JPH08162952A - Ad conversion value correction device for ad converter - Google Patents

Abstract

PURPOSE: To eliminate the error of an AD conversion value by obtaining a correction factor from the AD conversion value of a correction power supply voltage converted in an AD converter to which a desired reference voltage or the reference voltage is supplied. CONSTITUTION: By the AD converter 1 to which the desired reference voltage Vref* is supplied from a transistor 2, the AD conversion value Do of a voltage Vs for correction is obtained beforehand and stored in a microcomputer (MPU) 5A. Then, by the converter 1 to which the reference voltage Vref is supplied, the correction factor KH is obtained from the AD conversion value Ds of the voltage Vs for the correction of a power supply 9 for the correction connected by a switching circuit 10 and the AD conversion value Do. Then, the AD conversion value DH corrected by multiplying the factor KH with the AD conversion value DA of the analog voltage VA of an analog circuit 8 connected by the circuit 10 is obtained. The AD conversion value DH matches with the AD conversion value at the time of the voltage Vref = the voltage Vref* and the error of the AD conversion value is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AD converter, and more particularly to an AD conversion value correcting device for an AD converter of a type in which its reference voltage is supplied by a transistor.

[0002]

2. Description of the Related Art Conventionally, when an AD converter is used, a method of supplying a reference voltage to the AD converter by using a transistor has been often used for the reason of reducing current consumption. FIG. 4 is a block diagram showing a partial circuit diagram of such a conventional method. In the figure, reference numeral 1 is an AD converter that converts an input analog value into a digital value and outputs the digital value. Two
Is a transistor, for example, a pnp type transistor,
Its collector is connected to the terminal of the AD converter 1 to which the reference voltage Vref is supplied, and its emitter is connected to the desired reference voltage Vref.
It is connected to the terminal that supplies ref *, resistor 3 is connected between the emitter and base, and the base is another resistor 4
It is connected to the control terminal VRC of the control device, for example, MPU5 via. The input terminal Din of the MPU 5 is connected to the output side of the AD converter 1. An analog circuit 8 for supplying an analog voltage V _A representing a measured physical quantity such as smoke concentration or temperature to the input side of the AD converter 1 such as a smoke detecting section of a smoke type fire detector or a thermal type fire detector. A heat detector having a thermistor is connected.

The conventional system is constructed as described above, and the MPU 5 supplies an L level signal from its control terminal VRC through the resistor 4 to the base of the transistor 2 and thereby turns on the transistor 2.
The reference voltage Vref was supplied to the D converter 1. afterwards,
The analog voltage V _A of the analog circuit 8 is input to the AD converter 1 and AD-converted.

[0004]

However, the reference voltage Vref actually input to the AD converter 1 is the emitter-collector voltage V _EC (about 0V to 0.3V) of the transistor 2 from the desired reference voltage Vref *. Becomes (ie, Vref = Vref * −V _EC ). Therefore, the reference voltage Vref differs depending on the magnitude of V _EC , and a difference occurs with respect to the desired reference voltage Vref *. Therefore, the AD conversion value at the reference voltage Vref and the AD at the desired reference voltage Vref * are generated.
An error also occurs with the converted value. Further, the smaller the value of the reference voltage Vref input to the AD converter 1, the larger the error. As described above, the conventional method has a problem in that it is possible to make a determination only with an AD conversion value including an error, and it is not possible to catch a minute change.

Therefore, the present invention has been made in order to solve such a problem, and the AD of the AD converter is used.
It is an object of the present invention to obtain an AD conversion value correction device that corrects a conversion value and loses an error.

[0006]

An AD conversion value correction apparatus for an AD converter according to the present invention includes an AD converter, a transistor connected to the AD converter for supplying a reference voltage thereof, and a measured physical quantity. An analog circuit for supplying an analog voltage to be represented and a correction power supply for supplying a predetermined correction voltage, a switching means for switching and connecting the analog circuit and the correction power supply to the AD converter, the AD converter, and the transistor. And a control device for controlling the switching means.

[0007]

According to the present invention, the AD for which the correction voltage is AD-converted by the AD converter to which the desired reference voltage is supplied.
A conversion value D _O is obtained in advance, and the AD conversion value D _S obtained by AD converting the correction voltage of the connected correction power supply by the AD converter to which the reference voltage is supplied and the AD conversion value D _{O are obtained.} A correction function KH is obtained, and AD conversion is performed by multiplying the AD conversion value D _A obtained by AD conversion of the analog voltage of the connected analog circuit by the correction coefficient KH by the AD converter to which the reference voltage is supplied. The value D _H is obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the accompanying drawings will be described in detail below. FIG. 1 is a block diagram showing a partial circuit diagram of an embodiment of an AD conversion value correction device for an AD converter according to the present invention. In the figure, 1 to 4 and 6 to 8
Is the same as that shown in FIG. 4, and will not be described in detail here. Reference numeral 9 is a correction power source for supplying a predetermined correction voltage V _S (this V _S is set to be smaller than a voltage obtained by subtracting the maximum V _{EC of the} transistor 2 from a desired reference voltage Vref *), and 10 is an analog circuit. 8 and a correction power source 9 are switching means for switching and connecting to the input side of the AD converter 1, such as a switching circuit and a switching switch, and 5A has a control terminal SW for supplying a signal for switching the switching circuit 10. MPU (microcomputer), MPU5
The input terminal D _{cnt of} A is connected to the power supply V _cc via the resistor 6 and grounded via the switch 7.

For example, in the case of a fire detector, the analog circuit 8 detects a fire phenomenon and outputs an analog amount thereof. In the case of a machine tool, the analog circuit 8 detects the position of a material to be processed and outputs the analog amount. In the case of the position detecting circuit and the flow rate measuring device, the flow rate measuring circuit measures the flow rate and outputs the analog amount. The switch 7 is a switch that determines whether to correct the analog voltage with the same correction coefficient or to calculate the correction coefficient each time. In the former case, the switch 7 is off, that is, the D _cnt input of the MPU 5A is at the H level. The latter is when the switch 7 is on, that is, when the D _cnt input is at the L level. Further, the former is a case where it is not necessary to obtain the correction coefficient each time, for example, when the analog voltage V _A is taken in and AD-converted in a short time in which the emitter-collector voltage V _{EC of the} transistor 2 does not change.
When the latter takes in the analog voltage V _A , this emitter
When the collector voltage V _EC changes or is expected to change, for example, when the analog voltage V _A is taken in before dawn and 2:00 pm, which have the highest temperature difference in a day, or for a long period of time. This is a case in which it is not possible to predict how the emitter-collector voltage V _EC will change for measurement, and it is necessary to obtain a correction coefficient and take in the voltage V _EC to perform AD conversion to surely correct the AD conversion value. Whether the correction is performed by the former or the latter is determined in advance before measurement is started under measurement conditions such as measurement intervals or measurement periods, and the switch 7 is turned on or off accordingly.

Next, the operation of the AD conversion value correction apparatus will be described with reference to FIG.
First, AD will be described based on the flowchart shown in FIG.
The reference voltage Vref input to the converter 1 is made equal to the desired reference voltage Vref *, that is, Vref = Vref * (hence the emitter-collector voltage V _EC = 0 of the transistor 2) and the correction voltage V of the correction power supply 9. An AD conversion value D _O obtained by AD conversion of _S by the 8-bit AD converter 1 is calculated from the following formula (1).

D _O = INT (V _S / Vref * × 2 ⁸ ) (1)

However, INT is an integerizing function that truncates the numbers in parentheses after the decimal point. The AD conversion value D _o calculated in this way and stored in the ROM (not shown) in the MPU 5A is stored in the R (not shown) in the MPU 5A.
Call to AM (step S1). Next, input terminal Dcnt
The input level at is read into the MPU (step S
2).

Thereafter, a signal is sent from the control terminal SW of the MPU 5A to the switching circuit 10 to connect the correction power source 9 to the AD converter 1 (step S3). An L level signal is sent from the control terminal VRC of the MPU 5A to the transistor 2 to turn on the transistor 2, and the reference voltage Vref is AD
It is supplied to the converter 1 (step S4). Power source for correction 9
The correction voltage V _S supplied from the AD converter 1 is actually AD-converted by the AD converter 1, and the obtained AD conversion value D _S is input terminal Din.
The data is stored in the RAM (not shown) inside the MPU 5A through (step S5). AD conversion value D _O stored in RAM of MPU 5A and AD stored in RAM
The conversion value D _S is called and the correction coefficient KH is calculated from the following equation (2).

KH = D _O / D _S (2)

The correction coefficient KH thus calculated is stored in the RAM (step S6).

Next, a signal is sent from the control terminal SW of the MPU 5A to the switching circuit 10 and the analog circuit 8 is sent to the AD converter 1.
Are connected (step S7). The analog voltage V _A supplied from the analog circuit 8 is actually AD-converted by the AD converter 1.
The AD conversion value D _A obtained by the conversion is input to the MPU 5A (step S8). This input AD conversion value D _A
Is multiplied by the correction coefficient KH called from the RAM to obtain the corrected AD conversion value D _H (step S9). The corrected AD conversion value D _H is stored in the RAM of the MPU 5A (step S10).

Then, in step S11, it is determined whether or not the operation is completed, and if it is completed, step S12.
Then, the H level signal is sent from the control terminal VRC of the MPU 5A to the transistor 2 to turn off the transistor 2, and the process ends at step S13. However, if the determination in step S11 is not completed, step S1
4, the input level at the input terminal Dcnt of MPU5A is H
It is determined whether it is the level (“1”) or the L level (“0”), and in the former case, the process returns to step S8 to capture the analog voltage V _A once again (continuously) and AD-convert it. The correction can be made with the same correction coefficient KH. In the latter case, after the transistor 2 is turned off in step S15, the process returns to step S3, the correction voltage V _S is again taken in and AD-converted, and the analog voltage calculated in step S8 is obtained with the correction coefficient KH calculated each time. AD conversion value V _A
Can be corrected.

Next, the operation of the AD conversion value correction apparatus will be described with reference to FIG.
It will be explained based on the actual example shown in FIG. A. Desired reference voltage Vref * = 2.5V, maximum emitter
Collector voltage V _EC = 0.3 V and correction voltage V _S = 2.3.
In the case of 0V, the analog voltage V _A is 2.0V, 1.5V, 1.
An example in which the voltage is changed to 0V will be described first. AD conversion value D _O
Is 2.0V / 2.5V × 256 = 204.8 from the formula (1).
→ It becomes 204. (At this time, V _EC = 0 and V ref =
Vref *. ) The AD conversion value D _S is 2.0 V / (2.5 V-0.3 V) × 25
6 = 232.7 → 232. Then, the correction coefficient KH is 204/232 from the equation (2). The AD conversion value D _A is 2.0 V / (2.5 V-0.3 V) × 256 = 2, respectively.
32.7 → 232, 1.5V / (2.5V-0.3V) × 2
56 = 174.5 → 174, 1.0V / (2.5V-0.3
V) × 256 = 116.3 → 116. These AD
By multiplying the conversion value D _A by the above-mentioned correction coefficient KH, the corrected AD conversion values D _H = 204, 153, 102 are obtained. Finally, when the AD conversion value D * of the analog voltage V _A when Vref = Vref * is obtained, 204 and 1 respectively.
It becomes 53 and 102, which coincides with the corrected AD conversion value D _H, and it can be seen that this correction was made accurately.

B. Desired reference voltage Vref * = 1.5V, if the maximum emitter-collector voltage V _EC = 0.3V and correction voltage V _S = 1.0 V, the analog voltage V _A 1.0
An example in which the voltage is changed to V, 0.7V, and 0.5V will be described below. AD
From the formula (1), the converted value D _O is 1.0 V / 1.5 V × 256 =
170.6 → 170. (At this time, V _EC = 0
Therefore, Vref = Vref *. ) AD converted value D _S is 1.0 V / (1.5 V-0.3 V) × 25
6 = 213.3 → 213. Then, the correction coefficient KH becomes 170/213 from the equation (2). The AD conversion value D _A is 1.0 V / (1.5 V-0.3 V) × 256 = 2, respectively.
13.3 → 213, 0.7V / (1.5V-0.3V) × 2
56 = 149.3 → 149, 0.5V / (1.5V-0.3
V) × 256 = 106.6 → 106. These AD
By multiplying the conversion value D _A by the above-described correction coefficient KH, the corrected AD conversion values D _H = 170, 118, 84 are obtained. Finally, the analog voltage V when Vref = Vref *
_When the AD conversion value D * of A is calculated, it is 170 and 11 respectively.
The value is 9,85, which is in good agreement with the corrected AD conversion value D _H, and it can be seen that this correction was made accurately.

The difference between the AD conversion value D _A and the corrected AD conversion value D _H when the reference voltage Vref = 2.2 V and the analog voltage V _A = 1.0 V input to the AD converter 1 is 14. On the other hand, Vref = 1.2V, analog voltage V _A = 1.0
The difference between D _A and D _H when V is 22 is Vref
It can also be seen that the smaller the value of, the larger the error. In addition,
Although the AD converter and the MPU are used separately in this embodiment, an MPU (not shown) with a built-in AD converter may be used.

[0021]

The present invention provides an AD converter, a transistor which is connected to the AD converter and supplies a reference voltage thereof, an analog circuit which supplies an analog voltage representing a measured physical quantity, and a predetermined correction voltage. And a control device for controlling the AD converter, the transistor and the switching means, and a control device for controlling the AD converter, the analog circuit and the correction power source being switched to and connected to the AD converter. Is supplied with the reference voltage and first control means for previously obtaining an AD conversion value D _O obtained by AD-converting the correction voltage by the AD converter to which a desired reference voltage is supplied. A correction coefficient K is calculated from the AD conversion value D _S and the AD conversion value D _{O obtained} by AD converting the correction voltage of the connected correction power source by the AD converter.
By the second control means for obtaining H and the AD converter to which the reference voltage is supplied, the AD conversion value D _A obtained by AD converting the analog voltage of the connected analog circuit is multiplied by the correction coefficient KH. because it contains a third control means for determining a corrected AD conversion value D _H, corrected AD conversion value D _H of the analog voltage is very well matches the AD converted value D * when Vref = Vref *, the error It is no exaggeration to say that there is no such thing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit diagram according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the present invention.

FIG. 3 is a diagram illustrating an example of the present invention.

FIG. 4 is a block diagram showing a circuit diagram of a conventional method.

[Explanation of symbols]

 1 AD converter 2 transistor 5A MPU 8 analog circuit 9 correction power supply 10 switching circuit

Claims (5)

[Claims] 1. An AD converter, a transistor which is connected to the AD converter and supplies a reference voltage thereof, an analog circuit which supplies an analog voltage representing a measured physical quantity, and a correction circuit which supplies a predetermined correction voltage. The control device includes a power supply, switching means for switching and connecting the analog circuit and the correction power supply to the AD converter, and a controller for controlling the AD converter, the transistor, and the switching means. First control means for previously obtaining an AD conversion value D _O obtained by AD-converting the correction voltage by the AD converter to which the reference voltage is supplied; and the AD conversion to which the reference voltage is supplied. Depending on the vessel
Second control means for obtaining a correction coefficient KH from the AD conversion value D _S obtained by AD converting the correction voltage of the connected correction power source and the AD conversion value D _O, and the AD to which the reference voltage is supplied. With the converter,
AD, characterized in that it comprises a third control means for determining the connected AD conversion value D _H to the analog voltage is corrected by multiplying the correction coefficient KH to AD conversion value D _A which AD conversion of the analog circuit, the AD conversion value correction device of converter. 2. The AD conversion value D _O has the formula D _O = INT (Vs when the AD converter is an 8-bit converter.
/ Vref * × 2 ⁸ ) (calculated based on IN
T is an integer function that rounds off the number after the decimal point in parentheses, Vs is the correction voltage, and Vref * is the desired reference voltage. ) It is characterized by the above-mentioned.
AD conversion value correction device of the AD converter. 3. The correction coefficient is calculated based on the equation KH = D _O / D _S (where D _O and D _S are the AD conversion values). A of the AD converter
D conversion value correction device. 4. The control device further includes fourth control means for successively taking in the analog voltage, AD-converting the analog voltage, and correcting the AD conversion value D _A with the same correction coefficient KH. An AD conversion value correction device for an AD converter according to claim 1. 5. The control device alternately takes in the correction voltage and the analog voltage, performs AD conversion, and corrects the AD conversion value D _A obtained by AD-converting the analog voltage with a correction coefficient KH obtained each time. 5. The method according to claim 1, further comprising fifth control means for
AD conversion value correction device of D converter.