JPS58122436A - Automatic temperature measuring device with high accuracy using electronic computer - Google Patents

Abstract

PURPOSE:To measure the temp. of an object to be measured accurately by supplying the positive current and reverse current by a constant current source to a circuit for temp. measurement to offset components corresponding to thermoelectromotive force and correcting and operating the reading errors, full- scale errors, etc. of a voltmeter by a computer. CONSTITUTION:Electric currents of +1mA and -1mA are supplied to a circuit 8 for temp. measurement consisting of a standard platinum temp. measuring resistor 5, the 1st standard resistor 6 and the 2nd standard resistor 7 from a constant current source 4, and the values thereof are added to offset components corresponding to thermoelectromotive force. The reading errors, full- scale errors, etc. of a digital voltmeter are corrected by incorporating mathematical expressions to utilize a computer. Then, the errors to be produced result in quantization errors and the errors within the range of the accuracy of the standard platinum temp. measuring resistor and the accuracy of the standard resistors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic temperature measuring device using a standard platinum resistance temperature detector. Conventionally, in this type of device, temperature has been measured using various industrial meters. , due to the accuracy of the instrument itself,
Even if one attempts to measure the absolute temperature of a temperature-measuring object with a high precision of 1/100° C. or higher, it is impossible.

In other words, when trying to measure temperature with high accuracy,
Although a bridge measuring circuit such as a Wheatstone bridge or a Mueller bridge can be used, it is very difficult to automate the side temperature measurement due to the nature of the pudding 7 in such a device.

Therefore, it is already known to use digital voltmeters for automation, but these voltmeters have various measurement error elements called reading errors, full-scale errors, and quantization errors due to rounding down and rounding up. Even with the highest precision existing model, the reading error is 10.0034% and the full scale error is 2.3 μV.
(0, IV range), quantization error is 0,1μV (01
v Renn) occurs.

Therefore, if the temperature is measured using the conventional device using the standard platinum side temperature resistance element using the digital voltmeter described above, the accuracy of the standard platinum side temperature resistance element (standard pt) is ±0. 001°C, and the sensitivity of the standard pt is approximately 1
It may be about 00mΩ/deg or 1 with a measurement current of 1mA.
00μV/deg, and the resistance of standard PT at 0℃ is about 25.5Ω, so the measurement error with a digital voltmeter is 25.5 (Ω) for full scale Nira.
X 1 (mA)X±0.0034(%)=±0.86
7μV, and the reading scale error and quantization error are ±2.3μV and ±0.1μV, respectively, as mentioned above, so the error meter is ±3.267μV, and therefore its accuracy is ±3.267/100, or ±0. .03267d9
g, and the error due to digital pressure and i1 alone is 3
/100~4/100u, and in addition, this type of temperature measuring device has error factors based on the drift of the constant current source, deviation from the absolute value, and thermoelectromotive force generated within the measurement system. These errors are usually larger than the errors caused by the digital voltmeter.

The present invention aims to correct the above-mentioned unnecessary errors in conventional temperature measurement devices as much as possible to enable highly accurate automatic temperature measurement of ±0.00'7℃. This will be explained in detail by way of examples.

In the figure (11 indicates an electronic computer such as a microcomputer, and a digital voltmeter (21) and a scanner (3) are connected to the computer fil by a measurement line L1 sequentially shown as a solid line). Intuitively, I connected the standard platinum temperature resistor (5) to the first constant current source (4), and the first standard resistor (6).
), a second standard resistor (7) connected in series, and a temperature measuring circuit (8) formed by connecting the above-mentioned standard platinum temperature measuring resistor (5), the first standard resistor (7) in series, and the scanner (3) (6) is connected to both terminals of the second standard resistor (7), and the electronic computer 11) is connected to the control line L shown by the broken line in the figure.
2 is connected to the digital voltmeter (2), scanner (3), constant current source (4), and as is known, the standard platinum temperature resistance element (5), the first standard resistance (
6) The second standard resistor (7) is immersed in the object A to be measured.

Therefore, when temperature measurement is performed using the above-mentioned temperature measuring device, first, 1 mA flows in one direction through the temperature measuring circuit (8) by the constant current source (4), and at the time of the positive current, the standard platinum resistance thermometer (
5) The terminal voltages of the first standard resistor (6) and the second standard resistor (7) are measured by the digital voltmeter (2) during scanning by the scanner (3), and the absolute value of the measured voltage is Vφ10, vl+, and V2+ are respectively electronic computer 11.1
, and then a reverse current (-1 mA) in the opposite direction to the positive current is passed through the temperature measuring circuit (8),
As a result, the terminal voltage of each resistor (5), f6), +71 is measured, and the absolute value of the measured voltage is Vφ-, V
, , V2- is introduced into the electronic computer (,11) in the same manner as before.

Then, the electronic computer+11 that has obtained the above measurement information performs the following calculations.In other words, as mentioned above, errors in the measurement system include (a) reading error of the digital voltmeter, and (b) digital voltage. Quantization error of digital voltmeter) Error of constant current source (e) Error due to thermal electromotive force of measurement system (c) Accuracy of standard platinum side temperature resistor (g) Accuracy of standard resistance However, in the above errors, regarding the quantization error in H, the accuracy of the standard platinum side temperature resistor in (c), and the standard resistance product in (g), this cannot be avoided. It corrects the errors in (b) middle), (c), and (e).

Therefore, by calculation by the electronic computer (1), 1
f ”tfi + 10 V$ −/2 = Vφ', V
1++Vl/2=V1', v2++v2-/2-■
By performing the 2'-null average value calculation, the error caused by the thermoelectromotive force in the measurement system (c) can be eliminated by counterattack.

Here, Vφ', vk', and 2' obtained by the above calculation can be expressed by the following equations.

■φ'= ρφVφ1ηφ・・・・・・fi1 formula Vl'
= ρI Vl +11"" (2) Formula V2' =
7) 2 V2 +12 ”” f31 In the above equation, if the scanning by scanner (3) is short, then ρ
It can be regarded as φ=ρ1−ρ2=ρ, ηφ2ηl=η2=η, where ρ=1−(gl 4 E2 ), E□ indicates the reading error of the digital voltmeter, and E2 indicates the error of the constant current source. Also, η=E3, where E3 indicates the full scale error of the digital voltmeter.

In the above formulas (1) to (3), v', ■1', ■2'
Since φ has been introduced as described above, and V2 is a known value, ρ and η can be found by solving the simultaneous equations using this equation, and thus El, E2, and E
Since the electronic computer il+ can calculate the error of 3, Vφ', which cancels out the thermoelectromotive force of the measurement system, ■1', ■
2', it is possible to obtain measurement results in which the errors of E□, E2, and E3 are further corrected.

As embodied by the above-mentioned embodiment, the present invention connects an electronic computer such as a microcomputer, a digital voltmeter, a scanner, and a constant current source through control lines, and connects the computer to the electronic computer through a measurement line. A voltmeter and a scanner are connected, and a standard platinum resistance temperature detector, a first standard resistor, and a second standard resistor are connected in series to the constant current source to form a temperature measuring circuit. When a positive current and a reverse current are supplied from a constant current source to
The terminal voltage of the second standard resistor is made measurable by the digital voltmeter by scanning with the scanner, and the measured information is introduced into the electronic computer, and the thermoelectromotive force in the measurement line system is generated by the divider. At the same time, the reading caller of the digital voltmeter, the full scale error, and the error of the constant voltage power supply are corrected and calculated to calculate the resistance value of the standard platinum side temperature resistance element and measure the temperature of the temperature measured object. Therefore, according to the temperature measuring device according to the present invention, not only can measurement results be automatically obtained by an electronic computer, but also the errors are due to the quantization error in (c) above and the standard white in (f). ◆It is within the range depending on the accuracy of the resistance temperature sensor and the accuracy of the standard resistance (g), and these = 0.001 deg (g) mamma±0.001 deg (g)...
・The accuracy of standard resistance is about IOPPM, so 25Ω
When using one, 25 (Ω) Xi (mA) x ± 10 (PPM) x 2 (units)
=0.5μv1, so ±0.001±0.001±0.005=
It becomes possible to measure with an accuracy of ±0.007°C.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of an automatic temperature measuring device according to the present invention. +1)...Electronic computer [21-...Digital voltmeter (3)...E-scanner (4)-...Constant voltage source (5)...Standard platinum measurement Temperature resistor (6)...First standard resistance, (7)...Second
Standard resistance (8)・e...Temperature measurement circuit Patent applicant representative Patent attorney Makoto Ito

Claims (1)

[Claims] An electronic computer such as a microcomputer, a digital voltmeter, a scanner, and a constant current source are connected through control lines, and the digital voltmeter and scanner are sequentially connected to the electronic computer through measurement lines, and... The constant current source includes a standard platinum resistance thermometer and the first
A temperature measurement circuit is formed by connecting a standard resistor and a second standard resistance in series, and when a positive current and a reverse current are supplied from a constant current source to the temperature measurement circuit, respectively, the above standard platinum side temperature resistance The terminal voltages of the main body, the first standard resistor, and the second standard resistor can be measured by a digital voltmeter by scanning with the scanner, and the measured information is introduced into the computer and an Eri measurement line system is introduced into the computer. In addition to canceling the thermal electromotive force component in A high-precision automatic temperature measurement device that uses an electronic computer to measure temperature.