CN103424138B - Combined resistance formula instrument calibration device - Google Patents
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Abstract
The present invention relates to a kind of combined resistance formula instrument calibration device, comprise single machine unit, keyboard unit, display unit and by D/A change-over circuit, combined resistance output circuit, the combined resistance control module that proportional feedback circuit and range swithching control circuit are formed, keyboard unit, display unit, D/A change-over circuit, range swithching control circuit is connected with single machine unit respectively, the output terminal of D/A change-over circuit, the output terminal of range swithching control circuit is connected with the input end of combined resistance output circuit respectively, the combined resistance output terminal of combined resistance output circuit is connected with by check meter, proportional feedback circuit on one side connects combined resistance output terminal, the other end connects D/A change-over circuit.The present invention obtains the ratio of input voltage and electric current by programming, and obtain combined resistance able to programme and export, scope is wide, and precision is high, and load capacity is strong, has good versatility, meets the verification needs of multiple resistance sensor instrument.
Description
Technical field
The present invention relates to a kind of calibrating apparatus for general instruments, particularly relate to a kind of combined resistance formula instrument calibration device.
Background technology
The input signal of a lot of instrument is the resistance signal sent here by sensor, as fuel-quantity transducer, pressure transducer, temperature sensor many employings resistance sensor of automobile instrument, its resistance changes along with the change of oil level, oil pressure (air pressure), water temperature (or oil temperature), is all design according to resistance variations with indicating instrument such as fuel level gauge, brake pressure gage, the water-thermometer (oil thermometer) etc. that these sensors are supporting.
Early stage adopt several grades of fixed resistances when verifying this kind of instrument, the sensor often changing a kind of model must be changed a kind of measuring resistance and just can carry out simulating and verifying, and versatility is poor.Rotating resistance box and program-controlled resistor network type tester was more adopted to verify instrument afterwards.But these two kinds of verification modes exist following defect: (1) adopts rotating resistance box check meter, resistance box volume is large, troublesome poeration, and efficiency is low, owing to not having 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, reaches required resistance value by the short circuit of relay to corresponding resistor.Or adopt weighted resistance network in parallel, by analog switch break-make, combination is carried out to parallel resistance and obtains corresponding resistance value.Because after relay, the long-term break-make of analog switch, failure rate is higher, its resistor network need adopt more high-power nonstandard precision resistance, general employing self-control, there is the shortcoming that coiling difficulty, thermal stability are poor, its resistor network and pcb board all need to take cooling measure, thus cause that volume is large, cost is high, also limit and apply.
Summary of the invention
The present invention mainly solves original calibrating apparatus for general instruments verified resistance sensor instrument and there is volume greatly, troublesome poeration, and efficiency is low, and versatility is poor, the technical matters that reliability is lower; There is provided a kind of combined resistance formula instrument calibration device, it exports programmable resistance, and precision is high, and output resistance scope is wide, and have good versatility, easy to operate, raise the efficiency, have good thermal stability, 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 provide the power supply unit of operating voltage for whole combined resistance formula instrument calibration 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, and the combined resistance output terminal of combined resistance control module is connected with by check meter.The combined resistance value exported is needed by keyboard unit setting, setting signal send display unit to show on the one hand after single machine unit process, flow to combined resistance control module on the other hand, again through the process of combined resistance control module, the combined resistance value that output needs is given by check meter, thus just can the output of analog electrical resistive sensor by programming, realize the verification to the instrument of mating with resistance sensor.The programmable resistance that the present invention exports, precision is high, and output resistance scope is wide, has good versatility, easy to operate, raises the efficiency.
As preferably, described combined resistance control module comprises D/A change-over circuit, combined resistance output circuit and proportional feedback circuit, the input end of D/A change-over circuit is connected with the control signal output terminal of described single machine unit, 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 is connected with by check meter, the input end of described proportional feedback circuit is connected with the combined resistance output terminal of described combined resistance output circuit, the output terminal of proportional feedback circuit is connected with described D/A change-over circuit.After the setting signal of single machine unit to keyboard unit processes, flow to D/A change-over circuit, through process and the conversion of D/A change-over circuit, transmit signal to combined resistance output circuit, again through the process of synthesis electric resistance output circuit, obtain the ratio of voltage and electric current, thus obtain combined resistance able to programme, export to by check meter.Proportional feedback circuit can eliminate D/A change-over circuit to the impact exporting combined resistance by follower, guarantees that the combined resistance exported meets setting requirement further.
As preferably, described combined resistance control module comprises range swithching control circuit, and the input end of range swithching control circuit is connected with described single machine unit, and the output terminal of range swithching control circuit is connected with described combined resistance output circuit.The setting signal of single machine unit to keyboard unit processes, export corresponding signal to range swithching control circuit, range swithching control circuit exports control signal to combined resistance output circuit, guarantees the Standard resistance range of the combined resistance that combined resistance output circuit exports.Widen the output area of combined resistance further, precision is higher, and load capacity is stronger, can simulate the resistance sensor of more polytypic, more kinds of by the needs of check meter to meet, and improves versatility further.
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; then send signal to single machine unit; through single machine unit process; send the output that control signal turns off combined resistance output circuit; thus realize overcurrent protection, guarantee to be 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, then send control signal and start warning circuit and carry out overcurrent warning, be convenient to staff and make the process such as maintenance, replacing in time.
As preferably, described D/A change-over circuit comprises DA conversion chip U10, and DA conversion chip U10 adopts 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 swithching 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, electric capacity C101 is connected with 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 R71, the in-phase input end of amplifier U7 is through resistance R73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R72, another road is connected with the in-phase input end of amplifier U6, the inverting input of amplifier U6 is connected with 13 pin of analog switch chip U3, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R61, the drain electrode of field effect transistor Q61 is exactly the combined resistance output terminal of described combined resistance output circuit, it was both connected by check meter with described, be connected with one end of resistance R91 again, the other end of resistance R91 is through resistance R92 ground connection, resistance R91 is connected with the inverting input of amplifier U9 with the also contact of resistance R92, 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, field effect transistor Q12 is all connected with the source electrode of field effect transistor Q61 with the drain electrode of field effect transistor Q13, the source electrode of field effect transistor Q10 is through resistance R111 ground connection, the source electrode of field effect transistor Q11 is through resistance R112 ground connection, the source electrode of field effect transistor Q12 is through resistance R113 ground connection, the source electrode of field effect transistor Q13 is through resistance R114 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 R17, through resistance R18, through resistance R19, through resistance R110 ground connection, other three control signal output terminals of described single machine unit are connected with the base stage of triode Q14 through resistance R14 respectively, be connected with the base stage of triode Q15 through resistance R15, be connected with the base stage of triode Q16 through resistance R16, the collector of triode Q14 connects 9V voltage through resistance R11, the collector of triode Q15 connects 9V voltage through resistance R12, the collector of triode Q16 connects 9V voltage through resistance R13, triode Q14, the equal ground connection of emitter of triode Q15 and triode Q16, triode Q14 simultaneously, 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.16 multiplying-type D/A converter DAC8811 chips are selected, even if multiplying-type DA reference voltage is reduced to also can obtain the output of good ratio close to zero.Amplifier U6 ~ U8 adopts chopper-zero-stabilized amplifier, improves precision.Field effect transistor Q61 selects high-power N raceway groove insulation field effect transistor, solves the combined resistance imbalance that transistor Correctional tube saturation voltage drop causes, makes its loading range wider.Range swithching control circuit adopts 4052 chips, its have two 4 select 1 multi-channel analog selector switch, and have employed four high-power N raceway groove insulation field effect transistor, namely field effect transistor Q10, field effect transistor Q11, field effect transistor Q12 and field effect transistor Q13 are as the electronic switch of range swithching, realize the auto-shifted measurement 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 3V voltage and ground connection respectively, 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 connect 3V voltage and ground connection, amplifier U11 respectively, 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 four input ends of door U5 be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R52, 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 takes from the electric current on reference resistance R111 ~ R114, its pressure drop is respectively by amplifier U11, amplifier U12, amplifier U13 and amplifier U14 compares with the comparative voltage of setting, when in four road signals passes by stream, pressure drop on its reference resistance is greater than the comparative voltage of setting, amplifier overturns, four tunnels 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 INT0 signal to the interrupting input pin of single-chip microcomputer, start the interrupt service routine of single-chip microcomputer, make single-chip microcomputer export control signal to hold to the INH of analog switch chip U3, analog switch chip U3 turns off field effect transistor Q10, field effect transistor Q11, field effect transistor Q12 and field effect transistor Q13, cut off all passages, thus do not have combined resistance to export, realize overcurrent protection.
As preferably, described single machine unit comprises single-chip microcomputer U1, single-chip microcomputer U1 adopts STC2C5A60S2 single-chip microcomputer, described display unit is LCDs, described keyboard unit comprises ten six press keys lined up four lines four and arrange, 2 pin of same row button connect together output four column signal output terminals, 1 pin with a line button connects together output four row signal output parts, four column signal output terminals are connected with 21 ~ 28 pin of described single-chip microcomputer U1 respectively with four row 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 and 4 pin are connected with three input ends of described D/A change-over circuit respectively, 14 ~ 16 pin of single-chip microcomputer U1 are connected with the input end of described range swithching 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 R17 ground connection, crystal oscillator Y11 is connected 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 electric capacity C11 ground connection.In ten six press keys, become to arrange key, clear key, single step key, type selecting key, storage key, loop start/ESC Escape by software set, start acknowledgement key and measurement range selection 0.1 Ω key, 1 Ω key, 10 Ω keys, 100 Ω keys and 1000 Ω keys as required.Easy to operate, combined resistance output area is wide, and precision is high.
The invention has the beneficial effects as follows: use the one-port network that amplifier is formed, adopt low imbalance, Low-bias Current amplifier, high precision multiplication type d/a converter, the Correctional tube of wide range regulation ability, the ratio of input voltage and electric current is obtained by programming, obtain combined resistance able to programme to export, combined resistance is no-contact resistance analog network, in precision, thermal stability, reliability and volume etc., all have good superiority.The combined resistance that the present invention exports, 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.
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 swithching 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 calibration device of the present embodiment, as shown in Figure 1, comprise single machine unit 1, keyboard unit 2, display unit 3 and combined resistance control module 4 and provide the power supply unit 5 of operating voltage for whole combined resistance formula instrument calibration device.Combined resistance control module 4 comprises D/A change-over circuit 7, combined resistance output circuit 8, proportional feedback circuit 9, range swithching 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 is connected with by check meter 6, the input end of proportional feedback circuit 9 is connected with the combined resistance output terminal of combined resistance output circuit 8, and the output terminal of proportional feedback circuit 9 is connected with D/A change-over circuit 7.The input end of range swithching control circuit 10 is connected with single machine unit 1, and the output terminal of range swithching 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 STC2C5A60S2 single-chip microcomputer, display unit 3 is LCDs, keyboard unit 2 comprises ten six press keys lined up four lines four and arrange, 2 pin of same row button connect together output four column signal output terminals, 1 pin with a line button connects together output four row signal output parts, four column signal output terminals are connected with 21 ~ 28 pin of single-chip microcomputer U1 respectively with four row 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 R17 ground connection, crystal oscillator Y11 is connected 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 electric capacity C11 ground connection.13 pin of single-chip microcomputer U1 are connected with the base stage of triode Q31 through resistance R31, and the emitter of triode Q31 connects 5V voltage, and the collector of triode Q31 is connected with one end of hummer B3, 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 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 swithching 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, electric capacity C101 is connected with 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 R71, the in-phase input end of amplifier U7 is through resistance R73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R72, another road is connected with the in-phase input end of amplifier U6, the inverting input of amplifier U6 is connected with 13 pin of analog switch chip U3, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R61, the drain electrode of field effect transistor Q61 is exactly combined resistance output terminal, it both and be equivalent to by check meter by check meter 6(resistance R62, pull-up resistor) be connected, be connected with one end of resistance R91 again, the other end of resistance R91 is through resistance R92 ground connection, resistance R91 is connected with the inverting input of amplifier U9 with the also contact of resistance R92, 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, field effect transistor Q12 is all connected with the source electrode of field effect transistor Q61 with the drain electrode of field effect transistor Q13, the source electrode of field effect transistor Q10 is through resistance R111 ground connection, the source electrode of field effect transistor Q11 is through resistance R112 ground connection, the source electrode of field effect transistor Q12 is through resistance R113 ground connection, the source electrode of field effect transistor Q13 is through resistance R114 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 R17, through resistance R18, through resistance R19, through resistance R110 ground connection, 14 pin of single-chip microcomputer U1, 15 pin, 16 pin are connected with the base stage of triode Q14 through resistance R14 respectively, be connected with the base stage of triode Q15 through resistance R15, be connected with the base stage of triode Q16 through resistance R16, the collector of triode Q14 connects 9V voltage through resistance R11, the collector of triode Q15 connects 9V voltage through resistance R12, the collector of triode Q16 connects 9V voltage through resistance R13, triode Q14, the equal ground connection of emitter of triode Q15 and triode Q16, triode Q14 simultaneously, 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 3V voltage and ground connection respectively, 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 connect 3V voltage and ground connection, amplifier U11 respectively, 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 four input ends of door U5 be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R52, and the emitter of triode Q51 is connected with 12 pin of single-chip microcomputer U1 again.
One, resistance building-up process:
(1) combined resistance direct-current working volts are: 1.25V ~ 30V, and resistance R62 is pull-up resistor (being equivalent to accordingly by check meter).The drain terminal voltage Us of field effect transistor Q61 is the terminal voltage of combined resistance, and after resistance R91 and resistance R92 dividing potential drop 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 exports as an electrical current, converts to after voltage, output to amplifier U7 through amplifier U8.The output voltage V of amplifier U7
oUTwith input voltage V
rEFand CODE(is arranged by keyboard, 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, outputs to the in-phase input end of amplifier U6 after therefore anti-phase by amplifier U7.
(3) field effect transistor Q10 ~ Q13(adopts N raceway groove insulation field effect transistor) be range selector, resistance R111 ~ R114 is the reference resistance under each range, after analog switch chip 4052 switches, size according to setting combined resistance sends a signal behavior wherein road reference resistance line attachment by single-chip microcomputer, 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, make the pressure drop on reference resistance (the anti-phase input terminal voltage of amplifier U6) equal 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 combined resistance terminal voltage, and Is is the electric current flowing through combined resistance, and K is the intrinsic standoff ratio of divider resistance R91 and R92, and CODE is the input voltage control coding in formula (1-1), and RN is the voltage on the reference resistance of access.Equal from above-mentioned two formulas, combined resistance value is:
Rs=Us/Is=65536×K×RN/CODE （1-4）
In formula (1-4), K, RN are definite value, and namely under same range, if keep CODE constant, then combined resistance Rs is definite value.If arranged by keyboard and change CODE value, then can change the size of combined resistance Rs.
Two, range swithching implementation procedure:
According to the combined resistance size of keyboard unit setting, 14 pin of single-chip microcomputer and 15 pin export the break-make that control signal controls 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, realizes the automatic conversion of range.Detailed process is as follows:
(1) analog switch chip U3 selects the multi-channel analog selector switch CD4052 chip of 1 to realize by two 4, and A, B signal on 9 pin of analog switch chip U3 and 10 pin is 4 select 1 control signal, for channel selecting.INH signal on 6 pin of analog switch chip U3 is sheet gating signal, for cutting off all passages, carries out overcurrent protection.
(2) the Y group switch of CD4052 chip realizes range swithching selection, and the public termination 9V DC voltage of Y group switch controls the break-make of field effect transistor Q10 ~ Q13.The X group switch of CD4052 chip realizes reference resistance and selects, the inverting input of the public termination amplifier U6 of X group switch, selects the accurate ohmically voltage of a wherein roadbed 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) because CD4052 chip need the output of control 9V DC voltage, its working power voltage need reach 9V, and the control level of A, B and INH signal also must reach 9V.And P3.4, P3.5 and P3.6 mouth line of single-chip microcomputer U1 to export high level be 5V, cannot A, B, INH end of direct control 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 takes from the electric current on reference resistance R111 ~ R114, its pressure drop is compared with the comparative voltage of setting by amplifier U11 ~ U14, when in four road sampling currents passes by stream, the accurate ohmically pressure drop of this roadbed is greater than the comparative voltage of setting, the amplifier upset be then attached thereto, by four-input terminal or door U5 phase or after, control the break-make of triode Q51, the emitter of triode Q51 produces INT0 signal to 12 pin of single-chip microcomputer U1, single-chip microcomputer U1 is made to start interrupt service routine, 16 pin of single-chip microcomputer U1 export the control level that control signal produces CD4052 chip I NH end, thus turn off field effect transistor Q10 ~ Q13, cut off all passages, realize overcurrent protection.
The combined resistance scope that the present invention exports is: 1 ~ 1999.9 Ω, preset resistance resolution is 0.1 Ω, by the test of metering mechanism, precision is better than ± 0.1% ± 0.2 Ω, and this precision is the requirement of 0.5% far above precision in QC/T727-2007 automobile, motor vehicle instrument industry standard.Load capacity of the present invention is strong, maximum current IR=500mA.
Claims (3)
1. a combined resistance formula instrument calibration device, it is characterized in that comprising single machine unit (1), keyboard unit (2), display unit (3) and combined resistance control module (4) and provide the power supply unit (5) of operating voltage for whole combined resistance formula instrument calibration 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) is connected with by check meter (6), described combined resistance control module (4) comprises D/A change-over circuit (7), combined resistance output circuit (8) and proportional feedback circuit (9) and range swithching control circuit (10), 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) is connected with by check meter (6), 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), the input end of range swithching control circuit (10) is connected with described single machine unit (1), the output terminal of range swithching control circuit (10) is connected with described combined resistance output circuit (8), described D/A change-over circuit (7) comprises DA conversion chip U10, and DA conversion chip U10 adopts 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 swithching control circuit (10) comprises analog switch chip U3 and triode Q14, triode Q15, triode Q16, analog switch chip U3 adopts 4052 chips, analog switch chip U3 selects the multi-channel analog selector switch CD4052 chip of 1 to realize by two 4, A, B signal on 9 pin of analog switch chip U3 and 10 pin is 4 select 1 control signal, for channel selecting, INH signal on 6 pin of analog switch chip U3 is sheet gating signal, for cutting off all passages, carry out overcurrent protection, 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, electric capacity C101 is connected with 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 R71, the in-phase input end of amplifier U7 is through resistance R73 ground connection, the output terminal of amplifier U7, one tunnel is connected with the inverting input of amplifier U7 through resistance R72, another road is connected with the in-phase input end of amplifier U6, the inverting input of amplifier U6 is connected with 13 pin of analog switch chip U3, the output terminal of amplifier U6 is connected with the grid of field effect transistor Q61 through resistance R61, the drain electrode of field effect transistor Q61 is exactly the combined resistance output terminal of described combined resistance output circuit (8), it was both connected by school instrument (6) with described, be connected with one end of resistance R91 again, the other end of resistance R91 is through resistance R92 ground connection, resistance R91 is connected with the inverting input of amplifier U9 with the tie point of resistance R92, 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, field effect transistor Q12 is all connected with the source electrode of field effect transistor Q61 with the drain electrode of field effect transistor Q13, the source electrode of field effect transistor Q10 is through resistance R111 ground connection, the source electrode of field effect transistor Q11 is through resistance R112 ground connection, the source electrode of field effect transistor Q12 is through resistance R113 ground connection, the source electrode of field effect transistor Q13 is through resistance R114 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 R17, through resistance R18, through resistance R19, through resistance R110 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 R14 respectively, be connected with the base stage of triode Q15 through resistance R15, be connected with the base stage of triode Q16 through resistance R16, the collector of triode Q14 connects 9V voltage through resistance R11, the collector of triode Q15 connects 9V voltage through resistance R12, the collector of triode Q16 connects 9V voltage through resistance R13, triode Q14, the equal ground connection of emitter of triode Q15 and triode Q16, triode Q14 simultaneously, 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, described combined resistance control module (4) 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 3V voltage and ground connection respectively, 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 connect 3V voltage and ground connection, amplifier U11 respectively, 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 four input ends of door U5 be connected, or the output terminal of door U5 is connected with the base stage of triode Q51 through resistance R51, the grounded collector of triode Q51, the emitter of triode Q51 connects 5V voltage through resistance R52, and the emitter of triode Q51 is connected with the interrupting input pin of described single machine unit (1) again.
2. combined resistance formula instrument calibration device according to claim 1, it is characterized in that described combined resistance control module (4) comprises warning circuit (12), warning circuit (12) is connected with described single machine unit (1).
3. combined resistance formula instrument calibration device according to claim 1, it is characterized in that described single machine unit (1) comprises single-chip microcomputer U1, single-chip microcomputer U1 adopts STC2C5A60S2 single-chip microcomputer, described display unit (3) is LCDs, described keyboard unit (2) comprises ten six press keys lined up four lines four and arrange, 2 pin of same row button connect together output four column signal output terminals, 1 pin with a line button connects together output four row signal output parts, four column signal output terminals are connected with 21 ~ 28 pin of described single-chip microcomputer U1 respectively with four row 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 and 4 pin are connected with three input ends of described D/A change-over circuit (7) respectively, 14 ~ 16 pin of single-chip microcomputer U1 are connected with the input end of described range swithching 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 R17 ground connection, crystal oscillator Y11 is connected 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 electric capacity C11 ground connection.
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| CN104833934B (en) * | 2015-04-14 | 2018-05-04 | 北京华科兴盛电力工程技术有限公司 | Earth resistance tester calibration equipment |
| CN107976647A (en) * | 2018-01-24 | 2018-05-01 | 镇江市计量实验工厂 | A kind of high-voltage high resistance calibrating instrument intelligence calibrating installation |
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| US5257222A (en) * | 1992-01-14 | 1993-10-26 | Micron Technology, Inc. | Antifuse programming by transistor snap-back |
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