JPH0750132B2 - AC / DC difference comparison measurement method using U-shaped resistance thermoelectric AC / DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC difference comparison measuring method using a U-shaped resistance (heater) type thermoelectric AC / DC converter.

[0002]

2. Description of the Related Art In order to measure a low frequency AC voltage (current) with precision, it is necessary to compare the low frequency AC voltage (current) with a DC voltage (current).

Conventionally, for this comparison, a current is passed through a resistance wire (heater), and the temperature rise is detected by a thermocouple.
A so-called thermoelectric AC / DC converter is used. This thermoelectric type AC / DC converter has a single thermocouple type thermoelectric type AC / DC converter (hereinafter referred to as SJTC) and a large number of thermocouple type thermoelectric type DC / DC converters (hereinafter referred to as MJTC) depending on the number of thermocouples used. )
In both cases, the AC voltage (current) is applied to the converter, and the DC voltage (current) that produces the same thermoelectromotive force as the output is adjusted and compared with the DC voltage (current). By doing so, the effective value of the AC voltage (current) is obtained.

At the time of this comparison, there is a slight difference between the AC voltage and the DC voltage. This difference is called the AC / DC difference of the converter. A converter with a small AC / DC difference is desirable, and is used for precise measurement of low frequency AC voltage (current). Requires the use of a thermoelectric type AC / DC converter whose AC / DC difference is known in advance.

However, in the AC / DC difference measurement of the conventional thermoelectric type AC / DC converter, there is no standard device as a basis for the AC / DC difference measurement, and the absolute value of the AC / DC difference of the converter cannot be measured. Therefore, conventionally, two converters are taken out from each of the plurality of converters, and the AC / DC difference is comparatively measured, and the one having the smallest AC / DC difference is used.

FIG. 3 shows a circuit used for this comparative measurement. In this figure, TC ₁ and TC ₂ are the _first and _second converters for comparative measurement. First
Thermoelectromotive force E ₁ of the transducer TC ₁ is assumed second thermoelectromotive force E ₂ is greater than the converter TC _2.

The converters TC ₁ and TC ₂ are connected in series, and currents are continuously supplied from the precision current sources Va and Vd to the AC and DC forward directions and the DC reverse direction, respectively. In addition,
Divide the thermoelectromotive force E ₁ of the transducer TC ₁ with resistors R _1, R ₂ minute, and substantially equal to the thermoelectromotive force E ₂ of converter TC _2, the transducer TC ₂ comprising a difference voltage and standard, Two precision digital voltmeters DV
Measure with M1 and DVM2. At this time, the controller performs the switching of the power source, the data processing, and the calculation processing of the difference between the AC / DC difference.

[0008]

However, as described above, two converters are taken out from each of the plurality of converters, and the AC / DC difference is comparatively measured. The AC / DC difference is selected and the low frequency AC is selected. In the method used for precise measurement of voltage (current), the AC / DC difference of the converter used is not a standard value based on the standard, but is a relative value. Even in the measurement of (current), sufficient accuracy cannot be expected.

Further, in the above-mentioned method, the procedure for selecting the converter to be used is complicated, and at the same time, the converter to be used must be selected each time the low-frequency AC voltage (current) is precisely measured. There are difficulties.

Therefore, it is desired to measure the AC / DC difference of the converter as a measure of the AC / DC difference of the standard device in the comparative measurement of the AC / DC difference of the thermoelectric AC / DC converter, but there is no ideal standard device in the past. This method is not established.

On the other hand, for SJTC described above, the measurement formula of the AC / DC difference was introduced by Widdis, etc., but the MJTC has not been sufficiently analyzed, and the measurement formula of the AC / DC difference of SJTC is applied as it is. Was being done.

On the other hand, the inventor of the present application connects a large number of thermocouples in series on an insulating substrate, and brings a U-shaped heater close to a contact group on one side of the thermocouple, so that An exact solution of the heat transfer equation was obtained for an MJTC with a heat sink placed close to the contact group on the other side, and a more precise AC / DC difference was obtained. It was found that the value is close to. That is, it was found that it would be an ideal standard device.

[0013]

Therefore, the present invention is based on the above findings, in which a large number of thermocouples are connected in series on an insulating substrate, and a U-shaped heater is provided at a contact group on one side of the thermocouple. And a heat sink close to the contact group on the other side of the thermocouple as a standard device, a method for comparatively measuring the AC / DC difference of the thermoelectric AC / DC converter is proposed.

Regarding the MJTC of this U-shaped heater,
The following procedure is used to obtain an exact solution of the heat transfer equation and derive the equation for measuring the AC / DC difference from this. First, a general solution is obtained by including boundary conditions in the heat transfer equation when an AC current is applied to a linear heater MJTC heater, and a general solution is obtained by applying an AC current to a U-shaped heater MJTC heater. The solution.

On the other hand, the boundary condition when the linear heater is folded back in a U shape is added to the heat transfer equation when a direct current is applied to the heater of the MJTC linear heater, and the heater of the MJTC heater is a U-shaped heater. Obtain a general solution when a DC current is applied to, integrate these general solutions over the length of the heater, and substitute these integrated values into the definition formula of the AC / DC difference to obtain the AC / DC difference measurement formula. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 shows an MJTC of a linear heater. On a substrate 1 made of an insulating film, there are thermocouples 2 on both sides of which are arranged in series with contacts arranged in the longitudinal direction.

A linear resistance film 3 (heater) having a length of 2 L is provided on one side of the substrate 1, and terminal fittings 4 are connected to both ends thereof.

Further, the one side contact group 2a of the thermocouple 2 is brought close to the resistance film 3, and this is used as a hot junction of the thermocouple 2.

In this embodiment, the one side contact group 2a of the thermocouple 2 is extended from both ends of the resistance film 3.

On the other hand, on the other side of the substrate 1, there is provided a heat sink 5 composed of, for example, a copper block, and the other side contact group 2b of the thermocouple 2 is connected to the heat sink 5, and the temperature reference point (cooling point) Contact point).

When the current I is supplied from the input terminals 4a, 4a of the terminal fittings 4, 4 to the MJTC thus constructed,
The resistance film 3 generates heat and the temperature of the contact group 2a rises, a thermoelectromotive force is generated between the resistance film 3 and the contact group 2b kept at room temperature, the electromotive force of each thermocouple is added, and both ends of the thermocouple 2 are Appears at the output terminals 5a, 5a connected to the terminals.

On the other hand, FIG. 2 shows an MJTC of a U-shaped heater formed by folding back the linear resistance film 3 of FIG. 1 in a U-shape around the origin, and the U-shaped resistance film 3 (heater). The one side contact group 2a of the thermocouple 2 is close to the outer circumference of the above, and the other parts are the same as those in FIG.

Next, the procedure for obtaining the measurement formula of the MJTC AC / DC difference of the U-shaped heater will be described. First, in order to obtain the heat transfer equation when an alternating current is applied to the resistance film 3 of the MJTC of the linear heater of FIG. 1, the middle point of the resistance film 3 is set as the origin and the distance to one of the terminal fittings 4 is + L. , The distance to the other terminal fitting 4 is -L, the cross-sectional area of the resistance film is a ₁ , and its thermal conductivity is
Let k ₁ and resistivity be ρ.

Consider the heat flow from the resistance film 3 to the thermocouple 2. In this case, the cross-sectional area of the thermocouple 2 differs depending on the metal, and the thickness differs depending on where it is vapor-deposited, so use the equivalent cross-sectional area per unit length 7 to average the thickness. Then, the equivalent cross-sectional area of the thermocouple ₂ is a ₂ , and its equivalent thermal conductivity is k ₂ . This k ₂ is not the heat conductivity of thermocouple 2,
This is because the resistance film 3 and the thermocouple 2 are not in contact with each other.

Consider the heat flow from the micro-plane element dx to the cold junction at any x-ray of the resistive film 3. The heat conduction of the resistance film 3
a ₁ k ₁ (d ² θ / dx ² ) dx, and the heat transferred to thermocouple 2 is
a ₂ k ₂ (d ² θ / dx ² ) dx, and the Joule heat on this surface is (ρI ² / a ₁ ) dx.

Since these are in equilibrium, the following equation (2) is established as a heat transfer equation. a ₁ k ₁ (d ² θ / dx ² ) ＋ a ₂ k ₂ (d ² θ / dx ² ) ＋ ρI ² / a ₁ = 0 (2) This equation is obtained when there is no Thomson effect or Peltier effect, that is, when the AC current is It is when it flows.

Here, b = (ρI ² / a ₁ ) / (a ₁ k ₁ + a
₂ k ₂ ), (2) is transformed into the following equation (3). d ² θ / dx ² = -b (3)

When the boundary condition when an alternating current is applied to the resistance film 3 is x = ± L and the temperature is θ _0, and this boundary condition is substituted into the formula (3), the following formula (4) symmetrical with respect to the origin is obtained. The general solution represented is obtained.

Θ−θ ₀ = b / 2 (L ² −x ² ) (4)

Next, a heat transfer equation when a direct current is applied to the resistance film 3 will be obtained. In this case, heat is generated (or heat is absorbed) when a direct current is applied to a place having a temperature gradient. This is the Thomson effect.

When the Thomson coefficient is α, the amount of heat generated by the Thomson effect is αId θ. Therefore, the heat transfer equation is obtained as the following equation (5) by adding the Thomson effect to (2).

A ₁ k ₁ (d ² θ / dx ² ) + a ₂ k ₂ (d ² θ / dx ² ) + ρI ² / a ₁ + αId θ / dx = 0 (5)

Here, assuming that C = αI / (a ₁ k ₁ + a ₂ k ₂ ), equation (5) is transformed into equation (6) below. d ² θ / dx ² + Cd θ / dx + b = 0 (6)

Next, when a direct current flows through the contact point between the resistance film 3 and the terminal fitting 4, heat (or heat absorption) occurs at the contact point due to the Peltier effect, and the temperature becomes θ ₀ + Δθ at x = + L, and x =
At −L, the temperature becomes θ ₀ −Δθ.

By inserting this boundary condition into (6), a general solution represented by the following expression (7) is obtained. θ-θ ₀ = (bL / C + Δθ) {(1 / tanhCL) -e ^-Cx / sinhCL} -bx / C (7)

Next, when the resistance film 3 is folded back in a U-shape, the Thomson coefficient has the opposite sign at the position -x which is symmetrical with respect to the position x with respect to the origin, so that the temperature θ _{+ at} the position + x and the temperature θ at the position -x. _- than equation (7), it becomes: (8) (9).

Θ ₊ −θ ₀ = (bL / C + Δθ) {(1 / tanhCL) -e ^−Cx / sinhCL} −bx / C (8) θ ₋ −θ ₀ = (-bL / C + Δθ) {-(1 / tanhCL) + e ^-Cx / sinhCL} −bx / C (9)

The resistance film 3 is U-shaped and has positions x and -x.
Are close to each other, the temperature at any position x of the resistance film 3 is represented by the average value of the above equations (8) and (9). That is, it becomes like the following formula (10).

(Θ ₊ + θ _-- 2θ ₀ ) / 2 = (bL / C) {(1 / tanhCL) -e ^-Cx / sinhCL} -bx / C (10)

That is, there is a solution that the linear resistance film 3 has a temperature difference Δθ between both current terminals due to the Peltier effect.
As is clear from the equation (10), when the resistance film 3 is U-shaped, the term of the temperature difference Δθ (Peltier effect) disappears.

Further, as shown in FIG. 2, since both current terminals are provided close to each other on the same metal heat trap, it can be said that there is no temperature difference.

The thermoelectromotive force of the thermocouple 2 is proportional to the temperature θ at an arbitrary position x of the resistance film 3. If the proportional constant is K,
The thermoelectromotive force is obtained by integrating from x = -L to x = + L.

Therefore, the total thermoelectromotive force E _AC when an alternating current flows through the resistance film 3 is obtained by the above equation (4) from x = −L to x =
It is integrated up to L, and the integrated value is obtained by the following equation (11).

[0043]

Similarly, assuming that the total of the electromotive force E _DC when a direct current is applied is E _DC , E _DC can be calculated from the equation (10) by x = -L to x.
The integral value obtained by integrating up to = L is obtained as the following equation (12).

[0045]

Here, specifically, CL << 1 holds. Therefore, when the above equation (12) is approximately expanded, the following equation (13) is obtained.

E _DC = K2 / 3bL ³ (13)

By substituting the above equations (11) and (13) into the defining equation {(E _AC −E _DC ) / E _DC } of the direct-current difference δ, the following equation (14) is obtained. δ = (E _AC −E _DC ) / E _DC = 0 (14)

That is, the resistance film 3 is an MJTC of a U-shaped heater.
In, it was revealed that the AC / DC difference δ is very small, which is close to zero in the first-order approximation and close to zero in high-order infinity. Therefore, this MJTC can be an ideal standard.

The AC / DC difference comparison measurement of the thermoelectric type AC / DC converter using the MJTC of the U-shaped heater as a standard device can be performed by using, for example, the circuit shown in FIG. 3, in which case the second converter is used.
UJ-shaped heater MJTC that serves as a standard device at the location where TC ₂ is installed
Is installed, a converter for comparative measurement is installed at the installation location of the first converter TC ₁ , and the measuring method is the same as the above-mentioned conventional method.

[0051]

In summary, according to the present invention, since the MJTC of the U-shaped heater having the AC / DC difference of 0 or very close to 0 is used as the standard device, the AC / DC difference of the thermoelectric type AC / DC converter can be very accurately achieved. Comparative measurements can be made.

Although the MJTC of the U-shaped heater has been described here, the conventionally known three-dimensional MJTC.
A heater using a resistance wire as a C or U-shaped heater,
Alternatively, it can be applied to any one in which the resistance wire is a bifiller.

Further, in the present invention, since the ideal standard device is used, the comparative measurement of the thermoelectric type AC / DC converter can be easily performed.

[Brief description of drawings]

FIG. 1 is a plan view modeling the MJTC of a linear heater used for explaining the principle of the present invention.

FIG. 2 is a plan view modeling the MJTC of a U-shaped heater used for explaining the principle of the present invention.

[Fig. 3] Comparative measurement circuit of AC / DC difference of thermoelectric AC / DC converter

[Explanation of symbols]

 1 Insulating board 2 Thermocouple 3 Resistive film 4 Terminal fitting 5 Heat sink 2a Thermocouple contact group on one side 2b Thermocouple contact group on the other side

Claims (2)

[Claims] 1. A linear resistance film is formed in a U-shape centering on the origin.
Both current terminals of the U-shaped heater that is folded back
(1) It is provided close to the heat retaining metal, and further on the outer circumference of the heater.
Connection of one side of many thermocouples connected in series on an insulating substrate
Bring the point cloud close to each other and apply heat to the contact group on the other side of the thermocouple.
The thermoelectric type AC / DC converter with multiple thermocouples
U, characterized in that the thermoelectric type AC / DC converter is used as a standard device to compare and measure the AC / DC difference of the thermoelectric type AC / DC converter.
Measuring method for AC / DC difference of thermoelectric type AC / DC converter with resistance type. 2. The method according to claim 1, wherein a multi-thermocouple type thermoelectric type AC / DC converter having an AC / DC difference of zero or close to zero is used as a standard.