JPH0342513A - Differential transformer conversion system - Google Patents

Abstract

PURPOSE:To output the difference value between input voltages as it is as the measured output without dividing it by a reference value by using a reference voltage source, an error amplifier, and a multiplying circuit to fix the sum of inputs of a subtracting circuit to a set value. CONSTITUTION:An error amplifier 21 which amplifies the difference voltage V1 and the output voltage of a synchronous detecting circuit 16 on the addition to a voltage higher by at least by one figure, and a multiplying circuit 22 which multiplies the output of this amplifier 21 by the oscillation output of an oscillating circuit 11 and sends the result to the primary coil of a differential transformer 13 as the output signal from the transmission side are additionally provided to this system, and the output of the circuit 16 on the subtraction side is outputted as a measured output VP. That is, the sum of inputs VA and VB of a subtracting circuit 15 is fixed to a set value to accurately and stably output the difference value between voltages VA and VB as the output VP without dividing it by a reference value V0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal conversion system for a converter using a differential transformer.

[Prior art] Conventionally, when manufacturing a converter using a differential transformer, the conversion circuit and the differential transformer are often assembled in the same container, but this method is often used in cases where the converter is not recoverable like civil engineering instruments. For instruments that will be used for long periods of time, it is desirable to place the electronic circuits on the ground from the standpoint of reliability. From this,
A sensor cable is interposed between the differential transformer and the conversion circuit, and the resistance of this cable affects the conversion accuracy of the differential transformer. Therefore, from the secondary coil outputs VA and VB of the differential transformer, A+VB and vA-VB signals are generated. Synchronous detection is performed using the vA or VB signal, and input to the divider circuit (VA-V
a) / (VA + Vs) (7) A method is used in which calculation is performed to obtain an output that is not affected by cable resistance or the like.

Figure 2 shows the above f) (VA - Ve ) / (VA
+VB ) is a diagram showing the configuration of a method for calculating. The output voltage of the oscillation circuit 11 is applied to the primary side of the differential transformer 13 via the buffer amplifier 12 and the cable resistance, and the two secondary output signals generated on the secondary side are added via the cable resistance. The input voltages vA and V are applied to the circuit 14 and the subtraction circuit 15, and the addition value vA+VB obtained by the addition circuit and the subtraction value V^-V obtained by the subtraction circuit,
are synchronized by synchronous detection circuits 16 and 17, respectively,
The synchronized addition value and subtraction value are divided by the division circuit 18, and the measurement output (VA - Va) / (VA +V
! 1).

According to this method, the measured output is not the difference value itself between the two secondary output signals, but the value obtained by dividing this by the reference value of the sum of the two secondary output signals. It is possible to obtain a measured output value that is not affected by the coil resistance of the dynamic transformer 13.

[Problems to be Solved by the Invention] However, although the measurement output obtained in this manner is such that the influence of the cable resistance r can be ignored in appearance, it does not actually indicate an accurate value.

As can be seen from FIG. 2, a division circuit 18 is required to obtain the above measurement output. However, when this type of division circuit outputs an analog signal to the outside, the A/D section
Since a C/DC divider circuit is required, the influence of DC drift cannot be ignored, and accurate measurement output cannot be obtained.

Therefore, the present invention aims to provide a differential transformer conversion system that can obtain stable and accurate measurement outputs.

[Means for Solving the Problems] According to the present invention, an oscillation circuit and a differential transformer whose primary coil receives an output signal from the oscillation circuit and output two secondary output signals from the secondary coil are provided. an adder circuit that takes the sum of the two secondary output signals; a subtracter circuit that takes the difference between the two secondary output signals; and the adder circuit and the subtracter circuit that are synchronized with one of the two secondary output signals. A conversion circuit includes two synchronous detection circuits that individually perform detection of output signals of , and obtains a measurement output using the output of the synchronous detection circuit on the subtraction side. The difference voltage between the output voltages of the synchronous detection circuit on the addition side is at least 1
An error amplifier that amplifies the voltage to an order of magnitude higher, and a multiplier circuit that multiplies the oscillation output of the oscillation circuit by the output of the error amplifier and sends the resultant signal to the primary coil of the differential transformer as an output signal from the transmitting side. As a result, a differential transformer conversion system is obtained in which the output of the synchronous detection circuit on the subtraction side is used as the measurement output.

[Function] In the above circuit, the sum of the two secondary output signals (reference value) of the differential amplifier is always fixed to the reference voltage using an error amplifier with a high amplification factor, and the sum of the two secondary output signals of the differential amplifier is always fixed to the reference voltage. The synchronous detection circuit accurately and stably outputs the difference between two secondary output signals as a JIIJ constant output.

[Example] Next, an example of the differential transformer conversion system according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention. In this embodiment, the output voltage of the oscillation circuit 11 is vx1, the output voltage of the error amplifier 21 is My, the gain is 3, the product of vx and vv is the product of vx and vv in the multiplier circuit 22, and the output after passing through the rebuffer amplifier 12 is v11 on the addition side. The output voltage of the synchronous detection circuit 16 is V. , the reference voltage that is the output of the reference voltage source 23 is Vl, the coupling coefficient between the primary coil and the secondary coil of the differential dynamic transformer 13 is 2. the resistance of the primary coil is R1, and the resistances of the two secondary coils are both R2. , the two secondary output signals are v2 and Vl, the addition circuit 14 and the subtraction circuit 1
5 common input terminals vA and V.

is VA −RV2 / (r+R2+R)−(RV+
R2/ (2r+R+)-Va 1/(r+R
2+R) ... (1) Va "" RVs
/ (r +R2+R)-(RV, K2
/ (2r+R,) +V,]/(r×R2+R)
...It is expressed as (2). Here, R is the human power impedance of the addition/subtraction circuits 14 and 15, and Vd is a voltage depending on the core of the differential transformer 13.

Also, the common input terminals VA and V of the above-mentioned addition circuit 14 and subtraction circuit 15, and the output voltage V of the addition side synchronous detection circuit 16. has the following relationship.

Vo-VA ten V,, ++ (3)
This value has conventionally been used as a reference value.

On the other hand, the voltages VISVx1■1 and voSvR have the following relationship, as can be readily seen from the arrangement of each component in FIG.

V, -VX-VY -Vx - + (V, Vo, -(4)
Here, if we express VA and ■8 in formula (3) in the form of formulas (1) and (2), and insert the relationship of formula (4) into ■ contained in the obtained formula, we get Vo-2. 2 RVx Kl (V, -Vo)/(
(2r + R+) (r +R2+R) 1...
・(5) becomes. This formula (5) is written as ■. Solving for V, -2
2RV x K, V, / 1 (2r+R+) (r+R, +R) +2 to 2
RVX Kl ) −(6). If the value of is increased to such an extent that the first term of the denominator can be ignored, equation (6) becomes Vo-V, . . . (7). That is, the output voltage V of the addition side synchronous detection circuit 16, which is the sum of the input voltages VA and VB, is conventionally used as a reference value. is a value fixed to the reference voltage V.

Therefore, the output of the subtraction circuit 15, which can be expressed as the difference between the input voltages vA and VB, is obtained as is from the synchronous detection interval Fδ17 on the subtraction side as the 811 constant output VP without being divided by the reference value. That is, a measurement output can be obtained without using a division circuit that causes DC drift.

In section f, as the value of 1 for the amplification factor of the error amplifier 21, a value of about 10 can be used in calculations, but in terms of accuracy and stability, a value of 102 or more is used in practice. The setting of this amplification factor differs depending on whether the signal is AC or DC, and in the former case it is about 10 to 5X102 times, and in the latter case it is 10' to 10'.
The standard is approximately double that. This difference in range is mainly due to the fact that the stability of the circuit system decreases when AC signals are used.

[Effects of the Invention] As is clear from the above description, in the present invention, by fixing the sum of the subtraction circuit manual power VA and VB to a constant value using a reference voltage source, an error amplifier, and a multiplier circuit, The difference value between the input voltages vA and V is directly measured and output without dividing it by the reference value■.

It can be output as Therefore, the measurement output obtained is accurate and stable, improving the reliability of the device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a conventional differential transformer conversion system. Explanation of symbols: 11...Oscillation circuit, 12...Buffer 7
12.13...Differential transformer, 14...Addition circuit. 15... Subtraction circuit, 16... Synchronous detection circuit (
addition side), 17... synchronous detection circuit (subtraction side), 21.
...Error amplifier, 22...Multiplication circuit, 23...Adjudication voltage source.

Claims (1)

[Claims] 1. An oscillation circuit, a differential transformer whose primary coil receives an output signal from the oscillation circuit, and whose secondary coil outputs two secondary output signals; an addition circuit that takes the sum of the output signals; a subtraction circuit that takes the difference between the two secondary output signals; and a detection circuit that individually detects the output signals of the addition circuit and the subtraction circuit in synchronization with one of the two secondary signals. to do 2
A conversion circuit that includes two synchronous detection circuits and obtains a measurement output using the output of the synchronous detection circuit on the subtraction side. an error amplifier that amplifies the differential voltage to a voltage that is at least one order of magnitude higher; and a multiplier that multiplies the oscillation output of the oscillation circuit by the output of the error amplifier and sends the resultant signal to the primary coil of the differential transformer as an output signal from the oscillation circuit. A differential transformer conversion method comprising an additional circuit, wherein the output of the synchronous detection circuit on the subtraction side is used as the measurement output.