JPH05199111A - Input signal processing circuit of industrial instrument - Google Patents

Abstract

(57) [Abstract] [Purpose] The bias processing is facilitated and the A / D converter is simplified in order to process analog measurement signals including bias components used in industrial instruments with a microcomputer. The purpose of the present invention is to provide an input signal processing circuit of an industrial instrument that can be efficiently implemented by software built in. A bias signal is removed from an input signal A by an input processing unit, and a bias signal B is constantly periodically compared with a reference value signal to perform correction, whereby an input processing unit and an A / D conversion unit are provided. An industrial instrument that can remove the error amount of.

Description

Detailed Description of the Invention

[0001]

[Industrial application] In process control, etc., temperature, pressure, flow rate, etc. are measured, and PID control calculation etc. are carried out in a controller or a distributed instrumentation system. These analog measurement signals are output signals from the temperature converter, the pressure transmitter, and the flow rate transmitter, and are generally analog signals including a unified DC4 to 20 mA, DC1 to 5 V bias, The present invention relates to industrial instruments that use these signals as input signals.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional example. FIG. 1 shows that an analog measurement signal 2 including a bias is applied to an input terminal 1 of an industrial instrument.
Switch unit 3 which is connected to and switches between a plurality of input signals
Via the analog-to-digital converter 4 (hereinafter abbreviated as A / D converter).
The reference numeral 5 executes various control calculations and the like, and has a display unit, an operation unit (not shown) and outputs to the outside.
The adjustment unit 7 is an adjustment unit for accurately A / D converting an analog signal. In this example, analog measurement signal 2
Is taken into 5 while including the bias signal, and the bias signal is removed by software processing inside 5 by a microcomputer (not shown). Therefore, the high-resolution A / D converter 4 is required to accurately capture the 2 signal. The DC1 to 5V signal is digitized in the range of 0 to 5V, but the bias signal of 1V or less is unnecessary. Therefore, effective signal range 1
The A / D converter needs to have a high resolution in order to capture ˜5V with high accuracy, and the adjustment of the offset and the like of each A / D converter by the adjusting unit 7 is necessary.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate a bias component signal contained in an analog measurement signal in an input processing section and to A / D convert only a measurement value signal to improve resolution. The bias component signal used in the input processing unit is constantly monitored periodically by the digital processing calculation unit,
It is an object of the present invention to provide an input signal processing circuit of an industrial instrument that performs correction and can achieve high resolution at low cost.

[0004]

The means for achieving the object is to remove the bias component by inputting an analog measurement signal and a bias component signal which is constantly monitored and corrected periodically to a differential input amplifier. The converted signal is A / D converted and taken into the digital processing unit, and the bias component signal of the bias component signal generation unit is A / D converted and compared with the internal reference value determined by the digital processing unit to determine the error component. Is calculated and corrected to always generate an accurate bias signal,
Regarding the offset voltage and the like which each A / D conversion section has, a reference value signal is taken in and the measurement signal and the like are corrected by this reference value signal to achieve low cost and high accuracy.

[0005]

The bias component signal, which is one input of the differential amplifier of the input processing unit for removing the bias signal, is generated by the bias component signal generation unit, or this bias component signal generation unit includes a Zener diode or the like. Although it is possible to use a constant voltage generator, it is possible to use a digital processing arithmetic unit to keep periodical fluctuations in order to eliminate constant voltage fluctuations due to changes in external temperature and manual adjustment work such as variable resistors during initial adjustment. In addition to correcting the bias component signal from the bias component signal generation unit to automate the adjustment of external influences and initial values, the bias component signal of this bias component signal generation unit is also used for the offset of the input processing unit. Is input to the analog measurement signal side of the input processing unit to capture the offset signal component of the input processing unit into the digital processing calculation unit via the A / D conversion unit. Accordingly, to implement a correction in the digital processing operation section, thereby achieving a high accuracy.

[0006]

EXAMPLE An example shown in FIG. 2 is shown. FIG. 3 shows another embodiment.

In FIG. 2, contents having the same functions as those in FIG. 1 are designated by the same reference numerals. The input signal 2 is input to the input terminal 1 as A. 1 is connected to one end of the resistor 10, and the other end of 10 is connected to the non-inverting input terminal (+) side of the operational amplifier 8 and the resistor 11. The other end of 11 is connected to the reference value signal side. A resistor 12 and a resistor 13 are connected to the inverting input terminal (-) side of 8, and the other end of 13 is connected to the output of 8 and the input side of the switch 9. The other end of the resistor 12 is connected to the output of the voltage buffer unit 15 and the inverting input side and the other input terminal of the switch 9. The other input terminal of the switch 9 is connected to 0V used as a reference value signal, and the output of 9 is A / D.
It is input to the conversion unit 4. The output of 9 becomes the input of the A / D converter 4. Since 4 operates with 0V as the reference value, it is connected to the reference value 0V, and at the same time, it converts the analog input signal from 9 into the digital signal of the output signal, and this output signal is connected to the digital arithmetic processing unit 5 '. ..

5'is the output signal B of the voltage buffer 15.
Pulse width generator 1
The signal is output to 8. 18 inputs the digital signal from 5 ', converts this signal into a predetermined pulse width signal, and outputs it. The pulse width signal C is input to the resistor 17, and the other end of 17 is connected to the non-inverting input parts of the capacitors 16 and 15. The other end of 16 is connected to the reference value signal. In such a configuration, as the signals on the input side of the switch 9, the output signal (AB) ± e _{1 of 8} , the output signal B of 15 and the reference value signal 0V are input. Here, the signal A is a voltage signal including the bias component B, and e ₁ is the error component (offset voltage or the like) included in 8. The switch 9 switches these signals by a switching signal (not shown) from 5'and inputs them to the A / D converter 4 to convert them into digital signals. The signals fetched by 5'each have an error of 4 (offset, etc.) ± e ₂ for each input signal.
Is converted to (A−B) ± e ₁ ± e ₂ , B ± e ₂ , and 0V ± e ₂ .

From these signals, (B ± e ₂ ) − (± e ₂ ).
If the B value is not a predetermined reference value, the pulse width generation signal to 18 is corrected and correction is performed so that the bias signal B becomes correct. After this correction, the signal from 8 is again A / D converted and fetched.

FIG. 3 shows an input terminal 1'for correcting the error ± e ₁ of 8 and for connecting a plurality of analog measurement signals.
An example in the case of having The same functions as those in FIG. 2 are denoted by the same numbers. In this embodiment, a switching signal (not shown) from 5'input terminal 1, input terminals 1 ', 1
A switch 14 that receives the output signal B from 5 is provided, and the output of 14 is connected to the resistor 10. When the switch 9 is selecting the output signal of 8, the switch 14 is switched from 5'to capture the signal A and the bias value B of the terminal 1, and (AB) ± e ₁ ± e ₂ And (BB) ± e ₁ ± e ₂ are taken into 5 ′. Also, 9 takes in B ± e ₂ and 0V ± e _2, so that 5 ′
At, the value of ± e ₁ is obtained. As a result, the measured value signals (A-B) ± e ₁ ± e ₂ are corrected to the values of (A-B), and correct measured values are obtained. Since the bias component generator 19 of FIGS. 2 and 3 has a digital / analog conversion function, it may be implemented with another circuit configuration.

[0011]

As described above, according to the present invention, since the A / D conversion is performed so as to include the bias signal component included in the conventional measurement value, the required resolution of the A / D conversion of the measurement value is obtained. In order to do so, a higher resolution A / D converter was required,
A cheaper low-resolution A / D converter can be used, and the bias signal component and the reference value signal 0V are taken in in the same manner as the measurement signal, so that the digital arithmetic processing unit mainly composed of the 5'microcomputer is used as a formware. The bias value is corrected by the program built in as
The error component of the input processing unit and the A / D conversion unit can be removed, and the automation can be prepared without manually adjusting the components conventionally adjusted by the variable resistor or the like, which improves the economical efficiency. Also, with respect to changes in parts over time,
Since the correction can be executed periodically at all times, the performance is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional basic example.

FIG. 2 is a diagram showing a basic example of an embodiment of the present invention.

FIG. 3 is a diagram similarly showing a basic example.

[Explanation of symbols]

5 '... Digital arithmetic processing unit, 8 ... Differential amplifier, 9, 1
0 ... switch.

Claims (3)

[Claims] 1. An industrial instrument that receives an analog measurement signal having a constant bias signal as an input, an input processing section for removing the bias signal, a switch section for switching between the signal from the input processing section, the bias component signal and the reference signal, and a switch. A / for taking in the signal from the digital processing unit to the digital arithmetic processing unit
An industrial instrument comprising a D signal conversion section, a circuit section for converting an output signal from a digital operation processing section into a pulse width signal, and a bias component signal generation section formed by a resistor, a capacitor and an operational amplifier using the pulse width signal as an input, The bias component signal of the unlogged measurement signal is generated from the pulse width signal by the bias component signal generation unit, and the bias component signal and the reference signal are taken into the digital operation unit via the switch unit and the A / D signal conversion unit. An input signal processing circuit of an industrial instrument having a function of correcting a pulse width signal so that a bias component signal is always constant. 2. The input processing unit for removing a bias signal according to claim 1, further comprising a switch unit for switching between a plurality of analog measurement signals and a bias component signal from the bias generation unit, and an output signal from the switch unit. An input signal processing circuit for an industrial instrument, wherein the input signal processing circuit is configured to use as an input signal of an input processing unit. 3. The input signal processing circuit for an industrial measuring instrument according to claim 1, wherein the bias component signal generating section comprises a digital / analog converter which receives a signal from the digital arithmetic processing section.