CN201332319Y - Current input measuring range automatic switching circuit of electromotor protecting device - Google Patents

Abstract

The utility model relates to a current input measuring range automatic switching circuit of electromotor protecting device, which comprises a current mutual inductor and a sampling circuit, wherein the sampling circuit comprises three modules, a measuring range switching circuit is composed of a standard in-phase proportional amplifying circuit and an electronic switch, wherein the electronic switch is connected with a reverse-phase input end of an operational amplifier, four electric resistances are connected in series between an output end of the operational amplifier and the earth, four output end pins of the electronic switch are respectively connected between four resistances and on the output end of the operational amplifier, the output end of the operational amplifier is connected with a voltage rectification lifting circuit, the output of the voltage rectification lifting circuit is connected with the input of a single chip microcomputer, one output pin of the single chip microcomputer is connected with a display device, and the other two output pins are connected with control pins of the electronic switch. The volume of the measuring range switching circuit is greatly reduced, the power consumption is reduced, the switching speed is accelerated, the cost is greatly lowered, the measurement high precision is guaranteed on the basis of widening the measurement range, and the application range of the automatic measuring range switching circuit is greatly improved.

Description

The electric current input range automatic switch-over circuit of motor protection equipment

Technical field

The utility model relates to a kind of electric current input range automatic switch-over circuit of motor protection equipment, belongs to the motor protection field.

Background technology

Along with the continuous development of domestic field of electric control, increasing novel protector is popularizing progressively.Motor protector is integrated in one functions such as the measurement of motor, protection, control, communication, has replaced conventional electrical appliance elements such as conventional thermal relay, current transformer, auxiliary relay, transmitter.It progressively substitutes traditional motor protection conventional device with its high-tech advantage.And motor protector mainly is to rely on the collection of motor real work electric current is judged the state of motor and protected action.

In the actual motion; the running current of motor usually can be near rated current; but in starting process, can occur 6～8 times to the starting current of rated current; nonserviceable simultaneously and also can occur being several times as much as the fault current of rated current down; this has just proposed higher requirement to the current measuring range and the precision of this device, and measuring range is big, and precision will descend.And existing at present solution mainly contains two kinds: the one, only measure the following current value of 2 times of rated current, and do not do metering for electric current more than 2 times, precision is higher.Second kind of electric current that can measure 10 times exactly, but when rated current, certainty of measurement can only reach about 2%.So, must find a kind of both the assurance to make measuring range can reach 1%～1000% method of measurement again in rated current down-sampling precision at this type of contradiction.

Since measuring range need reach 1%～1000% of rated current, and need guarantee certainty of measurement in the maintenance of the electric current below 100% 0.2%, need select a kind of circuit that can carry out the range automatic switchover for use, guarantee under the electric current of different sizes, automatically carrying out range by device switches, the needs of wide-range can not only be satisfied like this, higher sampling precision can also be reached.

Use relay switch or electronic analog swtich switching mode mostly for range switch circuit at present.Though wherein its conducting resistance of relay switch is minimum, fairly simple on circuit is realized, because own vol is big, cost is high, power consumption is big, responsiveness waits shortcoming slowly, generally be commonly used in the medium-sized or above measuring instrument.The electronic analog swtich advantage is that its volume is little, power consumption is little, quick action, but its maximum shortcoming is that conducting resistance is higher, and this can directly cause the poor effect switched.There is segment chip manufacturer to develop the electronic analog swtich of low conduction impedance at present, but, causes except that a few high-end measuring instrument, seldom being used because it holds at high price.

The utility model content

In order to overcome the deficiencies in the prior art, the purpose of this utility model is to provide a kind of electric current input automatic range commutation circuit of the motor protection equipment of forming based on embedded platform, electronic analog swtich and amplifier.This patent has greatly improved the practicality of automatic range commutation circuit realizing greatly having saved device cost on wide region, the high-precision basis.

For achieving the above object, the utility model is achieved through the following technical solutions:

A kind of electric current input range automatic switch-over circuit of motor protection equipment comprises current transformer and sample circuit, and the output of described current transformer connects the input of sample circuit; It is characterized in that described sample circuit comprises range switch circuit, voltage commutation is raised circuit and three modules of single chip machine controlling circuit, described range switch circuit is made up of standard in-phase ratio amplifying circuit and electronic switch, electronic switch is that hilted broadsword eight is thrown electronic switch, be connected the inverting input of the operational amplifier in the standard in-phase ratio amplifying circuit, between the output of operational amplifier and ground, be in series with 4 resistance, 4 output pins of electronic switch are connected on respectively on the output that reaches operational amplifier between four resistance, form selectivity and insert resistance circuit, the output concatenation operation amplifier input terminal of current transformer; The output of operational amplifier connects voltage commutation and raises circuit, and it is basic operational amplifier add circuit that described voltage commutation is raised circuit; Described single chip machine controlling circuit comprises single-chip microcomputer, and voltage commutation is raised the input of the output connection single-chip microcomputer of circuit, and an output pin of single-chip microcomputer connects display unit, in addition the control pin of two output pins connection electronic switches.

The electric current input range automatic switch-over circuit of aforesaid motor protection equipment is characterized in that described single-chip microcomputer, is connected with decoupling capacitor on its pin.

The electric current input range automatic switch-over circuit of aforesaid motor protection equipment is characterized in that described single-chip microcomputer, is connected with the standard crystal oscillating circuit of being made up of electric capacity, resistance and crystal oscillator on its pin.

The beneficial effects of the utility model are: the utility model utilizes embedded platform, electronic analog swtich and amplifier to form the automatic range commutation circuit, make the volume of range switch circuit reduce greatly, power consumption reduces, switch speed is accelerated, cost reduces significantly, widen the high accuracy that has guaranteed measurement on the basis of measuring range, greatly improving the scope of application of automatic range commutation circuit.

Description of drawings

Fig. 1 is a standard in-phase ratio amplifying circuit schematic diagram;

Fig. 2 is the standard in-phase ratio amplifying circuit schematic diagram that inserts electronic switch at the operational amplifier inverting input;

Fig. 3 is the wiring schematic diagram of range switch circuit of the present utility model;

Fig. 4 is that voltage commutation of the present utility model is raised the circuit connection schematic diagram;

Fig. 5 is that range switch circuit of the present utility model and voltage commutation are raised the circuit connection diagram;

Fig. 6 is a single chip machine controlling circuit schematic diagram of the present utility model.

Embodiment

Below in conjunction with accompanying drawing the utility model is done concrete being described below.

In the utility model, as current sample, at first be primary side current to be carried out the proportional sampling conversion by current transformer, obtain a less ac voltage signal and supply with rear end sample circuit use.

Sample circuit of the present utility model can be divided into three modules: first module is a range switch circuit, its mainly act on be to front-end collection to ac voltage signal carry out the ratio gain amplifier, the multiple of its gain can change and switch by the high-low level of control pin.Second module is that voltage commutation is raised circuit, because the sampling AD of rear end is unipolarity AD, can't carry out the AD conversion to reverse voltage, so must raise processing to alternating voltage waveform.Three module is a single chip machine controlling circuit, mainly act as and utilize AD converter to gather the size of AC signal and calculating sampling value, after judging the sampled value size, utilize the IO mouth to export the gain ratio of the range switch circuit of controlling first module simultaneously, realize the automatic switchover of range.This part is finished by the MSP430 single-chip microcomputer.Below we just come specifically to introduce the operation principle of each module.

For first module, present existing commutation circuit normally adopts relay switch or electronic switch as switching device.And device is selected, though himself conducting resistance of relay switch is minimum, its operate time, long and big these two subject matters of consumed energy were that structural principle by relay itself causes, and can't improve by circuit design.So satisfy the design requirement of low-power consumption, fast-response, it is to be difficult to realize that the mode of employing relay switch designs automatic switch-over circuit.

Though yet common electronic switch has overcome two big shortcomings of traditional relay switch, the shortcoming that it brought is that conduction resistance value is bigger, can reach usually about 1000 ohm and bigger with the device individual difference.This shortcoming certainly will make utilizes the convert resistance circuit to realize that gain transformations becomes very difficult.Its conducting resistance of novel electronic switch can be done minimumly, but irrespective key factor also must not be in the cost of its cost.The new a MOS EFT electronic switch G3VM series of releasing of OMRON company, the I of its conducting resistance reaches below 0.1 ohm, but its price monolithic often surpasses 50 yuan, and common electronic switch monolithic price is about 1 yuan.At the design of meter meter, higher to cost requirement, adopt the novel electronic switch, be difficult to reach it and control cheaply.

For above problem, the utility model has been realized a kind of new-type circuit design that is based upon on the common electronic switch design direction basis.This kind new-type circuit can be on basis cheaply, and the gain that reaches high accuracy and quick low-power consumption is switched.

The electronic switch U2 that the utility model uses is the CD4051 of TI company, and this kind electronic switch principle is equivalent to a hilted broadsword eight and throws electronic switch.Which passage of switch connection, the 3 bit address sign indicating number ABC that imported by control end decide, and its truth table sees Table 1.Its switching time, contact resistance was at 470 ohm～1000 ohm during conducting about 30ns.Its input/output signal both can be an analog signal, also can be digital signal, and its operating voltage can reach 15V.

Table 1 electronic switch CD4051 truth table

C	B	A	Output
				0	0	0	“0”
0	0	1	“1”
				0	1	0	“2”
0	1	1	“3”
				1	0	0	“4”
1	0	1	“5”
				1	1	0	“6”
1	1	1	“7”

The input signal of front end is an ac voltage signal in this module, and this moment, this ac voltage signal entered in the in-phase proportion amplifying circuit of being made up of electronic switch U2 and operational amplifier U1A.

The in-phase proportion amplifying circuit (as Fig. 1) of standard, the short and empty disconnected principle of the void by operational amplifier U1A can analyze the electric current that flows through between the positive input of operational amplifier U1A and anti-phase input minimum, and can draw formula $\frac{\mathrm{Uo}}{\mathrm{Ui}}=1+\frac{R3}{R2}$ (formula 1)

Utilize this principle here just, we have revised the circuit (see figure 2), inverting input at operational amplifier U1A inserts electronic switch U2, the conducting resistance of being brought for electronic switch U2 we on Fig. 2 with resistance R 4 expressions, because the electric current that the anti-phase inlet flow of in-phase proportion amplifying circuit is crossed is minimum, so the pressure drop that is produced on resistance R 4 can be ignored, so formula 1 is still set up.

By above circuit theory, solved the problem of the conducting resistance that electronic switch U2 brought substantially.Simultaneously, we can be by a series of resistance of connecting at electronic switch U2 output, and the control pin by electronic switch U2 carries out the passage switching again, obtains different proportional gains.As Fig. 3, we have adopted R2=4K, R3=2K, and R4=1K, R5=1K forms resistor network.Simultaneously the QH1 of single-chip microcomputer U3, QH2 pin are connected with A, the B control pin of electronic switch U2, in order to the conducting pin of control electronic switch U2.

In conjunction with control truth table and the formula 1 of electronic switch U2, we draw following corresponding form:

By above form, we have realized the control switching of range gain by this module.

In second module, we have used basic operational amplifier add circuit, as shown in Figure 4.

According to above-mentioned schematic diagram, we can obtain by the operational amplifier basic principle:

$\mathrm{Uo}=\frac{-\mathrm{Ui}\&times;R8}{\mathrm{<figure-callout\; id="6"\; label="R"\; filenames="Y20082021585200111.png,Y20082021585200121.png"\; state="\{\{state\}\}">R</figure-callout>}6}+\frac{2.5\&times;R8}{R7}$ (formula 2)

For the AD of single-chip microcomputer U3, input signal must be between 0～3.3V.So herein, the utility model with reference to Fig. 4, is chosen the collocation of suitable resistance with the ac voltage signal of input, raises.Its output voltage values can calculate by formula 2. $\mathrm{Uo}=-\frac{\mathrm{Ui}}{2}+1.67$ Because Ui is a 1V left and right sides AC signal, its maximum amplitude is about 1.4V, so Uo just in time can satisfy the input request signal of rear end AD.

The three module single chip machine controlling circuit is the kernel control module of this circuit.12 AD of high accuracy by single-chip microcomputer MSP430 chip integration becomes carry out real-time sampling to the ac voltage signal of handling, and calculate the value of AD sampling AC signal simultaneously.Then sampled value be multiply by the coefficient of software ratio again, obtain final actual value, export to display unit.Be directed to the size of final actual value, we divide the sampling range.

If primary side 100% input current is 1A, be limited to 1000% on the measuring range.AD device sample range is 0～4095, sees Table 2

	The primary side input value	Module one gain amplifier	The AD original value of sampling	The software proportionality coefficient	Final actual value
						Range one	1.25A	8	4095	1/8	1.25A
Range two	2.5A	4	4095	1/4	2.5A
						Range three	5A	2	4095	1/2	5A
Range four	10A	1	4095	1	10A

As can be seen from the above table, because the sample range of AD is fixed, utilize this range switch circuit, can so that AD 125%, 250%, 500%, 1000% these 4 points reach the maximum of sampling original value respectively, so just make certainty of measurement obtain raising to a great extent.The software changeover program can be set switching law by the AD original value of sampling, and is controlled the different gains coefficient of range switch circuit again by the IO pin of output.As: AD＞4000 an o'clock range adds one, and AD＜2000 an o'clock range subtracts one, in the conversion range, changes the software proportionality coefficient that self calculates, and exports corresponding IO mouth simultaneously, controls the corresponding gain coefficient that obtains of range switch circuit.

R1～R8 is the RJJ-1/4W precision resister in Fig. 5, and operational amplifier is the double operational LM358 DIP-8 of TI company encapsulation.Because operational amplifier is a double operational, is expressed as two independent operational amplifiers of U1A and U1B in Fig. 5.By 4,8 pin access ± 5V working powers.U2 is the electronic switch CD4051DIP-16 of TI company encapsulation.+ 5V ,-5V ,-2.5V is the stability criterion voltage that power supply provided, it is all G1 with reference to ground.IA represents input signal, and IAIN represents to export to the signal of the AD mouth of single-chip microcomputer.QH1, QH2 connect single-chip microcomputer P2.0, P2.1 IO mouth is used to control the outlet of electronic switch U2 gating.

C41～C44 is the single-chip microcomputer decoupling capacitor in Fig. 6.C36, C37, R18 and XT1 form the standard crystal oscillating circuit.U3 is single-chip microcomputer MSP430F149IPM, adopts the QFP64 encapsulation.+ 3.3V is a microcontroller power supply, and VREF is an AD sampling reference voltage.QH1, QH2 connect control end A, the B of electronic switch U2, are used to control the outlet of electronic switch U2 gating.

The utility model compared with prior art, its major advantage sees Table 3

Table 3

Application scheme	Power consumption	Switch speed	The components and parts cost
				Relay switch	About 0.4W	About 20ms	About 10 yuan
The Low ESR electronic switch	Less than 0.1W	Less than 1ms	About 50 yuan
				The utility model	Less than 0.1W	Less than 1ms	About 2 yuan

Because single-chip microcomputer can select different model for use, and three kinds of schemes all need to use, so above cost does not comprise the single-chip microcomputer cost.

The utility model is through a large amount of experimental tests, and its certainty of measurement, measuring range and device cost all produce a desired effect.

Below disclose the utility model with preferred embodiment, so it is not in order to restriction the utility model, and all employings are equal to replaces or technical scheme that the equivalent transformation mode is obtained, all drops on protection range of the present utility model.

Claims (3)

1, the electric current input range automatic switch-over circuit of motor protection equipment comprises current transformer and sample circuit, and the output of described current transformer connects the input of sample circuit; It is characterized in that described sample circuit comprises range switch circuit, voltage commutation is raised circuit and three modules of single chip machine controlling circuit, described range switch circuit is made up of standard in-phase ratio amplifying circuit and electronic switch, electronic switch is that hilted broadsword eight is thrown electronic switch, be connected the inverting input of the operational amplifier in the standard in-phase ratio amplifying circuit, between the output of operational amplifier and ground, be in series with 4 resistance, 4 output pins of electronic switch are connected on respectively on the output that reaches operational amplifier between four resistance, form selectivity and insert resistance circuit, the output concatenation operation amplifier input terminal of current transformer; The output of operational amplifier connects voltage commutation and raises circuit, and it is basic operational amplifier add circuit that described voltage commutation is raised circuit; Described single chip machine controlling circuit comprises single-chip microcomputer, and voltage commutation is raised the input of the output connection single-chip microcomputer of circuit, and an output pin of single-chip microcomputer connects display unit, in addition the control pin of two output pins connection electronic switches.

2, the electric current input range automatic switch-over circuit of motor protection equipment according to claim 1 is characterized in that described single-chip microcomputer, is connected with decoupling capacitor on its pin.

3, the electric current input range automatic switch-over circuit of motor protection equipment according to claim 1 is characterized in that described single-chip microcomputer, is connected with the standard crystal oscillating circuit of being made up of electric capacity, resistance and crystal oscillator on its pin.

Images