JPH04135026U - Analog to digital converter - Google Patents

Abstract

(57) [Summary] [Purpose] Eliminate initial errors and errors due to temperature changes,
To realize an inexpensive AD conversion device. [Structure] The CPU 1 detects the ambient temperature using the temperature sensor 6, and converts it into a digital signal using the #0 AD conversion circuit 3. The CPU 1 determines which section of the reference temperatures stored in advance in the ROM 4 the ambient temperature corresponds to, and when it receives a digital value from any of the AD conversion circuits 2 from #1 to #n, it converts the digital value into Errors due to temperature changes are corrected using a reference conversion value that corresponds to the output AD conversion circuit 2 and corresponds to the reference temperature. The CPU 1 calculates a true converted value by correcting the initial error using the reference converted value in which the error due to temperature change has been corrected.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This idea converts analog signals into digital signals in control devices and data input/output devices. Analog-to-digital conversion device applied to the data input/output section that converts into a code and reads it. Regarding.

0002

[Conventional technology]

As shown in FIG. 3, the conventional analog-digital converter has a CPU 1 and this C Multiple (#1 to #n) analog-to-digital conversion circuits (hereinafter referred to as (abbreviated as the lower AD conversion circuit) 2. Each analog/digital conversion circuit 2 converts the input analog signal into a digital signal and outputs it.

0003 The AD conversion circuit 2 is generally configured as shown in FIG. Figure 4 shows 4-2 An analog/digital conversion circuit that converts a 0mA analog signal into a digital signal. This is an example. 4-20mA analog input from input terminal 10 The signal is converted to 1 to 5 V by a 250Ω reference resistor 20 and sent to an instrumentation amplifier 11. is input. The output voltage of this instrumentation amplifier 11 is determined by the gain adjusting variable resistor 25 and The voltage is adjusted within a predetermined range by the offset adjustment variable resistor 26, The voltage/frequency converter 12 converts the voltage into a pulse train with a frequency corresponding to the voltage value. This pulse train is electrically isolated by a photocoupler 13 and counted by a counter 14. and output to the address/data bus 15 as a digital signal.

0004 The elements that realize the analog-to-digital conversion circuit 2 described above are all sensitive to temperature changes. Its value or output value changes. Operating temperature of the above analog-digital conversion circuit 2 In order to minimize the error caused by this temperature change, it is conventional to Elements with minimal temperature changes, ie, low temperature coefficients, were used. especially, Instrumentation amplifier 1 is an element and device whose error due to temperature change directly affects the converted value. 1. Voltage/frequency converter 12, reference resistor 20, variable resistors 25, 26, and Integrating capacitor 27 and resistors 21 and 22 have very low temperature coefficients. Was.

[0005] In addition, regarding the initial error, please check the input terminal 1 before using the analog-to-digital converter. Input a reference signal from 0 and use a variable resistor for gain adjustment to ensure correct conversion. The problem was solved by adjusting the offset adjustment resistor 25 and the offset adjustment resistor 26.

[0006]

[Problem that the idea aims to solve]

However, the conventional method described above has the problem that the cost of realizing a highly reliable analog-to-digital conversion circuit is high because the cost of an element with a low temperature coefficient is extremely high. For example, taking a resistor as an example, a resistor with a temperature coefficient of 5 ppm/°C, that is, a resistance that changes by 5 × 10 ^-6 % with a temperature increase of 1°C, is usually more than 100 times as large as a resistor with a temperature coefficient of 200 ppm/°C. The price will be. Furthermore, even when looking at the entire circuit, if there is even one element with a high temperature coefficient, the error will become large even if other elements with low temperature coefficients are applied. Therefore, in order to ensure reliability, it is necessary to use elements with low temperature coefficients for all elements. Conventionally, the solution of applying low temperature coefficients to all elements is a method of minimizing errors due to temperature changes, but cannot eliminate temperature errors.

[0007] In addition, when operating the analog-to-digital conversion circuit, initial errors are removed. Adjust the variable resistor 25 for gain adjustment and the variable resistor 26 for offset adjustment to This will require time for adjustment.

[0008] This idea was made in view of the above circumstances, and uses elements that are unrelated to the temperature coefficient. can reduce costs and eliminate the need for adjustment to remove initial errors. The purpose is to provide an analog-to-digital conversion device.

[0009]

[Means to solve the problem]

The analog-to-digital conversion device according to this invention is controlled by a CPU. one or more analog-to-digital conversion circuits and analog-to-digital conversion devices Analog-to-digital conversion that measures the ambient temperature and converts this temperature into a digital value. circuit, and the above ambient temperature measurement and analog-to-digital conversion circuit. Reference temperature for the temperature specified, and each analog/digital conversion at that reference temperature A storage means for storing the reference conversion value output from the circuit, and a From the standard conversion value to the initial error of the analog-to-digital conversion circuit and temperature change during conversion. The present invention is characterized by comprising means for automatically correcting errors caused by the above.

0010

[Effect]

The data stored in the storage means in the analog-to-digital conversion device is corresponds to the temperature converted by the path and each AD conversion circuit at that reference temperature. This is the standard conversion value. Here, the reference conversion value is the reference input whose value is known accurately. It is a converted value of I can do the right thing. That is, the reference values are selected as 1V and 5V, and the reference converted values are aV and bV. Then, the correction for xV, that is, the calculation of the correct conversion value VANS, is VANS =5-1/(ba-a)×(x-a)+1 =4(x-a)/(ba-a)+1...(1) It can be done with Note that this conversion formula uses the same surroundings as when storing the standard conversion value. This is applied in the case of temperature conditions, and is a correction of the initial error of the circuit.

[0011] At different temperatures, reference conversion is performed to eliminate errors due to temperature changes that occur. It is necessary to correct the value itself. The standard conversion value at the standard temperature T1 is (a1, b1 ), and the reference conversion value at the reference temperature T2 is (a2, b2), then the temperature Tx(T The standard conversion values (ax, bx) at 1 < Tx < T2 are ax=(a2-a1)(Tx-T1)/(T2-T1)+a1...(2) bx=(b2-b1)(Tx-T1)/(T2-T1)+b1...(3) It is determined by

0012 Finally, the conversion value at temperature Tx is the standard conversion obtained by equations (2) and (3). Substitute the values (ax, bx) into the standard conversion values (a, b) of equation (1), and calculate the initial error and temperature. Obtain a digital conversion value in which errors due to degree changes are corrected.

[0013]

【Example】

An embodiment of this invention will be described below with reference to the drawings.

[0014] FIG. 1 is a block diagram showing the configuration of the analog-to-digital converter of this invention. . As shown in the figure, the CPU 1 includes a plurality of AD conversion circuits (analog converters) #1 to #n. ・Digital conversion circuit) 2, #0 AD conversion circuit 3, and as a reference value storage means A programmable ROM 4 is connected via a bus line 5. #1 to #n above The AD conversion circuit 2 converts the analog signal sent from the previous circuit (not shown) into a digital signal. The AD conversion circuit 3 converts the analog signal output from the temperature sensor 6 into a digital signal. Convert to digital signal. The temperature sensor 6 is designed to detect the ambient temperature. For example, a thermistor or a platinum resistor is used.

[0015] The above-mentioned ROM 4 is, for example, an electrical eraser that can be programmed and erased electrically. A writable ROM (EEPROM) is used. Also, in ROM4, A plurality of predetermined reference temperatures, a plurality of predetermined reference values, and each of the above reference temperatures. The reference conversion value at is stored. Here, the standard conversion value is a pre-accurate value. The converted value corresponding to the above reference value for which is known is shown. As will be explained in detail later, if the Correction of outside values requires multiple reference conversion values.

[0016] Furthermore, the CPU 1 is responsible for converting the reference values of the AD conversion circuits 2 #1 to #n. A storage command instructing to store the result in ROM 4 is sent via command signal line 7. It is given as follows. This storage command can be easily input using a pushbutton, for example. I can do that. Next, the operation of the above embodiment will be explained with reference to FIG. Figure 2 shows #m AD conversion times. A flowchart for determining the true converted value of path (any one of #1 to #n) 2 is shown.

[0017] The #0 AD conversion circuit 3 is connected to the surrounding area of the AD conversion device measured by the temperature sensor 6. Converts the temperature Tnow from an analog signal to a digital signal and outputs it to CPU1 ( ST1). CPU1 determines which section of the reference temperature stored in ROM4 the temperature Tnow is. It is determined whether or not this applies (ST2). In Figure 1, the reference temperatures are T1, T2, There are three points at T3, but the reference temperature and the reference conversion value corresponding to each reference temperature are The larger the number, the smaller the error due to temperature change.

[0018] Here, for example, the CPU 1 determines that the ambient temperature Tnow of the AD converter is the reference temperature Ti. , Tj, the CPU 1 executes the base code stored in the ROM 4. Read the quasi-converted values iref1 and jref1. Reference conversion values iref1, jref1 The relationship between and the reference temperature is shown in the reference value table of the AD conversion circuit 2 at #m in FIG. here, The reference conversion value 1 refers to the reference value ref1, and the reference conversion value 2 refers to the reference value ref2. This is the value converted at temperature. Therefore, the reference converted value iref1 is the reference value ref 1 at the reference temperature Ti, and the reference converted value jref1 is the reference value r This is the value obtained by converting ef1 at the reference temperature Tj. The CPU 1 calculates the reference conversion values iref1 and jref1 using the formula, nowref1=(jref1-iref1)(Tnow-Ti) /(Tj-Ti) + iref1 By substituting and calculating, now which is the reference conversion value 1 at temperature Tnow Calculate ref1 (ST3).

[0019] Furthermore, the CPU 1 also uses the reference conversion values iref2 and jre stored in the ROM4. Read f2. The reference conversion value iref2 is the reference value ref2 at the reference temperature Ti. It is a converted value, and the reference converted value iref2 is the value obtained by converting the reference value ref2 to the reference temperature Tj. (See Figure 3). CPU1 uses the reference conversion values iref2 and jref2 as formulas, nowref2=(jref2-iref2)(Tnow-Ti) /(Tj-Ti) + iref2 By substituting and calculating, now which is the reference conversion value 2 at temperature Tnow Calculate ref2 (ST4). The reference conversion value 1 and reference conversion value 2 obtained by the above calculations are For this purpose, errors occurring in the reference conversion values themselves are corrected.

[0020] The AD conversion circuit 2 of #m above receives an analog value input from the previous stage circuit (not shown). is converted into a digital value and output (ST5), and this value is set as mdata. Above C PU1 uses mdata, previously calculated nowref1 and nowref2, and Furthermore, using the reference values ref1 and ref2, the following formula result=(ref2-ref1)(mdata-nowref1) /(nowref2-nowref1) + ref1 By calculating the true conversion value result with the initial error of the circuit corrected, Calculate (ST6).

[0021] The above processing is executed for the values output from each AD conversion circuit 2 of #1 to #n. As a result, a true conversion value is obtained in which the initial error of the circuit and the error due to temperature changes are corrected. be able to.

[0022]

[Effect of the idea]

As detailed above, according to this invention, initial errors and errors due to temperature changes are included. The outputs of the AD conversion circuits 2 of #1 to #n are converted using the reference value, reference temperature, and reference conversion value. By correcting the error using the The elements used in the AD conversion circuit 2 of ~#n can be applied regardless of the temperature coefficient. follow It is possible to realize a very inexpensive AD converter in terms of circuit configuration and circuit adjustment, reducing costs. It is possible to reduce the

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an analog-to-digital converter according to an embodiment of the invention.

FIG. 2 is a flowchart for determining the true conversion value of #m AD conversion circuit in this invention.

FIG. 3 is a reference value table of #m AD conversion circuit in this invention.

FIG. 4 is a block diagram showing the configuration of a conventional analog-to-digital converter.

FIG. 5 is a block diagram showing the configuration of a conventional analog-to-digital conversion circuit.

[Explanation of symbols]

1...CPU, 2...AD conversion circuit (#1 to #n), 3...A
D conversion circuit (#0), 4...programmable ROM, 5...
Bus line, 6...Temperature sensor, 7...Command signal line, 1
0...Input terminal, 11...Instrumentation amplifier, 12...Voltage/frequency converter, 13...Photocoupler, 14...Counter, 15...
Address/data bus, 20...Reference resistance, 21-24...
Resistor, 25, 26... variable resistor, 27... capacitor.

Claims (1)

[Scope of utility model registration request] Claim 1: An analog/digital converter comprising one or more analog/digital conversion means controlled by a CPU.
In the digital conversion device, a temperature measurement means for measuring the temperature around the analog-to-digital conversion device; an analog-to-digital conversion means for converting the temperature measured by the temperature measurement means into a digital value; A reference temperature corresponding to the temperature measured by the digital conversion means, and each analog temperature at that reference temperature.
A reference value storage means for storing a reference conversion value by the digital conversion means, and an initial error of the analog-to-digital conversion means and an error during conversion due to temperature change are automatically corrected from the reference conversion value stored in the reference value storage means. An analog-to-digital conversion device characterized by comprising means.