JP4835207B2 - Temperature transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that any disconnection can not be detected when a wiring resistance line connecting a resistance thermometer sensor to a temperature transmitter is disconnected. <P>SOLUTION: The temperature transmitter for inputting voltage signals from the resistance thermometer sensor via two measurement wires and the wiring resistance line, converting the voltage signals into a temperature value by applying an arithmetic operation thereto and outputting a temperature signal, is equipped with a disconnection detecting means which detects the disconnection of the wiring resistance line by using the voltage signals. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a temperature transmitter that performs temperature measurement using a resistance temperature detector and transmits the temperature output as a temperature output, and in particular, a failure of a wiring resistance wire that connects the resistance temperature detector and the temperature transmitter, or a problem that leads to disconnection. The present invention relates to an improved temperature transmitter that can detect and ensure the reliability of temperature measurement.

  FIG. 4 shows a two-wire temperature transmitter having two measurement wires generally used in the past. In the temperature transmitter 10, one end of the resistance temperature detector 11 is connected to the main input terminal 13 of the temperature transmitter 10 by the measurement wiring 12, and the other end of the resistance temperature detector 11 is connected to the sensor ground terminal of the temperature transmitter 10 by the measurement wiring 14. 15 is connected. In the above configuration, the temperature is measured as a resistance change of the resistance thermometer 11 in the resistance thermometer 11, and the temperature transmitter 10 converts the resistance change into a temperature and outputs a temperature.

  FIG. 5 shows a three-wire temperature transmitter having one wiring resistance wire in addition to two measurement wires generally used conventionally. In the temperature transmitter 20, one end of the resistance temperature detector 11 is connected to the main input terminal 13 of the temperature transmitter 20 by the measurement wiring 12, and the other end of the resistance temperature detector 11 is connected to the sensor ground terminal of the temperature transmitter 20 by the measurement wiring 14. 15 and connected to the wiring resistance input terminal 22 of the temperature transmitter 20 by the wiring resistance wire 21.

  In the above configuration, the temperature is measured by the resistance temperature detector 11 as a resistance change of the resistance temperature detector 11, and the temperature transmitter 20 converts the resistance change into a temperature and outputs a temperature. The measurement accuracy is improved by correcting the influence of the measurement wiring by using the input terminal 22.

  FIG. 6 shows a four-wire temperature transmitter having two wiring resistance wires in addition to two measurement wires generally used conventionally. In the temperature transmitter 30, one of the resistance temperature detectors 11 is connected to the main input terminal 13 of the temperature transmitter 30 by the measurement wiring 12 and connected to the wiring resistance input terminal 32 of the temperature transmitter 30 by the wiring resistance wire 31. ing. The other end of the temperature resistor 11 is connected to the sensor ground terminal 15 of the temperature transmitter 30 by the measurement wiring 14 and is connected to the wiring resistance input terminal 22 of the temperature transmitter 30 by the wiring resistance wire 21.

  In the above configuration, the temperature is measured by the resistance temperature detector 11 as a resistance change of the resistance temperature detector 11, and the temperature transmitter 30 converts the resistance change into a temperature and outputs a temperature. The measurement accuracy is further improved by correcting the influence of the measurement wiring using the input terminals 22 and 32.

  The following Patent Document 1 discloses a temperature measuring instrument having a three-wire or four-wire wiring using a resistance temperature detector, and generally diagnoses whether or not these wirings are disconnected, and wiring is performed if they are disconnected. A temperature measuring instrument that switches these wirings by a switching circuit is disclosed.

JP 2005-233737 A

  As described above, there are various methods such as 2-wire, 3-wire, and 4-wire methods for temperature measurement using the resistance temperature detector 11, but any method is correct when one of the wires is disconnected. Measurement cannot be performed.

  When the measurement wirings 12 and 14 for passing current to the resistance temperature detector 11 are disconnected, the main input terminal immediately rises to a high potential, so that the disconnection can be detected, but the wiring resistance lines 21 and 31 are disconnected. Cannot detect disconnection.

  When the wiring resistance lines 21 and 31 are disconnected, the input of the A / D converter in the temperature transmitters 30 and 40 for measuring the potential of the wiring resistance lines 21 and 31 becomes an open potential, and the potential fluctuates halfway. Are A / D converted.

Therefore, the temperature value calculated using this potential as a parameter is a value that is not reliable at all. If the fluctuation of the open-circuit potential is large, the temperature calculation value changes significantly, so that an abnormality can be detected. However, since the open-circuit potential is indefinite, the temperature calculation value is also undefined.

  In view of the above, an object of the present invention is to improve the reliability of temperature measurement by improving the temperature measurement using a resistance temperature detector so that the disconnection of the wiring resistance wire can be accurately detected.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
Power supply, main input terminal, sensor ground terminal, wiring resistance input terminal, and arithmetic processing means,
One of the resistance temperature detectors having a resistance value Rpt is connected to the main input terminal via one measurement wiring having a wiring resistance R0, and the other temperature measurement resistor is connected to the other measurement wiring having a wiring resistance R0. Connected to the sensor ground terminal and connected to the wiring resistance input terminal via a wiring resistance line having a wiring resistance R0, and the sensor ground terminal is connected to a common potential point via a resistor R,
The arithmetic processing means inputs a current I of the power source to the main input terminal, and makes a path formed by the one measurement wiring, the temperature measuring resistor, the other measurement wiring, the sensor ground terminal, and the resistance R. Then, the measured values of the main input voltage V1 generated at the main input terminal, the sensor ground voltage V0 generated at the sensor ground terminal, and the wiring resistance voltage V2 generated at the wiring resistance input terminal are captured by flowing to the common potential point. ,
Rpt = (V0 + V1-2V2) / I
By calculating the resistance value Rpt of the resistance temperature detector,
R0 = (V2-V0) / I
In the temperature transmitter configured to calculate the resistance value R0 of the wiring resistance line by performing the calculation of
The arithmetic processing means calculates an initial wiring resistance value R00 of the wiring resistance line and stores it in a memory, and then calculates a wiring resistance current value RX of the wiring resistance line at a predetermined timing,
Rd = RX-R00
By calculating the difference resistance value Rd between the initial wiring resistance value R00 and the current wiring resistance value RX, the wiring resistance line is determined depending on whether or not the calculated difference resistance value Rd exceeds a predetermined set threshold value. It is characterized by detecting disconnection.

The invention according to claim 2 is the invention according to claim 1,
The predetermined timing for reading the current value of the wiring resistance is a fixed value, a fixed interval, or a user set value from an input means.

The invention according to claim 3 is the invention according to claim 1 ,
When the differential resistance value Rd exceeds the set threshold value, a disconnection of the wiring resistance line or a malfunction that leads to a disconnection is detected and an alarm is given.

The invention according to claim 4 is the invention according to claim 1 ,
When the differential resistance value Rd exceeds the set threshold value, backup means is provided for backing up by changing the transmission configuration of the wiring resistance line.

As is apparent from the above description, the present invention has the following effects.
According to the first aspect of the invention, the disconnection of the previous wiring resistance line is detected by the arithmetic processing means using the voltage signal input from the resistance temperature detector through the wiring resistance line together with the two measurement wirings. As a result, it is possible not only to detect disconnection using the voltage change of this voltage signal, but also to detect disconnection by computing this voltage signal, and detect disconnection of wiring resistance lines in various forms. And the reliability of temperature measurement can be improved.
Furthermore, since the disconnection detection is performed based on whether the difference resistance value between the initial value and the current value of the wiring resistance line exceeds the set threshold, not only the disconnection of the wiring resistance line but also the process leading to the disconnection There is an effect that disconnection can be accurately detected.

According to the second aspect of the present invention, since the reading timing of the current value of the wiring resistance is performed at a constant value, a constant interval, or a user set value from the input means, not only in the case of disconnection, but also periodically By performing the diagnosis, it is possible to detect a malfunction in which the wiring resistance gradually increases.

In addition, there is an effect that it is possible to predict the disconnection such as the resistance value gradually increasing by storing the measured wiring resistance value in time series and taking the trend. Furthermore, since the user can arbitrarily set the read timing by the input means, the wiring resistance value can be measured according to the situation at the site.

According to the third aspect of the present invention, when the differential resistance value exceeds the set threshold value, an abnormal state can be externally detected by detecting a disconnection of the wiring resistance line or a failure leading to the disconnection. Notification can be made promptly and early troubleshooting can be performed.

According to the fourth aspect of the present invention, when the differential resistance value exceeds the set threshold value, the backup unit can ensure temperature measurement while reducing the number of wiring resistance lines and minimizing a decrease in accuracy. There is an effect that can.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of a temperature transmitter according to the present invention. FIG. 1 is a flow chart showing the procedure of a disconnection detecting means for detecting disconnection of a wiring resistance wire that is executed by the temperature transmitter.

First, the structure of the temperature transmitter 40 according to the present invention will be described with reference to FIG. Here, an example in which the temperature transmitter 40 is a three-wire type is shown. In the following description, components having the same functions as those shown in the conventional temperature transmitter are denoted by the same reference numerals, and description thereof is omitted as appropriate.

On the input end side of the temperature transmitter 40, a main input terminal 13, a sensor ground terminal 15, and a wiring resistance input terminal 22 are provided. The main input terminal 13 is connected to one end of the resistance temperature detector 11 via a measurement wiring 12, and the sensor ground terminal 15 is connected to the other end of the resistance temperature detector 11 via a measurement wiring 14. Further, the wiring resistance input terminal 22 is connected to the other end of the resistance temperature detector 11 by a wiring resistance wire 21.

The resistance temperature detector 11 is the resistance value _{R pt,} measurement lines 12, 14, and the wiring resistance wire 21 has a wire resistance R0 both equal. From the power supply VDD of the temperature transmitter 40, the current I flows to the common potential point COM through the main input terminal 13, the measurement wiring 12, the resistance temperature detector 11, the measurement wiring 14, the sensor ground terminal 15, and the resistance R sequentially. Has been.

As a result, the main input voltage V1 is generated at the main input terminal 13, the sensor ground voltage V0 is generated at the sensor ground terminal 15, and the wiring resistance voltage V2 is generated at the wiring resistance line 21. These main input voltage V1, sensor ground voltage V0, and wiring resistance voltage V2 are input to an A / D converter 41 in the temperature transmitter 40, where these voltages are converted into digital data DD.

  The digital data DD of each voltage is input to the arithmetic processing means 42. Here, the CPU (Central Processing Unit) performs temperature calculation, detection of disconnection of the wiring resistance line, etc. using a memory 43 such as ROM (Read-Only Memory). An operation is performed. Further, calculation processing such as disconnection detection is performed in consideration of data input from the input means 46 such as a keyboard. These calculation results are output to the outside as a temperature output 44 and an alarm output 45.

  Next, the procedure of the disconnection detecting means 47 for detecting disconnection of the wiring resistance wire, which is executed by the temperature transmitter 40 according to the present invention, will be described with reference to the flowchart shown in FIG.

  Step 1 sets the wiring resistance disconnection detection ON to an initial state in which the disconnection of the wiring resistance line can be normally detected and the temperature can also be measured.

Then control proceeds to step 2, by measuring the wiring resistance value R0, calculated by the wiring resistance of the initial value R _00. Thereafter, the initial value R ₀₀ of the wiring resistance measured in step 3 is stored in the memory 43.

In step 4, temperature measurement is performed. In the temperature measurement, first, the resistance value Rpt of the resistance temperature detector 11 is calculated using the main input voltage V1, the sensor ground voltage V0, and the wiring resistance voltage V2 generated by passing the current I through the resistance temperature detector 11. This is performed based on equation (1).
Rpt = (V0 + V1-2V2) / I (1)
Thereafter, the temperature is calculated based on a resistance value-temperature conversion table defined by an international standard or the like built in the temperature transmitter 40, and is output as a temperature output 44 in step 5.

Thereafter, the process proceeds to step 6. Normally, the wiring resistance R0 does not appear in the resistance value calculation, but the wiring resistance R0 is measured based on the following equation (2).
R0 = (V2-V0) / I (2)

Therefore, it measured at an appropriate timing based on the current wiring resistance R _X (2) expression. The reading timing of the current value of the wiring resistance may be a constant value such as 1 hour, or may be periodically performed at regular intervals such as every 30 minutes, or may be set by the user through the input means 46. May be. Furthermore, when the user sets the read timing by the input means 46, the wiring resistance value can be measured according to the situation at the site.

Next, the process proceeds to step 7. In step 7, the arithmetic processing means 42 calculates a difference resistance value Rd (= R _X −R ₀₀ ), which is a difference between the initial wiring resistance value R ₀₀ and the current current wiring resistance value R _X , using a predetermined calculation program.

In step 8, the arithmetic processing means 42 determines whether or not the differential resistance value Rd has exceeded a predetermined threshold value SS by using a predetermined arithmetic program. When the differential resistance value Rd exceeds the set threshold value SS (Yes), the process proceeds to step 9 where the wiring resistance line is disconnected and disconnection is detected, and a disconnection alarm output is output at step 10. When the differential resistance value Rd does not exceed the set threshold value SS in step 8 (No), the process returns to step 4 and steps 6 to 8 are repeated.

With regard to the set threshold SS, for example, when the accuracy is 0.1 ° C., there is a resistance measurement accuracy of about 40 mΩ. Therefore, when the set threshold SS is set to 1Ω, disconnection occurs when the wiring resistance value increases to 1Ω or more. Will be detected.

  The setting threshold SS may be a fixed value such as 1Ω or may be set by the user using the input unit 44. However, since the resistance value of the wiring material varies depending on the ambient temperature, it is necessary to consider the variation of the wiring resistance value due to the wiring material when performing long distance wiring.

  The disconnection detection of the wiring resistance line shown in the flowchart of FIG. 1 is detected by a change in the resistance measurement value of the wiring resistance line, but it can be detected by replacing this with a change in the wiring resistance voltage V2.

  Further, not only in the case of disconnection, but also by detecting periodically, it is possible to detect a problem that the wiring resistance gradually increases. In this case, it is possible to detect that the resistance value has gradually increased by storing the measured wiring resistance value in time series and taking a trend.

  FIG. 3 is an explanatory view of the main part configuration of another embodiment of the present invention, and is an example of a four-wire temperature transmitter. In the temperature transmitter 50 in this case, when the wiring switching circuit 51 is disposed between the resistance temperature detector 11 and the temperature transmitter 50 and the wiring resistance wire detects the disconnection by the wiring switching signal ST from the temperature transmitter 50. The wiring resistance lines 21 and 31 are switched to each other.

  Thus, when the wiring resistance lines 21 and 31 are disconnected in the 4-wire system, the temperature measurement can be prevented from being interrupted by switching to the 3-wire system and performing the backup measurement, and the reliability of the temperature measurement is improved. Although not shown in the figure, similarly, when the wiring resistance wire 21 is disconnected in a three-wire system, it is possible to improve the reliability of temperature measurement by switching to the two-wire system and backing up in the same manner.

It is a principal part flowchart which shows the procedure of the disconnection detection means of this invention. It is a block diagram which shows one Example of the temperature transmitter which concerns on this invention. It is a block diagram which shows the other Example of this invention. It is composition explanatory drawing of the temperature transmitter generally used conventionally. It is another structure explanatory drawing of the temperature transmitter generally used conventionally. It is further another structure explanatory drawing of the temperature transmitter generally used conventionally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20, 30, 40 Temperature converter 11 Resistance thermometer 12, 14 Measurement wiring 13 Main input terminal 15 Sensor ground terminal 21, 31 Wiring resistance wire 22, 32 Wiring input terminal 41 A / D converter 42 Arithmetic processing means 43 Memory 44 Temperature output 45 Alarm output 46 Input means 47 Disconnection detection means R0 Wiring resistance R _X Current wiring resistance value R ₀₀ Initial wiring resistance value Rd Differential resistance value SS Setting threshold V1 Main input voltage V2 Wiring resistance voltage V0 Sensor ground voltage

Claims (4)

Power supply, main input terminal, sensor ground terminal, wiring resistance input terminal, and arithmetic processing means,
One of the resistance temperature detectors having a resistance value Rpt is connected to the main input terminal via one measurement wiring having a wiring resistance R0, and the other temperature measurement resistor is connected to the other measurement wiring having a wiring resistance R0. Connected to the sensor ground terminal and connected to the wiring resistance input terminal via a wiring resistance line having a wiring resistance R0, and the sensor ground terminal is connected to a common potential point via a resistor R,
The arithmetic processing means inputs a current I of the power source to the main input terminal, and makes a path formed by the one measurement wiring, the temperature measuring resistor, the other measurement wiring, the sensor ground terminal, and the resistance R. Then, the measured values of the main input voltage V1 generated at the main input terminal, the sensor ground voltage V0 generated at the sensor ground terminal, and the wiring resistance voltage V2 generated at the wiring resistance input terminal are captured by flowing to the common potential point. ,
Rpt = (V0 + V1-2V2) / I
By calculating the resistance value Rpt of the resistance temperature detector,
R0 = (V2-V0) / I
In the temperature transmitter configured to calculate the resistance value R0 of the wiring resistance line by performing the calculation of
The arithmetic processing means calculates an initial wiring resistance value R00 of the wiring resistance line and stores it in a memory, and then calculates a wiring resistance current value RX of the wiring resistance line at a predetermined timing,
Rd = RX-R00
By calculating the difference resistance value Rd between the initial wiring resistance value R00 and the current wiring resistance value RX, the wiring resistance line is determined depending on whether or not the calculated difference resistance value Rd exceeds a predetermined set threshold value. A temperature transmitter characterized by detecting disconnection.   2. The temperature transmitter according to claim 1, wherein the predetermined timing for reading the current value of the wiring resistance is a constant value, a constant interval, or a user set value from an input means.   2. The temperature transmitter according to claim 1, wherein when the differential resistance value Rd exceeds the set threshold value, a disconnection of the wiring resistance line or a failure leading to the disconnection is detected and alarmed.   The temperature transmitter according to claim 1, further comprising backup means for changing and backing up the transmission configuration of the wiring resistance line when the differential resistance value Rd exceeds the set threshold value.

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