JPS6054527A - A/d converting device - Google Patents

Abstract

PURPOSE:To adjust easily an A/D converting part by inputting two, high and low reference inputs to an A/D converter through an amplifier, and generating correction data with an obtained value and adjusting the A/D converting part with this data. CONSTITUTION:A correction mode is set by a switch input circuit 7, and a low reference input is inputted from an analog input circuit 1, and a digital value is obtained by an amplifier 2 and an A/D converter 3 and is displayed on a display circuit 9, and a value is set by the switch input circuit and is stored in an RAM6; and a high reference input value is stored in the RAM6 similarly, and correction data is obtained in a CPU4 by the calculation and is registered in the RAM6. In a measurement mode, the input signal is subjected to A/D conversion and is corrected on a basis of correction data, and a digital value is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an A/D conversion device that easily calibrates an A/D conversion output of an A/D converter including a preamplifier.

Conventional technology and its problems When constructing a digital control circuit using sensors that convert temperature, pressure, etc. into electrical signals, the outputs of these sensors are minute analog quantities, so after being amplified by an amplifier circuit. A configuration in which the signal is converted into a digital signal using an A/D converter and the digital output is used as an input signal to a digital control circuit is widely used. In such an A/Di converter, errors occur during digital conversion due to fluctuations in the reference voltage of the amplifier circuit and A/D converter. Therefore, when adjusting such an A/D conversion section, a variable resistor is used to provide the reference input of the minimum value and maximum value to be A/D converted to the input terminal of the amplifier circuit, and adjust the amplification factor of the amplifier circuit. using A/
The digital output of the D converter was adjusted to a predetermined value corresponding to each reference input. However, in this case, when either the minimum value or the maximum value is adjusted, the other is also affected and the output value often fluctuates. Therefore, there is a problem in that it is necessary to repeat such fine adjustments, and the calibration takes a lot of time and effort. Furthermore, since a highly accurate variable resistor is required, the price cannot be reduced. Furthermore, since the output of the variable resistor fluctuates due to temperature changes, aging, etc., there is a problem in that readjustment is often required depending on the usage environment.

Purpose of the Invention The present invention solves the problems of the conventional A/D converter, and provides an A/D converter that allows adjustment of the A/D converter extremely easily without using a variable resistor. /D conversion device.

Structure and Effects of the Invention The present invention is an A/D conversion device including an amplifier that amplifies an analog input and an A/D converter that converts the analog amplified output of the amplifier into a digital value. A/D that corresponds to the reference input signal to the two types of amplifiers, high and low.
Storage means for storing the digital output of the converter; and calculation means for calculating the input analog value by proportionally distributing the digital output value of the A/D converter obtained in response to the input of the analog signal based on the stored value of the storage means. It is characterized by comprising the following.

According to the present invention having such features, there is no need to use a variable resistor to finely adjust the amplification factor of the amplifier circuit or the reference voltage of the A/D converter, and there is no need to use a variable resistor to adjust the amplification factor during calibration. Since it is only necessary to store the digital conversion value corresponding to the reference input in the storage means using a button switch, etc., the A/
Calibration including the D conversion circuit and amplifier circuit becomes extremely easy. In addition, since a variable resistor is not used, readjustment is not required due to temperature changes or changes over time (and the cost can be reduced.Furthermore, readjustment can be made in response to changes in the amplifier circuit itself over time or changes in the environment). Even in this case, since the adjustment work is extremely easy, there is also the effect that it is easy to use the calibrated state.

DESCRIPTION OF EMBODIMENTS FIG. 1 is a block diagram of a control system using an A/D converter according to the present invention. In this figure, an analog input circuit 1 such as a temperature sensor or a pressure sensor is connected to an amplifier circuit 2 that amplifies its analog output, and further connected to an A/D conversion circuit 3 that converts the amplified analog output into a digital quantity. . The output of the A/D conversion circuit 3 is processed by the central processing unit (hereinafter referred to as CPU).
) given to 4. A read-only memory (hereinafter referred to as ROM) 5 for storing system programs and a random access memory (hereinafter referred to as RAM) 6 for holding temporary data are connected to the CPU 4 as storage means. In order for the RAM 6 to retain its stored contents even when the power is turned off, it is necessary to use a non-volatile memory or use a CMOS memory or the like to store the data in a bank using a battery. Further connected to the CPU 4 are a switch input circuit 7 for changing the control state using a dip switch or the like, and a digital input circuit 8 for inputting digital signals, and a display circuit 9 as an output means.
A digital output circuit 10, a D/A conversion circuit for converting an output digital signal into an analog quantity, and a constant current output circuit 12 driven by the D/A conversion circuit are connected.

FIG. 2 shows the front panel surface on which the switch input circuit 7 and display circuit 9 are provided.

In this figure, the numerical displays indicated by Pv and S■ at the top are indicators that show the current value and cent value, respectively, and the switch indicated by rD I PJ below them is a dip switch that changes the calibration mode, operation mode, etc. be. Also rTE
The AcHJ key is used to input the current value indicated by Pv into the cent value area, and the "↑", "↓", and "→" keys are numerical control keys that increase, decrease, and digit decrease the value of the parameter, respectively. The rWRITEJ key is a switch for writing set values.

Next, the operation of this embodiment will be explained with reference to the flowchart in FIG. First, instead of adjusting the amplification factor of the amplifier circuit 2 with a variable resistor, the A/D conversion circuit 3
．． A digital conversion value corresponding to the reference input signal within a range in which A/D conversion is possible is stored in the RAM 6. First, the dip switch of the 7-inch input circuit 7 is set to the calibration mode.

Then, step 1 in the flowchart of FIG. The process proceeds to step 21 via the block 2o, and an instruction (AJL) to input the low reference input via the analog input circuit 1 is given by the sV display as shown in FIG. 4(a). Furthermore, in step 24, the digital value "1o" for the already stored low reference input is displayed on the SV display. If the A/D conversion circuit 3 has a resolution of, for example, 8 bits, its digital output will be from 0 to 255.
It can take values up to. Further, the low reference input is set to an arbitrary value higher than the lowest value in the range in which A/D conversion is possible, for example, 4 mV. Then, this reference distance is given from the analog input circuit 1. Then, the process proceeds to step 24 via step 23, and the A/D conversion output method for that 4 mV is determined, for example, "12
" is displayed in the Pv territory. Then, in step 25, it waits for the rTEACHJ key to be pressed, and if the rTEACHJ key is pressed, the current value "12" is rewritten as the cent value of the low standard input in the s■ area (step 25).

If the rWRITEJ key is then pressed, the low reference input is stored in the RAM 6 (steps 26 and 27). Subsequently, as shown in FIG. 4 (bl), in step 28 an instruction is given to give a high reference input, and the digital value of the previously set high reference input is displayed on the S indicator (step 28.
29). And high standard input within the range that can be converted to A/D,
For example, if an input of 20 mV is given via the analog input circuit 1, the process proceeds to step 31 via step 3o, and the A/D converted value for that input is displayed on the PV display.

FIG. 4(b) shows this state, and the A/D conversion value r242J is displayed on the PV display. Similarly, if you press the r T E A CHJ key, the current value r24
2J is displayed on the Sv display as a cent value (step 32), and then when the "WRITE" key is pressed, that value is written to the RAM 6 (steps 33 and 34). [Instead of using the TEACHJ key, press "T""↓"
Already set values may be modified using the [→] numerical control key. In this way, digital inputs corresponding to the upper and lower reference values are stored in the RAM 6. Using this reference digital quantity, it is possible to digitally convert any analog input. For example, the current analog input signal Da t
a If the A/D conversion output of the A/D conversion circuit 3 when A is given to the analog input circuit 1 is DataD, then Da
taA is expressed by the following formula.

However, D20. D4 is the digital conversion value of the high and low reference inputs, ie, 242 and 12, respectively. Input data can be calculated by proportionally distributing the digital values converted in this way. In order to facilitate such calculations and speed up the calculations, it is preferable to calculate the constant part in advance. That is, the formula (11) is 2−−−−−−(2
1 However, such calibration data for Kl and K2 is calculated in step 35 and registered in the RAM 6 in step 36. In this way, the calibration of the A/D converter is completed.

Next, the A/D conversion operation using this A/D conversion device will be explained with reference to the flowchart shown in FIG. First, in step 40, if an input is given to the analog input circuit 1, it is read, and then the input signal is A/D converted (step 41).

Then, the calibration data Kl registered in step 36
, K2 are read, and the input data is calibrated based on equation (2) (steps 42 and 43). And input analog signal DataA corresponding to digital value DataD
is calculated and various controls are performed based on it (step 4
5). This calibration data is stored in RAM, which is a non-volatile memory.
6, the data is retained even if the power is turned off, and calculations based on equation (2) are always possible.

In this embodiment, the constant part of Equation (11) has already been calculated and stored as calibration data, but Equation (1) is calculated each time to obtain input analog data. Needless to say, this is a good thing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control device including an A/D conversion device of the present invention, FIG. 2 is a front panel diagram of a display circuit and a switch input circuit, and FIG. 3 is a flowchart showing a reference input signal setting operation. Figure 4(a). FIG. 4(b) is a diagram showing an example of the display on the display section at that time.
The figure is a flowchart showing the operation when calibrating and controlling input signals. 1--Analog input circuit 2--Amplification circuit 3--A/D conversion circuit 4-----CP
U 5-----ROM 6--------RAM
? , -------Sui, Chi input circuit 9-・--1-
-Display circuit patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) Figure 1 Figure 2 Figure 4 (a) -P1-S1-Pv~ SV - Figure 5

Claims (2)

[Claims] (1) An A/D conversion device including an amplifier that amplifies analog human power and an A/D converter that converts the analog amplified output of the amplifier into a digital value, the height and low range of the range in which A/D conversion is possible. storage means for storing digital outputs of the A/D converter corresponding to two types of reference input signals to the amplifier; and a storage means for storing digital output values of the A/D converter obtained in response to input of analog signals. A/
/D conversion device. (2) The low reference input given to the amplifier is selected to be higher than the lowest value that can be converted into A/D, and the high reference input given to the amplifier is selected to be lower than the maximum value that can be converted into A/D. An A/D conversion device according to claim 1.