JPS6225975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present application relates to a high frequency thermocouple and a compensating conductor.

In particular, this application aims to achieve high frequency isolation by adding common mode inductance to the conventionally used thermocouple/compensating conductor wire, to prevent high frequency electric field radiation radio waves by shielding this line again, and to further is intended for high-frequency thermocouples and compensating conductors that have the characteristics of increasing inductance and preventing electromagnetic field radiation by covering the coil with a material with high magnetic permeability.For example, it is used in engine spark plugs, It is used when the measurement point has a high frequency voltage relative to the earth's potential, such as when measuring the temperature of the electrodes of various discharge tubes, and it relates to a new structure of a so-called "cable".

Conventionally, cables using ordinary copper wire and cables for delay lines have been seen with shielded coiled core wires, but "cables" with thermocouples or compensating conductor wires as core wires are still on the market. Not realized.

Conventionally, in a temperature measurement method that uses a thermocouple or a combination of a thermocouple and a compensating conductor to guide the electromotive force of the thermocouple to a measuring device to determine the temperature at the measurement point, it is difficult to measure the temperature when the measurement point has a high frequency voltage with respect to the ground potential. There are mainly three obstacles:

That is, to explain _the conventional measurement method _{in FIG .}
Although it is related to L', the line causes radio wave radiation, which harms communications and broadcast reception.

(2) Measurement object with a measurement potential e ₀ where the amplitude of the high-frequency voltage is several thousand to tens of thousands of volts - for example, the electrodes of various discharge tubes, the center electrode of an engine spark plug, etc., that is, the case of the spark plug center electrode To explain, _{the ground voltage waveform of the concentric electrode is τ 1 hour} (approximately 40
After μs), the voltage of the center electrode peaks (point P)
(approximately 15 KV), then discharge starts, and during the spark discharge period τ ₂ (approximately 500 μs), the voltage decreases from 1 to
The voltage is discharged at 1.5 KV, and after the spark discharge ends, the voltage repeatedly oscillates in positive and negative directions around 0 V at a period of about 250 μs, indicated by period _τ3 . In addition, when the spark discharge reaches 1 to 1.5 KV from the peak voltage of the center electrode as the discharge starts, the section indicated by h in the figure changes at an extremely high speed of several ns (10 ^-9 seconds), and the period is several tens of seconds. It is considered to be a substantially step voltage containing frequency components up to megahertz. Note that the dotted line in FIG. 7 shows the waveform when no discharge occurs.

When the center electrode of the ignition plug as described above is the object of measurement, the high-frequency current i due to the inflow of the electrostatic capacitance C between the input terminals 5 _a and 5 _b of the measuring device and the measuring device housing 6 is This often results in destruction or malfunction of the internal circuit of the measuring instrument.

In other words, an example of the internal circuit of the measuring instrument will be explained with reference to Fig. 2. In the figure, the high frequency loss resistances r ₁ and r ₂ of the bypass capacitors C ₁ and C ₂ are assumed, and the difference Δr between the two resistances is 100Ω, and the resistance R ₁ = Assuming that R ₂ = 1000Ω (where R ₁ and R ₂ are input filter resistances), the ground high frequency voltage e ₀ of measurement object 1 is, for example, when a step voltage of 15 KV is applied, for example in the case of a spark plug. The instantaneous current of i ₁ ≒ i ₂ = 15KV/1KΩ = 15A Therefore, the potential difference between the + and - terminals of front stage amplifier _A1 is 15A x 100Ω = 1500V, which greatly exceeds the allowable voltage of the amplifier of 15V to 30V. Therefore, the amplifier is easily destroyed. However, in this case, the impedance of stray capacitances C ₃ , C ₄ , and C ₅ is ignored. In FIG. 2, reference numeral 22 indicates an isolator, and A ₂ indicates a rear-stage amplifier, and the output of the isolator passes through the amplifier A ₂ and is connected to a recorder or the like through its output terminals 20 and 21.

(3) In Fig. 1, the equivalent capacitance C between the measuring instrument input terminals 5 _a and 5 _{b and} the housing 6 is the ground electrostatic capacitance of the measuring object 1 via the compensating conductor and thermocouple. Since a capacitance is formed, the potential e ₀ of the measurement object 1 is obtained by dividing the operating voltage, that is, the voltage e _S of the high frequency source feeding the measurement object 1, by the internal impedance Z _S of the object and the capacitance C. This causes the inconvenience of changing the operating state of the object to be measured for measurement, which adversely affects the measurement results.

The present invention has been made in order to eliminate the drawbacks of the conventional example described above, and the configuration of the present invention will be described below with reference to one embodiment and the drawings.

FIG. 3a shows an embodiment of the present invention, which shows the basic structure of a thermocouple and a compensating conductor. As shown in the figure, the positive electrode wire 4 _a and negative electrode wire 4 _b are always connected. As a "pair", solenoids or helical coils are held insulated from each other in a flexible tubular shield _4c made of thin-walled tubes such as stainless steel, and the shield _4c is used for measurement. It has insulation performance that can withstand the voltage of the object.

Note that the inside of the flexible tubular shield _4c is filled with an electrical insulating material such as polyethylene or a rubber material made of a molded material, but it is also possible to fill it with a rubber material mixed with iron oxide powder as a high frequency magnetic material. Magnetic permeability can be increased.

Figure 3b shows compensation conductors 4 _a and 4 _b in Figure 3 a.
This is a cross-sectional explanatory diagram when a thermocouple is used in a conventional thermocouple structure. In the _example , chromel (+ _pole ) and alumel (- The wire is constructed by covering the outer periphery of each wire with an insulating material 23 such as glass fiber and storing it in a pipe 24 made of glass or vinyl having an oval cross section. As shown in the example of the shape and dimensions in this case, the oval pipe 24 has a long diameter.
The diameter is about 2.5 to 5 mm, and the short axis is about 1.3 to 3 mm.

In Fig. 1, regarding the distance L' from the measuring point _1a to the measuring instrument input terminals _5a , _5b , the thermocouple wires _2a , _2b are relatively short mainly for economic reasons, and the compensating conductor 4
Since it is common usage to allocate long portions a and 4 _b , in Fig. 3 a, in correspondence with Fig. 1, it is written as "compensating conductors 4 _a , 4 _{b "} , but in the same way, 4 _a , 4 _b Even if they are referred to as "thermocouple wires 2 _a and 2 _b ," it is consistent with the spirit of the present application. That is, in the embodiment shown in FIG. 3a, either the thermocouple wires 2 _a , 2 _b or the compensating lead wires 4 _a , 4 _b can be applied.

FIG _. 4a is an explanatory diagram _showing a second embodiment of the present invention. In contrast to the first embodiment shown in _FIGS . This was replaced by a generally known capillary thermocouple. 4 _d is the jacket capillary of the capillary thermocouple. That is, the jacket capillary tube _4d is a solenoid or a helical coil, and the capillary tube _4d and the measuring instrument input negative terminal _5b are connected at one end thereof.

Figure 4b is an explanatory cross-sectional view of the thin tube thermocouple in Figure 4a, and is a stainless steel pipe (outer diameter 1 mm).
The thermocouple wires 2 _a , 4 _a , 2 _b 4 _b are filled and housed in the thin tube 4 _d with a heat-resistant insulating material 24 ′ such as alumina.

In the embodiment shown in FIGS. 3a and 3b, the flexible tubular shield _4c is filled with a rubber material mixed with iron oxide powder as an insulating material between the compensation conductor solenoid or helical coil, and is transparent. It is even more effective to use a structure with increased magnetic flux.

Furthermore, in Figures 3a and 3b, compensation conductors 4 _a and 4 _b
In applications where the capacitance between the shield 4c and the shield _4c is to be reduced, it is natural to have a structure that does not provide a shield, or to reduce the total distance L' of the required thermocouples _2a , _2b and compensating conductors _4a , _4b . A partially shielded structure or a mixed connection configuration is also implemented.

The first embodiment shown in each of the above-mentioned embodiments (Fig. 3a,
By combining the deformed structures (see b) with each other, a more complex deformed structure can be created.

The configuration of the present invention has been described above with respect to embodiments and modified structures of the embodiments, and below, the operation and effects of the present invention will be explained. In addition, the compensation conductors 4 _a and 4 _b in the general example of the temperature measurement method using a thermocouple shown in Fig. 1 below
is replaced with the structure shown in Figure 3a,
In addition, the wire lengths of thermocouples 2 _a and 2 _b in contact with measurement point 1 _a are both short, and the compensating conductor wire 4 _a shown in FIG. 3 _a extends from terminals 3 _a and 3 _b to terminals 5 a and 5 _b . ,4 _b
The explanation will be given assuming that L' occupies most of the total line length L'.

In the present invention, from the terminals 3 _a and 3 _b to the terminals 5 _a ,
Since the line leading to _5b is a solenoid or helical coil that exhibits common mode inductive impedance with respect to the earth potential, the high-frequency voltage e ₀ is used to measure the inside of the measuring device 6' from terminals _5a and _5b . The high frequency current i flowing through the equivalent capacitance C between the terminals 5 _a , 5 _b and the measuring device housing 6 is reduced, and damage or malfunction of the internal circuit of the measuring device is prevented.

In addition, if this inductive impedance does not exist, the equivalent capacitance C will be directly connected between the measurement point _1a and the ground, inevitably causing a change in the ground high frequency voltage _e0 of the measurement object 1. In this case, the effect of the equivalent capacitance C can be reduced or eliminated by inserting this impedance.

In addition, in the case of Fig. 1, due to the high frequency voltage e ₀ , these pairs are connected to the ground common for the total line length L'.
The line will be excited as a mode, and the line will give electric field excitation to the space and radiate radio waves, but by making most of the total line length L' into a shield configuration as shown in Figure 3a. , this radio wave radiation can be significantly reduced.

When the same high-frequency voltage to ground, that is, common mode voltage, is applied to terminals 3 _a and 3 _b in Fig. 3a, the ground potentials of terminals 5 _a and 5 _b are not necessarily the same potential due to the difference in impedance. However, in the configuration shown in Fig. 4a, which uses a thin tube thermocouple, the high-frequency current flowing in the line does not flow through the wires 4 _a and 4 _b . Since the flow flows on the outer surface of the capillary tube _4d , which is the outer sheath, the impedance difference between the wires _4a and _4b becomes irrelevant, and the measuring instrument input terminal _5a has the same potential as the terminal _5b to which the capillary tube _4d is connected. Therefore, the unbalanced component no longer appears.

As already described in the embodiment shown in FIG. 3a, the flexible tubular shield _4c is filled with an electric insulating material made of rubber material mixed with iron oxide powder as a high-frequency magnetic material to increase the magnetic permeability. The equivalent capacitance C is increased by increasing the inductance per unit length of the solenoid or helical coil and increasing the common mode impedance between terminals 3 _a and 3 _b and terminals 5 _a and 5 _b . This has the effect of reducing the high frequency current i flowing to the ground and further reducing the influence of the capacitance C on the high frequency voltage e ₀ .
In other words, when the pair of compensation conductors _{4a and 4b} is viewed as a common mode, it is considered equivalent to one conductor for the shield _4c , so the configuration of Figure 5a is as shown in Figure 5b. It can be thought of as an equivalent circuit similar to a general coaxial cable with a single conductor.

In other words, L: inductance per unit length (for example, 1 cm) C: shielding capacitance of L R: internal resistance component of L (series component) G: internal conductance of C (parallel component) Then, the characteristic impedance Z is It is expressed as

Therefore, 1. By using a material with large high frequency loss, such as the carbon rubber material mentioned above, as the filling material between the core wire and the shield, the above R and G can be set large, and as a result, the equivalent capacitance C Reduction of high frequency current i flowing through to the ground and capacitance C
It has the effect of further reducing the influence on the high frequency voltage _e0 , and also particularly satisfies the matching with the characteristic impedance Z of each ground impedance of terminals 3 _a and 3 _b and each ground impedance of terminals 5 _a and 5 _b. The amplitude of the standing wave riding in the line direction of the outer shield 4 _c can be made small without causing any damage, and this has the effect of preventing the radiation of unnecessary radio waves from the surface of the shield 4 _c .

2. Also, if a rubber material mixed with iron oxide powder or the like is used as a filler, the magnetic permeability will increase and the inductance L will increase, but depending on the magnetic properties of the iron powder, if the iron powder has a large magnetic resistance at high frequencies. , 1 above
has the same effect as the term.

3. If carbon, iron powder, etc. are mixed together with the filler, it will have the synergistic effect of the above items 1 and 2.

4. When the above-mentioned cable is required to be insulated against high voltage, a two-layer insulating layer as shown in FIG. 6 may be used, and the same effect as above can be obtained. In addition, in FIG. 6, the compensation conductor 4
_a and 4 _b are center conductors, the surroundings of which are filled with an insulating material 31 made of a mixture of the insulating materials listed in items 1, 2, and 3 above, and the outer peripheral surface of which is further covered with a high-voltage insulating material 32. is stored in the shield _4c .

Furthermore, in the structure that increases magnetic permeability as described above, a long magnetic path column with a diameter larger than the diameter of the coil and high magnetic permeability is formed, so that the spatially excited electromagnetic field radiated from the coil wire is Since most of the energy is concentrated within this magnetic path column, external leakage radiation is minimal, making it possible to reduce radio wave interference.

In particular, in the case where electric field radiation is not a problem, the shield _4c may not be used and the above-mentioned high permeability magnetic path column alone may be configured as necessary, and the same effect as described above can be obtained.

As detailed above, in the present application, a thermocouple and a compensating lead wire are paired together to form a solenoid or helical coil, and this is filled and held in a flexible tubular shield with an electrical insulating material containing a high-frequency magnetic material. The gist is the structure of thermocouples and compensating conductors, and the measurement point has a high frequency voltage with respect to the earth potential, such as when measuring the temperature of the electrodes of engine spark plugs and various discharge tubes. This is a useful invention that is highly effective in the fields of high-frequency thermocouples and compensating conductors that are commonly used.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a temperature measuring device when the object to be measured has a high frequency voltage, Fig. 2 is an explanatory diagram of the internal circuit of the measuring instrument in Fig. 1, and Fig. 3a is a perspective view of the first embodiment of the present application. Explanatory drawings, FIG. 3b is an enlarged sectional explanatory view when a conventional thermocouple is used as the compensation conductor in FIG. 4a, FIG. 4a is a perspective explanatory view of the second embodiment of the present application, and FIG. Figure 5a is an enlarged cross-sectional explanatory view of the thin tube thermocouple in Figure a, and Figure 5a is a perspective explanatory view of a thermocouple cable in which two thermocouples _4a and _4b are arranged in parallel within the shield _4c . Fig. 5b is an equivalent circuit diagram of Fig. 5a, Fig. 6 is an enlarged cross-sectional diagram when a double insulation layer is used when high voltage insulation is required in Fig. 5a, and Fig. 7 is an illustration of engine ignition. It is an explanatory view of a voltage waveform in a stopper. 1... Measurement object, 1 _a ... Measurement point, 2 _a , 2 _b ... Thermocouple, 3 _a , 3 _b ... Terminal, 4 _a , 4 _b ... Compensation lead wire, 4 _c ...
Flexible tubular shield, 4 _d ... Thin tube, 5 _a , 5 _b ... Input terminal of measuring instrument 6', 6... Housing of measuring instrument 6', 6'...
Measuring instrument, 20, 21...A ₂ output terminal, 23...Insulating material, 24...Pipe, 31, 32...Insulating material, A ₁
...Pre-stage amplifier, A ₂ ... Post-stage amplifier, C... Equivalent capacitance, C ₁ , C ₂ ... Bypass capacitance, C ₃ , C ₄ ,
C ₅ ... Stray capacitance, e ₀ ... High frequency voltage, e _S ... Voltage,
...Waveform when no discharge occurs, G...Conductance, h...Step voltage, i...High frequency current, _i1 ,
i ₂ ...Current, L...Inductance per unit length,
L'...total length of 2 _a , 2 _b and 4 _a , 4 _b , l... unit length,
P...peak point of the voltage of the center electrode, R...resistance component,
R ₁ , R ₂ ... Input filter resistance, r ₁ , r ₂ ... High frequency loss resistance, t ₀ ... Ignition command time, Z ... Characteristic impedance, Z _S ... Internal impedance of 1, τ
₁ , τ ₂ , τ ₃ ...Time, 22...Isolator, 2
4'...Insulating material.

Claims (1)

[Claims] 1 It is held by an electrical insulating material containing a high-frequency magnetic material filled in a flexible tubular shield, and the positive and negative electrode wires are formed into a solenoid or helical coil as a pair. High frequency thermocouple and compensating conductor consisting of.