JPH0736026B2 - Comparison method of thermoelectric AC / DC converters - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for comparing thermoelectric type AC / DC converters used when performing precise measurement of AC voltage and AC current.

[Conventional technology]

In order to measure the low frequency AC voltage (current) with precision, it is necessary to compare the low frequency AC voltage (current) with the DC voltage (current). The converter used for this comparison is such that a current is passed through a resistance wire (heater) and the temperature rise is detected by a thermocouple. That is, AC voltage (current) to the converter
AC voltage (current) by comparing the DC voltage (current) that produces the same thermoelectromotive force
To obtain the effective value of. During this comparison, there is a slight difference between the AC voltage and the DC voltage, which is called the AC / DC difference of the converter.

Next, a conventionally known current comparison method will be described with reference to FIG. In this figure, the heaters of the converters TC ₁ and TC ₂ are connected in series to which the AC and DC forward directions from the precision AC power supply Va and the precision DC power supply Vd,
Current is continuously applied in the reverse direction of DC. However, in the circuit shown in FIG. 2, the thermoelectromotive force E ₁ of the first converter TC ₁ is assumed greater than thermoelectromotive force E ₂ of the second converter TC _2.

As shown in FIG. ₂ , thermoelectric powers E ₁ and E ₂ are connected to the respective converters TC ₁ and TC ₂ so as to have opposite polarities.
Therefore, the thermoelectromotive force E ₁ is divided by the resistors R ₁ and R ₂ , and the resistor R ₂
It is necessary to make the voltage between the terminals of R ₃ and R ₃ approximately equal.
This differential voltage and the thermoelectromotive force of the converter TC ₂ , which is the reference,
Measure with two precision digital voltmeters. At this time, the power supply switching, data acquisition, and AC / DC difference calculation processing are performed by the controller.

Now, assuming that the AC / DC difference between the converters TC ₁ and TC ₂ is δ ₁ and δ ₂ , respectively, it is necessary to find the difference in AC / DC difference when performing comparative measurement. That is, Becomes Here, Ea ₁ and Ea ₂ are thermoelectromotive force values when a rated AC current is applied to the converter, and Ed ₁ and Ed ₂ are DC currents (I
The thermoelectromotive force values when flowing d), ΔEd ₁ and ΔEd _2, are quantities proportional to the gradient of the input / output characteristics. This proportional amount is a resistor
Since R ₂ and R ₃ are set almost equal, ΔEd ₁ ΔEd ₂ . In addition, to measure the slope with the input / output characteristics, use the direct current
It is advisable to find the difference in the thermoelectromotive force between when Id is passed and when it is reduced by a minute amount ΔId.

In the above formula (1), the current ratio ΔId / Id is 1/100 to 1/10
About 000 is good. Further, it is necessary to make ΔEd ₁ and ΔEd ₂ of the denominator almost equal to each other, but how much they are equal to each other is specified in relation to the measurement accuracy.

Now, it is assumed that the relationship ΔEd ₁ = ΔEd ₂ (1 + ε) holds. In this embodiment, AC and DC forward E ⁺
Since d _i (i = 1, 2), DC reverse direction E ⁻ d _i , and AC and power supply are switched, the average value Ed _i Ed _i = (E ⁺ d _i + E ⁻ d _i ) / 2 is calculated by the formula ( Substituting into 1) and rearranging, Becomes

[Problems to be Solved by the Invention]

However, as shown in the above equation (2), there is a drawback in that it is complicated and complicated to use the analytical method of the mathematical formula when calculating the difference between the AC / DC difference between the two converters.

Therefore, an object of the present invention is to provide a method capable of simply and easily obtaining the difference between the direct-current difference between both converters.

[Means for Solving the Problems]

The present invention takes the thermoelectromotive force of a reference converter, out of the first and second thermoelectric type AC / DC exchangers, on one axis on a two-dimensional coordinate axis orthogonal to each other, and on the other axis, the first electromotive force is applied. Also, the differential thermoelectromotive force of the second converter is taken, and the difference between the AC / DC difference in both converters is obtained based on the obtained characteristics.

More specifically, the present invention takes the thermoelectromotive force of a second converter, which is a reference among the first and second thermoelectric AC / DC converters, on the horizontal axis, and The difference voltage of the converter is scaled on the vertical axis, the DC input differential voltage characteristic and the AC input differential voltage characteristic are drawn, and the value is changed to a value close to the rated voltage (current) on the horizontal axis and a minute amount from it. Of the reference converter when the rated DC voltage (current) is flowed, the gradient is obtained from the thermoelectromotive force of the reference converter generated by the quantity and the DC input voltage difference on the vertical axis corresponding to the thermoelectromotive force. The electromotive force is plotted on the abscissa, the intersection with the DC input differential voltage characteristic is the first point, and the thermoelectromotive force of the reference converter when a rated AC voltage (current) is passed is plotted on the abscissa. The resulting intersection points with the AC input differential voltage characteristic and the DC input differential voltage characteristic are the second point, As 4 points, the distance between the 2nd point and the 4th point is set to an amount proportional to the crossing difference between the 1st and 2nd transducers, and a line parallel to the horizontal axis is drawn through the 1st point. , The intersection of the line segment connecting the second point and the fourth point is the third point, and the length between the second point and the fourth point is the thermoelectromotive force of the DC rated voltage and its small amount. By dividing by the difference in thermoelectromotive force of the reference converter caused by the decrease, and further multiplying by the ratio of the input voltage (current) and its minute amount, the first
And the difference between the AC / DC difference of the second converter is obtained.

[Action]

In the present invention, by adopting the above-mentioned configuration, the difference in the direct-current difference between both converters can be graphically obtained. That is,
The abscissa plots the thermoelectromotive force of the converter as a reference, the ordinate plots the differential thermoelectromotive force of both converters, and the difference between the AC / DC difference is obtained by this characteristic.

As described above, the mathematical analysis requires complicated assumptions and inferences, whereas the present invention makes it possible to easily and clearly find the difference between the AC and DC differences by making a diagram.

〔Example〕

 Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 is a characteristic diagram showing the principle of the present invention. The current measurement will be described with reference to FIGS. 1 and 2. First
In the figure, the abscissa represents the thermoelectromotive force value of the reference converter (for example, the output E _{2 of} the second converter TC ₂ shown in FIG. ₂ ), and the ordinate represents the two converters TC ₁ , TC ₂ differential thermoelectromotive force (DVM ₁ reading shown in Fig. 2) is plotted. Thereby, the DC input differential current characteristic (broken line) and the AC input differential current characteristic (solid line) are drawn. Strictly speaking, the input / output characteristic of the converter is a curve, but can be regarded as a straight line in a minute range.

The denominator of the equation (2) for obtaining the difference between the AC / DC difference is as follows.

The thermoelectromotive force when a value close to the rated current is passed through the converter is S
(H), and the thermoelectromotive force when a minute resistor (ΔR in FIG. 2) for reducing a minute amount (ΔId) from the rated current is inserted in the power supply circuit is S (L).

S (H) and S (L) are plotted on the horizontal axis, and the intersections with the DC input differential current characteristic (broken line) are D (H) and D (L), respectively.
And Then, the difference on the horizontal axis is B (= S (H) −S
(L)). B is a quantity that is the denominator of the equation (2).
In addition, D (H) and D on the DC input differential current characteristic (broken line)
The difference of (L) is D ₁ (= D (H) −D (L)).

Then, from FIG. 1, the slope of the DC input differential current characteristic (broken line)
When D ₂ is obtained, D ₂ = D ₁ / B.

The main terms (parentheses) and the ε of the formula (2) for obtaining the difference between the AC and DC
The correction term of is as follows.

When the values close to the rated AC current and the rated DC current are input, the thermoelectric powers of the reference converter are E _AC and E _DC , respectively, and these are plotted on the horizontal axis. S (H) on the horizontal axis and E _DC should match at the rated DC current, but there is a drift because the measurement times are different. In particular, in FIG. 1, they are drawn apart for easier understanding.

The intersection of point E _DC and the DC input differential current characteristic (broken line) is A ₁ . The intersections of the point E _AC and both characteristics are A ₂ and A ₄ , respectively.

Next, draw a line that passes through point A ₁ and is parallel to the horizontal axis. The intersection with and is A ₃ . The difference between E _DC and E _AC on the horizontal axis is Y
(Y = E _AC −E _DC ). Furthermore, A ₁ on both characteristics
And the difference between A ₂ And If this is expressed by a measured value, D ₃ = D (DC) -D (AC). This is taken out of the molecule of formula ^{(2), (E + d} 1 -E + d 2) + is clear from _{-2 (Ea 1 -Ea 2) (} E - d 2 - d 1 -E).

It becomes the correction amount of the principal component D ₃ of the difference of the AC / DC difference. Be D ₄ . Although it is drawn large in FIG. 1, the actual measured value is small.

From the marking measurement, B: D ₁ = Y: D ₄ , so D ₄ =
D ₂ × Y = D ₁ Y / B.

Therefore, Then, D ₅ = D ₃ + D ₄ . After all, if you specifically write down the difference of the calculated direct difference δ ₁ −δ ₂ = (D ₅ / B) · ΔId / Id, Becomes

4 quantities D (H), D (L), S (H), S by marking
(L) is measured, AC current, DC current positive direction, DC current reverse direction, AC current are measured continuously, and D (AC), E _AC , D
_Find the amounts of (DC) and E _DC . These are substituted into the above equation (3). This is the most suitable measurement method for computer processing.

FIG. 3 shows an embodiment of the measuring device for AC voltage comparison to which the present invention is applied. Since the same theory as described above can be applied to the voltage measurement, description thereof will be omitted.

〔The invention's effect〕

As described above, according to the present invention, since the difference between the direct-current difference between the two converters can be graphically obtained, the processing can be performed quickly and easily using a computer or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a block diagram showing an example of an AC current comparison circuit, and FIG. 3 is a block diagram showing an example of an AC voltage comparison circuit. TC ₁ ... 1st converter, TC ₂ ... 2nd converter, t _{1 to} t ₄ ...
... Output terminal, DVM ₁ ... 1st precision digital voltmeter, DV
M ₂ …… Second precision digital voltmeter, R ₁ …… First resistor, R ₂ …… Second resistor, R ₃ …… Third resistor, C ……
Controller, P ... Printer.

Claims (2)

[Claims] 1. A thermoelectric electromotive force of a reference converter of the first and second thermoelectric type AC / DC converters is taken on one axis on a two-dimensional coordinate axis orthogonal to each other, and the thermoelectromotive force is taken on the other axis. A method for comparing thermoelectric AC / DC converters, characterized in that the difference thermoelectromotive force between the first and second converters is taken and the difference between the AC / DC difference in both converters is obtained based on the obtained characteristics. 2. A thermoelectromotive force of a second converter, which is a reference among the first and second thermoelectric type AC / DC converters, is plotted on the horizontal axis,
The differential thermoelectromotive force of the first and second converters is scaled on the vertical axis, the DC input differential voltage characteristic and the AC input differential voltage characteristic are drawn, and the rated direct current in which the resistors are connected in series on the horizontal axis From the difference between the voltage or the value close to the rated DC current and the thermoelectromotive force of the reference converter caused by an amount slightly changed from it, and the difference between the DC input differential voltage on the vertical axis corresponding to the thermoelectromotive force, Calculate the slope, plot the thermoelectromotive force of the reference converter on the horizontal axis when a value close to the rated DC voltage or rated DC current in which resistors are connected in series is flowed, and find the intersection with the DC input differential voltage characteristic. One point, the thermoelectromotive force of the reference converter when a value close to the rated AC voltage or rated AC current with resistors connected in series is taken on the horizontal axis, and the AC input differential voltage characteristics and DC input differential voltage Second at each intersection with the characteristic As the points and the fourth points, the distance between the second point and the fourth point is set as an amount proportional to the difference between the straightness of the first and second converters, and the point passes through the first point and is parallel to the horizontal axis. Draw a line, the second
The intersection between the point and the line segment connecting the fourth point is defined as the third point, and the length between the second point and the fourth point is the rated AC voltage or rated AC current of the reference converter and its minute amount. The difference in the AC / DC difference between the first and second converters is obtained by dividing by the difference in thermoelectromotive force generated by the decrease and further multiplying by the ratio of the input DC voltage or input DC current and its minute amount. A method of comparing thermoelectric AC / DC converters.