JPH07113585B2 - RTD connection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resistance temperature detector connecting device used for selectively connecting a resistance temperature detector in a two-wire system or a four-wire system.

[Conventional technology]

Traditionally, resistance thermometers made of platinum, copper, etc. (Resistance
Various temperature sensors using a Temperature Device (hereinafter referred to as RTD) are known. Further, when the temperature is measured using the thermocouple, it is necessary to perform cold junction compensation of the thermocouple. There are various cold junction compensation methods, one of which is to use the RTD as a temperature sensor for cold junction compensation.
A method of performing compensation at a room temperature level is known.

When using the RTD as various temperature sensors, generally,
As shown in FIG. 6, terminals 2 and 3 provided on the input device 1
Is connected to the RTD 4 via two conductors 5 and 6, and a current i is made to flow from the constant current source 7, the voltage V generated between the terminals 2 and 3 at this time is measured, and this voltage V is converted to temperature. I am trying to do it. However, using these two conductors 5,6
In the wire method, when the two conductors 5 and 6 are long and the conductor resistance r is large, a measurement error occurs due to a voltage drop of 2r, and accurate temperature measurement cannot be performed. As a countermeasure against this, as shown in FIG. 7, the RTD 4 is connected to the four terminals 2, 3, 10, 11 of the input device 1 by using the four conductors 5, 6, 8, 9 and the current i is supplied from the terminal 10.
A four-wire method in which the liquid is poured is often used. According to this method, since the current i does not flow through the conductors 5 and 6, the voltage V between the terminals 2 and 3 is not affected by the conductor resistance r and R
The voltage across the TD4 terminals can be measured. In addition to this, there is a three-wire method, but the description is omitted here.

[Problems to be Solved by the Invention]

Although the 4-wire method of FIG. 7 described above can perform accurate measurement, it has a drawback in that the number of wirings by the four conductors 5, 6, 8, 9 increases. When the conductors 5 and 6 are short and the conductor resistance r is small, the two-wire method shown in FIG. 6 is used. However, when the two-wire system and the four-wire system can be switched, the input device 1 has 4 units. It is necessary to provide the two terminals 2, 3, 10 and 11 and switch the tangential current source 7 to the terminal 10 or the terminal 2 or connect the measuring terminal for the voltage V to the terminal 2 or the terminal 10.

The present invention has been made to solve the above problems, and an object thereof is to obtain an RTD connection device capable of automatically switching and connecting an RTD to a two-wire system or a four-wire system. There is.

[Means for Solving the Problems]

In the present invention, the first to fourth terminals are provided, the power source is connected to the first terminal, and the diodes are respectively connected to the power source between the first and second terminals and between the third and fourth terminals. It is connected in the forward direction.

[Action]

When using the 2-wire system, connect the RTD between the second and third terminals to make the above two diodes conductive.
A current flows through the RTD, and a voltage is obtained between the second and third terminals. When using the 4-wire system, by connecting the RTD to the first to fourth terminals respectively, the two diodes become non-conductive, and the current flows from the first terminal to the fourth terminal through the RTD.
, And a voltage is obtained between the second and third terminals. In this way, the switching between the 2-wire system and the 4-wire system is automatically performed.

〔Example〕

An embodiment of the present invention in the case where an RTD is used as a temperature sensor for cold junction compensation of a thermocouple will be described with reference to the drawings.

4 and 5 show a system for input-processing the measurement signals of a large number of thermocouples.

FIG. 4 shows a case where a large number of thermocouples 20 and a thermocouple input device 21 for input-processing the measurement signals from these thermocouples 20 are arranged relatively close to each other. Figure 5 shows a large number of thermocouples
The case where 20 and the thermocouple input device 21 are arranged at a long distance is shown. The measurement signal of the thermocouple 20 is relayed by the terminal panel 22, and then input to the thermocouple input device 21 through the connector 23, the multicore cable 24 and the connector 25. A compensating lead wire may be connected between the thermocouple 20 and the thermocouple input device 21 or the terminal panel 22, but here, the thermocouple 20 may include a compensating lead wire.

In Figures 4 and 5, RT is used for cold junction compensation of thermocouple 20.
When using D, in FIG. 4, the RTD is provided inside the thermocouple input device 21, and in FIG. 5, the RTD is the terminal panel 2
It will be installed inside 2. In the case of FIG. 5, since the voltage V across the RTD provided on the terminal panel 22 is measured on the thermocouple input device 21 side through the multi-core cable 24, the length of the lead wire becomes long, so the above-mentioned lead wire resistance r is a problem. Therefore, the 4-wire system of FIG. 7 is used. In the case of FIG. 4, since the voltage V across the RTD is directly measured at the thermocouple input device 21, the conductor resistance r does not matter, so the two-wire system of FIG. 6 is used.

FIG. 1 shows an RTD connecting device according to the present invention for automatically switching between the 2-wire type and the 4-wire type. The connecting device is provided in a thermocouple input device 21.

In FIG. 1, 31, 32, 33, 34 are respectively the first, second, third,
The 4th terminal is shown. A constant current source 26 is connected to the first terminal 31, and a fourth terminal 34 is connected to a reference potential such as an installation potential. A diode 27 is provided between the first terminal 31 and the second terminal 32, with the anode connected to the first terminal 31 and the cathode connected to the second terminal 32. Third terminal
A diode 28 is provided between 33 and the fourth terminal 34, with the anode connected to the third terminal 33 and the cathode connected to the fourth terminal 34. The voltage V obtained between the second terminal 32 and the third terminal 33 is applied to the differential amplifier 29.

2 and 3 show a state in which the RTD 30 is actually connected to the RTD connecting device having the above configuration.

FIG. 2 shows the RTD 30 as a two-wire type having a first terminal 31 and a second terminal 32.
The case of connection between the two is shown and corresponds to FIG. The RTD 30 measures the temperature on the cold junction side of the thermocouple 20. In this case, the current i from the constant current source 26 flows through the path of the diode 27, the second terminal 32, the RTD 30, the third terminal 33 and the diode 28 as shown in the figure. The voltage V generated between the second and third terminals 32 and 33 is generated by the differential amplifier 2
Added to 9.

FIG. 3 shows a case where the RTD 30 is connected to the RTD 30 by a four-wire system and corresponds to FIG. The terminal panel 22 is provided with four conducting wires 35, 36, 37, 38 for connecting the RTD 30 by printed wiring. These conductors 35 to 38 are connected to the connector 23,
First to fourth terminals through the multi-core cable 24 and the connector 25
It is configured to be connected to 31 to 34, respectively. In this case, the potential difference between the first and second terminals 31 and 32 and the third
And the potential difference between the fourth terminals 33 and 34 becomes small, and the diodes 27 and 28 become non-conducting (in order for the diodes 27 and 28 to conduct, the voltage between the terminals of the diodes 27 and 28 is about 0.6 V or more) That is, the voltage Vr (= ri · i ₀ ) applied to the line resistance ( _{denoted by} ri) needs to be 0.6 V or more.However, in general, the current i ₀ is 0.
At about 5 mA, the line resistance ri is about 500 ohms or less, so the voltage Vr is about 0.25 V or less, which is 0.6 V or less, so that the diodes 27 and 28 do not conduct. ). Therefore, the current i from the constant current source 26 is
Terminal 31, connector 25, multi-core connector 24, connector 23,
Conductor 35, RTD30, conductor 38, connector 23, multi-core cable 2
4, through the path of the connector 25 and the fourth terminal 34. No current flows through the second terminal 32, the conductors 36, 37 and the third terminal 33, and a voltage V is generated between the second and third terminals 32, 33 and applied to the differential amplifier 29. .

As described above, according to the RTD connection device according to this embodiment, the RTD 30 is automatically changed to the 2-wire system of FIG. 2 or the 4-wire system of FIG. 3 according to the system of FIG. 4 or 5. Can be connected to.

Although the RTD is used as the temperature sensor for compensating the cold junction of the thermocouple in the above embodiment, the present invention can be applied to the case where the RTD is used as other various temperature sensors.

〔The invention's effect〕

According to the present invention, the first to fourth terminals are provided, the power source is connected to the first terminal, and the first and second terminals are connected to each other and the third terminal is connected.
Since the diode is connected between the fourth terminal and the fourth terminal in the forward direction with respect to the power supply, the RTD can be automatically switched and connected to the 2-wire type or the 4-wire type. In particular, when the RTD is applied to a thermocouple input processing device used for cold junction compensation of a thermocouple as in the embodiment, it is automatically switched to a 4-wire system when a multi-core connector or the like is connected. It is possible to obtain effects such as improved usability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a connecting device of a resistance temperature detector according to an embodiment of the present invention, FIG. 2 is a block diagram showing a state in which the device is used in a two-wire system, and FIG. 4 and 5 are configuration diagrams showing a thermocouple input processing system to which the present invention can be applied, and FIG. 6 shows a resistance thermometer as a two-wire type. FIG. 7 is a configuration diagram showing a case, and FIG. 7 is a configuration diagram showing a case where the resistance temperature detector is used in a four-wire system. 26 is a constant current source, 27 and 28 are diodes, 30 is a resistance temperature detector, 3
1 is the first terminal, 32 is the second terminal, 33 is the third terminal, 34
Is the fourth terminal. In the drawings, the same or corresponding parts with the same reference numerals are shown.

Claims (1)

[Claims] 1. A first terminal to which a power source is connected, a second terminal, a third terminal, a fourth terminal connected to a reference potential, and an anode connected to the first terminal. A resistance temperature detector connecting device comprising a diode having a cathode connected to the second terminal, and a diode having an anode connected to the third terminal and a cathode connected to the fourth terminal.