JPH0658604B2 - How to remove sinusoidal input noise - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a method for removing sinusoidal input noise, and more particularly to a signal input device for sampling an analog input signal at fixed time intervals and taking it into a computer. The present invention relates to a method of removing sinusoidal input noise having a period shorter than the included sampling period regardless of its amplitude.

(B) Prior Art In general, it is often the case that a plurality of analog input signals are switched by a multiplexer for A / D conversion and multichannel input signals are taken into a computer. In such a signal input device, a high-frequency noise having a short cycle or a sinusoidal low-frequency noise having a commercial power frequency of about 60 Hz (50 Hz) may be superimposed on an analog input signal to be added, and conventionally, these noises are removed. For this purpose, RC filters and active filters are used. The filter for removing high frequency noise is small, but there is no problem, but in the case of low frequency noise that is several to several tens of times the sampling frequency, for example, the electrostatic capacitance for the filter becomes large, and the cost and space are high. It is not desirable because it will occur. This is particularly remarkable in the case of multi-channel input. Furthermore, in the case of an analog filter, if the amplitude of noise is large, it cannot be attenuated sufficiently and the removal effect becomes insufficient.

(C) Objective The object of the present invention is to solve the drawbacks of the conventional noise removing method by the filter, does not require an installation space, does not increase the cost, and has a novel sine effect that does not change depending on the amplitude of the noise. It is to provide a method of removing wavy input noise.

(D) Configuration In order to achieve the above object, the present invention realizes removal of sinusoidal input noise by software processing of a CPU (central processing unit). That is, according to the sinusoidal input noise removing method of the present invention, the second sampling process is performed in synchronization with the normal sampling period (first) for three analog signal inputs in a period shorter than this sampling period. Input signal value y for each of these three samplings
1, y2, y3 are detected, and these input signal values y1, y
2 and y3 are constants determined by the frequency of the sinusoidal input noise and the second sampling period (However, ωΔt, ω: angular velocity of sinusoidal input noise) is multiplied to calculate K1y1 + K2y2 + K3y3, and b =
The true analog input signal value b is obtained from K1y1 + K2y2 + K3y3.

(E) Embodiment Hereinafter, the present invention will be described in more detail with reference to an embodiment shown in the drawings.

FIG. 1 is a block diagram of an input signal device in which the present invention is implemented. In the figure, the channel CH1 analog input signal applied to the input terminal 1 is applied to the multiplexer 3 via the high frequency noise elimination filter 2 including the resistor R and the capacitor C. Further, the analog input signals of the channels CH2, CH3, ... CHN (not shown) are also applied to the multiplexer 3 via the high frequency noise elimination filter. Multiplexer 3
Performs input switching according to a switching command from the CPU 5 which will be described later, and outputs input signals in a channel sequence to output the A / D converter 4
Add to. The A / D converter 4 converts the analog input signal into a digital signal based on the conversion command from the CPU 5,
It is supposed to be added to U5. According to the flow shown in FIG. 4 and FIG. 5, the CPU 5 executes the processing of removing the sinusoidal input noise of each channel and the processing of capturing the true input signal value. A one-shot multi-circuit 6 receives a trigger signal from the CPU 5 and outputs an active signal (high signal) to the CPU 5 for a certain period of time. The one-shot circuit 6 is used as a time signal circuit of the CPU 5, and therefore, instead of the one-shot circuit 6, a counter or a timer circuit that outputs a signal for a fixed time may be used.

In the signal input device shown in FIG. 1, the analog signal applied to the input terminal of each channel has high frequency noise removed by a high frequency noise removal filter 2, but a sine wave input noise of commercial frequency is superimposed on the multiplexer 3. It is input as it is. FIG. 2 shows an example of channels CH1 and C.
The input signal waveform time chart to the multiplexer 3 of H2 is shown. Also in the figure, b is the true value of the analog input signal, and sinusoidal input noise of amplitude a is superimposed on this signal b. The period Ta of sinusoidal input noise is about 1
It is 6.7 msec. Ts is a normal sampling period, and this value is several times to several tens times, that is, several hundred msec of the period Ta of the sinusoidal input noise.

In the apparatus shown in FIG. 1, the CPU 5 synchronizes with the normal sampling cycle Ts and performs a finer sampling process (hereinafter referred to as a short cycle sampling) every normal sampling cycle Ts at a cycle Δt sufficiently shorter than this cycle Ts. Are performed three times (t1, t2, t3 in FIG. 2).
-See t4, t5, and t6).

Here, the principle of removing the sinusoidal input noise in the signal input device will be described. When the input signal as shown in Figure 3 is assumed to be y = asinωt + b, short cycle △ when three sampling by _{t t 0 - △ t, t} 0, t 0 + △ each input signal value of t, respectively y1 _{= asin (ωt 0 -ω △ t} ) + b ...... y2 = asinωt 0 + b ...... y3 = asin (ωt 0 + ω △ t) + b ...... However ω: a sinusoidal input noise of the angular velocity. If θ = ωt ₀ , = ωΔt, the above equations ~ will be y1 = asin (θ −) + b …… y2 = asin θ + b …… y3 = asin (θ +) + b …….

Y1 + y3 = 2a sin θ cos + 2b …… When asin θ is deleted from the formula and the formula, y1 + y3 = 2 (y2-b) cos + 2b …… However In the above equation, K1, K2, and K3 are constants determined by the frequency of the sinusoidal input noise and the short-period sampling period, and therefore, as is clear from the equation, the input values y1, y2 obtained by three short-period samplings. , Y3, the true input value b can be obtained.

The CPU 5 of the embodiment signal input device shown in FIG. 1 is adapted to obtain a true input value for each channel based on the above principle.

Next, the operation of the signal input device of the above embodiment will be described with reference to the flow charts shown in FIGS.

When the operation starts, first, the counter i built in the CPU 5 is cleared [step ST (hereinafter referred to as ST).
1]. This counter i is for counting the number of short-period samplings performed within the normal sampling period Ts three times. After clearing the counter i, the one-shot multi-circuit 6 is triggered (ST2). Subsequently, the counter i is subjected to +1 processing (ST3). In the first operation cycle, i = 1. Then, input signal data for NCH from 1CH to NCH is taken in (ST
4). The detailed processing procedure of this data fetching routine is as shown in FIG. 5, where the counter n built in the CPU 5 is cleared (ST41), and then the counter n is incremented by 1 (S41).
T42), the multiplexer 3 is switched according to the contents of the counter n (ST43). Since n = 1 at the beginning, the multiplexer 3 first derives the input signal of the channel CH1. The derived analog input signal is converted into a digital signal by the A / D converter 4 (ST44). Subsequently, the digital data converted by the A / D converter 4 is stored in the yi data storage area of the channel n in the CPU 5 (ST4
5). Initially, y1 of the channel CH1 is stored. Next, it is determined whether the content of the counter n has reached the total number N of channels (ST46). Then, until the content of the counter n reaches N, that is, until the storage of the input data yi (initially i = 1) is completed for all the channels, the process returns to ST42, the counter n is incremented by 1, and the channel of the multiplexer 3 is switched to the next. Store the input data of the channel. That is, the processes of ST42 to ST46 are repeated N times. When ST42 to ST46 are repeated N times,
The input data yi of all channels are stored in the corresponding storage area of the CPU 5, the determination in ST46 is YES, the operation moves to ST5 in FIG. 4, and i = 3? judge. In the first operation cycle, this judgment is NO, and then the one shot end? That is, it is determined whether the output signal triggered by the one-shot multi-circuit 6 falls to low (ST
6). If the output of the one-shot multi circuit 6 has not fallen to low, it means that the short sampling period Δt has not elapsed since it was triggered, and ST6 is output until the output of the one-shot multi circuit 6 falls to low. Stay in time and wait.

When the output of the one-shot multi circuit 6 falls to low, it means that the time of Δt has passed from the first trigger, and ST
After returning to 2, the one-shot multi-circuit 6 is triggered again, and then the counter i is incremented by 1 to set i = 2 (S
T2), the data for N channels is taken in, that is, the second short cycle sampling is performed (ST4), and the sampling value y2 of each channel is stored in the storage area of the CPU 5. Even after the data of this sampling value y2 is taken in, S
After T5, in ST6, wait for the end of the one-shot time. When the one-shot time ends in ST6, that is, when the output of the one-shot multi-circuit 6 falls to low, the process returns to ST2 in the same manner as the previous time, and then ST2.
The processing from ST4 to ST4 is continued, the third short cycle sampling is performed, and the sampling value y3 of each channel is stored in the storage area of the CPU 5. Subsequent to the data acquisition of the sampling value y3, is i = 3 in ST5? The determination is made, but the determination is Y by the sampling of three short cycles.
It is ES, and then the true value of the signal input of each channel is calculated.

To calculate the true value, first clear the counter n (ST
7) Then, the counter n is incremented by 1 (ST
8). As a result, n = 1, so the channel CH continues.
The sampling values y1, y2, y3 of 1 are read from the storage area of the CPU 5, and b = K1 (y1 + y3) + K2y2
Then, the true value b of the signal input to the channel CH1 is calculated and stored in the storage area. Then, in ST10, n = N? (NO at the beginning is n = 1 <N), NO is returned to ST8, n = 2 is set, and the true value b of the signal input to the channel CH2 is calculated and stored by the same equation as above. ST1 after that
The process of 0 → ST8 → ST9 → ST10 is repeated to calculate the true value b of signal input for all channels. In this way, the true value from which sinusoidal input noise is removed can be obtained for all channel signal inputs.

As a special case of the above embodiment, the short period sampling period Δt is 1/4 of the period of sinusoidal noise noise (cos = 0 if the noise is 60 msec commercial frequency is 4.2 msec). , The true value b is Therefore, the true value b can be calculated only by the first and third sampling values y and y3 having a short period, and the true value of the signal input from which the sinusoidal noise is removed can be obtained by a simpler process.

In the above embodiments, a multi-channel signal input device is described, and the present invention is suitable for use in a multi-channel signal device, but multi-channel is not essential for the present invention, and the present invention is It can also be applied to a signal input device that receives a single input signal.

(F) Effect According to the sinusoidal input noise removing method of the present invention, the sampling process is performed three times with a period shorter than the period of the sinusoidal input noise, and thereafter, the sinusoidal input noise is obtained by performing a very simple operation. The true value of the signal from which noise is removed can be obtained, and a large analog filter for attenuating the commercial frequency of 60 Hz (50 Hz) is unnecessary. Therefore, the space for installing the analog filter is unnecessary, so the device can be downsized and the cost can be reduced. You can measure. Moreover, unlike an analog filter, noise can be removed regardless of the amplitude of the noise. Further, since the time required to obtain the true value of the signal input is short (2Δt), the response delay is small, and most of the extra time in the normal sampling cycle can be used for other calculations. it can.

[Brief description of drawings]

FIG. 1 is a block diagram of a signal input device in which the present invention is implemented, FIG. 2 is a time chart showing an example of a waveform of a signal input to a multiplexer of the signal input device, and FIG.
FIG. 4 is a waveform diagram for explaining the principle of removing the sinusoidal input noise by the signal input device shown in FIG. 4, FIG. 4 is a flow diagram for explaining the operation of the signal input device of FIG. 1, and FIG.
FIG. 9 is a flow chart showing in detail an N-channel data import routine of the flow shown in FIG. 1: Input terminal, 2: High frequency noise elimination filter, 3: Multiplexer, 4: A / D converter, 5: CPU, 6: One-shot multi-circuit.

Claims (1)

[Claims] 1. A method of removing a sinusoidal input noise having a period shorter than the sampling period included in the analog input signal in a signal input device for sampling the analog input signal at a constant time interval and loading it into a computer. In synchronization with the sampling cycle, the second sampling processing of the analog input signal is performed three times in a cycle shorter than the sampling cycle to obtain the input signal values y ₁ , y ₂ , y ₃ at each sampling. A constant determined by the frequency of the sinusoidal input noise and the second sampling period for the detected input signal values y ₁ , y ₂ , y _3. (However, ωΔt, ω: angular velocity of sinusoidal input noise) is multiplied to obtain a true analog input signal value b from K ₁ y ₁ + K ₂ y ₂ + K ₃ y ₃ How to remove input noise.