JPH0549945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a comparison device for a thermoelectric AC/DC converter that precisely measures AC voltage, current, etc.

[Conventional technology]

For direct current measurements, the voltage standard is provided by a Josephson voltage standard, but for alternating current measurements, there is no device that generates the same level of alternating current voltage (current). Therefore, for precise measurement of AC voltage (current), it is necessary to measure the measured voltage (current) and the equivalent DC voltage (current).
A method has been adopted in which the effective value of the measured voltage (current) is compared with a known DC voltage (current) using a device that produces equal outputs when inputted alternately. Devices used in this method include an AC/DC converter that converts an AC amount into a DC amount and an AC/DC comparator that compares the amount with the DC amount. Since it is possible to obtain a precise DC amount, the accuracy of this method is mainly determined by the errors of the AC/DC conversion and AC/DC comparators. These errors are sometimes called AC/DC differences, and determining AC/DC differences is used interchangeably with establishing AC voltage (current) standards.

Incidentally, AC voltage and current are generally precisely measured by using a thermoelectric AC/DC converter (TC) and comparing with a known DC amount. The TC used at this time consists of a heater (resistance wire) and a thermocouple close to it, and is a device that determines the magnitude of the input to the heater from the voltage generated in the thermocouple due to the heat generated at that time. If alternating current and direct current are input alternately and the temperature rise of the TC heater is equal, the effective value of alternating current and direct current will be equal, and the magnitude of alternating current can be determined from the known direct current.

A conventional comparison device for thermoelectric AC/DC converters connects a precision digital voltmeter to each of the two thermoelectric AC/DC converters, and calculates the value of thermoelectromotive force using a computer.

Figure 2 is a circuit diagram showing an example of a comparison device for a conventional thermoelectric AC/DC converter, where Va is a precision AC power supply, Vd
is a precision DC power supply, Ra ₁ , Ra ₂ , Rd ₁ , Rd ₂ are resistors, S ₁ to _{S 4} are switches, and a and b are switches.
The S ₄ contact, ΔR, represents a resistor with a small resistance value.

In addition, TC ₁ and TC ₂ are first and second thermoelectric AC/DC converters (hereinafter simply referred to as the first converter and second converter), and H ₁ and H ₂ are these heaters connected in series. A first precision digital voltmeter (hereinafter simply referred to as the first voltmeter) DVM ₁ is connected to the output terminals t ₁ and _t 2 of the first converter TC ₁ ,
A _second precision digital voltmeter (hereinafter simply referred to as the second voltmeter) DVM ₂ is connected to the output terminals t ₃ and t ₄ of TC 2.
is connected.

When measuring current, use the first and second voltmeters.
DVM ₁ and DVM ₂ measure the thermoelectromotive force caused by the thermocouple, and send the measurement results to computer C.
The calculation process is performed by the printer P, and the data is recorded by the printer P.
The computer C also controls power switching between the precision AC power supply Va and the precision DC power supply Vd. In addition, in order to compare the AC/DC difference due to the thermoelectromotive force obtained by the first and second converters TC ₁ and TC ₂ , the following calculation formula (from the following calculation formula , see page 5) δ ₁ − δ ₂ = (Ea ₂ − Ed ₂ / ΔEd ₂ − Ea ₁ − Ed ₁ / ΔEd ₁ ) ΔId
/Id……(1) is used.

In equation (1), δ ₁ and δ ₂ are the first and second converters
The AC/DC difference in TC ₁ and TC ₂ , Ea _{1 and} Ea ₂ are each thermoelectromotive force when AC current is passed through each heater H ₁ and _{H 2 of} the first and second converters TC 1 and TC 2, Ed ₁ and Ed ₂ are the respective thermoelectromotive forces when direct current is passed.
The denominators ΔEd ₁ and ΔEd ₂ are the differences in the respective thermoelectromotive forces when the rated DC current Id of the heaters H ₁ and H ₂ is changed (decreased) by the ratio ΔId/Id {(2/10000)}. These are the first and second converters TC ₁ , TC ₂
It is a quantity related to the input/output characteristics (gradient) of . This gradient tends to be approximately proportional to the thermoelectromotive force Ed ₁ , Ed ₂ when the rated DC current Id is passed through each heater H ₁ , H ₂ .

[Problem to be solved by the invention]

However, conventional comparison devices for thermoelectric AC/DC converters have the problem of being susceptible to noise caused by switch contacts and the like, and resulting in large variations in measured values.

In addition, some methods have solved the noise problem by using a photogalvanic meter, but this has the problem of being complicated for precise measurement of minute direct current electromotive force.

This invention was made to solve the above problems, and by taking the difference in thermoelectromotive force between two thermoelectric AC/DC converters, it is possible to perform measurements that are resistant to noise and have good reproducibility. The purpose is to obtain a comparison device for thermoelectric AC/DC converters.

[Means to solve the problem]

In the thermoelectric AC/DC converter comparison device according to the present invention, the output terminals of the first and second converters are connected with opposite polarities to each other, and the output terminal of the second converter having a small thermoelectromotive force is connected to the output terminal of the third converter. A resistor is connected in series to the output terminal of the first converter, which has a large thermoelectromotive force, and a first and a second resistor that divides the thermoelectromotive force are connected in series.
The voltage drop due to the resistor is reduced by a second resistor with a small thermoelectromotive force.
The first,
The connection point of the second resistor is used as an output terminal for the output of the first converter having a large thermoelectromotive force.

[Effect]

In this invention, by measuring the difference in thermoelectromotive force between the first and second converters connected in series, the influence of noise is reduced and measurements with good reproducibility can be performed. Furthermore, the voltage dividing resistor makes the input/output characteristics (gradient) at the dividing point almost equal to the input/output characteristics of the second converter having a low thermoelectromotive force.

〔Example〕

First, the principle of this invention will be explained.

In equation (1) explained in the prior art section, if the denominator is ΔEd ₁ ΔEd ₂ =ΔEd, equation (1) becomes simpler. When direct current flows, the thermoelectromotive forces Ed ₁ and Ed ₂ are thermoelectromotive forces Ed ₁ ⁺ and Ed ₂ ⁺ in the forward direction, and thermoelectromotive force Ed ₁ in the reverse direction.
⁻ , Ed ₂ ⁻ are taken as the average value Ed ₁ = (Ed ₁ ⁺ + Ed ₁ ⁻ )/2 and Ed ₂ = (Ed ₂ ⁺ + Ed ₂ ⁻ )/2.

Substituting this into equation (1) and slightly transforming it, we get δ ₁ − δ ₂ =
[(Ed ₁ ⁺ −Ed ₂ ⁺ ) + (Ed ₁ ^- −Ed ₂ ^- ) − 2 (Ea ₁ − Ea ₂ )/
2ΔEd〕ΔId／Id...(2)

In Equation (2), the first and second conversions are performed when the heaters H 1 _and H ₂ of the first and second converters TC ₁ and TC ₂ are sequentially supplied with AC power, DC forward direction, and DC reverse direction. device TC ₁ ,
Take the difference (numerator) of each thermoelectromotive force of TC ₂ , and further,
This shows that the voltage of the first converter TC ₁ having a larger thermoelectromotive force is divided to be almost equal to the smaller one (denominator ΔEd). An example of a circuit of a comparator for a thermoelectric AC/DC converter that realizes this principle is shown in FIG.

FIG. 1 is a circuit diagram showing an embodiment of this invention.
Similar to FIG. 2, this is the current measurement mode. The heaters H ₁ and H ₂ of the first converter TC ₁ and the second converter TC ₂ are connected in series, and the polarity (+, -) of each thermoelectromotive force E ₁ and E ₂ is changed as shown in Figure 1. Connect to. Note that the opposite polarity may be used. The same applies to the voltage comparator.

In Figure 1, if the thermoelectromotive force E ₁ is larger than E ₂ , E ₁
> indicates E ₂ . the third resistor R ₃ to the second converter
Connect to output terminals t ₃ and t ₄ of TC ₂ . One side is terminal t ₁
the first converter TC 1 with a first resistor R ₁ connected to the terminal t ₂ and a second resistor R ₂ connected on one side to the terminal t ₂
The thermoelectromotive force E ₁ of TC 2 is divided to make the voltage drop across the second resistor R ₂ approximately equal to the thermoelectromotive force E ₂ of the second converter TC ₂ . Since the accuracy of the measurement of the _AC / _DC difference is two digits, _the first
Choose the value of resistor _R1 . In the example, the second and third
Use metal film resistors with equal nominal values of about 10KΩ for resistors _R2 and _R3 . first and second converters TC ₁ ,
Since the thermoelectromotive force E ₁ , E ₂ of TC ₂ is in the range from 6.5 mV to 8.5 mV, the value of the first resistor R ₁ is determined by connecting an integer value resistor in parallel with a higher value resistor. Obtained by connecting. When first and second voltage dividing resistors R ₁ and R ₂ are connected to the first converter TC ₁ , a current flows. The third resistor R ₃ is the second converter
This is used to send current to TC ₂ and balance the circuit. As described above, the circuit can be configured entirely using fixed resistors.

The difference between both thermoelectromotive forces E ₁ and E ₂ is measured by the first voltmeter DVM ₁
This is the data to be measured and substituted into the numerator of equation (2). In addition, the thermoelectromotive force E ₂ of the second converter TC ₂ is
This is the data measured with the voltmeter DVM ₂ and substituted into the denominator of equation (2). These are calculated and processed by computer C, and comparative measurements are performed.

In this way, by connecting the respective thermoelectromotive forces E ₁ and E ₂ , the potentials of points 1 and 2 and the potentials of points 3 and 2 become almost equal, and the first and second converters TC ₁ ,
The input and output characteristics (slope) of TC ₂ become equal. Also,
The first and second converters TC ₁ and TC ₂ are connected between points 1 and 3.
The difference between the thermoelectromotive forces E ₁ and E ₂ appears.

〔Effect of the invention〕

As explained above, the present invention connects the output terminals of two thermoelectric AC/DC converters with opposite polarities, and connects the third resistor to the output terminal of the second converter, which has a small thermoelectromotive force. The first and second resistors that divide the thermoelectromotive force are connected in series to the output terminal of the first converter, which has a large thermoelectromotive force, and the voltage drop due to the second resistor is reduced to the thermoelectromotive force. The thermoelectromotive force of the second converter with a small thermoelectromotive force is set to be almost the same as that of the second converter, and the connection point between the first and second resistors is used as the output terminal of the first converter with a large thermoelectromotive force. Almost unaffected by mode noise and common mode noise. In addition, by using a fixed resistor in the differential voltage circuit, electrical instability caused by the opening and closing of contacts can be removed, allowing use with the highest sensitivity of precision digital voltmeters, making it possible to determine the grounding point, and eliminating noise with a simple circuit. It has the advantage of being able to perform measurements with good reproducibility, with little influence from

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional comparison device for a thermoelectric type AC/DC converter. In the figure, TC ₁ and TC ₂ are the first and second converters, t ₁ ~
_t4 is an output terminal, _DVM1 and _DVM2 are first and second precision digital voltmeters, and _R1 to _R3 are first to third resistors.

Claims (1)

[Claims] 1. A comparison device for thermoelectric AC/DC converters that measures thermoelectromotive forces by connecting precision digital voltmeters to first and second thermoelectric AC/DC converters having different thermoelectromotive forces, respectively. The output terminals of the second thermoelectric AC/DC converters are connected with opposite polarities to each other, and a third resistor is connected to the output terminal of the second thermoelectric AC/DC converter with a small thermoelectromotive force. first and second resistors that divide the thermoelectromotive force are connected in series to the output terminal of the first thermoelectric AC/DC converter with a large
The voltage drop caused by the second resistor is set to be almost the same as the thermoelectromotive force of the first thermoelectric AC/DC converter having a small thermoelectromotive force, and the connection point between the first and second resistors is set to A comparison device for a thermoelectric AC/DC converter, characterized in that the output terminal of the first thermoelectric AC/DC converter having a large thermoelectromotive force is used as an output terminal.