as X, Y, the signal input part of Z 3 D weak magnetic field.It is that sensor is magnetized and reduces forward and reverse polarization pulse generation circuit of measuring sensitivity and arranging in the magnetic-field measurement process in order to eliminate that hysteresis effect is eliminated peripheral circuit, can produce forward and reverse peak point current and reach the transient peak pulse of 4A, this pulse action is in the impulse polarization circuit of HMC2003 inside, realize the moment polarization of giant magnetoresistance, to improve the measurement sensitivity of giant magnetoresistance, forward and reverse polarization pulse is the SET that is sent by single-chip microcomputer, the RESET signal controlling.
Before the A/D conversion beginning, export a SET signal earlier, make sensor obtain the forward polarization, then start A/D converter and carry out the A/D conversion, in order to prevent that random disturbance from causing the A/D transformed error, the method that adopts 100 sampled values to average is carried out digital filtering, then single-chip microcomputer is exported a RESET signal, make sensor obtain reverse polarization, then start A/D converter and carry out 100 A/D conversions again, and average, the mean value with twice acquisition passes through numerical evaluation VOUT=(AVG1+AVG2)/2 then; Obtain a numerical value as a measured value, when the three dimensional signal of a sensor all disposes, then finished the three-dimensional magnetic field of a point and measured, after all finish the three-dimensional magnetic field of 5 sensors, just finished the measurement of frame data.After single-chip microcomputer is finished frame data collection, check the data request signal that serial communication has or not host computer to send, if the request signal that has host computer to send, then form sends frame data by appointment, finish after the data transmission, single-chip microcomputer enters the next employing cycle.Serial communication is made of private communication device MAX232.
HMC2003 is three-dimensional high sensitivity magnetic field survey sensor among the figure, 5 HMC2003 are according to arrangement shown in Figure 2, hysteresis effect is eliminated peripheral circuit and is cooperated with HMC2003 internal pulses degaussing circuit, finishes the forward and reverse polarization of giant magnetoresistance, makes sensor have highest measurement sensitivity; Data acquisition board is by MUX, analog to digital converter and single-chip microcomputer constitute, multi-way switch is the three-dimension sensor channel selector switch, X with 5 three-dimension sensors, Y, the timesharing gating is to three input channels of A/D converter ADS7825 respectively for Z, and ADS7825 is 16 A/D converters, and single-chip microcomputer is 8 STC single-chip microcomputers.
The HMC2003 chip internal comprises three-dimensional giant magnetoresistance measurement bridge, bridge circuit constant current power supply, accurate reference voltage, three-dimensional precision instrument amplifier, pulse degaussing circuit and background magnetic field are to canceling coil, its effect is at zero magnetic field state the variable quantity of Weak magentic-field to be converted into the variable quantity of output voltage, extrapolates the variation value of Weak magentic-field according to the corresponding relation of magnetic field and voltage.
Wherein to measure bridge be the base unit of measuring Weak magentic-field for three-dimensional giant magnetoresistance, and Weak magentic-field is exactly to measure bridge by giant magnetoresistance to be converted to differential output voltage.
The permanent power supply of bridge circuit provides constant current source for the three-dimensional magnetic field measurement, to reduce power-supply fluctuation to the influence of signal source, has reduced systematic error.
Accurate reference voltage is to provide a reference voltage for background magnetic field to canceling coil.
Three-dimensional precision instrument amplifier amplifies output with faint differential voltage signal, so that the transmission of voltage signal and conversion.
The two eliminates circuit in conjunction with forming hysteresis effect pulse degaussing circuit and hysteresis effect peripheral circuit, makes giant magnetoresistance measure the most highly sensitive state that bridge is in no hysteresis effect all the time, is used for eliminating hysteresis effect to measuring the influence of sensitivity.
Background magnetic field offsets coil circuit and the background magnetic field peripheral circuit is formed background magnetic field elimination circuit, is used for eliminating the working environment background magnetic field, makes the sensor real work in zero magnetic field environment, realizes the precision measurement of Weak magentic-field.
The effect of MUX be with 5 measurement points the analog signal voltage of totally 15 unit survey sensor outputs be transferred to an A/D converter, realize being finished by an A/D converter conversion of 15 tunnel simulating signals.
Single-chip microcomputer is finished the coordination of data acquisition and various functions as system control unit.
The GMR sensor is a kind of element of measuring magnetic field intensity, and different with a lot of other devices is that it is directly measured magnetic field intensity and is not the rate of change of induced field, is very easily so measure Weak magentic-field.The GMR sensor has that volume is little, highly sensitive, the range of linearity is wide, serviceability temperature height, low cost and other advantages
That the giant magnetoresistance sensor among the design is selected for use is HMC2003, this class magnetoresistive transducer is by 4 element wheat stone bridge configuration, have integrated set/reset band, can reduce temperature drift effect, nonlinearity erron and because the existence of highfield, the losing of the output signal that causes.And have integrated biasing band, can eliminate the influence that hard iron disturbs.Three-D magnetic field sensor HMC2003 can measure three-dimensional (x, y, z) direction of Weak magentic-field.
The amplifying circuit of HMC2003 periphery is prior art, does not elaborate at this.
The background magnetic field cancellation techniques
Around the giant magnetoresistance under the influence of hot-wire coil and terrestrial magnetic field, very strong background magnetic field is arranged around the giant magnetoresistance, background magnetic field has had a strong impact on the measurement of giant magnetoresistance to Weak magentic-field, detect the faint definition that changes the field in magnetic field for improving giant magnetoresistance sensor, on the giant magnetoresistance around on a circle coil, offset for one of giant magnetoresistance sensor size is identical, direction is opposite " compensating field " and background magnetic field by coil, make giant magnetoresistance work in zero magnetic field state.
Apply the compensating field and eliminate background magnetic field and bring by bias current and compensate, the bias current band can also drive current by the electric current band, offset measurement magnetic field accurately, this is known as closed loop configuration.Magnetic field biasing band (biasing+and setover-) can generate one with the just measured magnetic field that applies the magnetic field equidirectional.The electric current band of HMC2003 whenever can provide the magnetic field of 10e by the 50mA electric current, the electric current band of HMC2003 whenever can provide the magnetic field of 10e by the 5mA electric current.(1 Gauss in the air=10e).The bias current band appear to one the biasing+and biasing-pin between nominal resistance.
The bias current band can be as the feedback element in the closed loop circuit.Utilize the bias current band in the current feedback loop can measure expectation value.If will reach this purpose, the output terminal of amplifier of electrical bridge is connected to the current source that drives the bias current band.Utilize high-gain and reverse feedback in the loop.This will make the magnetic resistance bridge circuit be output as 0 (output +=output-).This method can provide the splendid linearity and temperature characterisitic, operates magnetoresistive bridge with the resistance mode of balance all the time.That is, no matter measure which type of magnetic field, all can be with it elimination by the electric current of bias current band.Electric bridge " is seen " zero magnetic field condition all the time, and being used for eliminating the resultant current that applies magnetic field is a direct examination question of this magnetic field intensity, and can be converted into magnetic field value.
The forward polarization is eliminated hysteresis effect with reverse polarization
Most of downfield sensors can be subjected to big magnetic interference (＞4～20 Gauss's) influence, may cause the decay of output signal.In order to reduce the output of this influence and maximum signal, can use the magnetic switch handoff technique in magnetoresistive bridge, eliminated the influence of degaussing history.The order ground of set/reset electric current band is exactly that magnetoresistive transducer is returned to the high sensitivity state of measuring magnetic field.This can be by realizing big pulsation of current by S/R electric current band.S/R electric current band looks like a resistance that is added between SR+ and the SR-pin.This electric current band is different with the bias current band, because it is magnetically coupled on the magnetoresistive transducer with Z-axis or insensitive direction.In case sensor is set (or resetting), can realize low noise and highly sensitive magnetic-field measurement.
When magnetoresistive transducer is exposed in the disturbing magnetic field, sensor element can be divided into some directions magnetic area at random, thereby causes the sensitivity decay.The pulse current (set) that peak point current is higher than the minimum requirements electric current will generate a high-intensity magnetic field by set/reset electric current band, and this magnetic field can be again aimed at magnetic area unified on a direction, will guarantee high sensitivity and reading repeatably like this.Reverse impulse (resetting) can rotate the direction of magnetic area with opposite direction, and changes the polarity of sensor output.If disturbing magnetic field do not occur, the state of this magnetic area can keep the several years.
S/R in the chip should aim at again by pulse current, or the magnetic area in " upset " sensor.This pulsewidth can be as short as 2 microseconds, and average power consumption is less than 1mA (DC) during continuous impulse.Can be chosen to be every 50ms has the pulse of 2 μ s pulsewidths, perhaps longer, with economize on electricity.Unique requirement is that each pulse only applies in one direction.That is, if+pulse of 3.5A is used to " set " sensor, and then impulse attenuation should not be lower than 0 electric current.Any negative (being lower than rated current) current pulse signal all can cause " can't set " sensor, and can not obtain best sensitivity.
Utilize S/R electric current band, can eliminate or reduce many influences, comprising: temperature drift, non-linear mistake, intersecting axle influence and because the existence of highfield losing of causing that signal exports.
The principle of 3 D weak magnetic field is to utilize the giant magnetoresistance resistance to change along with the variation in magnetic field, and the variation that will record resistance, the variation that can survey its output voltage then for particular current of resistance, because what we surveyed is voltage, so electric current is a steady state value preferably, so could not influence the linear changing relation between voltage and the resistance, and to constant current source of resistance, just can avoid electric current to be subjected to the influence of resistance variations, thereby avoid the influence of power-supply fluctuation to signal source. Fig. 5 is the constant-current source circuit that utilizes operational amplifier to form.
Because desirable operational amplifier input both end voltage equates, and the A point voltage is unaffected, so constant, corresponding B point voltage is also constant, so obviously can get electric current I
CConstant output.Field effect transistor in the circuit plays the effect of a fixed pressure drop.
Set/reset pulsing circuit (being that hysteresis effect is eliminated circuit)
In order to eliminate background magnetic field, must eliminate circuit for magnetic field effect by peripheral circuit a set/reset pulse is provided, require its oscillogram as shown in Figure 6.
Set in the design/and reset signal be by Single-chip Controlling output, to be converted into pulse signal by peripheral circuit then.Be exactly the set/reset pulsing circuit that utilizes IRF7106 to produce as shown in Figure 7.
There are two field effect transistor the IRF7106 the inside, and one is N channel enhancement field effect transistor, and one is the P-channel enhancement type field effect transistor, as Fig. 7, when being low level, triode Q18 ends when set end [i.e. set8 among the figure], and capacitor C 81 two ends all are high level, 4 pins of IRF7106 also are high level, no-voltage between s2 and the G2, thus the output of D2 end no current, when reset holds [i.e. reset8 among the figure] when being low level, no-voltage between s1 and the G1 is so D1 holds also no current output.In sum, because when set end and reset hold when being low level, D1 end and D2 hold equal no current output, and set end and reset end be alternating set/reset, and set holds and reset holds that field effect transistor of putting high level so we only need analyze when analyzing.
As the i.e. set8 among the figure of set[] when putting 1 (high level), triode Q18 conducting, the left end of capacitor C 81 sports low level, in the moment of this sudden change, capacitor C 81 is also uncharged, so capacitor C 81 right-hand members (4 pins of IRF7106) also are low levels, the conducting of P-channel field-effect transistor (PEFT) pipe, the D2 end has inverse current output, and when capacitor C 81 chargings finished, 4 pins of IRF7106 became high level again, the P-channel field-effect transistor (PEFT) pipe ends, no current output is so when set put 1, SR+8 had the output of reverse impulse electric current.
As the i.e. reset8 among the figure of reset[] when putting 1 (high level), the conducting of N channel field-effect pipe, the D1 end has forward current output (being assumed to be 1), and again because output terminal has capacitor C 83, so have only when electric current is 1 from 0 saltus step, SR+8 has the output of direct impulse electric current.
Described in combining, this circuit has satisfied the requirement of hysteresis effect elimination circuit aaset bit/reset pulse.
The design of magnetic field cancellation bias current control circuit
The effect of bias current band is exactly to eliminate background magnetic field, and three giant magnetoresistance sensors are arranged in the three-D magnetic field sensor, only analyzes the peripheral circuit of a giant magnetoresistance sensor here.
When DC current in the bias current band by the time bias current band multiple mode of operation can be arranged.
(1) balances outside unwanted magnetic field.
(2) the electric bridge biasing is set to zero.
(3) electric bridge output can drive bias current and bring the magnetic field of eliminating in the closed loop.
The bridge circuit gain can be calibrated in the system automatically when (4) receiving order.
The bias current band will produce a magnetic field opposite with tested magnetic direction when the electric current of specific size is tided over the bias current band, so can eliminate any environmental magnetic field.The bias current band whenever can provide the magnetic field of 10e by the 50m electric current.
Based on the characteristic of above bias current band, the biasing band can be as the feedback element in the closed loop circuit.In this kind application, the output terminal of amplifier of electrical bridge is connected on the drive current source of biasing band, utilizes high-gain and negative feedback in one tunnel to make electric bridge be output as zero.No matter measure which type of magnetic field, all can be with it elimination by the electric current of bias current band, electric bridge is seen zero magnetic field condition all the time.This method has the good linearity and temperature characterisitic.The electric current that is used for eliminating the external magnetic field is one of this magnetic field directly tolerance, and can be directly changed into magnetic field value.
The bias current band can also be used to calibrating automatically magnetoresistive bridge, and it is very useful to proofreading the electric bridge gain once in a while or adjusting in big temperature pendulum scope.Can power on or normal running during whenever carry out.Its principle is: get 2 points along a circuit, and determine the gradient of this line, be i.e. gain.When electric bridge was being measured stable external magnetic field, output was handed over and is kept constant.The reading of record stabilizing magnetic field is designated as H1. and applies specific currents at this moment by the bias current band, records this reading then, is designated as H2.Cause the variation in the magnetic field of magnetoresistive transducer measurement to be referred to as to apply magnetic field increment (Δ Ha), the magnetoresistive transducer gain can followingly be calculated:
Gain＝(H2-H1)/ΔHa.
Except the above, the bias current band also has many other purposes, and key is external environment condition magnetic field and bias magnetic field mutual superposition simply, is measured as single magnetic field by magnetoresistive transducer.
As Fig. 8 and shown in Figure 9 be exactly the peripheral circuit of bias current band, these two voltage followers mainly be play buffer compartment from effect.
The output port of these two voltage followers is received the HMC2003 background magnetic field respectively to two ends Xoff+1 and the Xoff-1 of canceling coil.One of them voltage follower input port connects accurate reference voltage, another voltage follower input is controlled by single-chip microcomputer, because the main effect of voltage follower be buffer compartment from, so background magnetic field can not be subjected to influence circuit to the voltage at canceling coil two ends, so just can provide stable " compensating field " to giant magnetoresistance sensor.
The data acquisition system (DAS) explanation
The design mainly finishes sensor and periphery circuit design, but the sensor check must have the cooperation of peripheral circuit, and the control of peripheral circuit is realized by single-chip data acquisition system, in order to illustrate that single-chip microcomputer is to control principle and the work schedule of sensor, now data collection and control section are briefly introduced, make the thinking of design more clear.
It is collection control, the A/D conversion and the mini system of communicating by letter of core with the single-chip microcomputer that data acquisition system (DAS) among the design is one.
In data acquisition system (DAS), need analog quantity is converted to data volume, and A/D is the device that analog quantity is converted to digital quantity that the index that he need consider has: resolution, switching time, transformed error etc.And single-chip microcomputer is the basic microprocessing systems of this system, and it finishes data read, processing and logic control, a series of task such as data transmission.We adopt the 89C52 Series chip in this system.。
This data acquisition circuit figure comprises following three parts.
The A/D analog to digital converter
In the design, select for use ADS7825 as analog to digital converter.ADS7825 is 4 passages that U.S. B-B company produces, 16 analog to digital converters.It is no more than data sampling and switching time 25 μ s by the power supply of list-5V power supply, can import-aanalogvoltage of 10V～10V.Data after the A/D conversion are line output also, also serializable output, and data transfer module also can be set to the continuous cyclic transformation of 4 interchannels, and it is extremely convenient to use.
When using the ADS7825 chip, will
Put 0, give then
Pin adds a negative edge namely can start the AD conversion.At this moment,
The output of pin keeps low level, finishes and the content of inner output register is updated until data-switching.During this period, ADS7825 no longer responds new conversion command.Must be noted that,
Before pin is output as high level,
Must be set to high level, otherwise can cause data not run through as yet, new conversion just begins, thereby makes loss of data.
Since the ADS7825 data converted can and line output, also serializable output is so reading of data also must divide parallel and the serial dual mode is discussed.Among the design be with
Be set to high level, select the parallel way of output for use, so will when data read
Pin is put low level, namely choose the ADS7825 chip after, give
Pin is imported a negative pulse, starts the AD conversion.AD conversion and the data time of latching are 25 μ s.Detect
The output level of pin can the judgment data transition status, works as state flag bit
The time, data-switching is still being carried out, and not can read data this moment.
The time, showing that data-switching has finished and data have entered output register, can read data this moment.Make parallel data output select position BYTE=0, can read the most-significant byte data, BYTE=1 reads the least-significant byte data.
Simulating signal by mode and the address of ADR0, ADRl and CONTC pin affirmation conversion, when CONTC=1, is selected continuous translative mode respectively from IN0, IN1, the input of IN2 pin, when
When being low level with the PWRD end, AD conversion and reading will circulate continuously at four interchannels of IN0～IN3 and carry out.When
After this EOC transfers high level to, A0 and A1 pin will be exported the used channel address of sampling next time, from which input channel begin to carry out cyclic transformation actually, depend on that CONTC is set to before the high level, the input value of A0 and A1 pin.The output of A0 and A1 pin and the relation that is sampled between the passage are listed as table 5.1.1.
When CONTC is set to low level, adopt intermittently translative mode.A0 and A1 pin are as input end, and its input value and sampling channel relation as table 5.1.2 are listed
Among the design, ADR0, ADRl, CONTC,
Pin all is by the control of single-chip microcomputer output signal, so its conversion regime should also be to be controlled by single-chip microcomputer.
Channel selecting when table 5.1.1 changes continuously
Channel selecting when table 5.1.2 intermittently changes
This designing requirement conversion regime should be to circulate continuously at IN0, IN1, three interchannels of IN2 to carry out.So should select continuous translative mode, and the initial value of A1, A0 is set to 01 before each circulation, so that circulate when beginning, data begin conversion from the AINO passage.When AIN2 passage EOC, immediately will
Put lowly, stop conversion, and next time circulation of beginning.So just, realized all data timesharing packet switched storages.
Single-chip microcomputer
Single-chip microcomputer is a kind of towards large-scale integrated circuit (IC) chip, is an important branch in the microcomputer.This system is by CPU, access data storer, read-only program memory, imput output circuit (I/O mouth) immediately, might comprise that also circuit such as Timer, serial communication port, display driver circuit (LCD and led drive circuit), pulse-width modulation circuit, analog multiplexer and A/D converter are integrated on the monolithic chip, have constituted a minimum but perfect computer task.Single-chip microcomputer will use specific group to translate and the composing software program compiler, with keiluvision2 program is being downloaded in the single-chip microcomputer.
Be the P89C52X2BN single-chip microcomputer and the design selects for use, P89C52X2BN is low-voltage, 8 single-chip microcomputers of high-performance CMOS, sheet includes can be the repeatedly erasable read-only program memory (PEROM) of 8k bytes and the Random Access Data storer (RAM) of 256bytes, device adopts high density, nonvolatile storage technologies production, with standard MCS-51 order set and 8052 product pin compatibilities, 8 central processing units of sheet built-in general-purpose (CPU) and Flash storage unit, powerful, the P89C52X2BN single-chip microcomputer is suitable for many comparatively complicated controls application scenario.
Wherein P0 is one group of two-way I/O mouth of 8 open-drain types, also is multiplexing mouthful of address/data bus.Here as the digital signal acquiring mouth.The P1 mouth is 8 two-way I/O mouths of a band internal pull-up resistor, and the output buffer stage of P1 can drive 4 TTL logic gates.In the design, the P1 mouth is that wherein P1.0～P1.5 is to analog-to-digital control as the control delivery outlet, and P1.6 and P1.7 are used for the control of aaset bit/reseting pulse circuit, and P2.0～P2.2 is used for controlling the timesharing gating of data.P3.0 and P3.1 mouth are as the serial input/output port,
RST is the input that resets.When oscillator is worked, two above high level of machine cycle appear in the RST pin will make single-chip microcomputer reset.
When visit external program memory or data-carrier store, ALE output pulse is used for the least-significant byte byte of latch address.Generally speaking, the pulse signal that ALE still fixes with 1/6 output of oscillation frequency clock, so it can externally be exported clock or be used for regularly purpose.
Program stores and allows
Output is the read strobe signal of external program memory, when single-chip microcomputer during by the external program memory instruction fetch, and twice of each machine cycle
Effectively, namely export two pulses.
XTAL1 is the input end of the internal clock generator of oscillator inverting amplifier.
XTAL2 is the output terminal of oscillator inverting amplifier.
Serial-port communication
I have selected standard RS-232 interface for use this serial port, and it is level and Transistor-Transistor Logic level conversion driving circuit.Chip commonly used is MAX232, and the advantage of MAX2321 is:
(1) a slice chip can be finished the dual-use function that sends conversion and receive conversion.
(2) single power supply+5V power supply
(3) its circuit design be connected fairly simple and multiple functional.
The MAX232 chip is that U.S. letter company is the interface circuit of the rs-232 standard serial ports design of computer specially, and use+5V single power supply can be realized the IC chip that Transistor-Transistor Logic level and RS-232 level are changed mutually.
Wherein pin 1-6 (C1+, V+, C1, C2+, C2-, V-) is used for the supply voltage conversion, as long as externally insert corresponding electrochemical capacitor; Pin 7-10 and pin 11-14 constitute the change-over circuit of two groups of TTL signal levels and RS-232 signal level, and corresponding pin can directly link to each other with the Transistor-Transistor Logic level pin of serial port of single chip computer and the RS-232C level pin of PC.
The design is the data of gathering three-dimensional, so when sampling, should gather the data of X, Y, Z-direction respectively, in four conversion input channels in A/D converter, passage 1 sampling directions X data, passage 2 sampling Y-direction data, passage 3 sampling Z directional datas.So during analog to digital conversion, should be respectively to passage 1, passage 2, the conversion of passage 3 gatings.Sampling routine is realized block diagram as shown in Figure 4.
Because the data of 8 points that the design has used 83 D weak magnetic field sensor measurements so a circulation will be set, make an A/D converter can change the data that 8 three-dimension sensors are measured.Owing to be 8 circulations, controlled so will export three bytes of ABC by single-chip microcomputer.
4 sensors of four jiaos, it is horizontal, and longitudinal pitch should be arranged in the maximum zone of sheet material drawing process distortion in theory, and the design obtains according to experimental summary, gets laterally=40mm, vertically=35mm
Figure 10-11 has provided the data and curves of experimental system, as Figure 10, the curve below has been set the different Show Color that needs 4 image data successively, (selected the numerical value (being magnetic field 2Y) of temperature, the displacement in the drawing process, the pulling force in the drawing process and second magnetic induction density sensor Y-direction that C orders among Figure 10, the upper right corner shows the infrared temperature image in the entire test, the user can select 4 temperature observation point arbitrarily in this image, and shows with curve form.In the curve from the graph as can be seen: displacement was directly proportional substantially with the time, just draw speed substantially at the uniform velocity, pulling force begins when reaching certain value to descend, show that test specimen begins fracture, the temperature that C is ordered sharply rises when beginning to rupture, and magnetic induction density rises also apparent in viewly when temperature rises.
Figure 10 and 11 shows: adopt the scheme of present embodiment, can realize the accurate detection of 5 three-dimensional magnetic fields, for the thermic magnetic effect of studying under many coupling conditions provides an outstanding experiment porch.
Claims (4)
1. three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect is characterized in that, comprises single-chip microcomputer, Magnetic Sensor, MUX, analog to digital converter, hysteresis effect elimination circuit and serial communication circuit; Described Magnetic Sensor is 5, is symmetricly set on 5 some positions in PCB front, and 4 Si Jiaochu that are arranged on pcb board wherein, another is arranged on the central authorities of pcb board; Each Magnetic Sensor has 3 signal output channels, exports the magnetic induction signal of X, Y, three directions of Z respectively;
Magnetic Sensor is connected with the input interface of single-chip microcomputer with analog to digital converter by MUX successively; The channel selecting termination single machine output end of MUX;
Two input ends of hysteresis effect elimination circuit connect reset terminal and the set end (set8 and reset8) of single-chip microcomputer respectively; Reset terminal and set end are the IO port of single-chip microcomputer; The output terminal of hysteresis effect elimination circuit links to each other with the impulse polarization circuit in the Magnetic Sensor;
Single-chip microcomputer is connected with host computer by described serial communication circuit.
2. three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect according to claim 1, it is characterized in that, described Magnetic Sensor adopts the HMC2003 chip, described MUX comprises 3 multi-way switchs: i.e. first multi-way switch, second multi-way switch and the 3rd multi-way switch, and analog multichannel switch adopts the 74HC4051 chip with 8 road signal input channels and 1 signal output channels; Analog to digital converter adopts the ADS7825 chip of sixteen bit; The ADS7825 chip has four input end of analog signal;
The X signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of first multi-way switch respectively;
The Y-signal output channel of 5 Magnetic Sensors is joined with 5 signal input channels of second multi-way switch respectively;
The Z signal output channels of 5 Magnetic Sensors joins with 5 signal input channels of the 3rd multi-way switch respectively;
3 signal output channels of 3 multi-way switchs join with 3 input end of analog signal of analog to digital converter respectively;
Three number word selecting sides of 3 multi-way switchs are corresponding in parallel.
3. three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect according to claim 2 is characterized in that, hysteresis effect elimination circuit is the pulse-generating circuit based on power MOSFET tube, and power MOSFET tube adopts the IRF7106 chip;
Join by the impulse polarization circuit in first electric capacity (C83) and the Magnetic Sensor behind the 5-8 pin short circuit of IRF7106 chip;
1 pin of IRF7106 chip and 3 pin are ground connection and direct supply anode VCC1 respectively;
2 pin (G1) of IRF7106 chip connect described reset terminal (reset8);
Another IO port of single-chip microcomputer is as set end (set8), and set end (set8) connects the base stage of the triode (Q18) of NPN type by first resistance (R81); The emitter grounding of triode (Q18), the collector of triode (Q18) meets VCC1 by second resistance (R82); The collector of triode (Q18) also connects 4 pin (G2 end) of IRF7106 chip by second electric capacity (C81); Be connected to the 3rd resistance (R83) between 4 pin of IRF7106 chip and the VCC1; Be connected to the 3rd electric capacity (C82) between VCC1 and the ground.
4. according to each described three-dimensional magnetic field, 5 positions measurement mechanism based on sheet material stretching thermic magnetic effect of claim 1-3, it is characterized in that serial communication circuit adopts private communication device MAX232, single-chip microcomputer adopts the STC89C54RD chip.
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