JPH04284028A - A/d converting method - Google Patents

Abstract

PURPOSE:To miniaturize an analog/digital(A/D) converter to convert the fluctuating values of various analog signals to digital values. CONSTITUTION:All the input signal ranges of an A/D converter 11 are decided so as to contain the fluctuation ranges of the analog signals and after the analog signals selectively inputted to an input terminal 10 are converted into digital signals at the A/D converter 11, those analog signals are converted into digital values corresponding to the fluctuation ranges of the inputted analog signals at a data processor 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting an analog signal into a digital signal (A/D conversion).

0002

2. Description of the Related Art Conventionally, analog-to-digital converters used in programmable controllers are provided with the following analog input signal ranges in order to meet various user requirements.

(1) -10V to +10V (2) 0 to +1
0V (3) 0 to +5V Also, the resolution for the input analog signal is 12
A/D converters are used to convert analog input into 12-bit digital signals.

[0004] When selectively A/D converting the above three types of analog signals using one A/D converter, it is necessary to commonize different signal levels.

For this reason, as shown in FIG. 3, an analog signal to be subjected to A/D conversion is selected by a signal changeover switch 5, and a voltage range is adjusted by gain adjusters 1a to 1c, an adder 2, and the like.

[0006] Any one of the adjusted signals Sa to Sc is selected by the changeover switch 5 according to an instruction from the data processing device 4 and guided to the A/D converter 3.

The output of the A/D converter 3 becomes a 12-bit digital signal and is input to a data processing device 4. The data processing device 4 performs predetermined data processing using this digital signal.

[0008] In addition to determining the selection conditions for the changeover switches 5a to 5c in FIG. be.

[0009]

[Problem to be Solved by the Invention] Conventional A method for selectively A/D converting a plurality of analog signals with different input ranges
As mentioned above, the /D conversion method requires an input circuit to share the analog signal range and an input selection circuit to select the signal, which has the disadvantage of making the device expensive and large. .

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide a method for digitally converting multiple types of analog signals having different fluctuation ranges without the need for an analog signal level conversion input circuit or signal selection circuit. The object of the present invention is to provide a possible analog-to-digital conversion method.

[0011]

[Means for Solving the Problems] In order to achieve such an object, the present invention sets the maximum allowable range of an input signal in an analog-to-digital converter so that the variation ranges of multiple types of analog signals to be input are all stipulated to be included;
An analog signal to be converted is input to the analog-to-digital converter, and the value indicated by the signal digitally converted by the analog-to-digital converter is calculated based on the maximum allowable range of the analog-to-digital converter and the analog to be converted. It is characterized by converting the fluctuation values indicated by a plurality of types of analog signals into digital values by performing arithmetic conversion into values proportional to the relationship between the signals and the maximum fluctuation range of the signals.

0012

[Operation] The present invention focuses on the fact that many devices that use digital values after A/D conversion have numerical calculation functions, such as CPUs and data processing devices, and convert the absolute values of various analog signals into digital values. After that, the fluctuation value of the analog signal is expressed as a digital value by proportionally converting the digital value in accordance with the fluctuation range of the analog signal.

[0013] By performing this arithmetic processing on the data processing device side, conventional level conversion circuits and signal selection circuits are no longer necessary, thereby reducing the size of the device and the manufacturing cost.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of a circuit configuration according to an embodiment of the present invention.

In FIG. 1, 10 is an input terminal for analog signals, and in this embodiment, one of three types of analog signals is input.

1d is a gain adjuster for analog signals, and there is no particular need to provide it.

11 is an analog-to-digital converter that converts the level value of the input analog signal into a digital value;
The resolution (number of output signal bits) is determined as follows.

[0019] The voltage fluctuation ranges of the plurality of analog signals to be input are respectively set as V1B to V1T, V2B to V2T...V.
When mB to VmT (m is any natural number, B indicates the minimum voltage value, and T indicates the maximum voltage value), when providing a resolution of at least n bits, The number l of output bits of the A/D converter is determined by the following equation.

[0020]

[Math 1]

Here, Vmax is the maximum value in the input signal range, and Vmin is the minimum value. Also, ΔVmin is the input signal range V1T-V1B, V2
Indicates the minimum fluctuation range among T-V2B...

For example, each range of the input signal is set to 0 to 5V.
, 0 to +10V, -10V to +10V, minimum 12
If you want to have a resolution of more than a bit, use A/
The number of output bits of the D converter 11 is determined to be at least 14 bits,
Further, in order to process the signals of Vmax and Vmix, an A/D converter is used whose allowable input signal range includes the variation range of all analog signals.

The data processing device 4 uses the 14-bit digital signal V14 output from the A/D converter 11 to
14-bit digital value V1 indicating the fluctuation value for each range
Convert to 2. There are three types of arithmetic expressions used for this conversion, and Equation 1 is selected to correspond proportionally to the maximum variation range VV of the input analog signal.

(1) Arithmetic formula used for analog signals of 0 to 5V (V1B to V1T)

[0025]

[Math 2]

(2) -10 to +10 (V2B to V2T)
Arithmetic formula used for the analog signal of

[0027]

[Math 3]

(3) Arithmetic formula used for analog signals of 0 to +10V (V3B to V3T)

[0029]

[Math 4]

The upper 12 bits of the 14-bit value obtained by such calculation are used as the final A/D.
Handled within the digital processing device as a converted output.

In such a configuration, for example, when using an analog signal of -10 to +10V to the input terminal, information indicating that Equation 4 is to be used is input to the data processing device from a keyboard input device (not shown) in advance. I'll go. For example, when an analog signal of 0V is input to the input terminal, the A/D converter 11 converts 2 in accordance with the conversion characteristic 20 in FIG.
000h (hexadecimal number) is output, but the top 12 of the results (2000h) of the calculation of number 1 in the digital processing device 4
Bit (5000h) is selected and used as the A/D converted value.

[0032] Furthermore, when a -10V analog signal is input, the final digital value indicating the fluctuation range is 0h, +10
When an analog signal of V is input, the final digital value becomes 1000h (163 = 212).

In this embodiment, even if analog signals with different signal ranges are input, the A/D converter 11 outputs a digital signal in accordance with the level conversion characteristic 20 shown in FIG. Next, on the data processing device 4 side, the conversion characteristics 21 to 23 of FIG.
The A/D output value is converted by calculation so that it matches the corresponding characteristic in . Therefore, it is not necessary to perform level conversion for commonization for each type of analog signal as in the past. Furthermore, since the data processing device 4 only needs to select the arithmetic expression to be used for the analog signal to be converted in advance, a signal switching circuit for the analog signal is not required.

In addition to this embodiment, the following examples can be given.

1) In this embodiment, when converting the range of variation from the reference value of an analog signal into a digital value, all analog signals are commonly converted into a 12-bit digital value. If it is desired to increase the resolution of the A/D conversion, it is possible to selectively use a bit number larger than 12 bits within the 14-bit output range of the A/D converter 11. In this example, the 14-bit output of the A/D converter 11 is used as is for the -10V to +10V analog signal, the 13-bit output is used for the 0V to +10V analog signal, and the 14-bit output is used for the 0V to 5V analog signal. 12 bits can be used for that.

2) In this embodiment, numerical calculation processing is executed in the data processing device 4, but a calculation circuit may be provided within the A/D converter. In this case, it is preferable to use a read-only memory or the like for the arithmetic circuit, and the output signal of the A/D converter 11 and the selection signal of the arithmetic expression are input as addresses, and the arithmetic results are output to the data bus in accordance with this address specification. It's good to let them do it.

3) In this embodiment, three types of analog signals are used as an example, but it goes without saying that the present invention is not limited to these.

[0038]

As described above, according to the present invention, there is no need to convert the levels of multiple types of analog signals to be converted using a level conversion circuit for analog signals as in the conventional case. It becomes possible to downsize the A/D conversion circuit.

[Brief explanation of the drawing]

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

FIG. 2 is an explanatory diagram showing the relative relationship between the output value of the A/D converter, the final digital value, and the analog signal value according to the embodiment of the present invention.

FIG. 3 is a block diagram showing the circuit configuration of a conventional analog-to-digital converter.

[Explanation of symbols]

1a to 1d Gain adjuster 2 Adder 3, 11 A/D converter 4 Data processing device 10 Input terminal 20 Characteristic curve 21 showing the relationship between the output value of the A/D converter 11 and the analog value 0 to 5 V range characteristic curve showing the digital value corresponding to the voltage value of the analog signal with

Claims (1)

[Claims] 1. The maximum allowable range of the input signal in the analog-to-digital converter is determined so as to include all the variation ranges of multiple types of analog signals to be input, and the analog signal to be converted is converted into the analog-to-digital converter. The value indicated by the signal input to the converter and digitally converted by the analog-to-digital converter is determined based on the relationship between the maximum allowable range of the analog-to-digital converter and the maximum variation range of the analog signal to be converted. An analog-to-digital conversion method characterized by converting fluctuating values indicated by a plurality of types of analog signals into digital values by performing arithmetic conversion into proportional values.