KR100745158B1 - An automatic measurement device for the ac-dc current transfer difference of the thermal current converter and method thereof - Google Patents

Abstract

A device and a method for automatically measuring AC-DC(Alternating Current-Direct Current) current transfer difference of a TCC(Thermal Current Converter) are provided to prevent the leaking current generated due to stray capacity from flowing and to minimize influence of a drift of a current generator by measuring the output of two TCCs at the same time. A device(100) for automatically measuring AC-DC current transfer difference of a TCC is composed of a current generating unit(120) generating forward and reverse DC and AC current and supplying the generated current to a standard TCC(20) and a TCC(30) to be measured; a scan unit(140) changing the polarities of each output of the TCCs receiving the forward and reverse DC and AC current; a first voltmeter(150a) measuring the output of the standard TCC induced through the scan unit; a second voltmeter(150b) measuring the output of the TCC to be measured, induced through the scan unit; and a calculating unit computing a relative value of AC-DC current transfer difference of the TCC to be measured for the AC-DC current transfer difference of the standard TCC on the basis of a value measured by the first and second voltmeters if the forward and reverse DC and AC current is supplied. The standard TCC and the TCC to be measured are connected in series.

Description

An automatic measuring device and method for measuring the AC-DC current conversion difference of a thermoelectric current transducer {AN AUTOMATIC MEASUREMENT DEVICE FOR THE AC-DC CURRENT TRANSFER DIFFERENCE OF THE THERMAL CURRENT CONVERTER AND METHOD THEREOF}

1 is a schematic circuit diagram of a thermoelectric current converter,

2 is a block diagram of an automatic measuring device of an AC-DC current conversion difference of a thermoelectric current converter according to the present invention;

3 is a flowchart of a method of measuring an AC-DC conversion difference difference of a thermoelectric current converter according to the present invention;

4 is a schematic diagram showing an example of the result when the thermoelectric current converters are compared with each other according to the present invention, and

5 is a graph of inconsistencies when comparing thermoelectric current transducers in accordance with the present invention.

Description of the main parts of the drawing

10, 20, 30: thermoelectric current transducer

100: automatic measuring device of AC-DC current conversion difference of thermoelectric current converter

110: reference voltage generator for the current generator

120: current generator

130: coaxial chalk

140: scanner

150a, 150b: first and second voltmeters

160: system controller

The present invention relates to an apparatus and method for automatically measuring the AC-DC current conversion difference of a thermoelectric current converter, and more particularly, to an AC-to-DC current converter comparator used for an AC current standard. The present invention relates to a dual channel measuring apparatus for automatically evaluating a DC conversion difference and a measuring method using the same.

The alternating current standard is derived from the direct current standard. AC-DC Current Transfer Comparator is used to maintain AC current standards and disseminate them to industry or calibration organizations. Accurate assessment of the AC-DC Current Transfer Difference (CCD) of the AC converter is the basis for maintaining and disseminating the standard. Recently, among the various types of teaching converters, thermoelectric teaching converters having a wide range of frequency and current and small teaching differences are widely used worldwide.

The thermoelectric current converter (TCC) is one of thermoelectric rectilinear converters, and based on a calorimeter method, an effective current value of alternating current is detected by detecting a direct current value having the same thermal effect as Joule heat caused by alternating current. Measure The details of TCC are described in Kwon Sung-won, Lee Rae-deok, M. Klonz, “Manufacture of Thermoelectric Current Transducers for Primary Current Standards,” Korean Journal of Sensors, Vol. 1, No. 1, pp. 77-83, 1992 ', the details of which are incorporated herein by reference. The structure of the TCC is shown in FIG. The TCC 10 has a structure in which a thermoelectric element 12 and an AC current shunt 14 are connected in parallel. The intersection difference δ _i of the TCC 10 is defined as in Equation 1 below.

Where I _ac and I _dc represent the alternating current and direct current inputs required to obtain the same output from the TCC 10, respectively, and the direct current input is the average value of the positive and negative two-way current inputs.

In order to evaluate the intersection difference δ _i of each TCC 10, a mutual comparison measurement with a standard TCC is required. Until now, cross-comparison measurement of TCC has been performed manually, which may cause personal error and long measurement time.

The present invention provides a device for measuring the cross-sectional difference of TCC and a method for measuring the cross-sectional difference of the measured TCC with respect to the standard TCC by using the same, thereby eliminating individual errors due to manual measurement, reducing measurement time and improving measurement system utilization. The purpose.

In order to achieve this object, the present invention is a device for automatically measuring the cross-section of the thermoelectric current transducer under measurement based on a standard thermoelectric current converter, the forward DC current, the reverse direction having a predetermined current value in a predetermined order Current generating means for generating a direct current and an alternating current having a predetermined current value and frequency and supplying the standard and measured thermoelectric current converters; Scanning means for changing the polarity of the outputs from standard and measured thermoelectric current transducers supplied with forward direct current, reverse direct current and alternating current; A first voltmeter for measuring the output from the standard thermoelectric current converter induced through the scanning means and a second voltmeter for measuring the output from the measured thermoelectric current converter induced through the scanning means; And the relative value of the crossover difference of the measured thermoelectric current converter to the crossover difference of the standard thermoelectric current converter based on the measured values measured by the first and second voltmeters in the case of forward direct current, reverse direct current and alternating current. Computing means for calculating; provides a cross-sectional automatic measuring device of the thermoelectric current converter comprising a.

The high (H) terminals of the standard and measured thermoelectric current transducers are connected to each other, and the low (L) terminals of the standard and measured thermoelectric current transducers are connected to the output terminals of the current generating means, respectively. It is preferable not to flow.

The current output from the current generating means is preferably output through the coaxial choke which wound the coaxial line to the toroidal core.

The current generating means may comprise current limiting means such that the predetermined current value from the current generating means does not exceed 105% of the reference current values of the standard and the measured thermoelectric current converters.

In addition, the present invention, in the device configured as described above, in the current generating means for outputting the forward and reverse direct current having a current value larger than the reference current value of the standard and the measured thermoelectric current converter in a predetermined order and Measuring the outputs from the standard and measured thermoelectric current transducers in the first and second voltmeters for each current case (S10); The current generating means outputs forward and reverse direct currents having a current value smaller than the reference current value in a predetermined order, and outputs the outputs from the standard and measured thermoelectric current converters in the first and second voltmeters, respectively. Measuring for the case (S20); The current generating means outputs a forward DC current having a reference current value, a reverse DC current and an AC current having a reference current value and a reference frequency in a predetermined order, from the standard and measured thermoelectric current converters in the first and second voltmeters. Measuring the output for each current case (S30); And calculating a relative value of the cross sectional difference of the measured thermoelectric current converter to the cross sectional difference of the standard thermoelectric current converter from the outputs of the standard and the measured thermoelectric current converters measured in the first and second voltmeters (S40). It provides a method for automatically measuring the cross-sectional difference of the thermoelectric current converter comprising a.

The scanning means reverses the polarity of the output from the standard and the measured thermoelectric current transducer once while the current having respective current characteristics is output from the current generating means, and the first and second voltmeters average the voltage values before and after reversing. It is desirable to measure the output from standard and measured thermoelectric current transducers.

Step S30 is preferably repeated a plurality of times.

It is preferable to wait at least 60 seconds when the characteristic of the current output from the current generating means is changed.

The present invention described above will be described in more detail with reference to the embodiments of the present invention with reference to the drawings.

1. TCC teaching automatic measuring device

2 is a block diagram of a TCC automatic cross-sectional measuring apparatus 100 according to the present invention. As shown in FIG. 2, the TCC automatic cross measuring device 100 automatically measures the relative value of the cross difference of the measured TCC 30 with respect to the standard TCC 20. The TCC automatic cross measuring apparatus 100 includes a reference voltage generator 110 for a current generator, a current generator 120, a scanner 140, two voltmeters 150a and 150b, and a system controller 160.

The reference voltage generator 110 for the current generator generates DC and AC reference voltages using the Fluke 5700A, which is a stable calibrator. The current generator 120 generates a current with a conductance of 1 A / V in proportion to the input voltage from the reference voltage generator 110 and applies the current to the standard TCC 20 and the TCC 30 under measurement.

Output from the standard TCC 20 and the TCC 30 under measurement is applied to the two voltmeters 150a and 150b via the dual channel scanner 140. The voltmeters 150a and 150b use two Keithley 182s with 10 nV resolution to simultaneously measure the output of the TCC, effectively minimizing the effects of output drift. In addition, using a dual channel scanner 140 with low thermoelectric power, the voltmeters 150a and 150b measure the output of the TCC twice in the forward and reverse directions and use the average as one measurement to connect with the offset of the voltmeter itself. Allow the thermal power of the circuit to be canceled.

The system controller 160 instructs the current generator reference voltage generator 110 to sequentially generate a direct current or alternating current having a predetermined current value and frequency in a predetermined order, and instructs the scanner 140 at a predetermined timing. Indicates a channel switch command. In addition, the system controller 160 measures the intersection difference of the TCC 30 under measurement based on the measurement values from the voltmeters 150a and 150b.

The crossover of the TCC is connected to the standard TCC 20 and the TCC 30 to be measured in series, and the output of the standard TCC 20 is adjusted after adjusting the output of the TCC 30 to be equally adjusted for AC and DC input currents. We measure each and apply the difference to the calculation of teaching differences. When connecting two TCCs 20 and 30, connect the two high (H) terminals with the shortest possible lead wires, and connect the two low (L) terminals to the output terminals of the current generator 120, respectively. Even if a leakage current flows through the stray capacitance between the casings 20 and 30 and the ground, the same current flows through the two TCCs 20 and 30, thereby minimizing the measurement error.

The output measuring wires of the TCCs 20 and 30 may use a special wire shielded by twisting two copper wires having a small thermoelectric power to reduce an error by reducing a loop coupling area by an external magnetic field.

In addition, by using a coaxial choke (coaxial choke or current equalizer) 130 made by winding a coaxial line 10 times on a toroidal core having a high permeability, as a current input, the amount of current flowing through the inner and outer conductors of the coaxial line is increased. It is preferable to make them the same. This is because, in the precision measurement, if the magnitude of the current flowing in the inner and outer conductors of the coaxial line is different, this difference current may be combined with a circuit near the coaxial line and cause a measurement error.

On the other hand, the use range of the TCCs 20 and 30 is 50 to 110% of the rated current. If a current larger than this range is supplied, the thermoelectric elements ('12' in FIG. 1) of the TCCs 20 and 30 are destroyed. In order to prevent damage of the TCCs 20 and 30 due to overcurrent in the automatic measurement process, it is preferable to employ a current limiting function such that the output current of the current generator 120 does not exceed 105% of the measured current.

2. How to measure TCC teaching difference

Hereinafter, a method of automatically measuring the crossing difference δ _t of the TCC 30 to be measured by the above-described TCC automatic crossing measurement apparatus 100 will be described. 3 is a flowchart illustrating an example of a method for measuring a TCC crossover difference.

As shown in FIG. 3, the current generator 120 includes a forward direct current (DCF (1)), a reverse direct current (DCR (2)), a forward direct current (DCF (3)), a reverse direct current (DCR (4)), Forward DC (DCF (5)), AC (AC (6)), Reverse DC (DCR (7)), Alternating Current (AC (8)), Forward DC (DCF (9)), Alternating Current (AC (10)) , Reverse direct current (DCR (11), alternating current (AC (12)), forward direct current (DCF (13)), alternating current (AC (14)), reverse direct current (DCR (15)), alternating current (AC (16)) 60 seconds interval in the order of forward direct current (DCF (17)), alternating current (AC (18)), reverse direct current (DCR (19)), alternating current (AC (20)) and forward direct current (DCF (21)) The output of TCC 20 and 30 for each input current is measured by inverting the polarity of the voltmeter input with scanner 140, and the average value is obtained, and the TCC after the contact of input current and scanner 140 is changed. (20, 30) output, and an output (E _t) of the scanner 140 after each waiting for 40 seconds, and 20 seconds for the contact is stable, the output of the normal TCC (20) (E _s) and the measured TCC (30) At the same time The intersecting difference δ _t of the TCC 30 to be measured is determined by three measurement stages (DCR (7) -AC (8) -DCF (9) or AC (10) -DCR (11) -AC (12). Calculate as in Equation 2 using the values measured in

Where δ _s is the intersection of the standard TCC, E _as and E _at are the outputs of the standard and measured TCCs 20 and 30 when an alternating current is supplied to each, and E _ds and E _dt are the direct currents respectively. When supplied, it is the output of the standard and measured TCCs 20 and 30. For direct current inputs, this is the average of the output voltages for the DCF and DCR input currents. The variables n _s and n _t are values representing the characteristics between the input and output of the standard and the measured TCCs 20 and 30, respectively ( n = ΔE · l / E · Δl ), and the measurement steps DCF (1) -DCR ( 2) -DCF (3) -DCR (4) (step S10 and step S20), using the measured values.

In very narrow sections near the measurement current, the linearity of the input-output characteristics of the TCCs 20 and 30 is as good as in thermoelectric voltage converters. In order to calculate n _s and n _t from the outputs of the TCCs 20 and 30, the measuring steps DCF 1 and DCR 2 supply a current of 100.1% of the test current (step S10), and the measuring step DCF ( 3) and DCR (4) supply the current of 99.9% of the test current (step S20), and calculate the slope of the input-output characteristic graph in the measurement steps DCF (1) to DCR (4). Calculate the new AC setpoint using the slope obtained previously so that the average value of the TCC (30) output under test in the DCF (5) and DCR (7) phases is equal to or less than 20 mA / V with the AC current output. In step (8), the AC current is adjusted.

δ _t is calculated from the data of the three measuring stages DCR (7) -AC (8) -DCF (9) following the measuring stage DCF (9) (step S30), using each corresponding data in the same order. The measurement step is calculated after the DCR 12, the DCF 15, the DCR 18, and the DCF 21, respectively, and the average value thereof is one cross-sectional difference δ _t measurement (step S40).

3. TCC teaching difference measurement result

Five 3 mA TCCs and three 200 mA TCCs of the same current and structure were compared to each other to analyze the measurement capability of the automatic cross-section automatic measuring device. One 3 A TCC and two 5 A TCCs were measured at 3 A. 4 is a representative example of cross-checking 5 mA TCC at 1 kHz. The number above the circle is the serial number of the TCC, and the number below the circle is the teaching difference of that TCC. The number next to the arrow is a difference between the difference between the two teaching _{TCC (δ s -δ t),} δ s and δ _t is the value of the primary teaching TCC has a head and a tail of each arrow.

If there is no comparative measurement error of the measurement system itself, the sum of the differences of the teaching differences along the arrows shall be zero. In the example of FIG. 4, the discrepancy between the result of the direct comparison measurement (020 → 022) and the indirect comparison measurement (020 → 021 → 022) is +0.1 dB / A. As a result of comparative measurements at the frequencies 40 Hz, 500 Hz, 1 kHz, and 10 kHz in this manner, as shown in FIG. 5, the maximum value of the mismatch value is 1.1 dB / A at 10 kHz, as shown in FIG. 5. As a result of the comparison measurement for the 200 mA TCC, the discrepancy value was found to be 3.1 dB / A or less, and the maximum value was 5.4 dB / A for the 3 A comparative measurement.

The present invention provides a device for automatically measuring the crossover difference of TCC and a method for automatically measuring the crossover difference of the measured TCC with respect to the standard TCC by using the same, thereby eliminating individual errors due to manual measurement, reducing the measurement time and measuring device. It is effective to improve utilization.

In addition, when connecting the TCC according to the present invention, there is an effect that the leakage current due to stray capacitance does not flow. The scanner of the present invention can reverse the polarity of the output of the TCC, measure and average twice to offset the offset voltage of the voltmeter itself. The present invention can minimize the effects of drift of the current generator by measuring two TCC outputs at the same time.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it will be readily apparent to those skilled in the art that various other modifications and variations are possible without departing from the spirit and scope of the present invention. Are all within the scope of the appended claims.

Claims (8)

A device for automatically measuring the AC-DC conversion difference of a measured thermoelectric current transducer based on a standard thermoelectric current transducer. Current generating means for generating a forward direct current, a reverse direct current, and an alternating current and supplying the standard and measured thermoelectric current converters; Scanning means for changing the polarity of the output from the standard and measured thermoelectric current converters supplied with the forward direct current, reverse direct current and alternating current; A first voltmeter for measuring the output from the standard thermoelectric current transducer induced through the scanning means and a second voltmeter for measuring the output from the measured thermoelectric current transducer induced through the scanning means; And The measured thermoelectric current converter for the AC-DC conversion difference of the standard thermoelectric current converter based on the measured values measured by the first and second voltmeters in the case of the forward DC current, the reverse DC current and the alternating current. Calculation means for calculating a relative value of the AC-DC conversion difference of And the standard and measured thermoelectric current transducers are connected by direct current. 2. The output terminal of claim 1, wherein the high (H) terminals of the standard and measured thermoelectric current converters are directly connected to each other, and the low (L) terminals of the standard and measured thermoelectric current converters are directly connected to each other. Automatic measurement device for the AC-DC conversion difference of the thermoelectric current converter, characterized in that connected to each of the leakage current through the stray capacitance does not flow. The apparatus of claim 1, wherein the current output from the current generating means is output through a coaxial choke obtained by winding a coaxial line to a toroidal core. 2. The alternating current of a thermoelectric current converter according to claim 1, wherein said current generating means includes current limiting means not to exceed 105% of the reference current values of said standard and measured thermoelectric current converters. Conversion difference automatic measuring device. In the device configured as described in claim 1, The forward and reverse direct currents larger than the reference current values of the standard and measured thermoelectric current converters are output in a predetermined order by the current generating means, and the first and second voltmeters are output from the standard and measured thermoelectric current converters. Measuring the output of each case of current (S10); The current generating means outputs forward and reverse direct currents smaller than the reference current value in a predetermined order, and outputs the output from the standard and measured thermoelectric current converters in the first and second voltmeters in the case of each current. Measuring (S20); The current generating means outputs a forward DC current having a reference current value, a reverse DC current, and an AC current having the reference current value and a reference frequency in a predetermined order, and the standard and measured thermoelectrics are output from the first and second voltmeters. Measuring the output from the type current converter for each current case (S30); And AC-DC conversion of the measured thermoelectric current converter to AC-DC conversion difference of the standard thermoelectric current converter from outputs from the standard and measured thermoelectric current converters measured in the first and second voltmeters Computing the relative value of the difference (S40); automatic measuring method of the AC-DC current conversion difference of the thermoelectric current converter comprising a. 6. The apparatus according to claim 5, wherein said scanning means reverses the polarity of the output from said standard and measured thermoelectric current converter once, while a current having respective current characteristics is output from said current generating means, The second voltmeter measures the output from the standard and the measured thermoelectric current converter by averaging the voltage values before and after the reversal, the AC-DC current conversion difference automatic measuring method of the thermoelectric current converter. The method of claim 5, wherein the step S30 is repeated a plurality of times. 6. A method according to claim 5, characterized by waiting at least 60 seconds when the characteristic of the current output from said current generating means changes.

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