Summary of the invention
In view of this, the invention provides a kind of protection conductor metering circuit and measurement mechanism, more accurately the resistance of measuring and protecting conductor.
For achieving the above object, the invention provides following technical scheme: a kind of metering circuit of protecting conductor comprises: current-limiting resistance, divider resistance, sample resistance, the positive and negative transfer relay of electric current and A/D converter;
Described current-limiting resistance, described divider resistance and described sample resistance are connected in series in D.C. regulated power supply and with reference between the ground, an end of wherein said current-limiting resistance links to each other with described D.C. regulated power supply, and an end of described sample resistance links to each other with reference ground;
The common port of described current-limiting resistance and described divider resistance links to each other with the positive and negative transfer relay of described electric current;
The common port of described divider resistance and described sample resistance links to each other with described analog to digital converter;
The positive and negative relay of described electric current links to each other with earthing of casing end with the protection conductor terminals of equipment under test.
Preferably, the positive and negative transfer relay of described electric current comprises: the first relay, the second relay and the 3rd relay;
One port of described the first relay links to each other another port ground connection with the common port of described current-limiting resistance and described divider resistance;
Described the second relay links to each other with described earthing of casing end;
Described the 3rd relay links to each other with described protection conductor terminals.
Preferably, the span of described current-limiting resistance is: the resistance of the magnitude of voltage/current-limiting resistance of D.C. regulated power supply〉200mA.
The present invention also provides a kind of protection conductor measuring device, comprises the above protection conductor metering circuit.
Can find out from above-mentioned technical scheme; current-limiting resistance, divider resistance, sample resistance, the positive and negative transfer relay of electric current and A/D converter have been comprised in a kind of protection conductor metering circuit provided by the invention; realize employing direct current bidirectional measurement technology by the positive and negative transfer relay of electric current, improved the precision of measuring and protecting conductor resistance.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that obtains under the creative work prerequisite.
Referring to Fig. 1, be a kind of connection diagram of protecting the metering circuit of conductor that the embodiment of the invention provides, this circuit comprises: current-limiting resistance 1, divider resistance 2, sample resistance 3, the positive and negative transfer relay 4 of electric current and analog to digital converter (ADC) 5;
Described current-limiting resistance 1, described divider resistance 2 and described sample resistance 3 are connected in series in D.C. regulated power supply 6 and with reference between the ground, an end of wherein said current-limiting resistance 1 links to each other with described D.C. regulated power supply 6, and an end of described sample resistance 2 links to each other with reference ground;
The common port of described current-limiting resistance 1 and described divider resistance 2 links to each other with the positive and negative transfer relay 4 of described electric current;
The common port of described divider resistance 2 and described sample resistance 3 links to each other with described digital to analog converter 4;
The positive and negative transfer relay 4 of described electric current links to each other with earthing of casing end with the protection conductor terminals of tested electric equipment 7.
Wherein, the positive and negative transfer relay of electric current comprises: the first relay, the second relay and the 3rd relay; referring to Fig. 2; be a kind of internal circuit connection diagram of protecting the positive and negative commutation circuit in the conductor metering circuit in the embodiment of the invention; the positive and negative transfer relay of electric current comprises the first relay 41, the second relay 42 and the 3rd relay 43; described the first relay 41, the second relay 42 and third phase relay 43 include eight ports
The first port 411 of described the first relay 41 is positive terminal, the 8th port 418 is negative terminals, the 4th port 414 links to each other with the common port of current-limiting resistance 1 with divider resistance 2, five-port 415 ground connection, the 3rd port 413 links to each other with the 6th port 436 with the 3rd port 433 of the 3rd relay 43 respectively with the 6th port 416.In addition, the first relay 41 also comprises the second port 412 and the 7th port 417.
The first port 431 of the 3rd relay 43 is positive terminal; the 8th port 438 is negative terminals; the second port 432 of the 3rd relay 43 is connected with its five-port 435; and link to each other with tested Electrical protection conductor earth terminal, the 4th port 434 of the 3rd relay 43 and 437 series connection of the 7th port are connected in the 6th port 426 of the second relay 42.
The first port 421 of the second relay 42 is positive terminal, and the 8th port 428 is negative terminals, and the second port 422 of the second relay 42 is connected with the 7th port 427, and with linked to each other by the earthing of casing end of electricity measurer.In addition, the second relay 42 also comprises the 3rd port 423, the 4th port 424, five-port 425.
Protection conductor metering circuit of the present invention can realize direct current bidirectional measurement technology.Current direction during the bipolarity test is:
The electric current forward is measured: direct supply VCC---current-limiting resistance R1---the first relay 41(is through the 4th, three ports)---the 3rd relay 43(is through the 3rd, two ports)---electrical appliance power cord PE holds J1---electric appliance casing earth terminal J2---the second relay (through the 7th, six ports)---the 3rd relay 43(is through the 7th, six ports)---the first relay 41(closes) (through the 6th, five-port)---ground;
Electric current is oppositely measured: direct supply VCC---current-limiting resistance R1---the first relay R L1(is through the 4th, three ports)---the 3rd relay 43(is through third and fourth port)---the second relay 42(is through the 6th, seven ports)---electric appliance casing earth terminal J2---electrical appliance power cord PE holds J1---the 3rd relay 43(is through the 5th, six ports)---the first relay 41(through the 6th, five-port)---ground.
Wherein, the span of current-limiting resistance R1 is: the resistance R1 of the magnitude of voltage VCC/ current-limiting resistance of D.C. regulated power supply〉200mA.
Wherein, the resistance of the resistance of described divider resistance R2 and described sample resistance R3 should be far longer than the resistance of current-limiting resistance R1, so that the partial pressure value of divider resistance R2 and sample resistance R3 can be ignored with respect to the partial pressure value of current-limiting resistance R1.And the ADC sampling voltage value (sampling in analog to digital converter) of sample resistance R3 should be less than the reference voltage of ADC.
Protection conductor electricity is tried to achieve by following formula one:
Wherein, the resistance of protection conductor is Rx, and V1 is the dividing potential drop on the resistance R x of protection conductor, and the magnitude of voltage of V1 can read at analog to digital converter.
Dividing potential drop to divider resistance R2 and sample resistance R3 is ignored, and the dividing potential drop of R1 is VCC-V1, and formula one becomes following formula two so:
(formula two)
Above formula two can be converted into the computing formula of protection conductor resistance, following formula:
Rx=(the ÷ (VCC-V1) (formula three) of R1 * V1)
Circuit of the present invention adopts direct current bidirectional measurement technology by the positive and negative transfer relay of electric current, has improved the precision of measuring and protecting conductor resistance.
In addition, the invention provides a kind of protection conductor measuring device, this device comprises aforesaid protection conductor metering circuit.
Each embodiment adopts the mode of going forward one by one to describe in this instructions, and what each embodiment stressed is and the difference of other embodiment that identical similar part is mutually referring to getting final product between each embodiment.
To the above-mentioned explanation of the disclosed embodiments, make this area professional and technical personnel can realize or use the present invention.Multiple modification to these embodiment will be apparent concerning those skilled in the art, and General Principle as defined herein can be in the situation that do not break away from the spirit or scope of the present invention, in other embodiments realization.Therefore, the present invention will can not be restricted to these embodiment shown in this article, but will meet the widest scope consistent with principle disclosed herein and features of novelty.