JPS61284608A - Signal processing unit for differential transformer - Google Patents

Abstract

PURPOSE:To precisely measure the displacement of a core without being affected by the conditions for manufacture, etc. by having a level detecting means for detecting the output voltage level on the secondary side of a differential transformer. CONSTITUTION:The primary voltage Ep obtd. by amplifying the sinusoidal output from an oscillation circuit 4 by an amplifier 8 is supplied to the primary winding of the differential transformer. The secondary voltage Es of the transformer 9 is amplified by an amplifier 10 and is applied to an analog-to-digital converter 6. On the other hand, the cosine wave output shifted in phase by 90 deg. from the sine wave applied to the amplifier 8 is applied from the circuit 4 to a synchronizing circuit 5. The circuit 5 applies a conversion command signal to the converter 6 at the respective points of the time when the cosine wave inputted thereto rises across the zero level. The converter 6 converts the analog output from the amplifier 10 to a digital signal and applies the digital signal to a buffer 7. The buffer 7 holds the previous input value in the period until the next input value is applied thereto. Said value is outputted as the measuring output to a measurement display circuit relating to the core displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a signal processing device for a differential transformer used as a displacement sensor or the like.

(Prior art and its problems) FIG. 7 shows the basic configuration of a differential transformer used for the purpose of detecting various amounts of displacement and dynamics.

In the figure, the primary winding I is given a negative voltage EI).
The secondary winding 2a,
2b. and,
The secondary windings 2a and 2b are differentially connected to each other, and the difference in induced voltage EE in each is extracted as the secondary voltage E11s2S. Conventionally, the core 3 is rectified by rectifying it. The amount of displacement is being measured.

This measurement characteristic is shown in FIG. 8, where the rectified secondary voltage E ideally changes in a V-shape as shown by a characteristic line C6 for a displacement amount of 1 of the core 3.

However, 1=O is a point where the core 3 is located between the secondary windings 2a and 2b.

However, as is well known, an actual differential transformer does not have a V-shaped characteristic as shown by the characteristic line C8, but has a finite offset voltage E near 1=O, as shown by the characteristic line C1. remains. This is thought to be a phenomenon caused by various factors (described later) in the manufacturing of the differential transformer itself, wiring cords, etc., and the soil used, but as a result, linearity in displacement measurement etc. is inhibited near the zero point. The result is that

This offset voltage E. As a technique for removing this, for example, there is a method in which the induced voltage EE of the secondary windings 2a and 2b is rectified by a bridge circuit to Sl and S2, respectively, and then the difference between them is taken and output ("Electric Measurement Handbook"). No. 780, Ohmsha, November 30, 1960). This method can largely prevent the effects of stray capacitance inside the differential transformer, but the length of the wiring cord from the differential transformer to this bridge circuit is often several tens of meters, for example when used for robot control. If the offset voltage E is caused by stray capacitance of the cord, etc. cannot be removed, and the above-mentioned problem still remains.

(Object of the Invention) The present invention is intended to overcome the above-mentioned drawbacks, and is capable of accurately measuring the amount of displacement of the core, including near the zero point, without being influenced by manufacturing conditions or usage conditions. The present invention aims to provide a signal processing device for a dynamic transformer.

(Means for Achieving the Object) In order to achieve the above-mentioned object, in the signal processing device for a differential transformer according to the present invention, near the zero cross point of the AC excitation voltage supplied to the primary side of the differential transformer, level detecting means for detecting the output voltage level on the secondary side of the differential transformer at a predetermined phase other than the above, and measuring the amount of displacement of the core of the differential transformer based on the detection output of the level detecting means. There is.

(Example) Before showing the specific structure of an example of this invention, the principle of this invention will be explained based on a specific example. For this purpose, first, the characteristics of the offset voltage Eo will be considered.

FIG. 2(a) is a vector diagram of a differential transformer in an ideal case, and as is well known, the phase is delayed by 90 degrees from the -order voltage F, and the primary current flows through the secondary winding 2a. ,2
b is the electromotive force EE, and Sl/S2 is shifted by 180°).・However, in reality, as shown in FIG. 2(b), between the negative voltage E and the secondary voltage E, with R6°1-6 as the resistance and inductance on the primary side, A phase difference of ``(R/ωm), , . . . (1) is generated. However, ω is a frequency. Also, for convenience of explanation, the phase difference is exaggerated in the drawing.

On the other hand, the resistance and inductance on the secondary side are R
, L, and the load resistance for measurement is RL,
The output type tan [ωL /
(R+R1)l・(2)S It's late.

In addition, iron loss occurs in the differential transformer and the angle α in the figure shifts, and the phase relationship between the induced electromotive forces EE and EE shifts depending on the position of the core 3, resulting in secondary voltages 1. The phase of is further changed.

In addition, the output voltage V
The phase of , also shifts due to various reasons.

In this way, the input/output relationship in a differential transformer is considered to be determined by various factors, including the offset voltage E; It is difficult to fundamentally eliminate the cause itself.

However, there is an empirical fact that the output of an actual differential transformer loses linearity only near the zero point, as shown by the characteristic line C1 in FIG. Therefore, if the possible displacement range of the core 3 is (-L)≦l≦L, and the voltage vector at 1-1 is (±El), then the core 3 can be sequentially displaced in the vertical direction in Fig. 7. When the secondary voltage E,
For example, as shown in Figure 3(a), the voltage vector (-
It can be thought of as starting from point E, ), bypassing zero point ○, and then changing along a trajectory C (or its opposite direction) l that reaches voltage vector E.

From this, the inventor of the present invention discovered that the secondary voltage vector E, without detecting the period proportional to the absolute value of the secondary voltage vector E (for example, the effective value after rectification), as in the conventional method. It has been discovered that by extracting only a specific phase component, a characteristic passing through the zero point O can be obtained. That is, of the secondary voltage vector E, for example, U in FIG. 3(a).

When we extract the phase component E [uo] along the direction shown in the figure, we obtain a component change that starts from the voltage (7E,), passes through the zero point O, and reaches the voltage E, as shown in Figure (b). It will be done.

A more quantitative representation of this is shown in Fig. 4(a). By extracting the phase component E [LJ,], it can be seen that it is substantially linear in the displacement range (-L)≦l≦L of the core 3. , and a characteristic line passing through the zero point 0 can be obtained.

By the way, in the above example, the phase to be extracted is the direction U parallel to the voltage vector (±E) in FIG. 3(a). I'm thinking. And if you do it like this, (-shi)≦l≦
This has the advantage that the change range of the phase component in L becomes larger, which improves detection accuracy, and that the influence of curvature of the trajectory C can be minimized. However, Fig. 3 (a
), when phase components E [u ] and E [L12] in other directions as shown by Ul and u2 are extracted, sl S is also as shown in FIG. 4(b) and (C), respectively. Considerable linearity is ensured, and it is fully possible to utilize these. In these figures, the deviation from the straight line is exaggerated for convenience of explanation, but it has been experimentally confirmed that the deviation is actually quite small.

However, the phase component in the direction of u3 in Figure 3(a), that is, in the direction perpendicular to the voltage vector (±E,), is the fourth
As shown in Figure (d), it is difficult to utilize this phase component. The situation is similar for the phase near this direction u3, but as mentioned above, the deviation from the straight line in the trajectory C in FIG. 3 is actually quite small, so the range in which it is difficult to use is small.

An embodiment of the present invention constructed based on the above considerations is shown in FIG. 1, and a time chart thereof is shown in FIG. 5. In FIG. 1, this signal processing device includes a differential transformer 9 of a commonly used type, and an oscillation circuit 4.
The primary voltage E, (excitation m voltage) obtained by amplifying the sine wave output (FIG. 5(a)) from the differential transformer 9 by the amplifier 8 is supplied to the primary winding of the differential transformer 9. In addition, the differential transformer 9
The secondary voltage E, after being amplified by the amplifier 10, is A/
The signal is applied to the D converter 6.

On the other hand, the oscillation circuit 4 supplies the synchronization circuit 5 with a signal (cosine wave output) whose phase is shifted by 90' with respect to the sine wave supplied to the amplifier 8 . This synchronization circuit 5 operates at points 1 and 12 when the input cosine wave crosses the zero level and rises.
．． ... gives a conversion command signal to the A/D converter 6. This timing is the negative voltage E
This corresponds to a phase shifted by 90'' from the zero cross point of p (that is, the peak position).When this conversion command signal is given, the A/D converter 6 converts the output of the amplifier 10 into A
/D conversion and provided to the buffer 77 (FIG. 5(b)).

This buffer 77 holds the previous input value as a measurement output until the next input value is given, and supplies desired circuits such as a measurement display circuit and a feedback circuit (both not shown) regarding the displacement of the core 3. Output to.

By the way, when the displacement mA of the core 3 is large and close to (±L), the deviation of the secondary voltage vector E from the ideal case is relatively small, and the secondary voltage vector E in this case , (that is, the voltage vector (±El)) and the −order voltage vector E.

The phase difference between them is considered to be considerably smaller than the phase difference between them near the zero point. Therefore, the peak position of the negative secondary voltage E almost coincides with the peak position of the secondary voltage E near jl=(±L).

Therefore, detecting the level of the secondary voltage E for various l at a phase corresponding to the peak of the negative secondary voltage E means U in FIG. 3(a). This is equivalent to extracting the phase component along the direction, and this embodiment embodies the above-mentioned principle.

Next, with this circuit configuration, the displacement 1 of the core 3 is (+L)
The detection operation when the voltage sequentially changes from -L to (-L) will be explained with reference to FIG. 6, which shows the change in the secondary voltage E. First, when the displacement l changes from (+L) to around ×1 in Fig. 8, the phase shift of the secondary voltage vector E8 is relatively small, so the peak level of the secondary voltage E, ( That is, the peak value) is A/D converted. This peak value monotonically decreases as l approaches ×1.

Next, as the displacement of the core 3 passes around x1 and moves toward x2, the peak value further decreases and the phase shift gradually increases (FIGS. 6(b) and (C)).

In the range where l changes roughly and goes from x3 through zero point 0 to x4 in Fig. 8, the peak value of the secondary voltage E does not change much, but mainly changes in phase. Then, the secondary voltage vector begins to bypass the zero point O as shown in Fig. 3(a).

However, as shown in FIGS. 6(C) to (e), since the level at a specific phase is detected here, the detection output has no offset voltage and monotonically decreases to O. After that, it will change monotonically in the negative direction. After that, from x5 to x7, the phase shift gradually slows down, and the change in peak value becomes the main change.

Therefore, by plotting the detection level V - V6 of FIG. 6 obtained in this manner against the displacement l of the core 3, the desired characteristics shown in FIG. 4(a) can be obtained.

In addition, in the case of this embodiment, in regions where the peak value of the secondary voltage E is large (Fig. 6 (a), (g), etc.), A/D conversion is performed at the peak. In areas other than those in which levels are extracted (such as (C) to (e) in the same figure), the level changes over time are gradual, so both detection times t1, t2. . . . no sudden level changes occur over time, and there is an advantage that there is no need to use a sampling and holding circuit for A/D conversion. Furthermore, since the level change range corresponding to the change in the displacement l is large, the measurement accuracy is also high. This is the negative voltage E
This advantage applies not only to the phase that is exactly 90° off from the zero crossing point of , but to the entire phase that is off about 90'.

Further, by appropriately changing the phase of the signal applied from the oscillation circuit 4 to the synchronization circuit 5 in FIG. 1 to change the phase of level detection, the characteristics as shown in FIGS. 4(b) and 4(c) can be realized as a circuit.

However, as mentioned above, it is difficult to use the phase component in the u3 direction in Figure 3, and this is due to the secondary voltage at the phase near the zero cross point of the -order voltage E (1o in Figure 6). Voltage E,
This means that it is not appropriate to perform level detection.

Note that the secondary voltage vector E shown in FIG. 3(a) etc.
The behavior of be. In other words, the secondary voltage vector E,
Regardless of the detailed structure of the phase shift, a characteristic line passing through the zero point O can be obtained, so there is no problem even if the wiring cord around the differential transformer 9 is quite long.

(Effects of the Invention) As explained above, in this invention, the effective value of the secondary voltage is not detected by rectification, but the level is detected at a predetermined phase. It is possible to obtain a signal processing device for a differential transformer that can perform precise measurements including those near the zero point.

[Brief explanation of the drawing]

Figure 1 is a schematic block diagram showing one embodiment of the present invention, Figures 2 and 4 are vector diagrams of a differential transformer, Figures 3 and 4.
The figure is a diagram explaining the principle of the present invention, Figures 5 and 6 are time charts showing the operation of the embodiment, Figure 7 is a configuration diagram of a differential transformer, and Figure 8 is an output characteristic diagram of a conventional device. . 1... - Secondary winding, 2a, 2b... Secondary winding 3... Core, 4... Oscillation circuit 5... Synchronous circuit, 6... A/r) converter 9 ...Differential 1
- Lance

Claims (2)

[Claims] (1) Level detection means for detecting the output voltage level on the secondary side of the differential transformer at a predetermined phase other than the vicinity of the zero cross point of the AC excitation voltage supplied to the primary side of the differential transformer, A signal processing device for a differential transformer, characterized in that the amount of displacement of the core of the differential transformer is measured based on the detection output of the detection means. (2) The signal processing device for a differential transformer according to claim 1, wherein the phase is shifted by about 90 degrees from a zero-crossing point of the AC excitation voltage.