JPH01291132A - Resistance bulb temperature converter - Google Patents

Abstract

PURPOSE:To always measure a temperature with high accuracy by changing a dynamic range of an A/D converter, based on a result of comparison by a comparing means. CONSTITUTION:A constant current (i) from a constant-current source 3 flows to a resistance bulb 1, and in one end of a lead wire 2, voltage signals VA-VC are generated, respectively. These voltage signals are selected successively by a switch 4, and converted to digital signals by an A/D converter 5. Also, a wiring resistance arithmetic means 61 calculates a wiring resistance r3 of a signal path. A comparing means 62 compares a value of this resistance r3 and a prescribed wiring resistance value which has been set in advance, and by its results, whether a current limiting resistance has been inserted into the signal path or not is known. When the wiring resistance is larger than a prescribed value, it is decided that the current limiting resistance has been inserted, and a dynamic range of the converter 5 is set to a regular mode, and when the wiring resistance is smaller than the prescribed value, it is decided that the current limiting resistance is not inserted, and the dynamic range is switched so as to become a high resolution mode.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a temperature conversion device using a resistance temperature sensor as a sensor for detecting temperature, and more specifically, to a temperature conversion device using a resistance temperature sensor as a sensor for detecting temperature. The present invention relates to a resistance temperature detector temperature converter that changes the dynamic range of an A/D converter according to the wiring resistance of the resistor and is capable of always obtaining a signal that accurately corresponds to the measured temperature with high precision.

(Prior Art) FIG. 4 is a block diagram showing an example of a device using a conventionally known resistance temperature detector as a temperature sensor.

In the figure, 1 is a resistance temperature detector, 2 is a connection path (lead wire) to the resistance temperature detector 1, and rl, , r2°r3 all represent lead wire resistances. 3 is a constant current source that supplies a constant current i to the resistance temperature sensor 1; 4 is a switch that sequentially switches and extracts the voltages VA, VB, and VC at one end of the lead wire; 5 is a voltage signal that is extracted by switch 4; A/I) converter for A/D conversion, 6 is a microprocessor;
A digital signal from the A/D converter 5 is input, and a predetermined calculation is performed to obtain a temperature signal.

In the device configured in this way, each resistance r1, r2 . Assuming that all r3 are equal and the resistance value of the temperature sensing resistor 1 is 1t, the following equations hold true.

rl=r2=r3 ・・・・・・(1
)VA-VC= (R+r 1+r3) ・i...
...(2) VB-VC= r 3- i ------
-(3) Formula (4) is obtained from formulas (1), (2), and (3).

VA-VC-2VB+2VC=R-i R-1=VA-2VR+VC...(4)(4)
In the equation, the current i is a constant value, and by calculating the equation (4), the microprocessor 6 can calculate the resistance value R of the resistance temperature detector 1, and from this, the temperature can be determined. It looks like this.

(Problem to be Solved by the Invention) In the conventional device configured as described above, the resistance temperature detector 1
For example, when a platinum resistance temperature sensor is used, its resistance value changes from 10-odd ohms to several hundred ohms depending on the ambient temperature. Therefore, the A/D converter that A/D converts the signals input through each lead wire and switch has its dynamic range set to a range convenient for receiving these signals and obtaining the necessary resolution. There is.

Incidentally, for reasons of intrinsic safety, a current-limiting resistor may be inserted in the signal path from the resistance temperature detector 1. In this case, the dynamic range set for the A/D converter is no longer a range that includes the current limiting resistor, and as a result, the necessary A/D conversion resolution cannot be obtained, making highly accurate temperature measurement impossible. The problem arises that it becomes impossible to do so.

The present invention has been made in view of these problems, and its purpose is to prevent current-limiting resistors from being inserted into the signal path from the resistance thermometer and when the lead wire resistance increases. Another object of the present invention is to realize a temperature conversion device that can automatically change the dynamic range of an A/D converter and constantly measure temperature with high accuracy.

(Means for Solving the Problems) FIG. 1 is a block diagram showing the basic configuration of the present invention. In FIG. 6, 1 is a resistance temperature detector;
Signal from! ! ! With i (lead wire),! -1, r2.
In both cases, r3 indicates lead wire resistance. 3 is a constant current source that supplies a constant current i to temperature measuring resistor #1; 4 is a switch that sequentially switches and extracts the voltages VA, VB, and VC at one end of the lead wire; 5 is a voltage signal that is extracted by switch 4;
A/r) converter that performs /D conversion, and is configured so that its dynamic range can be changed. 60 is a temperature signal calculation means that inputs the digital signal from the A/D converter 5 and performs a predetermined calculation to obtain a temperature signal; 61 is an A/D converter 5;
I) Input the digital signal from the converter 5 and convert the predetermined ?
Resistance calculation means 62 calculates the wiring resistance of the signal path 2 by performing calculation A, and 62 inputs the wiring resistance value obtained by the calculation means 61.
This is a comparison means for comparing with a predetermined value.

<Function> The calculation means can obtain the wiring resistance of the lead wire by inputting the voltage signal at each end of the lead wire and performing a predetermined calculation, and the wiring resistance value and the predetermined wiring resistance value are By comparing , it is possible to know whether a current limiting resistor is inserted in the signal path. If a current limiting resistor is inserted in the signal path, the dynamic range of the A/D converter including the current limiting resistor is changed to suit the fi.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. In FIG. 0, the same components as those in FIG. 1 are denoted by the same reference numerals.

A preamplifier 40 amplifies the voltage signal at one end of the lead wire selected by the switch 4, and its amplified output is applied to the A/D converter 5, where it is converted into a digital signal. This A/D converter 5, in combination with a preamplifier 40,
It is configured so that the dynamic range can be changed to the optimum dynamic range for the input voltage signal.

6 is a microprocessor to which the digital signal from the A/D converter 5 is input.

In this microprocessor 6, 71 is an arithmetic control unit ('CPU), 72 is a ROM that stores various programs and tables for performing arithmetic operations, and 73 is a ROM that stores arithmetic formula data, various externally given data, and ranges. 74 is a RAM for storing data related to calculations and spans; 74 is an EFF, PT (OM) for storing various data used for calculations, data given from the outside, etc.; 75 is a T10 boat; 76 is a
are communication boats, and these are interconnected via a bus BS.

The CPU 71 functions as the temperature calculation means 60, the wiring resistance calculation means 61, and the comparison means 62 in FIG. 1 by executing a program stored in the ROM 72.

Reference numeral 8 denotes a data input means, through which data such as the type of resistance temperature detector and range are inputted and given to the microprocessor 6, which includes the microprocessor, a keyboard for inputting data, a display, a communication means, etc. It consists of

A communication cable 9 is used to connect to the microprocessor 6 via a connector 90 when inputting data.

The operation of the apparatus configured in this way will be explained next.

First, it is assumed that necessary data is stored in the RAM 73 and EEPROM 74 of the microprocessor 6 by the data input means 8.

A constant current i from a constant current source 3 flows through a pair of temperature measuring resistors 1, and voltage signals VA, VB, and VC are generated at one end of a lead wire 2, respectively. These voltage signals are sequentially selected by the switch 4 and converted into digital signals by the A/D converter 5 via the preamplifier 40. In the microprocessor 6, the wiring resistance calculating means 61 calculates the wiring resistance r of the signal path (lead wire) by calculating the above-mentioned equation (3).
Calculate 3. The comparison means 62 compares the value of the wiring resistance r3 obtained by the calculation with a predetermined wiring resistance value set in advance, and determines whether a current limiting resistor is inserted in the signal path based on the comparison result. Know. and,
When the wiring resistance is larger than a predetermined value, it is determined that a current limiting resistor is inserted, and the dynamic range of the A/D converter 5 is set to normal mode (for example, a mode with a wide range that can measure resistance from 0 to 700Ω). When the wiring resistance is smaller than a predetermined value, it is determined that the current limiting resistor is not inserted, and the mode is switched to a high-resolution mode (for example, a mode with a small range that allows resistance measurement of 0 to 460Ω). −
After such mode switching is performed, the data is stored in the EEPROM without indicating this mode.

FIG. 3 is a flowchart showing an example of the above mode switching operation performed by the microprocessor 6.

When the power is turned on, the microprocessor 6 initially operates in the mode in which it was operating last time. Then, it is determined whether the mode is normal mode or high resolution mode (step 1.2).

If the normal mode is determined in step 2, the wiring resistance is measured and it is determined whether the wiring resistance value is, for example, 40Ω or more (step 3.4). If it is determined that the wiring resistance is 40Ω or more, the normal mode is selected. It is left as is, and predetermined processing is executed (step 6).

If it is determined in step 4 that it is 40Ω or less, it is assumed that no current limiting resistor is inserted in the signal path, and conversion processing to a high resolution mode is performed (step 5). The combination including the A/D converter 5 has a dynamic range of, for example, 0 to 4.
The resistance is changed to 60Ω.

If it is determined that the high resolution mode is selected in step 2, the wiring resistance is measured and it is determined whether the wiring resistance value is, for example, 60Ω or less (step 7.8). If it is determined that the resistance is 60Ω or less, the high-resolution mode remains and predetermined processing is executed (step 8). If it is determined that the resistance is 60Ω or more in step 8, a current limiting resistor is installed in the signal path. Assuming that it has been inserted, conversion processing to normal mode is performed (step 9). This mode conversion process is performed by the preamplifier 40, A
The combination including the /D converter 5 changes the dynamic range to, for example, 0 to 700Ω.

By performing such an operation, for example, when measuring the resistance ff17 to 340Ω of a platinum resistance thermometer, the dynamic range can be adjusted to 0, assuming that a current limiting resistor is inserted in the signal path. By automatically switching to the high resolution mode when no current limiting resistor is inserted, the accuracy can be increased by about 1.5 times.

In the above embodiment, the wiring resistance is measured when the power is turned on, but when changing the connection of the lead wire to the resistance temperature detector, it is possible to measure the wiring resistance based on a command from the data input means, etc. You may also do so.

(Effects of the Invention) As explained in detail above, according to the present invention, when a current limiting resistor or the like is inserted in the signal path from the resistance temperature sensor or when the value of the lead wire resistance becomes large, Also, the dynamic range of the A/D converter is automatically changed, and a temperature conversion device that can always measure temperature with high accuracy can be provided.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration block diagram of the present invention, FIG. 2 is a configuration block diagram showing an embodiment of the present invention, FIG. 3 is a flowchart showing an example of a mode change operation performed by a microprocessor, and FIG. 4 1 is a configuration block diagram showing an example of a conventional device. 1...Resistance temperature detector 2...Lead wire 3...Constant current source 4...Switch 5...A/D converter 6...Microprocessor 60...Temperature calculation means 61. ... Wiring resistance calculation means 62 ... Comparison means 8 ... Data input means Agent Patent attorney Nobuo Ozawa

Claims (1)

[Scope of Claims] A resistance temperature detector; a constant current source that supplies a constant current to the resistance temperature detector; a switch that sequentially switches and extracts the voltage at one end of a lead wire connected to the resistance temperature detector; An A/D converter configured so that the dynamic range of A/D conversion of the voltage signal taken out by the switch can be changed.
A D converter; A temperature signal calculation means that inputs the digital signal from the A/D converter and performs a predetermined calculation to obtain a temperature signal; A temperature signal calculation means that inputs the digital signal from the A/D converter and performs a predetermined calculation. resistance calculating means for calculating the wiring resistance of the signal path including the lead wire; and comparing means for comparing the wiring resistance value obtained by the resistance calculating means with a predetermined value, 1. A resistance thermometer temperature converting device, characterized in that the dynamic range of the A/D converter is changed based on the temperature.