JPH1137855A - Resistance temperature measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a sufficient countermeasure against noise through a simple structure by providing a first common mode choke coil between first and second lead wires and providing a second common mode choke coil between the first common mode choke coil and a third lead wire. SOLUTION: A temperature measuring resistor Ri has one end connected with a first lead wire r1 and the other end connected with second and third lead wires r2, r3 where each lead wire is provided with the terminal t1-t3 on a terminal board (t). A constant current (i) is fed from the lead wire r1 to the temperature measuring resistor R1 and the output between the lead wires r2, r3 is measured by a measuring circuit 3. Voltage output from the measuring circuit 3 is converted into a digital signal and expressed in terms of temperature thus measuring the temperature. In this regard, a first common mode choke coil 1 is provided between the lead wires r1, r2 and a second common mode choke coil 2 having short-circuited input and output is provided between the first common mode choke coil and the third lead wire r3. According to the arrangement, a pulse-like noise is canceled and the noise can be removed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a noise countermeasure circuit of a resistance temperature measuring device.

[0002]

2. Description of the Related Art When performing temperature measurement using a resistance temperature detector, a constant current is supplied to a lead wire connected to the resistance temperature detector, and a voltage is measured to convert the voltage into a temperature. In this case, various noises come from the measurement environment, leading to measurement errors and malfunctions, so that noise countermeasures are required. Many require earth ground,
High voltage capacitors connected to each input line were connected to earth ground to eliminate noise.

[0003]

However, in this case, the capacitor requires a withstand voltage of 3000 V or more, has a large shape, and is difficult to miniaturize. Further, this alone cannot remove high-speed noise, and requires an LC filter including a coil and a capacitor at a subsequent stage. In addition, in the resistance-type temperature measurement circuit, the variation in the resistance of the lead wire of each input line causes a measurement error. Therefore, it is necessary to reduce the resistance value of the coil of the LC filter, but the coil shape becomes large. There is a problem.

An object of the present invention is to provide a resistance-type temperature measuring device that can take sufficient noise countermeasures with a simple configuration in view of the above points.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a first terminal is provided at one end.
And a constant-temperature resistor having a second and a third conductor at the other end, and supplying a constant current from at least the first conductor to the temperature-measuring resistor to measure an output between the first and second conductors. A measurement circuit to be performed; a first common mode choke coil provided between the first and second conductors; and a second common having an input and an output short-circuited between third conductors. A resistance type temperature measuring device comprising a mode choke coil, a plurality of channels provided with this circuit, and a switching switch for selection.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention. In FIG. 1, Ri is the first at one end.
, And a resistance temperature detector having second and third conductors r2, r3 at the other end, and each of the conductors r1, r2, r3 is provided with terminals t1, t2, t3 of the terminal plate t on the way, and A constant current i is supplied to the resistance thermometer Ri from at least the first conductor r1 of the resistance thermometer Ri, and the first and second conductors r1,
The output between r2 is measured by the measuring circuit 3 to constitute a well-known one-current or two-current resistance-type temperature measuring circuit. The voltage output of the measuring circuit 3 can be converted into a digital signal by an A / D converter (not shown) and converted into a temperature by a processing means to measure the temperature. The first common mode choke coil 1 and the third conductor r are provided between the first conductor r1 and the second conductor r2.
3 is provided with a second common mode choke coil 2 whose input and output are short-circuited. Further, capacitors C1 and C2 are provided between the first conductor r1 or the second conductor r2 and the ground G. Note that this ground G
Is circuit earth, not earth ground.

Here, the common mode choke coil 1
Is formed by winding two coils L1 and L2 around the iron core in opposite directions and providing them on the conductors r1 and r2, respectively, to cancel pulse-like noise and effectively remove the noise. The common mode choke coil 2 short-circuits both input terminals of the two coils L3 and L4,
Further, both output terminals are short-circuited and connected in parallel, and provided in the middle of the conducting wire r3 to cancel and remove pulse-like noise. Also, if necessary, a capacitor C1, which has a relatively low withstand voltage, may be provided between the first conductor r1 or the second conductor r2 and the ground G.
By providing C2, the noise attenuation effect can be further enhanced. The terminal plate t and the common mode choke coils 1 and 2 are made of surface-mounted components (chip components) and provided on a printed circuit board, so that the size can be reduced. Then, a metal plate is provided on a printed circuit board on which the circuit including the common mode choke coils 1 and 2 is provided, or a metal area is provided on the printed circuit board. Can be noise-resistant.

That is, the high-speed pulse-shaped noise can be effectively removed by the small-sized surface-mounted common mode choke coils 1 and 2, and no special LC filter or grounding is required at the subsequent stage. It can be installed in any part of, and it can achieve a significant miniaturization. The resistance values r01 and r02 of the coils L1 and L2 of the common mode choke coil 1 and the combined resistance value r03 of the coils L3 and L4 of the common mode choke coil 2 are small and uniform. If r01 = r02 = r03, a measurement error due to variation in wiring resistance does not occur, and the size can be reduced as described above. And if necessary,
Capacitors C1 and C2 are provided between the first conductor r1 and the second conductor r2 and the ground G to further enhance the noise attenuation effect.

FIG. 2 shows another embodiment of the present invention.
In FIG. 1, an EMI (elect) comprising a coil and a capacitor is further provided between the third conductor r3 and the ground G.
A filter 4 for removing a magnetic interference (electromagnetic interference) is provided. The filter 2 includes two coils L5 and L5 connected in series to a third conductor r3.
L6 is connected, and a capacitor C0 is connected between the midpoint of the coils L5 and L6 and the ground G, so that high-frequency noise can be further attenuated. This capacitor C0 may be a feedthrough capacitor, and the filter 4 can remove bidirectional noise.

FIG. 3 is an explanatory diagram showing the configuration of an embodiment of the present invention for achieving multi-channeling. The same reference numerals as those in FIGS. 1 and 2 denote the same components. In FIG. 3, the first conductor r1 is provided at one end and the second and third conductors r are provided at the other end as shown in FIG.
, Rn having resistances R1, R2,.
Are provided in a plurality of channels, and a first conductor r1 of each channel is provided.
And second changeover switches S11, S12, S21, S2 such as photoMOS optical semiconductor switches connected to
, Sn1, Sn2, and third changeover switches S13, S23,..., Sn3 such as photo-MOS optical semiconductor switches connected to the second conductor r2 of each channel. Changeover switches S11, S1
2, S13, S21, S22, S23,..., Sn1, S
n2 and Sn3 are sequentially driven by a drive circuit 8 via a light emitting element such as a light emitting diode (not shown) to perform input switching, and a constant current i is supplied from at least the first conductor r1 of each channel to the temperature measuring resistors R1. Supply first and second conductors r
The output of each channel between 1 and r2 is measured by a measuring circuit 3 as a resistance-voltage conversion circuit. Then, the output of each point of the measurement circuit 3 measured by the three-contact switching of the one-wire common is converted into a digital signal by the A / D conversion circuit 5, and is converted into a temperature by the processing means 6 having the memory 7 for storing data and the like. And other data processing and the like to configure a data acquisition device or to output the data to the network N, thereby configuring a multi-point, multi-channel resistance temperature measuring device.

As in FIG. 1 and the like, first common mode choke coils 11, 12,..., 1n are provided between a first conductor r1 and a second conductor r2 for each channel.
The second common mode choke coils 21, 22,..., 2n are provided on the third conductor r3 for each channel. Also, a first conductor r1 and a second conductor r2 for each channel
And capacitors G11, C12, C21,
, Cn1, Cn2 are provided. Further, the common mode choke coils 11,..., 21,..., The changeover switch S11, etc. are constituted by surface mount components and provided on a printed circuit board. That is, the common mode choke coil 1
A circuit including 1,..., A changeover switch S11, etc. is provided on a printed circuit board and a metal plate is provided, or a metal region is provided on the printed circuit board and connected to the ground G to form a ground plate and a shield plate. be able to.

Although FIG. 3 shows an example in which the second common mode choke coils 21,... Are provided for each channel, each third conductor r3 is connected to the measuring circuit 3 as shown in FIG. One common mode choke coil 20 may be provided in common to all the components, so that the number of components can be reduced, the size and cost can be reduced, and sufficient noise can be removed.

In FIG. 4, if necessary, filters 41 and 4 each including a coil and a capacitor are provided between each third conductor r3 and a ground as a circuit ground as shown in FIG.
, 4n may be provided for each channel to further attenuate bidirectional high frequency noise. FIG.
The same reference numerals as those in FIGS. 1 to 3 denote the same components.

[0014]

As described above, the present invention relates to a temperature measuring resistor having a first conducting wire at one end and second and third conducting wires at the other end, and a temperature measuring resistor at least from the first conducting wire. A measurement circuit for supplying a constant current to the first and second conductors and measuring an output between the first and second conductors; a first common mode choke coil provided between the first and second conductors; A second common mode choke coil having an input and an output short-circuited between the third conductors, and a plurality of channels of the circuit, and a switching switch for selecting a circuit. is there. For this reason, two sets of common mode choke coils of small surface mount components can effectively eliminate particularly high-speed pulse-like noise, and do not require a special LC filter or earth ground at the subsequent stage. It can be installed in such a part, and the size can be significantly reduced. Further, if necessary, a filter can be provided between the third conductor and the ground, or a capacitor with a low withstand voltage can be used between the first conductor or the second conductor and the ground, so that the size and the size can be further reduced. It is possible to increase the noise attenuation effect at low cost. In addition, if the resistance values of the coils and the like of both common mode choke coils of the surface mount component are selected to be small and uniform, and these resistance values are made equal, measurement errors do not occur and the size can be reduced as described above. In addition, a circuit including a common mode choke coil, a filter, and a changeover switch is provided on a printed circuit board, and a metal plate is provided or a metal region is provided on the printed circuit board, and connected to a ground, and a ground plate and a shield plate can be provided. , And can be more resistant to noise. Then, the output of the measurement circuit is converted into a digital signal by the A / D conversion circuit, and data processing is performed by the processing means.
The data acquisition device can be configured or output to a network, and can be used for various purposes. For example, in the circuit of the present invention, even if impulse noise of 2000 V or more is experimentally applied between the input terminal and the ground, this noise is removed and sufficient performance is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing one embodiment of the present invention.

FIG. 2 is a configuration explanatory view showing one embodiment of the present invention.

FIG. 3 is a configuration explanatory view showing one embodiment of the present invention.

FIG. 4 is a configuration explanatory view showing one embodiment of the present invention.

[Explanation of symbols]

1, 11, 12 to 1n First common mode choke coil 2, 21, 22, 2n, 20 Second common mode choke coil 3 Measurement circuit 4, 41 to 4n Filter Ri, R1, R2 to Rn Resistance thermometer r1, r2, r3 Conducting wires S11, S12, S13 to Sn1, Sn2, Sn3 selector switches C0, C1, C2, C11, C12, to Cn1, Cn2
Capacitor L1, L2, L3, L4, L5, L6 Coil G Ground

Claims (4)

[Claims] An RTD having a first conductor at one end and second and third conductors at the other end, and supplying a constant current from at least the first conductor to the RTD to supply a first and a second current. A measurement circuit for measuring the output between the two conductors, a first common mode choke coil provided between the first and second conductors, and an input provided between the third conductors. And a second common mode choke coil whose output is short-circuited. 2. A plurality of channels each having a first conducting wire at one end and second and third conducting wires at the other end, and a first and a second connected to the first conducting wire of each channel. A changeover switch, a third changeover switch connected to the second conductor of each channel, a drive circuit for sequentially switchingly driving the changeover switch of each channel, and at least a first circuit of each channel.
And a measuring circuit for supplying a constant current to the resistance bulb from the lead wire and measuring the output of each channel between the first and second lead wires, and between the first lead wire and the second lead wire for each channel. And a second common mode choke coil provided for each channel or in common and connected to the third conductor, and having a short-circuited input and output. Type temperature measuring device. 3. The resistance type temperature measuring device according to claim 1, wherein a filter comprising a coil and a capacitor is provided between said third conductor and ground. 4. A capacitor is provided between said first conductor or said second conductor and a ground.
The resistance type temperature measuring device according to any one of claims 1 to 3.