CN103424138A - Combined resistance type instrument calibration device - Google Patents
Combined resistance type instrument calibration device Download PDFInfo
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- CN103424138A CN103424138A CN2013103783831A CN201310378383A CN103424138A CN 103424138 A CN103424138 A CN 103424138A CN 2013103783831 A CN2013103783831 A CN 2013103783831A CN 201310378383 A CN201310378383 A CN 201310378383A CN 103424138 A CN103424138 A CN 103424138A
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Abstract
The invention relates to a combined resistance type instrument calibration device. The combined resistance type instrument calibration device comprises a single-chip microcomputer unit, a keyboard unit, a displaying unit and a combined resistance control unit composed of a D/A switching circuit, a combined resistance output circuit, a proportional feedback circuit and a range switching control circuit. The keyboard unit, the displaying unit, the D/A switching circuit and the range switching control circuit are respectively connected with the single-chip microcomputer unit. The output end of the D/A switching circuit and the output end of the range switching control circuit are respectively connected with the input end of the combined resistance output circuit. The combined resistance output end of the combined resistance output circuit is connected with an instrument to be calibrated, one end of the proportional feedback circuit is connected with the combined resistance output end, and the other end of the proportional feedback circuit is connected with the D/A switching circuit. The specific value of the input voltage to the input current is obtained through programming, and programmable combined resistance output is obtained, the range is wide, the precision is high, the load capacity is strong, and the combined resistance type instrument calibration device is very good in universality and can meet demands for calibration of various resistance type sensor instruments.
Description
Technical field
The present invention relates to a kind of calibrating apparatus for general instruments, relate in particular to a kind of combined resistance formula instrument check device.
Background technology
The input signal of a lot of instrument is resistance signals of being sent here by sensor, as fuel-quantity transducer, pressure transducer, the temperature sensor of automobile instrument adopts resistance sensor more, its resistance changes along with the variation of oil level, oil pressure (air pressure), water temperature (or oil temperature), and the indicating instrument supporting with these sensors is all to design according to resistance variations as fuel level gauge, brake pressure gage, water-thermometer (oil thermometer) etc.
Adopt several grades of fixed resistances while in early days this class instrument being carried out to verification, the sensor of a kind of model of every replacing must be changed a kind of measuring resistance and just can be simulated and verification, and versatility is poor.More adopted afterwards rotating resistance box and program-controlled resistor network type tester to carry out verification to instrument.But there is following defect in these two kinds of verification modes: (1) adopts the rotating resistance box check meter, and the resistance box volume is large, troublesome poeration, and efficiency is low, owing to there is no corresponding protection circuit, often occurs that resistance burns phenomenon; (2) adopt program-controlled resistor network type tester, the structure of its resistor network generally adopts the frame mode of 8421BCD code, by relay, the short circuit of corresponding resistor is reached to needed resistance value.Or adopt weighted resistance network in parallel, by the analog switch break-make, parallel resistance is combined and obtains corresponding resistance value.Because failure rate after relay, the long-term break-make of analog switch is higher, its resistor network need adopt more high-power nonstandard precision resistance, the general employing made by oneself, there are coiling difficulty, the poor shortcoming of thermal stability, its resistor network and pcb board all need to take cooling measure, thereby cause that volume is large, cost is high, also limited and applied.
Summary of the invention
The present invention mainly solves original calibrating apparatus for general instruments that the resistance sensor instrument is carried out to verification and exists volume large, troublesome poeration, and efficiency is low, and versatility is poor, the technical matters that reliability is lower; A kind of combined resistance formula instrument check device is provided, and it exports programmable resistance, and precision is high, and the output resistance scope is wide, has good versatility, easy to operate, raises the efficiency, and good thermal stability is arranged, and reliability is high, and volume is also less.
Above-mentioned technical matters of the present invention is mainly solved by following technical proposals: the present invention includes single machine unit, keyboard unit, display unit and combined resistance control module and reach the power supply unit that operating voltage is provided for whole combined resistance formula instrument check device, keyboard unit, display unit are connected with single machine unit respectively, the control signal output terminal of single machine unit is connected with the input end of described combined resistance control module, the combined resistance output terminal of combined resistance control module with by check meter, be connected.Set the combined resistance value that needs output by keyboard unit, setting signal send on the one hand display unit to show after single machine unit is processed, flow on the other hand the combined resistance control module, through synthetic resistance control module, process again, the combined resistance value that output needs is given by check meter, but thereby, by the just output of analog electrical resistive sensor of programming, realize the verification to the instrument with the resistance sensor coupling.The programmable resistance of the present invention's output, precision is high, and the output resistance scope is wide, has good versatility, easy to operate, raises the efficiency.
As preferably, described combined resistance control module comprises the D/A change-over circuit, combined resistance output circuit and proportional feedback circuit, the control signal output terminal of the input end of D/A change-over circuit and described single machine unit is connected, the output terminal of D/A change-over circuit is connected with the input end of combined resistance output circuit, the combined resistance output terminal of combined resistance output circuit with by check meter, be connected, the combined resistance output terminal of the input end of described proportional feedback circuit and described combined resistance output circuit is connected, the output terminal of proportional feedback circuit is connected with described D/A change-over circuit.After single machine unit is processed the setting signal of keyboard unit, flow to the D/A change-over circuit, processing and conversion through the D/A change-over circuit, transmit signal to the combined resistance output circuit, through synthetic electric resistance output circuit, process again, obtain the ratio of voltage and electric current, thereby obtain combined resistance able to programme, export to by check meter.The proportional feedback circuit can be eliminated the impact of D/A change-over circuit on the output combined resistance by follower, further guarantees that the combined resistance of output meets the setting requirement.
As preferably, described combined resistance control module comprises the range conversion control circuit, and the input end of range conversion control circuit is connected with described single machine unit, and the output terminal of range conversion control circuit is connected with described combined resistance output circuit.Single machine unit is processed the setting signal of keyboard unit, the output corresponding signal is to the range conversion control circuit, range conversion control circuit output control signal, to the combined resistance output circuit, is guaranteed the Standard resistance range of the combined resistance of combined resistance output circuit output.Further widen the output area of combined resistance, precision is higher, and load capacity is stronger, can simulate the more resistance sensor of polytypic, more kinds of by the needs of check meter to meet, and further improves versatility.
As preferably, described combined resistance control module comprises current foldback circuit, and the input end of current foldback circuit is connected with described combined resistance output circuit, and the output terminal of current foldback circuit is connected with described single machine unit.Current foldback circuit detects the output current of combined resistance output circuit; once the output current detected is too high; send signal to single machine unit; through single machine unit, process; send control signal and turn-off the output of combined resistance output circuit; thereby realize overcurrent protection, guarantee can not damaged because of overcurrent by check meter.
As preferably, described combined resistance control module comprises warning circuit, and warning circuit is connected with described single machine unit.When single machine unit receives the over-current signal that current foldback circuit sends here, send control signal and start warning circuit and carry out the overcurrent warning, be convenient to the staff and make in time the processing such as maintenance, replacing.
As preferably, described D/A change-over circuit comprises DA conversion chip U10, and DA conversion chip U10 adopts the DAC8811 chip, described combined resistance output circuit comprises amplifier U6, amplifier U7, amplifier U8 and field effect transistor Q10, field effect transistor Q11, field effect transistor Q12, field effect transistor Q13, field effect transistor Q61, described proportional feedback circuit comprises amplifier U9, described range conversion control circuit comprises analog switch chip U3 and triode Q14, triode Q15, triode Q16, and analog switch chip U3 adopts 4052 chips, 1 pin of DA conversion chip U10, 2 pin, 8 pin are connected with three control signal output terminals of described single machine unit respectively, 7 pin of DA conversion chip U10 connect 5V voltage, the 6 pin ground connection of DA conversion chip U10, be connected with capacitor C 101 between 7 pin of DA conversion chip U10 and ground, 5 pin of DA conversion chip U10 are connected with the inverting input of amplifier U8, the in-phase input end ground connection of amplifier U8, the output terminal of amplifier U8, one tunnel is connected with 3 pin of DA conversion chip U10, another road is connected with the inverting input of amplifier U7 through resistance R 71, the in-phase input end of amplifier U7 is through resistance R 73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R 72, another road is connected with the in-phase input end of amplifier U6, 13 pin of the inverting input of amplifier U6 and analog switch chip U3 are connected, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R 61, the drain electrode of field effect transistor Q61 is exactly the combined resistance output terminal of described combined resistance output circuit, it both was connected by check meter with described, with an end of resistance R 91, be connected again, the other end of resistance R 91 is through resistance R 92 ground connection, the also contact of resistance R 91 and resistance R 92 is connected with the inverting input of amplifier U9, the in-phase input end of amplifier U9 is connected with the output terminal of amplifier U9, the output terminal of amplifier U9 is connected with 4 pin of DA conversion chip U10, field effect transistor Q10, field effect transistor Q11, the drain electrode of field effect transistor Q12 and field effect transistor Q13 all is connected with the source electrode of field effect transistor Q61, the source electrode of field effect transistor Q10 is through resistance R 111 ground connection, the source electrode of field effect transistor Q11 is through resistance R 112 ground connection, the source electrode of field effect transistor Q12 is through resistance R 113 ground connection, the source electrode of field effect transistor Q13 is through resistance R 114 ground connection, field effect transistor Q10, field effect transistor Q11, the source electrode of field effect transistor Q12 and field effect transistor Q13 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, field effect transistor Q10, field effect transistor Q11, the grid of field effect transistor Q12 and field effect transistor Q13 respectively with 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are connected, 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are again respectively through resistance R 17, through resistance R 18, through resistance R 19, through resistance R 110 ground connection, other three control signal output terminals of described single machine unit are connected with the base stage of triode Q14 through resistance R 14 respectively, through resistance R 15, with the base stage of triode Q15, be connected, through resistance R 16, with the base stage of triode Q16, be connected, the collector of triode Q14 connects 9V voltage through resistance R 11, the collector of triode Q15 connects 9V voltage through resistance R 12, the collector of triode Q16 connects 9V voltage through resistance R 13, triode Q14, the equal ground connection of the emitter of triode Q15 and triode Q16, while triode Q14, the collector of triode Q15 and triode Q16 respectively with 9 pin of analog switch chip U3, 10 pin, 6 pin are connected, 3 pin of analog switch chip U3, 16 pin all connect 9V voltage, the 16 foot meridian capacitor C11 ground connection of analog switch chip U3, 7 pin of analog switch chip U3 and 8 pin ground connection.Select 16 multiplication type DA converter DAC8811 chips, even multiplication type DA reference voltage is reduced to, approached the zero ratio output preferably that also can obtain.Amplifier U6～U8 adopts the chopper-zero-stabilized amplifier, improves precision.Field effect transistor Q61 selects high-power N raceway groove insulation field effect transistor, has solved the combined resistance imbalance that the transistor adjustment is guaranteed adequate food and pressure drop causes, and makes its loading range wider.The range conversion control circuit adopts 4052 chips, it has two 4 to select 1 multi-channel analog selector switch, and four high-power N raceway grooves insulation field effect transistor have been adopted, be field effect transistor Q10, field effect transistor Q11, field effect transistor Q12 and the field effect transistor Q13 electronic switch as the range conversion, realize the automatic range conversion of 4 ranges.
As preferably, described combined resistance control module comprises current foldback circuit, and described current foldback circuit comprises amplifier U11, amplifier U12, amplifier U13, amplifier U14, or door U5 and triode Q51, amplifier U11, the in-phase input end of amplifier U12 connects 3V voltage, the in-phase input end of amplifier U13 is connected with the movable end of variable resistor RW32, two stiff ends of variable resistor RW32 connect respectively 3V voltage and ground connection, the in-phase input end of amplifier U14 is connected with the movable end of variable resistor RW31, two stiff ends of variable resistor RW31 meet respectively 3V voltage and ground connection, amplifier U11, amplifier U12, amplifier U13, the inverting input of amplifier U14 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, amplifier U11, amplifier U12, amplifier U13, the output terminal of amplifier U14 respectively with or the door U5 four input ends be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R 51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R 52, and the emitter of triode Q51 is connected with the interrupting input pin of described single machine unit again.The sampling current of current foldback circuit is taken from the electric current on reference resistance R111～R114, its pressure drop is respectively by amplifier U11, amplifier U12, the comparative voltage of amplifier U13 and amplifier U14 and setting relatively, one pass by when stream in four road signals, pressure drop on its reference resistance is greater than the comparative voltage of setting, the amplifier upset, four tunnel output signals of four amplifiers by four-input terminal or door U5 phase or after export to the base stage of triode Q51, after the level conversion of triode Q51, the emitter of triode Q51 produces the interrupting input pin of INT0 signal to single-chip microcomputer, start the interrupt service routine of single-chip microcomputer, make the INH end of single-chip microcomputer output control signal to analog switch chip U3, analog switch chip U3 turn-offs field effect transistor Q10, field effect transistor Q11, field effect transistor Q12 and field effect transistor Q13, cut off all passages, thereby there is no combined resistance output, realize overcurrent protection.
As preferably, described single machine unit comprises single-chip microcomputer U1, single-chip microcomputer U1 adopts the STC2C5A60S2 single-chip microcomputer, described display unit is LCDs, described keyboard unit comprises ten six press keys of lining up four lines four row, 2 pin of same row button connect together and export four column signal output terminals, with 1 pin of a line button, four the capable signal output parts of output that connect together, four column signal output terminals are connected with 21～28 pin of described single-chip microcomputer U1 respectively with four capable signal output parts, 1 pin of single-chip microcomputer U1 is connected with described power supply unit, 3～6 pin of single-chip microcomputer U1, 17 pin and 32～39 pin are connected with the signal input pin of LCDs respectively, 2 pin of single-chip microcomputer U1, 3 pin are connected with three input ends of described D/A change-over circuit respectively with 4 pin, 14～16 pin of single-chip microcomputer U1 are connected with the input end of described range conversion control circuit respectively, 9 pin of single-chip microcomputer U1 are connected with the negative pole of electrochemical capacitor C12, the positive pole of electrochemical capacitor C12 connects 5V voltage, 9 pin of single-chip microcomputer U1 are again through resistance R 17 ground connection, connect crystal oscillator Y11 between 18 pin of single-chip microcomputer U1 and 19 pin, the 18 foot meridian capacitor C12 ground connection of single-chip microcomputer U1, the 19 foot meridian capacitor C13 ground connection of single-chip microcomputer U1, the 20 pin ground connection of single-chip microcomputer U1, 40 pin of single-chip microcomputer U1 connect 5V voltage, 40 pin of single-chip microcomputer U1 are again through capacitor C 11 ground connection.In ten six press keys, can become to arrange key, clear key, single step key, type selecting key, store key, loop start/ESC Escape, start acknowledgement key and measurement range selection 0.1 Ω key, 1 Ω key, 10 Ω keys, 100 Ω keys and 1000 Ω keys by software set as required.Easy to operate, the combined resistance output area is wide, and precision is high.
The invention has the beneficial effects as follows: the one-port network that uses amplifier to form, adopt low imbalance, Low-bias Current amplifier, the high precision multiplication type d/a converter, the adjustment pipe of wide range regulation ability, obtain the ratio of input voltage and electric current by programming, obtain combined resistance output able to programme, combined resistance is the no-contact resistance analog network, at aspects such as precision, thermal stability, reliability and volumes, all has superiority preferably.The combined resistance of the present invention's output, scope is wide, and precision is high, and load capacity is strong, has good versatility, easy to operate, raises the efficiency, to meet the verification needs of multiple resistance sensor instrument.
The accompanying drawing explanation
Fig. 1 is a kind of circuit theory syndeton block diagram of the present invention.
Fig. 2 is a kind of circuit theory diagrams of combined resistance control module in the present invention.
Fig. 3 is a kind of circuit theory diagrams of current foldback circuit in the present invention.
Fig. 4 is a kind of circuit theory diagrams of single machine unit and display unit in the present invention, keyboard unit.
1. single machine unit in figure; 2. keyboard unit, 3. display unit, 4. combined resistance control module; 5. power supply unit; 6. by check meter, 7. D/A change-over circuit, 8. combined resistance output circuit; 9. proportional feedback circuit; 10. range conversion control circuit, 11. current foldback circuits, 12. warning circuits.
Embodiment
Below by embodiment, and by reference to the accompanying drawings, technical scheme of the present invention is described in further detail.
Embodiment: the combined resistance formula instrument check device of the present embodiment, as shown in Figure 1, comprise that single machine unit 1, keyboard unit 2, display unit 3 and combined resistance control module 4 reach the power supply unit 5 that operating voltage is provided for whole combined resistance formula instrument check device.Combined resistance control module 4 comprises D/A change-over circuit 7, combined resistance output circuit 8, proportional feedback circuit 9, range conversion control circuit 10, current foldback circuit 11 and warning circuit 12.Keyboard unit 2, display unit 3 are connected with single machine unit 1 respectively, the control signal output terminal of single machine unit 1 is connected with the input end of D/A change-over circuit 7, the output terminal of D/A change-over circuit 7 is connected with the input end of combined resistance output circuit 8, the combined resistance output terminal of combined resistance output circuit 8 with by check meter 6, be connected, the combined resistance output terminal of the input end of proportional feedback circuit 9 and combined resistance output circuit 8 is connected, and the output terminal of proportional feedback circuit 9 is connected with D/A change-over circuit 7.The input end of range conversion control circuit 10 is connected with single machine unit 1, and the output terminal of range conversion control circuit 10 is connected with combined resistance output circuit 8.The input end of current foldback circuit 11 is connected with combined resistance output circuit 8, and the output terminal of current foldback circuit 11 is connected with single machine unit 1.Warning circuit 12 is connected with single machine unit 1.
As shown in Figure 4, single machine unit 1 comprises single-chip microcomputer U1, single-chip microcomputer U1 adopts the STC2C5A60S2 single-chip microcomputer, display unit 3 is LCDs, keyboard unit 2 comprises ten six press keys of lining up four lines four row, 2 pin of same row button connect together and export four column signal output terminals, with 1 pin of a line button, four the capable signal output parts of output that connect together, four column signal output terminals are connected with 21～28 pin of single-chip microcomputer U1 respectively with four capable signal output parts, 1 pin of single-chip microcomputer U1 is connected with power supply unit 5, 3～6 pin of single-chip microcomputer U1, 17 pin and 32～39 pin are connected with the signal input pin of LCDs respectively.9 pin of single-chip microcomputer U1 are connected with the negative pole of electrochemical capacitor C12, the positive pole of electrochemical capacitor C12 connects 5V voltage, 9 pin of single-chip microcomputer U1 are again through resistance R 17 ground connection, connect crystal oscillator Y11 between 18 pin of single-chip microcomputer U1 and 19 pin, the 18 foot meridian capacitor C12 ground connection of single-chip microcomputer U1, the 19 foot meridian capacitor C13 ground connection of single-chip microcomputer U1, the 20 pin ground connection of single-chip microcomputer U1,40 pin of single-chip microcomputer U1 connect 5V voltage, and 40 pin of single-chip microcomputer U1 are again through capacitor C 11 ground connection.13 pin of single-chip microcomputer U1 are connected with the base stage of triode Q31 through resistance R 31, and the emitter of triode Q31 connects 5V voltage, and the end of the collector of triode Q31 and hummer B3 is connected, the other end ground connection of hummer B3.
As shown in Figure 2, D/A change-over circuit 7 comprises DA conversion chip U10, and DA conversion chip U10 adopts the DAC8811 chip; Combined resistance output circuit 8 comprises amplifier U6, amplifier U7, amplifier U8 and field effect transistor Q10, field effect transistor Q11, field effect transistor Q12, field effect transistor Q13, field effect transistor Q61; Proportional feedback circuit 9 comprises amplifier U9; Range conversion control circuit 10 comprises analog switch chip U3 and triode Q14, triode Q15, triode Q16, and analog switch chip U3 adopts 4052 chips.1 pin of DA conversion chip U10, 2 pin, 8 pin respectively with 4 pin of single-chip microcomputer U1, 3 pin, 2 pin are connected, 7 pin of DA conversion chip U10 connect 5V voltage, the 6 pin ground connection of DA conversion chip U10, be connected with capacitor C 101 between 7 pin of DA conversion chip U10 and ground, 5 pin of DA conversion chip U10 are connected with the inverting input of amplifier U8, the in-phase input end ground connection of amplifier U8, the output terminal of amplifier U8, one tunnel is connected with 3 pin of DA conversion chip U10, another road is connected with the inverting input of amplifier U7 through resistance R 71, the in-phase input end of amplifier U7 is through resistance R 73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R 72, another road is connected with the in-phase input end of amplifier U6, 13 pin of the inverting input of amplifier U6 and analog switch chip U3 are connected, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R 61, the drain electrode of field effect transistor Q61 is exactly the combined resistance output terminal, it both and by check meter 6(resistance R 62 was equivalent to by check meter, pull-up resistor) be connected, with an end of resistance R 91, be connected again, the other end of resistance R 91 is through resistance R 92 ground connection, the also contact of resistance R 91 and resistance R 92 is connected with the inverting input of amplifier U9, the in-phase input end of amplifier U9 is connected with the output terminal of amplifier U9, the output terminal of amplifier U9 is connected with 4 pin of DA conversion chip U10, field effect transistor Q10, field effect transistor Q11, the drain electrode of field effect transistor Q12 and field effect transistor Q13 all is connected with the source electrode of field effect transistor Q61, the source electrode of field effect transistor Q10 is through resistance R 111 ground connection, the source electrode of field effect transistor Q11 is through resistance R 112 ground connection, the source electrode of field effect transistor Q12 is through resistance R 113 ground connection, the source electrode of field effect transistor Q13 is through resistance R 114 ground connection, field effect transistor Q10, field effect transistor Q11, the source electrode of field effect transistor Q12 and field effect transistor Q13 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, field effect transistor Q10, field effect transistor Q11, the grid of field effect transistor Q12 and field effect transistor Q13 respectively with 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are connected, 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are again respectively through resistance R 17, through resistance R 18, through resistance R 19, through resistance R 110 ground connection, 14 pin of single-chip microcomputer U1, 15 pin, 16 pin are connected with the base stage of triode Q14 through resistance R 14 respectively, through resistance R 15, with the base stage of triode Q15, be connected, through resistance R 16, with the base stage of triode Q16, be connected, the collector of triode Q14 connects 9V voltage through resistance R 11, the collector of triode Q15 connects 9V voltage through resistance R 12, the collector of triode Q16 connects 9V voltage through resistance R 13, triode Q14, the equal ground connection of the emitter of triode Q15 and triode Q16, while triode Q14, the collector of triode Q15 and triode Q16 respectively with 9 pin of analog switch chip U3, 10 pin, 6 pin are connected, 3 pin of analog switch chip U3, 16 pin all connect 9V voltage, the 16 foot meridian capacitor C11 ground connection of analog switch chip U3, 7 pin of analog switch chip U3 and 8 pin ground connection.
As shown in Figure 3, current foldback circuit 11 comprises amplifier U11, amplifier U12, amplifier U13, amplifier U14, or door U5 and triode Q51, amplifier U11, the in-phase input end of amplifier U12 connects 3V voltage, the in-phase input end of amplifier U13 is connected with the movable end of variable resistor RW32, two stiff ends of variable resistor RW32 connect respectively 3V voltage and ground connection, the in-phase input end of amplifier U14 is connected with the movable end of variable resistor RW31, two stiff ends of variable resistor RW31 meet respectively 3V voltage and ground connection, amplifier U11, amplifier U12, amplifier U13, the inverting input of amplifier U14 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, amplifier U11, amplifier U12, amplifier U13, the output terminal of amplifier U14 respectively with or the door U5 four input ends be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R 51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R 52, and the emitter of triode Q51 is connected with 12 pin of single-chip microcomputer U1 again.
One, resistance building-up process:
(1) the combined resistance direct-current working volts are: 1.25V～30V, resistance R 62 is pull-up resistor (being equivalent to accordingly by check meter).The terminal voltage that the drain terminal voltage Us of field effect transistor Q61 is combined resistance, after resistance R 91 and resistance R 92 dividing potential drops and amplifier U9 proportional feedback, the output end voltage of amplifier U9 is as the changing voltage of DAC8811 chip.
(2) result of DAC8811 chip conversion is exported with current forms, after amplifier U8 converts voltage to, outputs to amplifier U7.The output voltage V of amplifier U7
OUTWith input voltage V
REFAnd CODE(is by the keyboard setting, the control coding generated by single-chip microcomputer) relation is shown in following formula:
（1-1）
From formula 1-1, V
OUTIts value is negative, so outputs to the in-phase input end of amplifier U6 after anti-phase by amplifier U7.
(3) field effect transistor Q10～Q13(adopts N raceway groove insulation field effect transistor) be range selector, resistance R 111～R114 is the reference resistance under each range, after analog switch chip 4052 switchings, send signal according to the size of setting combined resistance by single-chip microcomputer and select the wherein accurate resistance line attachment of a roadbed, and voltage on selected reference resistance is added to the inverting input of amplifier U6.Because field effect transistor Q61(adopts N raceway groove insulation field effect transistor) and the corrective action of amplifier U6, the pressure drop (the anti-phase input terminal voltage of amplifier U6) on reference resistance is equated with the in-phase input end voltage of amplifier U6.And the in-phase input end voltage of amplifier U6 is:
V+=（Us/K）×（CODE/65536） （1-2）
The anti-phase input terminal voltage of amplifier U6 is:
V-=RN×Is （1-3）
In above-mentioned two formulas, Us is the combined resistance terminal voltage, and Is is the electric current that flows through combined resistance, the intrinsic standoff ratio that K is divider resistance R91 and R92, and CODE is the input voltage control coding in formula (1-1), RN is the voltage on the reference resistance of access.From above-mentioned two formulas, equated, the combined resistance value is:
Rs=Us/Is=65536×K×RN/CODE （1-4）
In formula (1-4), K, RN are definite value, and, under same range, if keep CODE constant, combined resistance Rs is definite value.If change the CODE value by the keyboard setting, can change the size of combined resistance Rs.
Two, range conversion implementation procedure:
The combined resistance size of setting according to keyboard unit, 14 pin of single-chip microcomputer and 15 pin output control signal are controlled the break-make of triode Q14 and triode Q15, obtain corresponding A, B value, control the reference resistance that 4052 chip selections are corresponding, access combined resistance control circuit, realize the automatic conversion of range.Detailed process is as follows:
(1) analog switch chip U3 selects 1 multi-channel analog selector switch CD4052 chip to realize by two 4, and 9 pin of analog switch chip U3 and the A on 10 pin, B signal are 4 to select 1 control signal, for channel selecting.INH signal on 6 pin of analog switch chip U3 is the sheet gating signal, for cutting off all passages, carries out overcurrent protection.
(2) Y of CD4052 chip group switch is realized range conversion selection, the public termination 9V DC voltage of Y group switch, the break-make of control field effect transistor Q10～Q13.The X of CD4052 chip group switch realizes that reference resistance selects, and the inverting input of the public termination amplifier U6 of X group switch selects the accurate ohmically voltage of a roadbed wherein to be added to the inverting input of amplifier U6.The break-make of field effect transistor Q10～Q13 is selected to select corresponding with the access of reference resistance R111～R114.
(3) need control the output of 9V DC voltage due to the CD4052 chip, its working power voltage need reach 9V, and the control level of A, B and INH signal also must reach 9V.And the P3.4 of single-chip microcomputer U1, P3.5 and P3.6 mouth line output high level are 5V, can't directly control A, B, the INH end of CD4052 chip, therefore, by triode Q14～Q16, realize the conversion of 5V and 9V level.
Three, overcurrent protection implementation procedure:
The sampling current of current foldback circuit is taken from the electric current on reference resistance R111～R114, its pressure drop is compared by the comparative voltage of amplifier U11～U14 and setting, one pass by when stream in four road sampling currents, the accurate ohmically pressure drop of this roadbed is greater than the comparative voltage of setting, the amplifier upset be attached thereto, by four-input terminal or the door U5 phase or after, control the break-make of triode Q51, the emitter of triode Q51 produces 12 pin of INT0 signal to single-chip microcomputer U1, make single-chip microcomputer U1 start interrupt service routine, the 16 pin output control signals of single-chip microcomputer U1 produce the control level of CD4052 chip I NH end, thereby turn-off field effect transistor Q10～Q13, cut off all passages, realize overcurrent protection.
The combined resistance scope of the present invention's output is: 1 ~ 1999.9 Ω, preset resistance resolution is 0.1 Ω, by the test of metering mechanism, be better than ± 0.1% ± 0.2 Ω of precision, this precision is far above requirement that in QC/T727-2007 automobile, motor vehicle instrument industry standard, precision is 0.5%.Load capacity of the present invention is strong, maximum current IR=500mA.
Claims (8)
1. a combined resistance formula instrument check device, it is characterized in that comprising single machine unit (1), keyboard unit (2), display unit (3) and combined resistance control module (4) reach the power supply unit (5) that operating voltage is provided for whole combined resistance formula instrument check device, keyboard unit (2), display unit (3) is connected with single machine unit (1) respectively, the control signal output terminal of single machine unit (1) is connected with the input end of described combined resistance control module (4), the combined resistance output terminal of combined resistance control module (4) with by check meter (6), be connected.
2. combined resistance formula instrument check device according to claim 1, it is characterized in that described combined resistance control module (4) comprises D/A change-over circuit (7), combined resistance output circuit (8) and proportional feedback circuit (9), the input end of D/A change-over circuit (7) is connected with the control signal output terminal of described single machine unit (1), the output terminal of D/A change-over circuit (7) is connected with the input end of combined resistance output circuit (8), the combined resistance output terminal of combined resistance output circuit (8) with by check meter (6), be connected, the input end of described proportional feedback circuit (9) is connected with the combined resistance output terminal of described combined resistance output circuit (8), the output terminal of proportional feedback circuit (9) is connected with described D/A change-over circuit (7).
3. combined resistance formula instrument check device according to claim 2, it is characterized in that described combined resistance control module (4) comprises range conversion control circuit (10), the input end of range conversion control circuit (10) is connected with described single machine unit (1), and the output terminal of range conversion control circuit (10) is connected with described combined resistance output circuit (8).
4. according to the described combined resistance formula of claim 2 or 3 instrument check device; it is characterized in that described combined resistance control module (4) comprises current foldback circuit (11); the input end of current foldback circuit (11) is connected with described combined resistance output circuit (8), and the output terminal of current foldback circuit (11) is connected with described single machine unit (1).
5. combined resistance formula instrument check device according to claim 4, is characterized in that described combined resistance control module (4) comprises warning circuit (12), and warning circuit (12) is connected with described single machine unit (1).
6. combined resistance formula instrument check device according to claim 3, is characterized in that described D/A change-over circuit (7) comprises DA conversion chip U10, and DA conversion chip U10 adopts the DAC8811 chip, described combined resistance output circuit (8) comprises amplifier U6, amplifier U7, amplifier U8 and field effect transistor Q10, field effect transistor Q11, field effect transistor Q12, field effect transistor Q13, field effect transistor Q61, described proportional feedback circuit (9) comprises amplifier U9, described range conversion control circuit (10) comprises analog switch chip U3 and triode Q14, triode Q15, triode Q16, and analog switch chip U3 adopts 4052 chips, 1 pin of DA conversion chip U10, 2 pin, 8 pin are connected with three control signal output terminals of described single machine unit (1) respectively, 7 pin of DA conversion chip U10 connect 5V voltage, the 6 pin ground connection of DA conversion chip U10, be connected with capacitor C 101 between 7 pin of DA conversion chip U10 and ground, 5 pin of DA conversion chip U10 are connected with the inverting input of amplifier U8, the in-phase input end ground connection of amplifier U8, the output terminal of amplifier U8, one tunnel is connected with 3 pin of DA conversion chip U10, another road is connected with the inverting input of amplifier U7 through resistance R 71, the in-phase input end of amplifier U7 is through resistance R 73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R 72, another road is connected with the in-phase input end of amplifier U6, 13 pin of the inverting input of amplifier U6 and analog switch chip U3 are connected, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R 61, the drain electrode of field effect transistor Q61 is exactly the combined resistance output terminal of described combined resistance output circuit (8), it both was connected by school instrument (6) with described, with an end of resistance R 91, be connected again, the other end of resistance R 91 is through resistance R 92 ground connection, the also contact of resistance R 91 and resistance R 92 is connected with the inverting input of amplifier U9, the in-phase input end of amplifier U9 is connected with the output terminal of amplifier U9, the output terminal of amplifier U9 is connected with 4 pin of DA conversion chip U10, field effect transistor Q10, field effect transistor Q11, the drain electrode of field effect transistor Q12 and field effect transistor Q13 all is connected with the source electrode of field effect transistor Q61, the source electrode of field effect transistor Q10 is through resistance R 111 ground connection, the source electrode of field effect transistor Q11 is through resistance R 112 ground connection, the source electrode of field effect transistor Q12 is through resistance R 113 ground connection, the source electrode of field effect transistor Q13 is through resistance R 114 ground connection, field effect transistor Q10, field effect transistor Q11, the source electrode of field effect transistor Q12 and field effect transistor Q13 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, field effect transistor Q10, field effect transistor Q11, the grid of field effect transistor Q12 and field effect transistor Q13 respectively with 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are connected, 1 pin of analog switch chip U3, 5 pin, 2 pin, 4 pin are again respectively through resistance R 17, through resistance R 18, through resistance R 19, through resistance R 110 ground connection, other three control signal output terminals of described single machine unit (1) are connected with the base stage of triode Q14 through resistance R 14 respectively, through resistance R 15, with the base stage of triode Q15, be connected, through resistance R 16, with the base stage of triode Q16, be connected, the collector of triode Q14 connects 9V voltage through resistance R 11, the collector of triode Q15 connects 9V voltage through resistance R 12, the collector of triode Q16 connects 9V voltage through resistance R 13, triode Q14, the equal ground connection of the emitter of triode Q15 and triode Q16, while triode Q14, the collector of triode Q15 and triode Q16 respectively with 9 pin of analog switch chip U3, 10 pin, 6 pin are connected, 3 pin of analog switch chip U3, 16 pin all connect 9V voltage, the 16 foot meridian capacitor C11 ground connection of analog switch chip U3, 7 pin of analog switch chip U3 and 8 pin ground connection.
7. combined resistance formula instrument check device according to claim 6, is characterized in that described combined resistance control module (8) comprises current foldback circuit (11), and described current foldback circuit (11) comprises amplifier U11, amplifier U12, amplifier U13, amplifier U14, or door U5 and triode Q51, amplifier U11, the in-phase input end of amplifier U12 connects 3V voltage, the in-phase input end of amplifier U13 is connected with the movable end of variable resistor RW32, two stiff ends of variable resistor RW32 connect respectively 3V voltage and ground connection, the in-phase input end of amplifier U14 is connected with the movable end of variable resistor RW31, two stiff ends of variable resistor RW31 meet respectively 3V voltage and ground connection, amplifier U11, amplifier U12, amplifier U13, the inverting input of amplifier U14 respectively with 12 pin of analog switch chip U3, 14 pin, 15 pin, 11 pin are connected, amplifier U11, amplifier U12, amplifier U13, the output terminal of amplifier U14 respectively with or the door U5 four input ends be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R 51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R 52, and the emitter of triode Q51 is connected with the interrupting input pin of described single machine unit (1) again.
8. according to claim 3 or 6 or 7 described combined resistance formula instrument check devices, it is characterized in that described single machine unit (1) comprises single-chip microcomputer U1, single-chip microcomputer U1 adopts the STC2C5A60S2 single-chip microcomputer, described display unit (3) is LCDs, described keyboard unit (2) comprises ten six press keys of lining up four lines four row, 2 pin of same row button connect together and export four column signal output terminals, with 1 pin of a line button, four the capable signal output parts of output that connect together, four column signal output terminals are connected with 21～28 pin of described single-chip microcomputer U1 respectively with four capable signal output parts, 1 pin of single-chip microcomputer U1 is connected with described power supply unit (5), 3～6 pin of single-chip microcomputer U1, 17 pin and 32～39 pin are connected with the signal input pin of LCDs respectively, 2 pin of single-chip microcomputer U1, 3 pin are connected with three input ends of described D/A change-over circuit (7) respectively with 4 pin, 14～16 pin of single-chip microcomputer U1 are connected with the input end of described range conversion control circuit (10) respectively, 9 pin of single-chip microcomputer U1 are connected with the negative pole of electrochemical capacitor C12, the positive pole of electrochemical capacitor C12 connects 5V voltage, 9 pin of single-chip microcomputer U1 are again through resistance R 17 ground connection, connect crystal oscillator Y11 between 18 pin of single-chip microcomputer U1 and 19 pin, the 18 foot meridian capacitor C12 ground connection of single-chip microcomputer U1, the 19 foot meridian capacitor C13 ground connection of single-chip microcomputer U1, the 20 pin ground connection of single-chip microcomputer U1, 40 pin of single-chip microcomputer U1 connect 5V voltage, 40 pin of single-chip microcomputer U1 are again through capacitor C 11 ground connection.
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