JPH0542632B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is directed to a microcomputer (hereinafter referred to as μCPU).
This invention relates to an analog signal input device using an analog signal input device.

In recent years, due to advances in μCPU and its peripheral technology,
Opportunities to apply μCPUs to measurement control equipment for various processes are increasing. All signals that can be processed by the μCPU are digital signals, so when an external analog signal is input to the μCPU, it must be done through an AD conversion circuit. Further, it is common to provide signal insulation between various process signals and the inside of the equipment, and generally process signals are isolated from the inside of the equipment via a signal isolator.

FIG. 1 shows a configuration diagram in which an analog signal is input to a μCPU using a voltage-frequency conversion circuit (hereinafter abbreviated as a VF conversion circuit). In the same figure, VF
The conversion circuit 1 receives an analog signal from the outside and converts it into a frequency signal. The signal insulator 2 insulates the frequency signal from the VF conversion circuit 1 using a photocoupler or the like. The interval timer 3 measures the frequency signal input from the signal isolator 2 and outputs it to the μCPU 4. Based on the frequency signal measured by μCPU4,
Calculate the input voltage.

Figure 2 shows details of the VF conversion circuit 1.
It is composed of an integrator 5, a comparator 6, a one shot 7, and a constant current source 8. To explain the operation of this VF conversion circuit 1, when the voltage V _c input to the comparator 6 is "0" or less, the one shot 7 is activated, the output ₀ becomes "H", and at the same time the switch SW
1 to turn on the constant current source 8. At this time, the capacitor C1 of the integrator 5 starts charging and _Vc rises at a slope of _dv / _dt =( _Ic -Vin/R)/C1 during the one-shot time T. After one-shot time T, output ₀ becomes “L” and at the same time the constant current source is turned on.
To turn off, capacitor C1 starts discharging at a slope of d _v /d _t = -Vin/R1C1. Capacitor C as it is
1 continues discharging, and when V _c becomes "0", one shot 7 works again, output ₀ becomes "H", and the constant current source is turned on. After that, this operation is repeated, and the output ₀ repeats "H" and "L".

FIG. 3 is a time chart showing the relationship between the voltage V _c of the VF conversion circuit 1 and the output ₀ .

The signal “L” from this VF conversion circuit 1 is output to the interval timer 3 via the signal isolator 2,
The interval timer 3 measures the "L" time t and outputs it to the μCPU 4. In μCPU4, (I _c −Vin/R ₁ )/C1×T=Vin/R1C1×t……(1
) Rearranging equation (1), Vin=I _c R ₁ /1+t/T=K/1+t/T...(2) (K, T are constants specific to the circuit) By performing the calculation, input voltage Vin can be calculated. demand.

In this way, external analog signals can be transferred to the μCPU.
However, in a system that repeatedly compares and judges the setting value preset in the μCPU with an external analog signal, the analog input method described above cannot be used. That is, in addition to the time required to measure t of the external analog signal, a considerable amount of time is required to perform the calculation of equation (2) above, and the cycle of repeated comparison and judgment operations cannot be shortened. However, in a system with a cycle shorter than this repetition cycle, the above analog input method could not cope with the problem.

The present invention has been made in view of the above circumstances, and its purpose is to provide an analog input device that can compare and judge analog signals using a VF conversion circuit in a short time. It is something.

Hereinafter, the present invention will be explained in detail based on FIGS. 4 and 5.

In FIG. 4, two analog signals V _s and V _p are connected to the Oobu preamplifiers 9 and 9 a, the VF conversion circuits 1 and 1 a, and
Isolators 2 and 2a and interval timers 3 and 3a
Input to μCPU4 via.

FIG. 5 shows a functional block diagram of the μCPU 4. In the same figure, 41 is a measured value input section, and the measured values ts and tp measured by each interval timer 3 and 3a.
Enter. Reference numeral 42 denotes a correction unit that performs a correction calculation on the measured value ts as a set value from the measured value input unit 41 to obtain a pulse width, and stores this pulse width in the set value storage unit 43. This correction is for example analog 2
This is a correction performed to match the level of the other when comparing quantities. In this correction calculation, as shown in FIG. 4, assuming that each analog signal _{is Vs} , _Vp , the set value voltage calculation means calculates the analog signal _Vs based on the measured value ts using equation (3).

V _s = K _s /1 + t _s /T _s -1 ...(3) t _s : Measured value K _s , T _s : Constant In equation (3), adding "-1" to equation (2) means that
Setting the positive phase input of the integrator in the VF conversion circuit to -1V prevents the pulse width from becoming infinite when the input voltage is "0" and making measurement by the interval timer impossible. This is to ensure that the pulse width does not become unnecessarily long even for a minute input voltage and remains within a certain pulse width. Then, the set value correction means calculates the pulse width tps for the analog signal V _p to be compared using equation (4).

tps=Tp×(Kp/V _s +1−1) (4) Store this tps in the setting value storage section 43.

44 is a comparison/judgment section that compares the pulse width stored in the set value storage section 43 with the measured value inputted from the measured value input section 41, that is, the pulse width.

Next, the operation of the device configured as described above will be explained.

Now, when comparing analog signals V _s and V _p with different levels, the analog signal V _s is input to the preamplifier 9,
The measured value ts as a set value is input to the measured value input section 41 via the VF conversion circuit 1, the insulator 2, and the interval timer 3. This measured value ts is calculated by the correction unit 42
Then, calculations of equations (3) and (4) are performed to obtain the pulse width tps, and this pulse width tps is stored in the set value storage section 43.

In this way, the pulse width tps of the analog signal _Vs is stored in advance as a set value. Then, the analog signal Vp is sent to the preamplifier 9a and the VF conversion circuit 1.
a. The measured value tp is input to the measured value input section 41 via the insulator 2a and the interval timer 3a, and the comparison/judgment section 44 compares this measured value tp with the set value tps stored in the set value storage section 43. Compare and judge the size.
After the comparison and determination, the analog signal Vp is taken in again and the same processing is performed continuously.

In this way, based on a certain analog signal,
When reading other analog signals at certain cycles and comparing and determining them, there is no need to perform calculations compared to the conventional method, and it is possible to handle even very short cycles.

In other words, if the conventional method is used as shown in Figure 6,
As shown in the flowchart showing the comparison between (a) and the case (b) when the comparison is made according to the present invention, in the case of the conventional method (a), the measurement of the pulse width ts of the set value ( S1), calculation of set value V _s (S2), analog signal Vp
In contrast to the processing steps of measuring the pulse width tp (S3), calculating the analog signal value Vp (S4), and comparing the set value V _s and the analog signal Vp (S5), in the case of the present invention,
(b) Measures the pulse width ts of the set value (S11), and
Calculation of V _s (S12), calculation of pulse width tps for analog signal Vp (S13), measurement of pulse width tp of analog signal Vp (S14), comparison with pulse width, tps, tp (S15), and once. The time required for judgment can be significantly shortened, and analog signals can be detected in short cycles.

Also, in equation (3), suppose K _s = 10V, T _s =
When _Vs = 0V, ts=900μsec, and when _Vs >0, ts<900μsec. Therefore, the time required for the μCPU to input data using the interval timer is about 1 msec or less. On the other hand, the calculation of equation (3) is performed by μCPU4
If you use this program, it will take about 10 msec. Considering these times, in the conventional method, (1 msec + 10 msec) x 2 = 2 msec
It is impossible to judge the magnitude of V _s and Vp in a cycle shorter than this. In contrast, in the present invention, the time required to compare the magnitudes of each analog signal V _s and Vp once is only the time to measure tp, which is within 1 msec in the above example, which is faster than the conventional method. The time required for judgment can be significantly shortened, and therefore, when large/small judgments are made continuously, the period of detection can be significantly shortened.

In this embodiment, a method has been described in which two analog quantities are taken in and compared, but it goes without saying that the comparison can also be made using set values from the operator console.

As described above, the present invention uses a μCPU to input analog quantities of various processes while maintaining signal isolation, and compares and judges them with preset analog quantities. By using a conversion circuit, a frequency signal isolator, and an interval timer to measure the pulse width corresponding to the input voltage and having the μCPU calculate the input voltage, a simpler and more compact circuit can be realized compared to other methods. On the other hand, it takes a certain amount of time for the μCPU to calculate the input voltage, so it takes that much time to compare one analog signal, and when comparing analog signals continuously, it takes a certain amount of time to calculate the input voltage. However, in the present invention, before continuously comparing analog signals, a preset analog quantity is input, and the corresponding analog signal pulse width is calculated. When comparing analog signals, the set value and analog signal are compared by measuring the pulse width corresponding to the analog signal and comparing it with the previously calculated pulse width corresponding to the set value. Furthermore, since the time required for one analog signal comparison is approximately the time required to measure the pulse width corresponding to the analog signal, the cycle can be shortened even when analog signals are compared continuously.

In other words, when comparing analog signals while insulating the signals, (1) the circuit configuration is simple, small, and low cost;

(2) Compared to conventional methods, there is no need to take the time to calculate analog values, allowing for faster comparisons and judgments.

(3) Even when comparing continuously, it has excellent advantages such as being able to process in short cycles.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an analog input device using a conventional VF conversion circuit, Fig. 2 is a detailed circuit diagram of the conventional VF conversion circuit, and Fig. 3 is a graph diagram for explaining the conventional VF conversion circuit. FIG. 4 is a block diagram showing an embodiment of the present invention, FIG. 5 is a functional block diagram of the μCPU 4 of the present invention, and FIG. 6 is a flow chart comparing the present invention with the conventional system. 1 and 1a are VF conversion circuits, 2 and 2a are signal isolators, 3 and 3a are interval timers, 4 is μCPU, 5 is integrator, 6 is comparator, 7 is one shot, 8 is constant current source, 9 and 9a are A preamplifier, 41 is a measured value input section, 42 is a correction section, 43 is a set value storage section, and 44 is a comparison/judgment section.

Claims (1)

[Claims] 1. A microcomputer is provided to input analog signals of set values and measured values through a voltage-frequency conversion circuit, a signal isolator, and an interval timer, respectively, and the microcomputer is provided with: A measurement value input section that receives the set value from the timer and the pulse width of the measured value, and a setting that calculates the voltage of the set value from the pulse width of the set value and the circuit constant of the voltage-frequency circuit on the set value input side. Correction comprising a value voltage calculation means and a set value correction means for correcting the pulse width of the set value from the voltage of this set value and the circuit constant of the voltage-frequency conversion circuit on the measured value input side so as to correspond to the measured value input side. a set value storage unit that stores the value from the correction unit; and a comparison determination unit that compares the value stored in the set value storage unit with the pulse width of the measured value. An analog signal input device characterized by: 2. Claim 1, characterized in that the setting values are input from the operator console.
The analog signal input device described in Section 1.