Temperature Measurement System

Abstract

To provide a temperature measurement system that can detect a temperature at a measurement point with high precision using a two-terminal method and can be configured simply and inexpensively.SOLUTION: A temperature measurement system includes a thermistor 20(k) installed at a measurement point 18(k), an analyzer 22 in which a continuous function equation KS(k) is prescribed, and a wiring cable 24(k) connecting the thermistor 20(k) and the analyzer 2. The continuous function equation KS(k) is a mathematical expression of the relationship between a combined resistance value R and temperature T, by defining a value obtained by adding a resistance value Rc-a(k) to a resistance value Rt(k) in a single uniform way as the combined resistance value R, based on temperature characteristics of the resistance value Rt(k) of the thermistor 20(k) measured in an experimental thermostatic chamber 28, and the resistance value Rc-a(k) of the wiring cable as a round trip line measured in the thermostatic chamber 28 in which an internal temperature T is set to a value equal to an average temperature Ta. The analyzer 22 calculates a temperature Tx(k) at the measurement point 18(k) based on a received resistance value signal TKS(k) and the continuous function equation KS(k).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a temperature measurement system for measuring the temperature of a measurement point in an indoor space, and more particularly to a temperature measurement system using a thermistor as a temperature-sensitive element. [Background technology]

[0002] Thermistors and platinum resistance thermometers are widely used as temperature-sensing elements for temperature measurement. Thermistors, in particular, have the advantage of being able to detect small temperature changes with high sensitivity, since their resistance changes relatively more with respect to temperature changes than platinum resistance thermometers. Another attractive feature of thermistors is that they are significantly cheaper.

[0003] Conventional temperature measurement systems using thermistors include a system in which a thermistor is installed at a measurement point and the temperature at the measurement point is detected by a four-terminal method, as disclosed in, for example, Figure 6 of Patent Document 1. In the four-terminal method, a pair of lead wires 23a and 23b are connected to a constant current generator to pass a constant current, and a voltage generated across the thermistor 21 in accordance with its temperature-dependent resistance is input to a high-impedance amplifier 25 via lead wires 23c and 23d and detected. The three-terminal method has the advantage that the influence of the resistance of the lead wires 23a and 23b, which are located in series with the thermistor 21, is canceled out, and even if the lead wires 23a and 23b are somewhat long, this does not cause an error.

[0004] Furthermore, Figure 3 of Patent Document 1 describes a system in which a thermistor is installed at a measurement point and the temperature at the measurement point is detected using a simple two-terminal method. This system has a pair of lead wires 2 that supply a specified voltage and current to the thermistor 1, and is characterized in that the lead wires 2 are made of silicon carbide ceramic. Since silicon carbide ceramic is a material whose resistance value is extremely stable with temperature changes, the lead wires 2 connected in series to the thermistor 1 can simply be regarded as a fixed resistor. Therefore, the influence of the lead wires 2 can be easily and accurately eliminated, making it possible to measure temperature with high precision even using the conventional two-terminal method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-249716 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a growing demand for strict control of storage and environmental temperatures when storing and transporting pharmaceuticals, precision instruments, etc. For this reason, there has been active research into temperature measurement systems that continuously measure and manage the temperature distribution in indoor spaces such as pharmaceutical warehouses and truck compartments.

[0007] For example, in a pharmaceutical warehouse, an air conditioning system is operated to maintain a constant average temperature in the indoor space. However, structures such as racks containing pharmaceuticals are installed in the indoor space, and these structures may block the air from the air conditioning system, and each structure (or each part of the structure) has its own heat capacity, making it difficult to achieve a completely uniform temperature distribution in the indoor space. Therefore, it is important to measure the temperature at multiple measurement points in the indoor space and understand the temperature distribution.

[0008] Large pharmaceutical warehouses have very large indoor spaces, so thermistors must be placed at multiple measurement points that are far apart. Therefore, the wiring cables connecting each thermistor to an analyzer installed in a specific location (a device that analyzes the received resistance signal to determine the temperature at the measurement point) can be as long as 5 to 100 meters. Even in the case of refrigerated trucks, the wiring cables connecting thermistors installed at measurement points inside the cargo area to an analyzer installed outside the cargo area can be as long as 5 to 20 meters.

[0009] The four-terminal temperature measurement system shown in Figure 6 of Patent Document 1 can cancel the effect of the resistance value of the wiring cable (lead wires 23a, 23b), so even if the wiring cable is long, it does not pose a major problem. The same is true for three-terminal temperature measurement systems. However, four-terminal and three-terminal temperature measurement systems require a multi-core cable with three or more conductors as the wiring cable, and the analytical device has a complex configuration that combines a constant current generator and a high-impedance amplifier, making the system very expensive overall.

[0010] Furthermore, the two-terminal temperature measurement system shown in Figure 3 of Patent Document 1 can, in principle, eliminate the influence of the resistance value of the wiring cable even if the wiring cable (lead wire 2) is long. However, when considering the need to prepare multiple wiring cables with lengths of 5 to 100 m, cables made of special materials such as silicon carbide ceramics are difficult to use due to their cost and availability.

[0011] The present invention has been made in consideration of the above-mentioned background art, and aims to provide a temperature measurement system that can detect the temperature at a measurement point with high accuracy using a two-terminal method and can be configured simply and inexpensively. [Means for solving the problem]

[0012] The present invention is a temperature measurement system for measuring a temperature Tx at a measurement point in an indoor space managed so that the average temperature Ta is a constant value, a thermistor that is installed at the measurement point and whose resistance value Rx changes in response to the temperature Tx; an analyzer that defines a continuous function equation with the temperature T and the combined resistance value R as variables and calculates the temperature Tx based on a received resistance value signal and the continuous function equation; and a cable that forms a round-trip line with two conductors, that is arranged in the indoor space and connects a pair of terminals of the thermistor to a pair of receiving terminals of the analyzer, and that outputs the resistance value signal to the receiving terminals, The continuous function equation is a mathematical expression of the relationship between the combined resistance value R and the temperature T, where the combined resistance value R is defined as the resistance value Rt uniformly added to the resistance value Rc-a based on the temperature characteristics of the resistance value Rt of the thermistor measured in a bath whose internal temperature T can be varied to a known value, and the resistance value Rc-a of the distribution cable as a return line measured in a bath whose internal temperature T is set to a value equal to the average temperature Ta, The analytical device is a temperature measurement system that calculates the temperature T corresponding to the resistance value Rs by substituting the resistance value Rs recognized from the resistance value signal for the combined resistance value R, which is a variable in the continuous function equation, and sets the calculation result as the detected value of the temperature Tx.

[0013] The present invention also provides a temperature measurement system for measuring a temperature Tx at a measurement point in a predetermined indoor space, comprising: a thermistor that is installed at the measurement point and whose resistance value Rx changes in response to the temperature Tx; an analyzer that defines a continuous function equation with the temperature T and the combined resistance value R as variables and calculates the temperature Tx based on a received resistance value signal and the continuous function equation; and a cable that forms a round-trip line with two conductors, that is arranged in the indoor space and connects a pair of terminals of the thermistor to a pair of receiving terminals of the analyzer, and that outputs the resistance value signal to the receiving terminals, The continuous function formula is a mathematical expression of the relationship between the combined resistance value R and the temperature T, based on the temperature characteristics of the resistance value Rt of the thermistor measured in a bath whose internal temperature T can be varied to a known value and the temperature characteristics of the resistance value Rc of the distribution cable as a return line measured in a bath whose internal temperature T can be varied to a known value, and the combined resistance value R is defined as the sum of the resistance values ​​Rt and Rc measured at the same temperature T, The analytical device is a temperature measurement system that calculates the temperature T corresponding to the resistance value Rs by substituting the resistance value Rs recognized from the resistance value signal for the combined resistance value R, which is a variable in the continuous function equation, and sets the calculation result as the detected value of the temperature Tx.

[0014] The analysis device applies a DC voltage to the thermistor and the distribution cable, detects the current flowing through the thermistor and the distribution cable due to the application of the DC voltage and the voltage drop occurring in the thermistor and the distribution cable as the resistance value signal, and recognizes the resistance value Rs by dividing the voltage drop by the value of the current.Furthermore, the analysis device may be configured to include a plurality of pairs of thermistors and distribution cables, and the continuous function formula may be individually defined for each combination of thermistor and distribution cable. [Effects of the Invention]

[0015] The temperature measurement system of the present invention can easily and accurately determine the temperature at the measurement point even if the resistance signal received by the analytical device contains information about the resistance of the distribution cable. Furthermore, because the detection method is the two-terminal method, the system can be configured simply and inexpensively. [Brief explanation of the drawings]

[0016] [Figure 1] 1A is a front view showing the interior of a warehouse in which an embodiment of the temperature measurement system of the present invention is installed, and FIG. 1B is a cross-sectional view taken along the line AA. [Figure 2] FIG. 1 is a system configuration diagram of a temperature measurement system according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing an example of a continuous functional formula defined in the analysis device shown in FIG. 2. [Figure 4] 3 is a diagram showing another example of a continuous functional formula defined in the analysis device shown in FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the temperature measurement system of the present invention will be described below with reference to the drawings. As shown in FIGS. 1(a) and 1(b), a temperature measurement system 10 of this embodiment is installed in a warehouse 12 for storing items and is used for temperature mapping of a large indoor space 14. In the indoor space 14, n racks 16(1) to 16(n) containing various items are installed at appropriate positions. In the following description, any one of the n racks will be referred to as rack 16(k).

[0018] In this warehouse 12, one measurement point 18(k) is set for each rack 16(k), and the temperature measurement system 10 measures the temperatures Tx(k) at n measurement points 18(k). The measurement point 18(k) is, for example, the air temperature near the rack 16(k).

[0019] Next, the configuration of the temperature measurement system 10 will be described with reference to Figures 1 and 2. The temperature measurement system 10 is made up of n thermistors 20(k), one analyzer 22, and n distribution cables 24(k).

[0020] The thermistor 20(k) is installed at the measurement point 18(k) and is an element whose resistance value Rx(k) changes in response to the temperature Tx(k). The thermistor 20(k) is often housed in a housing 26a(k) and handled as a temperature measurement probe 26(k), but it can also be handled as a standalone element.

[0021] The analysis device 22 is provided with a predetermined continuous function formula KS(k), and upon receiving the resistance signal TKS(k), calculates the temperature Tx(k) based on the resistance signal TKS(k) and the continuous function formula KS(k). Details will be explained later.

[0022] The wiring cable 24(k) is a cable that forms a round-trip line with two conductors, and is arranged in the indoor space 14 to connect a pair of terminals of the thermistor 20(k) to a pair of receiving terminals 22a(k) of the analysis device 22, and outputs a resistance value signal TKS(k) to the receiving terminal 22a(k).

[0023] The internal configuration of the analyzer 22 will be explained in detail below. The analyzer 22 includes a resistance signal detector 22b, a calculator 22c, and a selector switch 22d.

[0024] Resistance value detection unit 22b applies DC voltage Vref to thermistor 20(k) and wiring cable 24(k) via changeover switch 22d, and detects current Is(k) flowing through thermistor 20(k) and wiring cable 24(k) and voltage drop Vs(k) occurring across thermistor 20(k) and wiring cable 24(k) by applying DC voltage Vref. In other words, the resistance value signal TKS(k) received by analysis device 22 here is current Is(k) and voltage drop Vs(k).

[0025] The calculation unit 22c defines continuous function expressions KS(1) to KS(n) corresponding to the measurement points 18(1) to 18(n), respectively. When the calculation unit 22c receives the resistance value signal TKS(k) for the measurement point 18(k), the calculation unit 22c calculates the temperature T corresponding to the resistance value Rs(k) by dividing the voltage drop Vs(k) by the current Is(k) and substituting this resistance value Rs(k) for the combined resistance value R, which is a variable in the continuous function expression KS(k), and outputs the calculation result as the detected value of the temperature Tx(k).

[0026] Next, the continuous function formula KS(k) will be explained. The content of the continuous function formula KS(k) is determined according to the situation of the indoor space 14 of the warehouse 12. Below, two examples (first and second situations) assumed as situations of the indoor space 14 and a method for deriving the continuous function formula KS(k) suitable for each situation will be explained in order.

[0027] First, the first situation of the indoor space 14 will be described. In the first situation, the indoor space 14 is well managed to maintain a constant average temperature Ta, and the temperature Ty(k) of the distribution cable 24(k) can be considered to be maintained at approximately the average temperature Ta when the temperature measurement system 10 is installed in the indoor space 14. For example, this situation occurs when a small number of racks 16(k) are distributed throughout the indoor space 14 and the distribution cables 24(k) are installed in wide corridors or spaces between the racks.

[0028] When the first situation is assumed, the continuous function formula K S (k) can be derived using the procedure shown in Figure 3. First, in an experimental thermostatic chamber 28 (a chamber whose internal temperature T can be varied to a known value), the temperature T is discretely changed and the change in resistance Rt(k) of thermistor 20(k) is measured. Also, in the thermostatic chamber 28 whose internal temperature T is set to a value equal to the average temperature Ta, the resistance Rc-a(k) of the return line of distribution cable 24(k) is measured.

[0029] Then, the sum of the resistance Rc-a and each resistance Rt(k) is defined as the combined resistance R, and a continuous function KS(k) that expresses the relationship between the combined resistance R and the temperature T is derived and stored in the calculation unit 22c. The continuous function KS(k) is, for example, R=f(T) or T=f -1 It can be expressed in the form (R).

[0030] When actually measuring the temperature Tx(k) at measurement point 18(k) in warehouse 12, calculation unit 22c uses the continuous function formula KS(k) corresponding to that measurement point 18(k). For example, when measuring the temperature Tx(1) at measurement point 18(1), calculation unit 22c uses the continuous function formula KS(1) corresponding to measurement point 18(1).

[0031] First, current Is(k) and voltage drop Vs(k), which are resistance signal TKS(k), are acquired from resistance detector 22b. Voltage drop Vs(k) is divided by current Is(k) to determine resistance Rs(k), which is the combined resistance Rt(k) of thermistor 20(k) and resistance Rc(k) of distribution cable 24(k). Then, the determined resistance Rs(k) is substituted for combined resistance R, which is a variable in continuous function KS(k), to calculate temperature T corresponding to resistance Rs(k). The calculation result is output as the detected temperature Tx(k). This allows temperature Tx(k) at measurement point 18(k) in the first situation to be detected with extremely high accuracy (for example, ±0.01°C).

[0032] Next, the second situation of the indoor space 14 will be described. In this situation, with the temperature measurement system 10 installed in the indoor space 14, the temperature Ty(k) of the distribution cable 24(k) is approximately equal to the temperature Tx(k) of the measurement point 18(k), and the temperature Ty(k) can be considered to change together with the temperature Tx(k). For example, this situation occurs when the temperature of the indoor space 14 is not adequately controlled and is prone to change.

[0033] When the second situation is assumed, the continuous function formula KS(k) can be derived using the procedure shown in Figure 4. First, the temperature T is changed discretely in an experimental thermostatic chamber 28, and the change in the resistance value Rt(k) of thermistor 20(k) and the change in the resistance value Rc(k) of the return line of distribution cable 24(k) are measured.

[0034] Then, the sum of the resistance values ​​Rt(k) and Rc(k) measured at the same temperature T is defined as a combined resistance value R, and a continuous function KS(k) that mathematically expresses the relationship between the combined resistance value R and the temperature T is derived and stored in the calculation unit 22c. In this case, the continuous function KS(k) can be, for example, R=f(T) or T=f -1 It can be expressed in the form (R).

[0035] When actually measuring the temperature Tx(k) at the measurement point 18(k) in the warehouse 12, the calculation unit 22c uses the continuous function formula KS(k) corresponding to the measurement point 18(k), as described above.

[0036] To explain the operation of the calculation unit 22c again, first, the current Is(k) and voltage drop Vs(k), which are the resistance signal TKS(k), are obtained from the resistance detection unit 22b. Then, the voltage drop Vs(k) is divided by the current Is(k) to determine the combined resistance Rs(k) of the thermistor 20(k) and the resistance Rc(k) of the distribution cable 24(k). The calculated resistance Rs(k) is then substituted for the combined resistance R, which is a variable in the continuous function KS(k), to calculate the temperature T corresponding to the resistance Rs(k). The calculated result is used as the detected temperature Tx(k). This allows the temperature Tx(k) at the measurement point 18(k) in the second situation to be detected with extremely high accuracy (e.g., ±0.01°C).

[0037] Note that, common to both the first and second situations, the continuous function formulas KS(1) to KS(n) are individually defined for each combination of thermistors 20(1) to 20(n) and distribution cables 24(1) to 24(n) in the analysis device 22. Because the resistance and temperature coefficients of thermistors 20(1) to 20(n) vary even among elements of the same manufacturer and model, and because the lengths of distribution cables 24(1) to 24(n) differ, the relationship between the combined resistance R and temperature T varies for each combination. Therefore, if there are n combinations of thermistors 20(k) and distribution cables 24(k), a total of n continuous function formulas KS(k) are defined. For the same reason, it is preferable to re-derive the continuous function formula KS(k) when replacing a deteriorated thermistor 18(k) or distribution cable 24(k).

[0038] As described above, the temperature measurement system 10 can easily and accurately determine the temperature Tx(k) at the measurement point 18(k) even if information about the resistance value Rc(k) of the distribution cable 24(k) is included in the resistance value signal TSK(k) received by the analysis device 22. Furthermore, because the detection method is the two-terminal method, the system can be configured simply and inexpensively.

[0039] The temperature measurement system of the present invention is not limited to the above embodiment. For example, the above temperature measurement system 10 is a system used for temperature mapping inside a warehouse 12 for storing goods, and therefore has a plurality of measurement points 18(k). However, since the use of the temperature measurement system of the present invention is not particularly limited, a single measurement point 18(k) may be sufficient. In this case, the thermistor 20(k) and the distribution cable 24(k) may be used as a single set, and the type of continuous function formula KS(k) specified for the analysis device 22 may also be one type. Furthermore, the substance used as the measurement point may be a gas (air) as in the above embodiment, or it may be a liquid or solid.

[0040] 2 shows a preferred example of the internal configuration of the analyzer 22, and can be freely modified as long as the intended operation of the present invention is possible. For example, the analyzer 22 is provided with a changeover switch 22d so that one resistance signal detector 22b can detect n resistance value signals TKS(1) to TKS(n), but when n is small, the changeover switch 22d can be eliminated and the n resistance value signal detectors 22b can individually detect the n resistance value signals TKS(1) to TKS(n).

[0041] 2, the internal configuration of the resistance value signal detection unit 22b is represented by symbols for an ammeter and a voltmeter, but this is merely a simplified diagram that clearly shows the function of the resistance value signal detection unit 22b. In reality, it is generally configured by combining a current detection circuit, a current-voltage conversion circuit, a voltage detection circuit, a digital processor, etc. Furthermore, the calculation unit 22c can also be configured within the same digital processor. [Explanation of symbols]

[0042] 10 Temperature Measurement System 14 Indoor space 18(k) measurement point 20(k) thermistor 22 Analyzer 22a(k) receiving terminal 24(k) distribution cable Is(k) current Vs(k) voltage drop KS(k) continuous function formula Rt(k) Thermistor resistance Rc(k), Rc-a(k) Resistance value of wiring cable Ta: Average temperature of the internal space Tx(k) Temperature at the measurement point TKS(k) resistance signal Rs(k) Resistance value recognized from the resistance signal

Claims

1. In a temperature measurement system that measures the temperature Tx at a measurement point in an indoor space that is managed so that the average temperature Ta is a constant value, a thermistor that is installed at the measurement point and whose resistance value Rx changes in response to the temperature Tx; an analyzer that defines a continuous function equation with the temperature T and the combined resistance value R as variables and calculates the temperature Tx based on a received resistance value signal and the continuous function equation; and a cable that forms a round-trip line with two conductors, that is arranged in the indoor space and connects a pair of terminals of the thermistor to a pair of receiving terminals of the analyzer, and that outputs the resistance value signal to the receiving terminals, The continuous function equation is a mathematical expression of the relationship between the combined resistance value R and the temperature T, where the combined resistance value R is defined as the resistance value Rt uniformly added to the resistance value Rc-a based on the temperature characteristics of the resistance value Rt of the thermistor measured in a bath whose internal temperature T can be varied to a known value, and the resistance value Rc-a of the distribution cable as a return line measured in a bath whose internal temperature T is set to a value equal to the average temperature Ta, The temperature measurement system is characterized in that the analytical device calculates the temperature T corresponding to the resistance value Rs by substituting the resistance value Rs recognized from the resistance value signal for the combined resistance value R, which is a variable in the continuous function equation, and sets the calculation result as the detection value of the temperature Tx.

2. In a temperature measurement system for measuring a temperature Tx at a measurement point in a specified indoor space, a thermistor that is installed at the measurement point and whose resistance value Rx changes in response to the temperature Tx; an analyzer that defines a continuous function equation with the temperature T and the combined resistance value R as variables and calculates the temperature Tx based on a received resistance value signal and the continuous function equation; and a cable that forms a round-trip line with two conductors, that is arranged in the indoor space and connects a pair of terminals of the thermistor to a pair of receiving terminals of the analyzer, and that outputs the resistance value signal to the receiving terminals, The continuous function equation is a mathematical expression of the relationship between the combined resistance value R and the temperature T, where the combined resistance value R is defined as the sum of the resistance values ​​Rt and Rc measured at the same temperature T, based on the temperature characteristics of the resistance value Rt of the thermistor measured in a bath whose internal temperature T can be varied to a known value, and the temperature characteristics of the resistance value Rc of the distribution cable as a return line measured in a bath whose internal temperature T can be varied to a known value, The temperature measurement system is characterized in that the analytical device calculates the temperature T corresponding to the resistance value Rs by substituting the resistance value Rs recognized from the resistance value signal for the combined resistance value R, which is a variable in the continuous function equation, and sets the calculation result as the detection value of the temperature Tx.

3. 3. The temperature measurement system according to claim 1, wherein the analysis device applies a DC voltage to the thermistor and the wiring cable, detects the current flowing through the thermistor and the wiring cable and the voltage drop occurring in the thermistor and the wiring cable as the resistance value signal, and recognizes the resistance value Rs by dividing the voltage drop by the value of the current.

4. 3. The temperature measurement system according to claim 1, further comprising a plurality of pairs of thermistors and wiring cables, wherein the continuous function formula is individually defined for each combination of thermistor and wiring cable in the analysis device.

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