CN102466750A - Circuit and method for measuring alternating current of digital universal meter - Google Patents
Circuit and method for measuring alternating current of digital universal meter Download PDFInfo
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- CN102466750A CN102466750A CN2010105311456A CN201010531145A CN102466750A CN 102466750 A CN102466750 A CN 102466750A CN 2010105311456 A CN2010105311456 A CN 2010105311456A CN 201010531145 A CN201010531145 A CN 201010531145A CN 102466750 A CN102466750 A CN 102466750A
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Abstract
The invention discloses a circuit and a method for measuring alternating current of a digital universal meter. The circuit comprises a program-controlled gain level circuit, a first fixed gain level circuit, a second fixed gain level circuit and a third fixed gain level circuit which are connected in series with one another sequentially, an alternating current voltage input terminal which is directly coupled to the input end of the program-controlled gain level circuit, a first switch which is connected in series between the program-controlled gain level circuit and the first fixed gain level circuit, an alternating current input terminal which is coupled to the input end of the first fixed gain level circuit through a second switch, a third switch which is connected in series between the first fixed gain level circuit and the third fixed gain level circuit, a fourth switch which is connected in series between the first fixed gain level circuit and the second fixed gain level circuit, a fifth switch which is connected in series between the second fixed gain level circuit and the third fixed gain level circuit and a sixth switch which is connected in series between the program-controlled gain level circuit and the third fixed gain level circuit. The circuit and the method can be used for measuring small/weak alternating current.
Description
Technical field
The present invention relates to electronic measuring technology field, relate in particular to the AC measurment circuit and the AC measurement method of digital multimeter.
Background technology
General digital multimeter can be measured the size of ac voltage signal, the size of ac current signal.In order comparatively accurately to measure measured signal, the ac voltage measurement function of digital multimeter and ac current measurement function are all divided has a plurality of measurement ranges.For example: the ac voltage measurement function is divided into 100mV, 1V, 10V, 100V, 750V totally 5 ranges; The ac current measurement function is divided into 1A, two ranges of 3A.Each range all has identical reading figure place, so input signal amplitude can obtain maximum valid reading significance bits when selected range 10%～100% scope, and precision is also higher.
Shown in Figure 1 is a kind of AC measurment circuit of digital multimeter of prior art.It is the AC measurment circuit block diagram of the Agilent 34401A type digital multimeter of U.S. Agilent company production.The 100mV, 1V, 10V, 100V, 750V that this this circuit will be realized the ac voltage measurement function be two ranges of 1A, 3A of totally 5 ranges and ac current measurement function.The real effective converter for example can be: the AD637 of Analog Device company, and its best input effective value is 2V, the measurement bandwidth of real effective converter is maximum in this input range scope, measuring accuracy is the highest, the input signal crest factor maximum.For making the performance that keeps the real effective converter in the various range input ranges best, do processing and amplifying to the signal of various range input ranges.Be the method that this circuit of example explanation is realized all ranges of ac voltage measurement function and ac current measurement function below with Fig. 1.
The AC measurment circuit of the digital multimeter of prior art as shown in Figure 1 comprises: functional select switch S6, programme-controlled gain level circuit, fixed gain level circuit 1, fixed gain level circuit 2, fixed gain level circuit 3, real effective converter and AD (modulus) converter of connecting successively; Functional select switch S6 is connected between the sub-V alternating current of ac voltage input input terminal I and the programme-controlled gain level circuit.Be in series with switch S 1 between programme-controlled gain level circuit and the fixed gain level circuit 1; Be in series with switch S 2 between programme-controlled gain level circuit and the fixed gain level circuit 2; Be in series with switch S 3 between fixed gain level circuit 1 and the fixed gain level circuit 2; Be in series with switch S 5 between fixed gain level circuit 2 and the fixed gain level circuit 3, be in series with switch S 4 between programme-controlled gain level circuit and the fixed gain level circuit 3.The gain of programme-controlled gain level circuit is 0.2 times or 0.002 times; The gain of fixed gain level circuit 1 is 10 times; The gain of fixed gain level circuit 2 is 10 times; The gain of fixed gain level circuit 3 is 1 times.The real effective converter is the AD637 of Analog Device company.
Processor system receives steering order from input media, according to the steering order CS S1 that receives～S6 handover measurement function and measurement range.Input exchange signal is coupled to the real effective converter after amplifying through a plurality of gain stage circuit (programme-controlled gain level circuit and fixed gain level circuit); The direct current signal that the output of real effective converter equates with the AC signal effective value that coupling is come in, AD converter is coupled to processor system after converting this direct current signal into digital quantity.Digital quantity after processor system is changed AD converter carries out processing such as filtering, calibration, and the gained measurement result is delivered to output unit.
During the ac voltage measurement function, processor system CS S6 connects its terminal 2 and terminal 3, and the AC signal of the sub-V of ac voltage input is coupled to the input end of programme-controlled gain level circuit.Other circuit of each range of ac voltage measurement function is provided with as shown in table 1.
The circuit setting of the different alternating voltage ranges of table 1
During the ac current measurement function, processor system CS S6 connects its terminal 2 and terminal 1, and the signal of alternating current input terminal I is coupled to the input end of programme-controlled gain level circuit.Other circuit of each range of ac current measurement function is provided with as shown in table 2.
The circuit setting of the different alternating current ranges of table 2
Said from table 1 and table 2; The voltage that is coupled to real effective converter input end under each range of ac voltage measurement function and ac current measurement function is all near the best input voltage (2V) of real effective converter, thereby makes the precision of AC measurment best.
This shows; AC measurment circuit of the prior art and method can make each range of ac voltage measurement function and ac current measurement function is coupled to the real effective converter when full scale is imported signal all near 2V, have solved the problem of each range real effective converter processing accuracy.
But the inventor finds that also there is following deficiency in above-mentioned prior art in realizing process of the present invention:
The ac current measurement range of the AC measurment circuit of digital multimeter is less in the prior art, is not suitable for measuring milliampere little electric current of level interchange and exchanges weak current with microampere order;
As everyone knows, under the constant prerequisite of the first amplifying circuit noise figure, the gain of the first order of multistage amplifier circuit is more little, and then the overall noise factor of multistage amplifier circuit is poor more.The maximum gain of the AC measurment circuit first order programme-controlled gain level circuit of digital multimeter is 0.2 in the prior art, has limited the overall noise coefficient, therefore is not suitable for measuring faint AC signal, particularly faint ac current signal;
The maximum full gain of the AC measurment circuit of digital multimeter is 20 in the prior art, and the little range of energy measurement is 0.1V under the situation that satisfies real effective converter best operating condition, has limited the ability of METHOD OF MEASURING WEAK SIGNALS.
Summary of the invention
The embodiment of the invention provides a kind of AC measurment circuit of digital multimeter, exchanges little electric current and exchanges weak current in order to measure, and this circuit comprises:
Programme-controlled gain level circuit, the first fixed gain level circuit, the second fixed gain level circuit, the 3rd fixed gain level circuit, modulus AD converter and the processor system of connecting successively;
Ac voltage input is sub, couples directly to the input end of programme-controlled gain level circuit;
First switch is series between the programme-controlled gain level circuit and the first fixed gain level circuit;
The alternating current input terminal is coupled to the input end of the first fixed gain level circuit through second switch;
The 3rd switch is series between the first fixed gain level circuit and the 3rd fixed gain level circuit;
The 4th switch is series between the first fixed gain level circuit and the second fixed gain level circuit;
The 5th switch is series between the second fixed gain level circuit and the 3rd fixed gain level circuit;
The 6th switch is series between programme-controlled gain level circuit and the 3rd fixed gain level circuit;
Processor system connects input media, output unit, programme-controlled gain level circuit, first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch respectively.
The embodiment of the invention also provides a kind of AC measurement method of digital multimeter, exchanges little electric current and exchanges weak current in order to measure, and said data multimeter adopts above-mentioned AC measurment circuit; This method comprises:
Input media is to the processor system sending controling instruction;
Processor system receives the steering order that input media sends, and controls first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch disconnection or closed;
AC signal after the amplification exports processor system to through the output of the 3rd fixed gain level circuit and after AD converter converts digital quantity into;
Processor system is handled digital quantity, and the output measurement result is to output unit.
The embodiment of the invention is adjusted the annexation of each switch and other circuit in the digital multimeter AC measurment circuit of prior art, makes adjusted digital multimeter AC measurment circuit possess more ac current measurement range; And ac current signal directly inserts the first fixed gain level circuit, inserts programme-controlled gain level circuit with ac current signal in the prior art and compares, and the first order gain of multistage amplifier circuit is improved relatively, improves the overall noise factor of circuit; In addition, also can possess higher maximum full gain; Exchange little electric current and exchange weak current thereby be suitable for measuring.
Description of drawings
In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art; To do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below; Obviously, the accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills; Under the prerequisite of not paying creative work property, can also obtain other accompanying drawing according to these accompanying drawings.In the accompanying drawings:
Fig. 1 is the structured flowchart of the AC measurment circuit of digital multimeter in the prior art;
Fig. 2 is the structured flowchart of the AC measurment circuit of digital multimeter in the embodiment of the invention;
Fig. 3 is the actual circuit structure figure of the AC measurment circuit of digital multimeter in the embodiment of the invention;
Fig. 4, Fig. 5 are the actual circuit structure figure of programme-controlled gain level circuit in the embodiment of the invention;
Fig. 6 is the actual circuit structure figure of fixed gain level circuit 1 or fixed gain level circuit 2 in the embodiment of the invention;
Fig. 7 is the actual circuit structure figure of fixed gain level circuit 3 in the embodiment of the invention.
Embodiment
For the purpose, technical scheme and the advantage that make the embodiment of the invention is clearer, the embodiment of the invention is explained further details below in conjunction with accompanying drawing.At this, illustrative examples of the present invention and explanation thereof are used to explain the present invention, but not as to qualification of the present invention.
The AC measurment circuit of the digital multimeter in the embodiment of the invention comprises:
Programme-controlled gain level circuit, the first fixed gain level circuit, the second fixed gain level circuit, the 3rd fixed gain level circuit, modulus AD converter and the processor system of connecting successively;
Ac voltage input is sub, couples directly to the input end of programme-controlled gain level circuit;
First switch is series between the programme-controlled gain level circuit and the first fixed gain level circuit;
The alternating current input terminal is coupled to the input end of the first fixed gain level circuit through second switch;
The 3rd switch is series between the first fixed gain level circuit and the 3rd fixed gain level circuit;
The 4th switch is series between the first fixed gain level circuit and the second fixed gain level circuit;
The 5th switch is series between the second fixed gain level circuit and the 3rd fixed gain level circuit;
The 6th switch is series between programme-controlled gain level circuit and the 3rd fixed gain level circuit;
Processor system connects input media, output unit, programme-controlled gain level circuit, first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch respectively.
For clearly demonstrating the digital multimeter AC measurment circuit of the embodiment of the invention, be illustrated below.
In the AC measurment circuit of the digital multimeter that this is routine, the first fixed gain level circuit is designated as fixed gain level circuit 1, the second fixed gain level circuit and is designated as fixed gain level circuit 2, the three fixed gain level circuit and is designated as fixed gain level circuit 3; First switch is designated as switch S 1, and second switch is designated as switch S 2, the three switches and is designated as switch S 3, the four switches and is designated as switch S 4, the five switches and is designated as switch S 5, the six switches and is designated as switch S 6.The 200mV, 2V, 20V, 200V, 750V that the AC measurment circuit of this digital multimeter will be realized the ac voltage measurement function be 200uA, 2mA, 20mA, 200mA, 2A, 10A totally six ranges of totally 5 ranges and ac current measurement function.
The structure of the AC measurment circuit of this digital multimeter is as shown in Figure 2, comprising: programme-controlled gain level circuit, fixed gain level circuit 1, fixed gain level circuit 2, fixed gain level circuit 3, real effective converter, AD converter and the processor system of connecting successively.Be in series with switch S 1 between programme-controlled gain level circuit and the fixed gain level circuit 1; Be in series with switch S 6 between programme-controlled gain level circuit and the fixed gain level circuit 3; Be in series with switch S 4 between fixed gain level circuit 1 and the fixed gain level circuit 2; Be in series with switch S 5 between fixed gain level circuit 2 and the fixed gain level circuit 3, be in series with switch S 3 between fixed gain level circuit 1 and the fixed gain level circuit 3.The sub-V of ac voltage input couples directly to the input end of programme-controlled gain level circuit, and alternating current input terminal I is coupled to fixed gain level circuit 1 through switch S 2.
The gain of programme-controlled gain level circuit is 0.2 times or 0.002 times; The gain of fixed gain level circuit 1 is 5 times; The gain of fixed gain level circuit 2 is 10 times; The gain of fixed gain level circuit 3 is 1 times.The real effective converter is the AD637 of Analog Device company.Certainly, those skilled in the art can change the real effective converter into other form according to common practise, for example: and the AD737 of Analog Device company, perhaps use the real effective converter of digital sample.In addition, can also adjust the gain size of each gain stage circuit according to the optimal input range of used real effective converter, to realize optimum performance.Here; The real effective converter is optional device, in the AC measurment circuit of the digital multimeter of the embodiment of the invention, and can be through in processor system, adding software; Realize the function of real effective converter, to substitute the real effective converter in the side circuit.
In the AC measurement method of the digital multimeter in the embodiment of the invention, digital multimeter adopts foregoing circuit structure (for example shown in Figure 2); This method can comprise:
Input media is to the processor system sending controling instruction;
Processor system receives the steering order that input media sends, and controls first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch disconnection or closed;
AC signal after the amplification is through the output of the 3rd fixed gain level circuit and after AD converter converts digital quantity into; (AC signal of the 3rd fixed gain level circuit output converts the direct current signal that effective value equates into by the real effective converter among Fig. 2, exports AD converter to export processor system to; Also can realize the function of real effective converter during enforcement by processor system software);
Processor system is handled digital quantity, and the output measurement result is to output unit.
Still the AC measurment circuit with digital multimeter shown in Figure 2 is an example; The AC measurement method of digital multimeter comprises in this example: processor system receives steering order from input media, according to the steering order CS S1 that receives～S6 handover measurement function and measurement range; Input exchange signal is coupled to the real effective converter after amplifying through a plurality of gain stage circuit (programme-controlled gain level circuit, fixed gain level circuit); The direct current signal that the output of real effective converter equates with the AC signal effective value that coupling is come in, AD converter is coupled to processor system after converting this direct current signal to digital quantity.Digital quantity after processor system is changed AD converter carries out processing such as filtering, calibration, and the gained measurement result is delivered to output unit.
In the AC measurement method of the digital multimeter in the embodiment of the invention, when measuring alternating voltage:
When range was 200mV, the gain that processor system is controlled first switch closure, second switch disconnection, the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.2 times;
When range was 2V, the gain that processor system is controlled first switch closure, second switch disconnection, the 3rd switch closure, the disconnection of the 4th switch, the disconnection of the 5th switch, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.2 times;
When range was 20V, the gain that processor system is controlled first switch closure, second switch disconnection, the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.002 times;
When range was 200V, the gain that processor system is controlled first switch closure, second switch disconnection, the 3rd switch closure, the disconnection of the 4th switch, the disconnection of the 5th switch, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.002 times;
When range was 750V, the gain that processor system is controlled the disconnection of first switch, second switch disconnection, the disconnection of the 3rd switch, the disconnection of the 4th switch, the disconnection of the 5th switch, the 6th switch closure, programme-controlled gain level circuit was 0.002 times.
Still the AC measurment circuit with digital multimeter shown in Figure 2 is an example, and when measuring alternating voltage, the signal of the sub-V of ac voltage input is coupled to the input end of programme-controlled gain level circuit.The circuit of each range of ac voltage measurement function is provided with as shown in table 3.
The circuit setting of the different alternating voltage ranges of table 3
In the AC measurement method of the digital multimeter in the embodiment of the invention, when measuring alternating current:
Processor system is controlled the disconnection of first switch, closed, the 6th switch disconnection of second switch;
When range was 200uA, 20mA or 2A, processor system was controlled the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure;
When range was 2mA, 200mA or 10A, processor system controlled that the 3rd switch closure, the 4th switch break off, the 5th switch breaks off.
Still the AC measurment circuit with digital multimeter shown in Figure 2 is an example, and when measuring alternating current, processor system CS S2 is closed, and switch S 1 is broken off, and switch S 6 is broken off, and alternating current input terminal I is coupled to fixed gain level circuit 1.Being provided with of the switch S 3 of each range of ac current measurement function, switch S 4 and switch S 5 is as shown in table 4.
The circuit setting of the different alternating current ranges of table 4
Can find out that from table 3 and table 4 in the embodiment of the invention, the voltage that is coupled to real effective converter input end under each range of ac voltage measurement function is the best input voltage of real effective converter; The voltage that is coupled to real effective converter input end under each range of ac current measurement function is all near the best input voltage of real effective converter, thereby makes the precision of AC measurment best.
Fig. 3 is a kind of possible actual use circuit structure diagram of AC measurment circuit of the digital multimeter of the embodiment of the invention.This circuit structure comprises: programme-controlled gain level circuit, fixed gain level circuit 1, fixed gain level circuit 2, Hi-pass filter, fixed gain level circuit 3, real effective converter, AD converter and the processor system of connecting successively.Be in series with switch S 1 between programme-controlled gain level circuit and the fixed gain level circuit 1; Be in series with switch S 6 between programme-controlled gain level circuit and the Hi-pass filter; Be in series with switch S 4 between fixed gain level circuit 1 and the fixed gain level circuit 2; Be in series with switch S 5 between fixed gain level circuit 2 and the Hi-pass filter, be in series with switch S 3 between fixed gain level circuit 1 and the Hi-pass filter.The sub-V of ac voltage input couples directly to the input end of programme-controlled gain level circuit, and alternating current input terminal I is coupled to fixed gain level circuit 1 through switch S 2.
That is, can also comprise in the AC measurment circuit of the digital multimeter of the embodiment of the invention: Hi-pass filter is series between the second fixed gain level circuit and the 3rd fixed gain level circuit; At this moment, the 3rd switch series is coupled between the first fixed gain level circuit and the Hi-pass filter; The 5th switch series is coupled between the second fixed gain level circuit and the Hi-pass filter; The 6th switch series is coupled between programme-controlled gain level circuit and the Hi-pass filter.
During practical implementation, in the AC measurment circuit of the digital multimeter of the embodiment of the invention, programme-controlled gain level circuit can comprise:
First resistance, second resistance, the 3rd resistance, operational amplifier and the minion that is connected with processor system are closed;
The two ends of first resistance connect the inverting input of ac voltage input and operational amplifier respectively;
The two ends of second resistance are concatenation operation amplifier's inverting input and output terminal respectively;
The two ends of the 3rd resistance connect first end of minion pass and the output terminal of operational amplifier respectively; The second end concatenation operation amplifier's inverting input that minion is closed;
The positive input end grounding of operational amplifier;
Processor system closes through the control minion and breaks off or closure, the gain of adjustment programme-controlled gain level circuit.
Lift an example and specify above-mentioned programme-controlled gain level circuit, in this example first resistance is designated as resistance R 1, the second resistance and is designated as resistance R 2, the three resistance and is designated as resistance R 3, operational amplifier is designated as operational amplifier U1, and minion is closed and is designated as switch S 7; With circuit structure shown in Figure 3 is example, and programme-controlled gain level circuit comprises resistance R 1, resistance R 2, resistance R 3, operational amplifier U1 and switch S 7 in this example.The resistance of resistance R 1 is 5 times of resistance of resistance R 2, and the resistance of resistance R 1 is 500 times of resistance of resistance R 3.When switch S 7 was broken off, resistance R 1, resistance R 2 and operational amplifier U1 formed sign-changing amplifier, and its low-frequency gain is suc as formula shown in 1:
During switch S 7 closures, resistance R 3 is passed through switch S 7 parallel connections with resistance R 7, forms sign-changing amplifier with resistance R 1 with operational amplifier U1, and its low-frequency gain is suc as formula shown in 2:
Programme-controlled gain level circuit can also adopt other circuit form during practical implementation, for example adopts the implementation method of some circuit function blocks of adjustment, reaches identical effect.For example, the annexation that the 3rd resistance in the adjustment in the example and minion are closed, concrete can be: the two ends of the 3rd resistance connect first end of minion pass and the inverting input of operational amplifier respectively; The output terminal of the second end concatenation operation amplifier that minion is closed.As shown in Figure 4, the two ends of resistance R 3 connect first end of switch S 7 and the inverting input of operational amplifier respectively; The output terminal of the second end concatenation operation amplifier of switch S 2.
Lift an example again, programme-controlled gain level circuit can also be to comprise:
First resistance, second resistance, the 3rd resistance, operational amplifier and the minion that is connected with processor system are closed;
The two ends of first resistance connect ac voltage input and second resistance respectively;
The two ends of second resistance connect first resistance and the 3rd resistance respectively;
The two ends of the 3rd resistance connect second resistance and ground respectively;
The output terminal of the inverting input concatenation operation amplifier of operational amplifier;
Minion is closed the normal phase input end of an end concatenation operation amplifier, and the other end select to connect in the two ends of second resistance a wherein end; Processor system closes through the control minion and breaks off or closure, the gain of adjustment programme-controlled gain level circuit.
Lift an example and specify above-mentioned programme-controlled gain level circuit, in this example first resistance is designated as resistance R 1, the second resistance and is designated as resistance R 2, the three resistance and is designated as resistance R 3, operational amplifier is designated as operational amplifier U1, and minion is closed and is designated as switch S 1; Obtain programme-controlled gain level circuit structure as shown in Figure 5, switch S 1 has adopted functional select switch among Fig. 5.
Among Fig. 5, resistance R 1, resistance R 2, resistance R 3 are composed in series potential-divider network successively, and this potential-divider network comprises two kinds of intrinsic standoff ratios.First kind of intrinsic standoff ratio is by resistance R 1 being composed in series with resistance R 2 and resistance R 2; Second kind of intrinsic standoff ratio is made up of with resistance R 3 series connection of resistance R 1 and resistance R 2.Operational amplifier U1 connects into unity gain amplifier.Switch S 1 can be program control electronic switch, electromagnetic relay, photoswitch etc.Switch S 1 is connected its terminal 2 and is selected first kind of intrinsic standoff ratio with terminal 3, and switch S 1 is connected its terminal 2 and selected second kind of intrinsic standoff ratio with terminal 1, thereby realizes programme-controlled gain.
During practical implementation, in the AC measurment circuit of the digital multimeter of the embodiment of the invention, the first fixed gain level circuit can comprise: first resistance, second resistance and operational amplifier; The normal phase input end of operational amplifier connects first switch and second switch; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier.
Lift an example and specify the above-mentioned first fixed gain level circuit, in this example the first fixed gain level circuit is designated as fixed gain level circuit 1, the first resistance and is designated as resistance R 4, the second resistance and is designated as resistance R 5, operational amplifier is designated as operational amplifier U2; With circuit structure shown in Figure 3 is example, and fixed gain level circuit 1 comprises resistance R 4, resistance R 5 and operational amplifier U2 in this example.The size of resistance R 5 is 4 times of size of resistance R 4.Resistance R 4, resistance R 4 and operational amplifier U2 form in-phase amplification circuit, and its low-frequency gain is 5.
The first fixed gain level circuit can also adopt other circuit form during practical implementation, for example adopts the implementation method of some circuit function blocks of adjustment, reaches identical effect.For example, the first fixed gain level circuit comprises: first resistance, second resistance and operational amplifier; The positive input end grounding of operational amplifier; The two ends difference concatenation operation amplifier's inverting input of first resistance and the output terminal of operational amplifier; Second resistance, one end connects first switch and second switch, other end concatenation operation amplifier's inverting input.
Lift an example and specify the above-mentioned first fixed gain level circuit, in this example the first fixed gain level circuit is designated as fixed gain level circuit 1, the first resistance and is designated as resistance R 1, the second resistance and is designated as resistance R 2, operational amplifier is designated as operational amplifier U2; Obtain fixed gain level circuit 1 as shown in Figure 6.Resistance R 1 resistance was 5 times of resistance R 2 resistances when fixed gain level circuit 1 used reverse amplification shown in Figure 6 to realize.
During practical implementation, in the AC measurment circuit of the digital multimeter of the embodiment of the invention, the second fixed gain level circuit can comprise: first resistance, second resistance and operational amplifier; The normal phase input end of operational amplifier connects the 4th switch; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier.
Lift an example and specify the above-mentioned second fixed gain level circuit, in this example the second fixed gain level circuit is designated as fixed gain level circuit 2, the first resistance and is designated as resistance R 6, the second resistance and is designated as resistance R 7, operational amplifier is designated as operational amplifier U3; With circuit structure shown in Figure 3 is example, and fixed gain level circuit 2 comprises resistance R 6, resistance R 7 and operational amplifier U3 in this example.The size of resistance R 7 is 9 times of size of resistance R 6.Resistance R 6, resistance R 7 and operational amplifier U3 form in-phase amplification circuit, and its low-frequency gain is 10.
The second fixed gain level circuit can also adopt other circuit form during practical implementation, for example adopts the implementation method of some circuit function blocks of adjustment, reaches identical effect.For example, the second fixed gain level circuit comprises: first resistance, second resistance and operational amplifier; The positive input end grounding of operational amplifier; The two ends difference concatenation operation amplifier's inverting input of first resistance and the output terminal of operational amplifier; The two ends of second resistance connect the inverting input of the 4th switch and operational amplifier respectively.
Lift an example and specify the above-mentioned second fixed gain level circuit, in this example the second fixed gain level circuit is designated as fixed gain level circuit 2, the first resistance and is designated as resistance R 1, the second resistance and is designated as resistance R 2, operational amplifier is designated as operational amplifier U3; Obtain fixed gain level circuit 2 as shown in Figure 6 (identical) with fixed gain level circuit 1.Resistance R 1 resistance was 10 times of resistance R 2 resistances when fixed gain level circuit 2 used reverse amplification shown in Figure 6 to realize.
Hi-pass filter among Fig. 3 is used to isolate the direct current offset that prime produces, and it comprises capacitor C 1 and resistance R 8.Capacitor C 1 is generally 0.22s with the Hi-pass filter time constant that resistance R 8 is formed.It can be 220nF that size is held in actual power taking, and resistance sizes is 1M Ω.
During practical implementation, the 3rd fixed gain level circuit can comprise: operational amplifier; The normal phase input end of operational amplifier connects the output terminal of Hi-pass filter, the output terminal of the inverting input concatenation operation amplifier of operational amplifier.
With Fig. 3 is example, and the 3rd fixed gain level circuit is designated as fixed gain level circuit 3, and fixed gain level circuit 3 comprises operational amplifier U4 among Fig. 3.Operational amplifier U4 connects into the unity gain amplifier structure, and its low-frequency gain is 1.
Certainly, the 3rd fixed gain level circuit also can adopt other circuit form during practical implementation, for example adopts the implementation method of some circuit function blocks of adjustment, reaches identical effect.For example, the 3rd fixed gain level circuit comprises: first resistance, second resistance and operational amplifier; The normal phase input end of operational amplifier connects the output terminal of Hi-pass filter; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier.
Lift an example and specify above-mentioned the 3rd fixed gain level circuit, in this example the 3rd fixed gain level circuit is designated as fixed gain level circuit 3, the first resistance and is designated as resistance R 1, the second resistance and is designated as resistance R 2, operational amplifier is designated as operational amplifier U4; Obtain the fixed gain level circuit 3 that employing in-phase amplifier as shown in Figure 7 is realized.
What the real effective converter among Fig. 3 used is the AD637 real effective conversion chip of Analog Device company.Those skilled in the art can also change the real effective converter into other form according to common practise; For example: the real effective conversion chip of models such as the AD737 of Analog Device company, AD736, AD636 is realized; Perhaps remove the real effective converter among Fig. 2 and Fig. 3, and use processor system to realize that through software the real effective converter of digital sample substitutes the effect of real effective converter in the side circuit.Certainly, can also adjust the gain size of each gain stage circuit according to the optimal input range of used real effective converter, to realize optimum performance.
In sum, the embodiment of the invention is adjusted the annexation of each switch and other circuit in the digital multimeter AC measurment circuit of prior art, makes adjusted digital multimeter AC measurment circuit possess more ac current measurement range; And ac current signal directly inserts the first fixed gain level circuit; Inserting programme-controlled gain level circuit (0.2 times of maximum gain) with ac current signal in the prior art compares; The first order gain (gain of the first fixed gain level circuit is 5 times) of multistage amplifier circuit is improved relatively, improve the overall noise factor of circuit; In addition, also possesses higher maximum full gain (full gain can reach 50 times during ac current measurement, can very weak signal be amplified to the best effort scope of real effective converter); Exchange little electric current and exchange weak current thereby be suitable for measuring.
In addition; As conventionally known to one of skill in the art; The gain that increases programme-controlled gain level circuit in the prior art improves the overall noise coefficient and also might solve prior art with entire gain and be not suitable for measuring little electric current and the problem that exchanges weak current of exchanging; But this can increase the complicacy of circuit greatly, increases the difficulty of debugging, also can increase cost.Compared with prior art; The present invention also possesses following advantage: under the situation of the quantity that does not increase gain stage circuit and change-over switch; Reached and improved maximum full gain of gain stage circuit and the purpose that improves the overall noise coefficient, thereby realized exchanging little electric current and exchanged if the measurement function of electric current.Owing to do not increase gain stage circuit and change-over switch quantity,, can not increase cost yet so can not increase the complexity and the debugging difficulty of control.
Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; And be not used in qualification protection scope of the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (12)
1. the AC measurment circuit of a digital multimeter is characterized in that:
This circuit comprises:
Programme-controlled gain level circuit, the first fixed gain level circuit, the second fixed gain level circuit, the 3rd fixed gain level circuit, modulus AD converter and the processor system of connecting successively;
Ac voltage input is sub, couples directly to the input end of programme-controlled gain level circuit;
First switch is series between the programme-controlled gain level circuit and the first fixed gain level circuit;
The alternating current input terminal is coupled to the input end of the first fixed gain level circuit through second switch;
The 3rd switch is series between the first fixed gain level circuit and the 3rd fixed gain level circuit;
The 4th switch is series between the first fixed gain level circuit and the second fixed gain level circuit;
The 5th switch is series between the second fixed gain level circuit and the 3rd fixed gain level circuit;
The 6th switch is series between programme-controlled gain level circuit and the 3rd fixed gain level circuit;
Processor system connects input media, output unit, programme-controlled gain level circuit, first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch respectively.
2. circuit as claimed in claim 1 is characterized in that, programme-controlled gain level circuit comprises:
First resistance, second resistance, the 3rd resistance, operational amplifier and the minion that is connected with processor system are closed;
The two ends of first resistance connect the inverting input of ac voltage input and operational amplifier respectively;
The two ends of second resistance are concatenation operation amplifier's inverting input and output terminal respectively;
The two ends of the 3rd resistance connect first end of minion pass and the output terminal of operational amplifier respectively; The second end concatenation operation amplifier's inverting input that minion is closed; Perhaps, the two ends of the 3rd resistance connect first end of minion pass and the inverting input of operational amplifier respectively; The output terminal of the second end concatenation operation amplifier that minion is closed;
The positive input end grounding of operational amplifier;
Processor system closes through the control minion and breaks off or closure, the gain of adjustment programme-controlled gain level circuit.
3. circuit as claimed in claim 1 is characterized in that, programme-controlled gain level circuit comprises:
First resistance, second resistance, the 3rd resistance, operational amplifier and the minion that is connected with processor system are closed;
The two ends of first resistance connect ac voltage input and second resistance respectively;
The two ends of second resistance connect first resistance and the 3rd resistance respectively;
The two ends of the 3rd resistance connect second resistance and ground respectively;
The output terminal of the inverting input concatenation operation amplifier of operational amplifier;
Minion is closed the normal phase input end of an end concatenation operation amplifier, and the other end select to connect in the two ends of second resistance a wherein end; Processor system closes through the control minion and breaks off or closure, the gain of adjustment programme-controlled gain level circuit.
4. circuit as claimed in claim 1 is characterized in that, the first fixed gain level circuit comprises:
First resistance, second resistance and operational amplifier;
The normal phase input end of operational amplifier connects first switch and second switch; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier;
Perhaps, the positive input end grounding of operational amplifier; The two ends difference concatenation operation amplifier's inverting input of first resistance and the output terminal of operational amplifier; Second resistance, one end connects first switch and second switch, other end concatenation operation amplifier's inverting input.
5. circuit as claimed in claim 1 is characterized in that, the second fixed gain level circuit comprises:
First resistance, second resistance and operational amplifier;
The normal phase input end of operational amplifier connects the 4th switch; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier;
Perhaps, the positive input end grounding of operational amplifier; The two ends difference concatenation operation amplifier's inverting input of first resistance and the output terminal of operational amplifier; The two ends of second resistance connect the inverting input of the 4th switch and operational amplifier respectively.
6. circuit as claimed in claim 1 is characterized in that, this circuit also comprises:
Hi-pass filter is series between the second fixed gain level circuit and the 3rd fixed gain level circuit;
The 3rd switch series is coupled between the first fixed gain level circuit and the Hi-pass filter;
The 5th switch series is coupled between the second fixed gain level circuit and the Hi-pass filter;
The 6th switch series is coupled between programme-controlled gain level circuit and the Hi-pass filter.
7. circuit as claimed in claim 6 is characterized in that, the 3rd fixed gain level circuit comprises:
Operational amplifier; The normal phase input end of operational amplifier connects the output terminal of Hi-pass filter, the output terminal of the inverting input concatenation operation amplifier of operational amplifier;
Perhaps, the 3rd fixed gain level circuit comprises:
First resistance, second resistance and operational amplifier; The normal phase input end of operational amplifier connects the output terminal of Hi-pass filter; The two ends of first resistance are concatenation operation amplifier's inverting input and ground respectively; The two ends difference concatenation operation amplifier's inverting input of second resistance and the output terminal of operational amplifier.
8. circuit as claimed in claim 1 is characterized in that, this circuit also comprises:
The real effective converter is series between the 3rd fixed gain level circuit and the AD converter.
9. like each described circuit of claim 1 to 8, it is characterized in that the gain of programme-controlled gain level circuit is 0.2 times or 0.002 times; The gain of the first fixed gain level circuit is 5 times; The gain of the second fixed gain level circuit is 10 times; The gain of the 3rd fixed gain level circuit is 1 times.
10. the AC measurement method of a digital multimeter is characterized in that, said data multimeter adopts the described AC measurment circuit of claim 9; The AC measurement method of said digital multimeter comprises:
Input media is to the processor system sending controling instruction;
Processor system receives the steering order that input media sends, and controls first switch, second switch, the 3rd switch, the 4th switch, the 5th switch and the 6th switch disconnection or closed;
AC signal after the amplification exports processor system to through the output of the 3rd fixed gain level circuit and after AD converter converts digital quantity into;
Processor system is handled digital quantity, and the output measurement result is to output unit.
11. method as claimed in claim 10 is characterized in that, when measuring alternating voltage:
When range was 200mV, the gain that processor system is controlled first switch closure, second switch disconnection, the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.2 times;
When range was 2V, the gain that processor system is controlled first switch closure, second switch disconnection, the 3rd switch closure, the disconnection of the 4th switch, the disconnection of the 5th switch, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.2 times;
When range was 20V, the gain that processor system is controlled first switch closure, second switch disconnection, the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.002 times;
When range was 200V, the gain that processor system is controlled first switch closure, second switch disconnection, the 3rd switch closure, the disconnection of the 4th switch, the disconnection of the 5th switch, the disconnection of the 6th switch, programme-controlled gain level circuit was 0.002 times;
When range was 750V, the gain that processor system is controlled the disconnection of first switch, second switch disconnection, the disconnection of the 3rd switch, the disconnection of the 4th switch, the disconnection of the 5th switch, the 6th switch closure, programme-controlled gain level circuit was 0.002 times.
12. method as claimed in claim 10 is characterized in that, when measuring alternating current, processor system is controlled the disconnection of first switch, closed, the 6th switch disconnection of second switch;
When range was 200uA, 20mA or 2A, processor system was controlled the disconnection of the 3rd switch, the 4th switch closure, the 5th switch closure;
When range was 2mA, 200mA or 10A, processor system controlled that the 3rd switch closure, the 4th switch break off, the 5th switch breaks off.
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| CN201010531145.6A CN102466750B (en) | 2010-11-03 | 2010-11-03 | Circuit and method for measuring alternating current of digital universal meter |
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| CN201010531145.6A CN102466750B (en) | 2010-11-03 | 2010-11-03 | Circuit and method for measuring alternating current of digital universal meter |
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| CN102466750B CN102466750B (en) | 2015-05-20 |
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| CN103884888A (en) * | 2012-12-20 | 2014-06-25 | 北京普源精电科技有限公司 | Oscilloscope having universal meter function |
| CN106568997A (en) * | 2016-11-15 | 2017-04-19 | 深圳市鼎阳科技有限公司 | Switching control method and device of multimeter current range |
| RU2685062C1 (en) * | 2018-07-17 | 2019-04-16 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Томский государственный университет" (ТГУ, НИ ТГУ) | Digital measurer of acting signal value |
| CN110780103A (en) * | 2018-07-31 | 2020-02-11 | 罗伯特·博世有限公司 | Measuring device |
| CN111398668A (en) * | 2020-04-07 | 2020-07-10 | 中国原子能科学研究院 | Measuring circuit and device |
| CN111413533A (en) * | 2019-12-26 | 2020-07-14 | 北京航天测控技术有限公司 | Portable intelligent multimeter |
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| RU2742695C1 (en) * | 2020-07-17 | 2021-02-09 | Федеральное государственное автономное образовательное учреждение высшего образования «Национальный исследовательский Томский государственный университет» | Digital meter of parameters of random processes based on the nakagami distribution |
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| CN103884888A (en) * | 2012-12-20 | 2014-06-25 | 北京普源精电科技有限公司 | Oscilloscope having universal meter function |
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| CN110780103A (en) * | 2018-07-31 | 2020-02-11 | 罗伯特·博世有限公司 | Measuring device |
| CN111413533A (en) * | 2019-12-26 | 2020-07-14 | 北京航天测控技术有限公司 | Portable intelligent multimeter |
| CN111398668A (en) * | 2020-04-07 | 2020-07-10 | 中国原子能科学研究院 | Measuring circuit and device |
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