JPS61209331A - Input apparatus of temperature measuring resistor - Google Patents

Abstract

PURPOSE:To attain to reduce the number of parts, by inputting the differential voltage of a plurality of bridge circuits having temp. measuring resistors connected thereto and that of non-equilibrium bridge circuits and using an amplifying means and a correction means for performing linear correction and temp. correction in common. CONSTITUTION:Resistors 21, 31, 41, resistors 22, 32, 42 and resistors 26, 36, 46 are respectively connected to temp. measuring resistors 1, 2, 6 to form first, second and sixth bridge circuits and these bridge circuits come to non- equilibrium by the change in temp. to output differential voltages. Resistors 27, 37, 47 and resistors 28, 38, 48 are connected to resistors 7, 8 to form seventh and eighth non-equilibrium bridge circuits and constant differential voltages are always outputted from said bridge circuits. These differential voltages are inputted to a digital correction device 64 through an analogue multiplexer 61, a differential amplifier 62 and A/D converter 63 to perform linear correction, temp. span correction and offset and temp. drift correction. By this method even if measuring points increase, the number of parts can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a resistance temperature detector input device, and more specifically, a temperature detector equipped with a resistance temperature detector that utilizes the fact that the resistance value changes due to temperature changes. The present invention relates to a resistor input device.

[Conventional technology]

FIG. 2 is an overall configuration diagram showing an example of a conventional resistance temperature detector input device, and FIG. 3 shows the circuit configuration of the input circuit in the conventional resistance temperature detector input device shown in FIG. FIG. In FIG. 2, three-wire resistance temperature detectors (hereinafter simply referred to as "resistance temperature detectors") 1, 2.6 are made of Pt.
It is a resistor with a resistance value of 100Ω. These resistance temperature detectors 1, 2.6 are connected to converters 11, 12, respectively.
It is connected to the input side of ゜16. Said converter 11°1
2.16 converts the resistance values of the temperature measuring resistors 1, 2, and 6 that have changed due to temperature changes into a standard voltage of about 1 to 5 V, and outputs the voltage signal. The analog input card 9 converts the standard voltage signal output from the converters 11, 12, 16 into a digital signal and outputs the digital signal. The internal structure of the converters 11, 12 and 16 is as shown in FIG.

FIG. 3 shows the details of the relationship between the resistance temperature detector 1 and the converter 11, and the relationships between the resistance temperature detector 2 and the converter 12, and the relationship between the resistance temperature detector 6 and the converter 16 are also similar. be. In FIG. 3, the resistance temperature detector 1 and a resistor 21, a resistor 31, and a resistor 41 constitute a bridge circuit. The differential voltage when the bridge is unbalanced is extracted and output.

The input filter 51 removes an AC induced component at approximately 2 K11z -3d B from the signal output from the bridge circuit and outputs the signal. The input terminal of the preamplifier 52 is connected to the output terminal of the input filter 51, and amplifies and outputs the signal output from the input filter 51. The linearizer 53 is connected to the feedback loop of the preamplifier 52, and linearizes the differential voltage caused by the change in resistance of the resistance temperature sensor 1, which exhibits nonlinearity with respect to the temperature change amplified by the preamplifier 51. ~Output as a 5v signal. The isolator 54 insulates between the input and the output to reduce the influence of wraparound in a humid environment, and also receives the 1-5V signal and outputs it to the analog input card 9.

For example, when measuring from 0°C to 100°C using the conventional resistance temperature detector input device configured as described above, the measurement temperature range from 0°C to 100°C is set using a volume control (not shown) in the preamplifier 52. adjust. The resistance value of each resistance temperature detector 1, 2.6 varies depending on the temperature to be measured between 0°C and 100°C. Then, as mentioned above, the balance of the bridge in the bridge circuit constituted by the measuring resistor 1°2.6 and the resistances in the converters 11 and 12.16, respectively, is lost, and the difference voltage is reflected in the converter 11. ,1
2.16 to the analog input card 9. Then, the analog input card 9 performs A/D conversion.

Note that the above-mentioned isolator 54 is not necessary in an environment with little moisture or the like.

[Problem that the invention seeks to solve]

By the way, in the conventional resistance temperature detector input device configured as described above, a converter is connected to each resistance temperature detector, so the number of measurement points increases and the arrangement of the resistance temperature detectors becomes difficult. As the number of converters increases, the number of converters must also increase, resulting in an increase in the number of parts and higher costs.

This invention was made to solve the above-mentioned problems, and provides a resistance temperature detector input device that does not require an increase in the number of parts even if the number of measurement points increases, and can reduce costs. The purpose is to obtain.

[Means for solving problems]

The resistance temperature detector input device according to the present invention includes a first plurality of bridge circuits to which the resistance temperature detectors are connected, and a second plurality of bridge circuits whose resistance values are selected in advance so as to be unbalanced. input selection means for selectively taking in differential voltage signals output from the first and second groups of bridge circuits according to input control signal numbers; and digitizing the differential voltage signals amplified by the amplification means. and a correction means for linearly correcting the signal and performing temperature span correction.

[For production]

The resistance temperature detector input device according to the present invention receives a differential voltage output from a plurality of bridge circuits to which resistance temperature detectors are connected;
By selectively inputting the differential voltage output from the bridge circuit whose resistance value is pre-selected to be unbalanced to the input selection means, the amplification means, linear correction, and correction means for temperature correction can be shared. This becomes a pivot and contributes to cost reduction by reducing the number of parts. In addition, by using the differential voltage from the bridge circuit whose resistance value is selected in advance to be unbalanced as the correction voltage, it is possible to extremely minimize the effects of offset and temperature drift, and the adjustment of the input device is made easier. Unnecessary 0 [Example] An example of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a resistance temperature detector input device according to an embodiment of the present invention. In FIG. 1, resistance temperature detector 1,
2 and 6 are made of Pt and have a resistance value of 100.
It is a resistor of Ω. The resistance temperature detector 1 is a resistance 2 of IOKΩ.
The resistor 41 of 1.31 and 1000 constitutes a first bridge circuit.

The resistance temperature detector 2 has a resistance of IOKΩ of 22.32 and 1000
A second bridge circuit is constituted by the resistor 42. Similarly, the resistance temperature detector 6 has resistances of IOKΩ of 26°36 and 10
A sixth bridge circuit is configured with a 0Ω resistor 46. An element with a resistance value of 1100 is used for the resistor 7, and a resistor 27°37 of Ω and a resistor 47 of 100 Ω are used for the resistor 10.
and constitute an unbalanced seventh bridge circuit. Similarly, an element with a resistance value of 900 is used for the resistor 8, and an unbalanced eighth bridge circuit is formed by the resistor 28.38 of 10Ω and the resistor 48 of 1000Ω. The first to sixth bridge circuits to which the above-mentioned resistance temperature detectors 1 to 6 are connected are arranged such that the resistance temperature detectors 1 to 6 are connected to each other due to temperature changes.
By varying the resistance value of the bridge circuits, the bridge circuits become unbalanced and a differential voltage is output from each bridge circuit. Moreover, the above-mentioned unbalanced first . A constant differential voltage is always output from each of the second bridge circuits.

The input selection means, that is, the analog multiplexer 61 selectively takes in and outputs the differential voltage signals output from the respective bridge circuits based on the input control signal output from the control section 66 via the input control terminal. The amplifying means, that is, the differential amplifier 62 receives each differential voltage signal outputted in time series from the analog multiplexer 61, amplifies it, and outputs it. The A/D converter 63 is driven by a drive command signal output from the control section 66, and the differential amplifier 6
The signal output from 2 is converted into a digital signal and output. For example, an electronic circuit control device such as a microprocessor is used for the digital corrector 64, and the resistance values of the temperature sensing resistors 1 to 6, which have a nonlinear relationship with temperature changes, are varied to adjust the resistance values of the first to sixth temperature sensing resistors 1 to 6. The differential voltage signal generated in the bridge circuit and digitized is linearly corrected. At the same time, the digital corrector 64 has an unbalanced seventh,
Based on the differential voltage signals output from the eighth bridge circuits and digitized, the voltages are output from the first to sixth bridge circuits by fluctuations in the power supply voltage, the differential amplifier 62, the A/D converter 63, etc. It also corrects offsets, temperature drifts, etc. that occur in differential voltage signals. For example, a microcomputer CPU is used as the control unit 66, and the analog multiplexer 61, A/
Drive command signals are output to the D converter 63, digital corrector 64, and input/output interface 65, respectively.

The span (storage unit) 67 stores measurement temperature range data for each point of the resistance temperature detectors 1 to 6, and outputs the data to the digital corrector 64.

In the resistance temperature detector input device lζ configured as described above, when the respective resistance values of the resistance temperature detectors 1 to 6 change due to temperature changes, the first to sixth bridge circuits become unbalanced, respectively. Therefore, a differential voltage is generated. For example, if we look at the first bridge circuit, the value of the resistor 21.31 is IOKΩ, the value of the resistance temperature detector 1 is around 100Ω, and the resistor 41 is 100Ω, so the resistor 21.31
Since the value of is sufficiently larger, this value is generated as a value proportional to the difference between these resistance values. The differential voltage is input to a differential amplifier 62 via an analog multiplexer 61, amplified by the differential amplifier 62, and then sent to an A/D converter 63.
It is converted into a digital signal at The digital signal is then linearly corrected in a digital corrector 64.
Temperature span correction (ie, correction of the measured temperature range), offset, and temperature drift correction are performed.

Details of the linear correction, temperature span correction and offset, and temperature drift correction performed in the digital corrector 64 described above are as follows.

(1) First, offset and temperature drift correction using the differential voltages output from the unbalanced seventh and eighth bridge circuits having resistors 7 and 8 will be explained. Since the power supply voltage (15V) fluctuates depending on the temperature to be measured and individual differences between the resistance temperature detectors 1 to 6, the resistance temperature detectors 1 to 6
The differential voltages output from the first to sixth bridge circuits each having a variable voltage vary, and as a result, the gain and offset of the differential amplifier 62 also vary.

The true value of the temperature sensing resistor 1, 2.6 is R8, 几2゜R8
, the true values of the resistors 7 and 8 are R,, R, and the first to sixth
bridge circuit, the seventh bridge circuit is set to be unbalanced in advance. The differential voltage output from the eighth bridge circuit is selectively taken in by the analog multiplexer 61, amplified by the differential amplifier 62, and the values converted by the A/D converter 63 are dI + d2.
*d@,d? *d8, the following relational expression holds true.

R, = to d, +a, , R2= to, d2+8
2゜t6 ”Wk6 d, +a, ,
R,=to,d,+a,.

R,=to dg +a@ where resistance 21, 31, 41, 22, 32, 42, 26
゜36.46, 27, 37, 47.28, 38.48
If we use a device with sufficiently high accuracy of element values,
Since the differential amplifier 62 and the A/D converter 63 are shared, it can be considered that the following relationships hold: . Therefore, the following relational expression holds true.

7. Since R1 is known, even if the values of d, , d, , d change due to temperature drift, etc., d〒.

By measuring d at the same time, the true values R1, R,, R, of the resistance temperature sensor can be calculated using the above-mentioned relational expression.

From the above relational expression, the offset and temperature drift correction performed by the digital corrector 64 can be expressed by the following general expression.

几: True resistance value of the resistance temperature detector d: Digital value after A/D conversion In the above-mentioned offset and temperature drift correction, if a highly accurate resistor is used in the bridge circuit along with the resistance temperature detector, the power supply voltage can be reduced. , differential amplifier 62 A/D converter 6
It is possible to reduce the influence of the offset and temperature drift described in No. 3, and eliminate adjustment points.

(2) Next, linear correction and temperature span correction will be explained. Since the relationship between the variable resistance value of the resistance temperature detector and the change in the surrounding temperature is non-linear, it is necessary to correct it. Also, since the digital value that you want to convert differs depending on the measurement temperature range (for example, resistance temperature detector 1 is for measuring 0 to 100°C, resistance temperature detector 2 is for measuring -100°C to +100°C, and you want to convert the digital value to 800 to 4000. ) Span correction must also be performed.

The above-mentioned linear correction is shown by the following equation 0, and the correction of the measurement temperature range is shown by the equation 0 below.

T=f(R)...Linearization (correction of nonlinearity)...■ T: Ambient temperature of the resistance thermometer...■ TTB: Temperature to be measured (Span storage unit 671 has this information...Setting by switch is also possible) Dm, DB: Digital values corresponding to Tm, TB [Effect of the invention] As described above, this According to the invention, the first plurality of bridge circuits to which the resistance temperature detectors are connected, the second plurality of bridge circuits whose resistance values are selected in advance so as to be unbalanced, and the first plurality of bridge circuits connected to the resistance temperature detectors by an input control signal. input selection means for selectively taking in the differential voltage signals output from the second plurality of bridge circuits; and digitizing the differential voltage signals amplified by the amplifying means, linearly correcting the digitized signals, and converting the temperature span. Since the present invention includes a correction means for performing correction, even if the number of measurement points increases, the number of parts does not increase accordingly, and it is possible to obtain a resistance temperature detector input device that can reduce costs. .

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a resistance temperature detector input device according to an embodiment of the present invention, FIG. 2 is an overall configuration diagram showing an example of a conventional resistance temperature detector input device, and FIG. FIG. 2 is a diagram showing a circuit configuration of an input circuit in FIG. In the figure, 1, 2.6 are resistance temperature sensors, 21, 31° 22
．． 32, 26, 36, 27, 37, 28, 38 are resistors of the same value, 41, 42, 46.47 are resistors of the same value, 47.48 are resistors of different values, 61 is an analog multiplexer, 62 is a resistor of a different value. Differential amplifier, 63 is A/D converter, 6
4 is a digital corrector, 65 is an interface section with other parts, 66 is a control section, 67 is a span having a measurement temperature range,
11, 12. 16 is a converter that converts the resistance value of the resistance temperature sensor into a standard voltage of 1 to 5, etc., 9 is an analog input device that converts the standardized voltage into a digital value, and 51 is for removing noise. 52 is a preamplifier, 53 is a linearizer, and 54 is an isolator. In the figures, the same reference numerals indicate the same.

Claims (1)

[Claims] A first plurality of bridge circuits to which a resistance temperature detector is connected and which become unbalanced due to a change in resistance value due to a change in temperature of the resistance temperature detector and generate a differential voltage; are selected and selectively take in the differential voltage signals output from the second plurality of bridge circuits, each of which generates a different voltage difference, and the first and second plurality of bridge circuits according to the input control signal. input selection means; amplification means for amplifying and outputting the differential voltage signal outputted from the input selection means; converting the signal amplified by the amplification means into a digital signal and transmitting the signal to the temperature measuring resistor; What is claimed is: 1. A resistance temperature detector input device comprising correction means for performing linear correction according to the variable resistance value of the body and temperature span correction.