JP2012137372A - Temperature measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measuring instrument in which a temperature sensor itself can hold its own R-T information without using any lead for a memory besides the own leads of the sensor and which permits combined use of the sensor holding the R-T information with diverse sensors having no R-T information by virtue of the use of only the own leads of the temperature sensor.SOLUTION: A temperature measuring instrument comprises a measuring instrument body B and a measuring unit A connected thereto. The measuring unit A comprises a temperature sensor 1 whose resistance varies with temperature and a memory 2 that is connected in parallel between two leads of the temperature sensor 1 with a diode 3 in-between and stores R-T information on correspondence between the resistance of the temperature sensor 1 and the temperature, and a current flows to the memory 2 only at the time of reading out the R-T information but does not at the time of measuring the temperature.

Description

  The present invention relates to a temperature measuring instrument, more specifically, a temperature measuring instrument using a temperature sensor whose resistance value changes with temperature, and the temperature sensor itself carries information on its own resistance temperature characteristic. It is about a vessel.

  In temperature measurement, as the measurement accuracy improves, uncertainty (in short, the reliability of the measured value) becomes a problem, and it is related to international standards to increase reliability. It has become important. As temperature measuring methods (sensing methods), various methods using various phenomena and effects are known, and they are properly used according to applications and purposes.

  Commonly used temperature measurement means include a temperature sensor (thermistor or RTD (temperature measuring resistor)) whose resistance changes with temperature, a thermocouple that measures electromotive force between different metals, and a forward voltage of a semiconductor. Although an IC sensor using change can be mentioned, the present invention is intended for a temperature sensor whose resistance value changes with temperature.

  This type of temperature sensor has a resistance value that varies depending on the temperature. In this case, the relationship between the temperature and the resistance value is called RT (resistance value-temperature) characteristics (resistance temperature characteristics), etc. Its characteristics vary from one sensor to another and are not uniform. Therefore, the manufacturer defines an RT characteristic for each sensor before shipment.

  Among the temperature sensors whose resistance values change depending on the temperature, the RT characteristic in the case of a resistance temperature detector is close to a linear type, but the RT characteristic in the case of a thermistor changes logarithmically. Become. In any of these cases, the relationship between the temperature and the resistance value is not simple, and a third-order or fourth-order correction becomes necessary as the accuracy requirement increases.

  The thermistor is widely used because of its large resistance change with temperature and low cost. However, as described above, there is no standard for RT characteristics, and several tens of standards for each manufacturer. In general, there are a huge number of thermistors with different characteristics supplied. Each high-precision sensor is provided with an individually calibrated RT table (a conversion table indicating correspondence between resistance values and temperature) or a polynomial constant indicating the relationship between RT. The RT information is supplied to the user from the manufacturer by characters, USB memory, mail file, etc., and the user reads the information into the memory of the measuring device and uses it.

  Prior art documents related to these technologies include, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. Hei 10) which discloses a temperature measuring instrument in which memory means retains RT data for a low temperature region and a high temperature region and can be used for switching. 5 or 45231), or a RAM or ROM that performs conversion using a voltage-temperature cross-reference table and a temperature-increment table instead of using an RT table, thereby holding the RT table Patent Document 2 (Japanese Patent Laid-Open No. 11-258068) discloses a device for converting a voltage to a temperature in which the capacity and cost of the battery are reduced.

  In addition, the coefficient of each term of a high-order polynomial that approximates a theoretical expression representing the relationship between the resistance value of the thermistor and the temperature is held without requiring a memory resource for holding the RT table online. Patent Document 3 (Japanese Patent Application Laid-Open No. 2007-113921), etc., which discloses a conversion arithmetic device that enables high-precision and high-speed conversion processing.

JP-A-5-45231 JP-A-11-258068 JP 2007-113921 A

  For example, a high-precision temperature sensor is required when calculating the temperature distribution using a large number of sensors, or calculating the temperature difference, and a temperature with calibration is required to ensure measurement reliability. A sensor is used. In this case, as described above, the information related to the calibration is supplied by characters, a USB memory, a mail file, etc., and the user reads the calibration information into the measuring device and uses it. Since they are supplied separately, it becomes difficult to manage when a large number of sensors are used, and mistakes are likely to occur.

  Of course, it is possible to hold RT information in the temperature sensor itself, but in order to do so, the terminals of the temperature sensor itself (generally, the temperature sensor has two lead wires and the RTD has 3 In addition, there is a need for a separate memory terminal. In addition, the temperature sensor configured in this manner is specific to a specific manufacturer, so it lacks versatility, is limited in use, and is difficult to use with a wide variety of sensors supplied by multiple manufacturers. It becomes.

  The present invention has been made to solve such a problem, and the sensor itself retains its own RT information without using a memory lead other than the temperature sensor itself. It is possible to provide a temperature measuring instrument that can use both a sensor that holds RT information and a variety of sensors that do not have this because only the lead of the temperature sensor is used. Is an issue.

  The invention according to claim 1 for solving the above-described problem comprises a measuring instrument main body and a measuring unit connected to the measuring instrument, wherein the measuring unit includes a temperature sensor whose resistance value changes according to temperature, and the temperature sensor. And a memory for storing RT information on the correspondence between the resistance value of the temperature sensor and the temperature, which is connected in parallel via a diode between two lead wires. The memory includes the R- The temperature measuring device is characterized in that a current flows only when reading T information and a current does not flow when measuring temperature.

  In one embodiment, the measuring instrument main body includes a temperature measuring unit that operates at the time of temperature measurement, and an RT information reading unit that operates at the time of reading out the RT information from the memory, and the temperature measuring unit Includes a pair of FETs for controlling the direction of the voltage applied to the temperature sensor, a stabilization power supply for measurement that applies a high stabilization reference voltage as a temperature measurement reference to the temperature sensor during temperature measurement, and the temperature A reference resistor connected in series to the temperature sensor to form a sensor and a voltage dividing circuit, and an AD converter that performs AD conversion of a measurement value by the temperature sensor.

  In one embodiment, the RT information reading unit is turned on when reading RT information from the memory and an AD converter for reading RT information built in the CPU. An analog switch that connects a load and the AD converter for reading the RT information, a reading power supply that applies a reading voltage to the memory when the RT information is read, and a serial connection to the memory And including a resistor which becomes a load resistance of the memory.

  In one embodiment, the measurement stabilization power supply is turned off, the pair of FETs are turned on and off, the analog switch is turned on, the CPU input / output port is disconnected, and the memory has a resistance. With the load applied, the H output level of the memory is recorded using the AD converter, and then output from the input / output port of the CPU at the L level to reset the memory. The output port is disconnected, the L output level of the memory is recorded using the AD converter for reading RT information, and the intermediate point between the H output level and the L output level is set as the threshold level of the output signal of the memory. Set.

  Further, in one embodiment, the RT information of the memory is read out by outputting the signal level at an L level from the input / output port of the CPU, then disconnecting the input / output port and setting the signal level after a predetermined time to the RT time. An AD converter for reading information checks to determine the H level and L level, confirms that the output of the memory has become H level, and reads the next bit from the I / O port of the CPU. After the output at the level, the input / output port is disconnected, and the operation for determining the H level and the L level by the AD converter for reading RT information is repeated.

  The present invention is as described above, and since the temperature sensor itself carries the memory storing the RT information without using the memory lead other than the temperature sensor lead, the RT There is no risk of misuse or the like due to the supply of information on another medium, and there is an effect that no problem occurs when the sensor holding the RT information is mixed with a wide variety of sensors that do not have this information.

  Even when a large number of temperature sensors are rearranged and used for another measurement, since the sensors themselves hold RT information, there is no possibility of setting the RT table by mistake. Even when only the temperature sensor damaged during measurement is replaced, there is no need for recalibration or manual table setting, and the reliability of the measuring device can be ensured.

It is a block diagram which shows the structure of the temperature measuring device which concerns on this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a temperature measuring instrument according to the present invention. This measuring instrument comprises a measuring instrument main body B and a measuring section A connected to the measuring instrument main body B.

  The measuring unit A includes a temperature sensor 1 such as a thermistor whose resistance value changes according to temperature, and a memory 2 connected in parallel via a diode 3 between two lead wires of the temperature sensor 1. . The memory 2 stores RT information relating to the correspondence between the resistance value and temperature of the temperature sensor 1 to which the memory 2 is attached. As the memory 2, for example, 1-WireEEPROM (DS2431) (manufactured by Maxim Integrated Products) is used. In addition, a discharge resistor 4 is connected in parallel to the memory 2 in order to discharge the power.

  If the memory 2 is arranged in parallel with the temperature sensor 1, the measured value is affected by the current consumed by the memory 2, and as a result, highly accurate measurement cannot be performed. Therefore, in the present invention, the diode 3 is arranged in series with the memory 2 as described above, and current flows through the memory 2 only at the time of reading RT information, and the current flows through the memory 2 at the time of temperature measurement. Is prevented from flowing.

  The measuring instrument main body B to which the measuring unit A is connected includes a temperature measuring unit that operates during temperature measurement and an RT information reading unit that operates when reading out RT information from the memory 2.

  The temperature measurement unit stabilizes the measurement by applying a pair of FETs 5 and 6 that control the direction of the voltage applied to the temperature sensor 1 and a highly stabilized reference voltage that is a reference for temperature measurement to the temperature sensor 1 during temperature measurement. A power source 7, a temperature sensor 1 and a voltage dividing circuit are formed, and a reference resistor 8 connected in series to the temperature sensor 1 in order to convert a resistance variation into a voltage variation, and an AD that performs AD conversion of a measurement value in the temperature sensor 1 A converter 9 is included. The FET 5 is turned on when RT information is read from the memory 2 to form a pseudo GND, and turned off when the temperature is measured. Further, the FET 6 is turned on at the time of temperature measurement to form a pseudo GND, and turned off at the time of reading RT information from the memory 2.

  The RT information reading unit is an analog switch that is used when reading RT information, and an analog switch that is turned on when RT information is read from the memory 2 and connects the load of the memory 2 and the AD converter 15. 11, a read stabilized power supply 12 that supplies a read voltage to the memory 2 when the analog switch 11 is turned on when the RT information is read, and a resistor 13 that serves as a load resistance of the memory 2.

  The AD converter 15 is built in the CPU 14 connected to the measuring instrument main body B. The CPU 14 includes calculation means for calculating the measured temperature from the AD converted measurement value and the RT information of the temperature sensor 1 read from the memory 2, and input / output for outputting an L signal to the memory 2. A port 16 is provided.

  When a temperature measuring instrument incorporating a plurality of temperature sensors 1 is used, the measuring unit A and the measuring instrument main body B are required for the channels, and are connected to a common CPU 14 respectively.

In the above configuration, at the time of temperature measurement, the FET 5 is turned off, the FET 6 is turned on, and the analog switch 11 is turned off to disconnect the input / output port 16 of the CPU 14. At that time, to form a pseudo GND becomes FET6 is the ON, by FET5 is OFF, the high stabilizing the reference voltage V _R is the temperature sensor 1 becomes the reference temperature measurements from the measuring power stabilizing 7 To be applied.

  A reference resistor 8 for forming a voltage dividing circuit is connected in series to the temperature sensor 1, and the change in resistance of the temperature sensor 1 that changes with the change in ambient temperature is changed to the change in voltage. The voltage fluctuation is AD-converted by the AD converter 9 and then sent to the calculation means of the CPU 14 where it is converted into temperature based on the RT information read from the memory 2 at the start-up, and is appropriately displayed. Is displayed. At this time, since no current flows through the memory 2 due to the action of the diode 3, the memory 2 does not consume the current and does not affect the measurement value, thereby ensuring high-precision measurement.

  On the other hand, when the RT information is read from the memory 2, the analog switch 11 is turned on to connect the load of the memory 2 and the AD converter 15, which is a power source for reading data from the memory 2. A voltage is applied to the memory 2 by the stabilized power supply 12 via the load resistor 13.

  Since the memory 2 is connected to the temperature sensor 1 in parallel, the output level of the signal from the memory 2 is small and changes greatly depending on the resistance value of the temperature sensor 1, so that it is difficult to read out at a normal logic level. is there. Therefore, in the present invention, the AD converter 15 uses the intermediate level between the H output level and the L output level of the signal from the memory 2 as the threshold level to read the stored information.

  That is, the measurement stabilization power supply 7 is turned off, the FET 5 is turned on, the FET 6 is turned off, and the analog switch 11 is turned on to disconnect the input / output port 16 of the CPU 14 and the memory 2 is loaded with the resistor 13. The H output level of the memory 2 is recorded using the AD converter 15. Next, after output from the input / output port 16 of the CPU 14 at the L level and resetting the memory 2, the input / output port 16 of the CPU 14 is disconnected and the L output level of the memory 2 is recorded using the AD converter 15. An intermediate point between the H output level and the L output level thus measured is set as the threshold level of the output signal of the memory 2.

  The RT information in the memory 2 is read from the input / output port 16 of the CPU 14 at the L level, then the input / output port 16 is disconnected, the signal level after a predetermined time is checked by the AD converter 15, and the Determine the L level. Then, after confirming that the output of the memory 2 becomes H level and outputting the next bit from the input / output port 16 of the CPU 14 at the L level, the input / output port 16 is disconnected and the AD converter 15 is disconnected. The determination of the H level and the L level is performed. Thereafter, by repeating the above operation, RT information recorded in the memory 2 is read.

  As the information is read from the memory 2, current flows through the temperature sensor 1 and self-heating occurs. Therefore, reading the information from the memory 2 is true only when the measuring device is started up or when the temperature sensor 1 is replaced. Do this only when necessary.

1 Temperature Sensor 2 Memory 3 Diode 4 Discharge Resistance 5 FET
6 FET
7 Stabilized power supply for measurement 8 Reference resistance 9 AD converter 11 Analog switch 12 Stabilized power supply for reading 13 Load resistance 14 CPU
15 AD converter 16 I / O port

Claims (5)

It consists of a measuring instrument body and a measuring unit connected to it,
The measurement unit includes a temperature sensor whose resistance value varies with temperature, and an RT that relates to the correspondence between the resistance value of the temperature sensor and the temperature connected in parallel via a diode between two lead wires of the temperature sensor. And a memory for storing information,
A temperature measuring device characterized in that a current flows through the memory only when the RT information is read, and no current flows during temperature measurement.   The measuring instrument main body includes a temperature measuring unit that operates at the time of temperature measurement, and an RT information reading unit that operates at the time of reading out the RT information from the memory. The temperature measuring unit is connected to the temperature sensor. A pair of FETs that control the direction of the voltage, a measurement stabilization power source that applies a high stabilization reference voltage that is a reference for temperature measurement to the temperature sensor at the time of temperature measurement, and the temperature sensor and a voltage dividing circuit The temperature measuring device according to claim 1, comprising a reference resistor connected in series to the temperature sensor to form and an AD converter that performs AD conversion of a measured value by the temperature sensor.   The RT information reading unit is an AD converter for reading RT information built in the CPU, and is turned on when RT information is read from the memory, and the memory load and the RT information reading are read out. An analog switch for connecting the analog-to-digital converter, a stabilized power supply for reading that applies a read voltage to the memory when the RT information is read, and a load resistance of the memory connected in series to the memory The temperature measuring instrument according to claim 2, comprising a resistor.   The measurement power supply is turned off, the pair of FETs are turned on and off, the analog switch is turned on, the CPU input / output port is disconnected, and a load of resistance is applied to the memory. The H output level of the memory is recorded using an AD converter for reading RT information, and then output at the L level from the input / output port of the CPU to reset the memory, and then the input / output of the CPU Disconnect the port, record the L output level of the memory using the AD converter for reading RT information, and set the intermediate point between the H output level and the L output level as the threshold level of the output signal of the memory The temperature measuring instrument according to claim 3.   Reading out the RT information of the memory is performed by outputting the signal level at an L level from the input / output port of the CPU, then disconnecting the input / output port, and converting the signal level after a predetermined time into an AD converter for reading the RT information. To check the H level and L level, confirm that the output of the memory has become H level, and output the L level from the input / output port of the CPU to read the next bit. The temperature measuring device according to claim 4, wherein the temperature measuring device is performed by repeating the operation of separating the entry output port and performing the determination of the H level and the L level by the AD converter for reading RT information.

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