CN201449402U

CN201449402U - Protection circuit for leakage current tester

Info

Publication number: CN201449402U
Application number: CN2009200432349U
Authority: CN
Inventors: 李求龙
Original assignee: NANJING MINSHENG ELECTRONIC INSTRUMENTS CO Ltd
Current assignee: NANJING MINSHENG ELECTRONIC INSTRUMENTS CO Ltd
Priority date: 2009-07-03
Filing date: 2009-07-03
Publication date: 2010-05-05
Anticipated expiration: 2019-07-03

Abstract

The utility model proposes a protection circuit for a leakage current tester, which comprises a current mutual inductor, an operational amplifier, a wave detector, a voltage follower, a comparator and an optocoupler. The current mutual inductor is arranged on the high end of an automatic coupling voltage regulator of the leakage current tester; the operational amplifier receives the output of the current mutual inductor; the wave detector receives the output of the operational amplifier; the voltage follower receives the output of the wave detector; the comparator compares the output of the voltage follower with a reference signal; the optocoupler receives the output of the comparator and outputs to the processing unit of the leakage current tester. The protection circuit can prevent the power of the tested instrument from being higher than that of the leakage current tester, avoids burning the leakage current tester and reduces the economic loss for users.

Description

The holding circuit of leakage current tester

Technical field

The utility model relates to a kind of holding circuit, and particularly relevant for a kind of holding circuit of leakage current tester.

Background technology

Leakage current testing is a test among many safety tests, common safety executable unit, and for example UL, CSA, IEC, BSI, VDE, TUV and JSI etc. can require some product must do this test.The test specification of leakage current is looked various product and is very different, and place that product is used and function different also can be caused the difference of specification standards.Electric current electric leakage and power supply leak and are common test clause, and the fact can be divided into three kinds of different tests, are respectively over the ground leakage current, to the leakage current of casing with to the leakage current of application object.Main difference is the difference of prod measuring position, and earth leakage current is that leakage current flows back to the earth via the ground wire on the power lead, and the casing leakage current is when touching body owing to personnel, and leakage current flows back to the earth via human body.Using the object leakage current in addition or be called the treatment leakage current, is to use between the object or flowing to the leakage current of using object, having only Medical Instruments that the requirement of this test is arranged usually.The fundamental purpose of these tests and is unlikely the danger of the injury of getting an electric shock for allowing the user in operation or hold when using object as safe as a housely.

Leakage current testing is that a kind of leakage current of product is simulated body impedance circuitry as the test that measures foundation via one group, and this simulation body impedance circuitry is called as " metering circuit (MD) ".The impedance of human body is different owing to the flow direction of position, area and the electric current of human-machine interface contact, and based on above-mentioned these reasons, the selection of metering circuit specification must decide according to the maximum leakage magnitude of current that will do which kind of test and can allow.The measurement of product leakage electric current can be avoided when product during in the mxm. of input voltage (be generally input voltage ratings 110% or 106%) work, for some reason barrier or improper use and the problems and the danger that cause.

Because the test of leakage current all is a dynamic test is that tested electrical appliance is in running order test down, so the tester power of leakage current must be higher than the power of tested electrical appliance, otherwise can burn out tester.But the situation that superpower is used takes place through regular meeting in user in actual use, brings economic loss to them.

The utility model content

The purpose of this utility model is the holding circuit that proposes a kind of leakage current tester, can prevent that tested power with instrument is higher than the power of leakage current tester, avoids burning out leakage current tester, has reduced economic loss of user.

For reaching above-mentioned purpose, the utility model proposes a kind of holding circuit of leakage current tester, comprise current transformer, operational amplifier, wave detector, voltage follower, comparer and optocoupler.Current transformer is arranged at automatic coupling voltage regulator high-end of leakage current tester; The output of operational amplifier received current mutual inductor; Wave detector receives the output of above-mentioned operational amplifier; Voltage follower receives the output of above-mentioned wave detector; Comparer, the output of more above-mentioned voltage follower and a reference signal; Optocoupler receives the output of above-mentioned comparer and exports it processing unit of leakage current tester to.

The utility model prevents that tested power with instrument is higher than the power of leakage current tester, avoids burning out leakage current tester, has reduced economic loss of user.

Description of drawings

Fig. 1 is the internal circuit diagram of the leakage current tester of known technology.

Fig. 2 is applied to the circuit diagram of leakage current tester for the utility model embodiment.

Embodiment

For above-mentioned and other purpose, feature and advantage of the present utility model can be become apparent, preferred embodiment cited below particularly, and conjunction with figs. are described in detail below.

Fig. 1 is the internal circuit diagram of the leakage current tester of known technology.Concrete element that leakage current tester inside comprises and the annexation between each element belong to common practise for the people who has common knowledge in this area, do not repeat them here.Hereinafter only simply introduce the use of leakage current tester, as shown in Figure 1, during test, attracting electric relay JK2 is added to civil power on the automatic coupling voltage regulator B1, through boost elementary again by the secondary equipment under test D that exports to of isolating transformer B2 to isolating transformer B2 of pressure regulator B1.Suction by relay J K1 in the test process with close, the switch branch is clipped to 1,2 position measurement leakage current, gets the leakage current values of bigger value as this electrical appliance in two leakage current values.The user generally by the standard-required of electrical appliance, sets leakage current value, and in the test process, processor (CPU) surpasses setting value as long as detect leakage current value, will cut off output voltage and send the sound and light alarm signal simultaneously to loudspeaker (SPEAKER).

Fig. 2 is applied to the circuit diagram of leakage current tester for the utility model embodiment.As shown in Figure 2, the holding circuit of leakage current tester comprises current transformer G, operational amplifier 10, wave detector 20, voltage follower 30, comparer 40, optocoupler 50.Current transformer G connects leakage current tester automatic coupling voltage regulator B1, the output of operational amplifier 10 received current mutual inductor G, wave detector 20 receives the output of operational amplifier 10, voltage follower 30 receives the output of wave detector 20, comparer 40 receives the also output and a reference voltage signal of comparative voltage follower 30, optocoupler 50 receives the output of comparer 40, and the result is exported to the processing unit (CPU) of Hi-pot Tester.

In the present embodiment, current transformer G is 100 to 1 current transformer.

Wave detector 20 comprises wave detector U2A and wave detector U2B.Voltage follower 30 comprises voltage follower U3A and voltage follower U3B.For the people who has common knowledge in this area, the internal circuit of current transformer 10, wave detector 20, voltage follower 30, comparer 40, optocoupler 50 has in this area and belongs to common practise the people of common knowledge, does not repeat them here.

Comparer 40 is integrated transporting discharging nonlinear application circuit, and it is compared an analog quantity voltage signal and one with reference to fixed voltage, the two amplitude equate near, output voltage will produce transition, corresponding output high level or low level.

In test process, input current obtains sampled signal by current transformer G, amplifies through operational amplifier 10, exports wave detector 20 to, and wave detector 20 carries out " detection " to the received signal.Though the principle of detection and rectification is the same, the purpose of rectification is just in order to obtain direct current, and detection then is to take out signal content from modulated wave.Characteristics such as to have junction capacity low because of detector diode, and the high and inverse current of frequency of operation is little are so can select in4148 for use.It is low that detector diode has junction capacity, characteristics such as frequency of operation height and inverse current are little, principle of work is for to pass through detector diode with signal, because the unilateal conduction characteristic of detector diode, the negative-going portion of amplitude-modulated signal is clipped, and only stays its forward part, and this moment is as average in each signal period (low-pass filtering), the ripple bag of gained signal is the base band low frequency signal, has realized the detection function.

Voltage follower 30 receives the output signal of wave detector 20; voltage follower 30 is used to reduce circuit output impedance; improve load capacity; and making that the signal of output is more stable. the output of voltage follower 30 is connected to the negative terminal of comparer 40. and comparer 40 is integrated transporting discharging nonlinear application circuit; it is compared an analog quantity voltage signal and one with reference to fixed voltage; the two amplitude equate near; output voltage will produce transition; corresponding output high level or low level. the size in when debugging according to each model power of leakage current tester; regulator potentiometer VR5; the voltage signal of regulating is sent into the anode of comparer 50 by voltage follower; obtain the comparative voltage of comparer 50. when sampled signal during greater than comparative voltage; the output end voltage upset of comparer 50; output voltage is by high step-down. and send into CPU after optocoupler 50 is isolated, after CPU received low level signal, execution stopped test command; the instrument output voltage cuts off, thereby reaches the purpose of protection instrument.

In sum, the utility model is set with comparative voltage according to the size of each model power of leakage current tester, the size that compares sampled signal and comparative voltage, when when sampled signal during greater than comparative voltage, cut off the leakage current tester output voltage, prevent that leakage current tester from being burnt out, reduced economic loss of user.

Concrete case study on implementation only is a preferable case study on implementation of the present utility model described in the utility model, is not to be used for limiting practical range of the present utility model.Be that all equivalences of doing according to the content of the utility model claim change and modification, all should be as technology category of the present utility model.

Claims

1. the holding circuit of a leakage current tester is characterized in that, comprising:

Current transformer is arranged at automatic coupling voltage regulator high-end of leakage current tester;

Operational amplifier, the output of received current mutual inductor;

Wave detector receives the output of above-mentioned operational amplifier;

Voltage follower receives the output of above-mentioned wave detector;

Comparer, the output of more above-mentioned voltage follower and a reference signal;

Optocoupler receives the output of above-mentioned comparer and exports it processing unit of leakage current tester to.