JPH0755952A - Hot-wire sensor - Google Patents

Abstract

PURPOSE:To avoid occurrence of false information due to noise in a hot-wire sensor. CONSTITUTION:An average value computing part 24 determines an average value of four consecutive data. By this averaging processing, white noise is removed. These average value data are made an absolute value by an absolute value attaining part 25 and this value is compared by a comparator 26 with a threshold value stored in a threshold value storage part 28. Only when all of the four consecutive average value data exceed the threshold value, the comparator 26 outputs an alarm signal SAL. In the other signal system, the data digitized by an A/D conversion part 30 are made an absolute value in an absolute value attaining part 31 and an average value of effective data in prescribed numbers is determined by an average value computing part 32. This average value represents an average level of noise, and based on this average value, the threshold value written in the threshold value storage part 28 is updated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat ray sensor, and in particular, it is an object of the invention to provide a heat ray sensor capable of avoiding occurrence of false alarm due to noise.

[0002]

2. Description of the Related Art A heat ray sensor for detecting an intruder by detecting far infrared rays emitted from a human body by a pyroelectric element is widely used in an alarm system and has a structure shown in FIG.

In FIG. 5, the light receiving means 1 comprises a pyroelectric element 2, a charging / discharging resistor 3, an FET 4, a load resistor 5 and the like. When far infrared rays from the warning zone are received by the light receiving optical system (not shown in FIG. 5), the amount of electric charge accumulated in the pyroelectric element 2 changes, but at this time, the pyroelectric element 1
Is charged and discharged through the resistor 3, and as a result, a voltage is generated across the resistor 3. This voltage is output to the load resistor 5 via the FET 4. This is the output voltage of the light receiving means 1. Here, the FET 4 is for impedance conversion.

As shown in FIG. 6, the output voltage of the light receiving means 1 is obtained by superimposing an AC signal generated by a change in the charge amount of the pyroelectric element 1 on a certain DC bias voltage V _BA . This output voltage is amplified by the amplifier 6 and further converted into an absolute value by the absolute value circuit 7 with reference to the DC bias voltage V _BA as shown in FIG. The comparator 8 compares the level of the input signal with a predetermined threshold value V _TH, and outputs a pulse when the level of the input signal exceeds the threshold value V _TH .

The output pulse of the comparator 8 can be used as it is as an alarm signal indicating an intruder, but normally, for the purpose of preventing the alarm signal from being output by a small animal, the comparator 8 outputs a pulse. A means for counting the output pulses is provided, and the alarm signal is output only when a predetermined number or more of pulses are output within a predetermined time from the first output pulse. That is,
Far-infrared rays are not emitted only by humans, but small animals such as cats and rats are also emitted. Normally, when humans cross one zone, 2-3 pulses are output, but in the case of small animals, one pulse is emitted. The pulse of is often output. This is because the amount of energy change received by the pyroelectric element differs depending on the size difference between humans and small animals. Therefore, the number of output pulses within a certain period of time is counted, and if the predetermined number is not reached, an alarm signal is not issued as a small animal, and thereby false alarm due to the small animal can be prevented. This function is usually called a pulse counting function.

The reason for providing the absolute value circuit 7 is as shown in FIG.
In order to set the threshold value of the comparator 8 to one as shown in FIG. 6, when the absolute value circuit 7 is not provided, the comparator 8 receives the DC bias voltage V _BA as indicated by V _TH1 and V _TH2 in FIG. Two central thresholds are needed.

[0007]

However, the output signal of the light receiving means 1 is not a beautiful signal as shown in FIG. 6 or 7, and usually contains a lot of noise as shown in FIG. Due to these noises, an alarm signal may be output even though there is no intruder. In addition,
In FIG. 8, 9 is an original signal, that is, a signal when an intruder or a small animal is detected, 10 is white noise, 1
1 indicates disturbance noise.

As noise, first, there is noise generated from a circuit element such as the FET 4, but in most cases this is white noise. In particular, it is known that the pyroelectric element 2 has a property that the amount of white noise generated increases when the ambient temperature changes rapidly. It has been confirmed that the peak of the white noise may exceed the threshold value of the comparator 8 by being amplified by the amplifier 6.

Further, since the pyroelectric element 2 responds to far infrared rays, if there is a change in heat around it, it will respond to it. Therefore, the output signal from the light receiving means 1 becomes large even when the temperature of the room suddenly changes due to the air conditioner, or when the temperature of the room suddenly rises due to the sun such as sunrise or cloud breaks. , False information may occur. That is, the alarm signal may be output even if there is no intruder. The noise generated by such a cause is generated by a change in the surrounding environment, and thus can be called disturbance noise.

As described above, there are various types of noise,
Moreover, since these noises may be combined, in that case, there is a higher possibility that a false alarm will occur.

As a method of avoiding such false alarm due to noise, it is conceivable to increase the threshold level of the comparator 8. Actually, the threshold level of the comparator 8 is set to about 10 times the level of white noise, and it is usual to avoid false alarm due to white noise, but the disturbance noise is larger than the white noise. In many cases, it is difficult to deal with disturbance noise by raising the threshold value of the comparator 8.

Of course, the threshold value of the comparator 8 can be set higher than the level of the disturbance noise, but in that case, it becomes difficult to detect an intruder, and the possibility of false alarm increases. That is, even if there is an intruder, there is a high possibility that the alarm signal will not be output.

As another method for avoiding false alarm due to noise, it is conceivable to set a large number of pulses to be counted when using the above-mentioned pulse counting function. In other words, if you increase the number of pulses to be counted,
If the noise disappears within that time, false alarm due to the noise can be avoided. However, increasing the number of pulses to be counted is nothing but making detection of an intruder more difficult, which increases the possibility of false alarm.

The present invention is intended to solve the above-mentioned problems, and it is possible to satisfactorily avoid false alarms due to noise without increasing the threshold value of the comparator and without increasing the number of pulse counts. It is intended to provide a sensor.

[0015]

In order to achieve the above object, the heat ray sensor according to claim 1 samples light receiving means including a pyroelectric element and an output signal of the light receiving means at a predetermined cycle, A signal processing means for obtaining an average value of a first predetermined number of consecutive sample values for each sampling and generating an alarm signal when the average value exceeds a threshold value for a predetermined number of times in succession. To do.

Further, the heat ray sensor according to claim 2 is the heat ray sensor according to claim 1, wherein the signal processing means is
Further, the output signal of the light receiving means is sampled at a predetermined cycle, an average value of absolute values of the sample values is obtained for every second predetermined number of sample values, and the threshold value is updated based on the average value. It is characterized by

[0017]

The output signal from the light receiving means is input to the signal processing means. The signal processing means samples the input signal at a predetermined cycle, and obtains an average value of a first predetermined number of consecutive sample values each time sampling is performed. Then, this average value is compared with a threshold value, and an alarm signal is generated when the average value continuously exceeds the threshold value a predetermined number of times.

The above is the operation of the heat ray sensor according to the first aspect. Thus, in this heat ray sensor, the output signal from the light receiving means is not directly compared with the threshold value as in the conventional case, but rather the light receiving means is used. The output signal of S is sampled to obtain the average value of the first predetermined number of sample values,
The average value and the threshold value are compared.

Therefore, the white noise as shown by 10 in FIG. 8 becomes almost zero when the average value is obtained, so that the white noise can be removed, and as a result, the threshold level becomes higher than necessary as in the conventional case. It is possible to satisfactorily avoid false alarm due to noise without increasing the height. That is,
It is not necessary to consider white noise when setting the threshold value.

The alarm signal can, of course, be used as it is as an alarm signal indicating the presence of an intruder, but a predetermined alarm signal is generated within a predetermined time by the pulse counting function as described above. Only in such a case, an alarm signal can be output when an intruder exists.

However, with the above configuration, the white noise can be removed, but the disturbance noise as indicated by 11 in FIG. 8 cannot be removed. This is because the disturbance noise is hardly zero even if the average value of a predetermined number of samples is calculated.

Therefore, as described in claim 2, the output signal of the light receiving means is sampled at a predetermined cycle, and the average of absolute values of the sample values is calculated for every second predetermined number of sample values. The threshold is updated based on the average value.

According to this, since the average value of the absolute values of the sample values is obtained, if there is white noise, a value corresponding to the level is obtained, and similarly, the disturbance noise as shown by 11 in FIG. If there is, a value corresponding to that level will be obtained.

That is, since this average value represents the noise level, the threshold value can be adaptively tracked to the noise level by updating the threshold value based on this average value. When disturbance noise or noise occurs, the threshold value increases according to the noise level, so that false alarms due to noise can be avoided.

[0025]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an embodiment of a heat ray sensor according to the present invention. In the figure, 20 and 21 are amplifiers, 22 is a signal processing means, 23 is an A / D conversion section, and 24 is an average value calculation section. , 25
Is an absolute value conversion unit, 26 is a comparator unit, 27 is a counter unit, 28 is a threshold value storage unit, 29 is a comparator unit, 30 is an A / D conversion unit, 31 is an absolute value conversion unit, 32 is an average value calculation unit, 33 Is a display control unit, 34 and 35 are display elements, S _A is an alarm signal, and S _K is an alarm signal. The same components as those shown in FIG. 5 are designated by the same reference numerals.

In FIG. 1, the light receiving means 1 has a structure similar to that shown in FIG.
Is amplified by. Then, the output signal of the amplifier 6 is branched into two, one signal is amplified by the amplifier 20 and input to the signal data input terminal AD ₁ of the signal processing means 22,
The other signal is amplified by the amplifier 21 and is processed by the signal processing means 22.
Is input to the noise data input terminal AD ₂ .

Here, the amplification factor of the amplifier 21 is equal to that of the amplifier 20.
The amplification factor is N times (where N> 1). This is for the following reason. The signal processing means 22 is composed of a microprocessor and its peripheral circuits, and its resolution is uniquely determined by the number of bits that can be handled. For example, when using an 8-bit microprocessor, the resolution is 1/256 with respect to the power supply voltage.

However, as will be described later, the input terminal AD ₁
In the signal system of (1), the intruder is detected based on the original signal generated by a human or the like among the signals output from the light receiving means 1, whereas the signal system of the input terminal AD ₂ detects the amount of noise. and is intended to, therefore, the level of the signal handled in the signal system of AD ₂ is sufficiently small compared to the level of the signal handled in the signal system of the AD _1, AD ₁ of the signal in the signal system of AD ₂ It requires higher resolution than the system.

Therefore, the amplification factor of the amplifier 21 is set to the amplifier 20.
Therefore, the resolution of the AD ₂ signal system is made equal to the resolution of the AD ₁ signal system.
The value of N is the resolution of the microprocessor used,
Alternatively, it may be determined in consideration of the amplification factor of the amplifier to be used, etc. It has been confirmed that, for example, when an 8-bit microprocessor is used as the signal processing means 22, N = 4 is sufficient.

The signal processing means 22 comprises a microprocessor and its peripheral circuits.
The configuration shown in FIG. The operation of each part of the signal processing means 22 will be described below.

The signals input to the input terminals AD ₁ and AD ₂ are synchronously sampled by the A / D converters 23 and 30 in a predetermined cycle, respectively, and converted into digital data of a predetermined number of bits, for example, 8 bits. It Synchronous sampling here does not necessarily mean that sampling is performed at the same time, and may be slightly deviated in time. However, it goes without saying that the time lag needs to be always constant. Note that sampling is performed here every 10 msec.

When the n-th data is output from the A / D converter 23, the average value calculator 24 outputs the (n-3) -th data, the (n-2) -th data, and the (n-th) data. -1) Obtain an arithmetic mean value (hereinafter, simply referred to as an average value) of the 4th data of the nth data and the nth data generated this time. Then, 10 msec later, the A / D converter 23 outputs (n +
1) When the second data is output, the average value calculator 24
Is an average value of four data of the (n-2) th data, the (n-1) th data, the nth data, and the (n + 1) th data generated this time. .

As described above, the average value calculation unit 24 uses the A / D
The above process is repeated every time the conversion unit 23 generates digital data every 10 msec.

As described above, the average value calculation unit 24 is 10 mse.
The average value data is generated for each c, and the average value data is converted into an absolute value by the absolute value conversion unit 25. Hereinafter, the average value data converted into absolute values will be referred to as signal data.

FIG. 2 shows this process in the figure.
That is, in the A / D converter 23, S ₁ , S ₂ , and S in FIG.
_{As shown by 3} , S ₄ , S ₅ , S _6, ..., Digital data is generated every 10 msec. Then, the average value calculator 24
Is, S ₄ data S ₄ are Once generated, which is generated this time
Then, the average value of the _three data S ₁ , S ₂ , and S ₃ immediately before is calculated to generate average value data. Then, this average value data is converted into an absolute value by the absolute value conversion section 25 and becomes the signal data D _{1 of} FIG. 2B. Average calculator 24 Similarly, generates the data S ₅ is generated, and S _5, which is generated this time, the average value data obtains an average value of the three data S ₂ immediately before, S _3, S ₄ To do. Then, this average value data is converted into an absolute value by the absolute value conversion section 25, and the signal data D _{2 of} FIG.
Becomes

It is clear that the white noise is removed by the averaging process and the absolute value process described above.
Now, for example, considering that no human or small animal crosses the warning zone for easy understanding, the input terminal A
As shown in FIG. 3A, a signal in which an AC signal of white noise is superimposed on the DC bias voltage V _BA is input to D ₁ , and this signal is sampled as described above to obtain an average value. It is clear that when averaged by, it becomes approximately V _BA . Therefore, when this average value data is converted into an absolute value, it becomes as shown in FIG. 3B.

The signal data from the absolute value conversion section 25 is input to the comparator 26. The comparator 26 compares the signal data with the threshold value V _TH stored in the threshold value storage unit 28, and only when all the values of four consecutive signal data exceed the threshold value V _TH , the alarm signal S _AL. Is output.
For example, in FIG. 2B, four pieces of signal data D ₁ , D ₂ ,
When all the values of D ₃ and D ₄ exceed the threshold value V _TH ,
The comparator 26 outputs the signal data D ₄ as shown in FIG. 2C.
The alarm signal S _AL is output at the timing.

As described above, the reason that the alarm signal is output only when the four signal data continuously exceed the threshold value V _TH is that a human walking speed is 0.3 m / sec to 2 m.
Since it takes m / sec, it takes at least 40 msec for a human to cross the warning zone, and the signal data D should exceed the threshold value V _TH during that time. Then, even when spike-like noise or the like which shows a high level momentarily but disappears in a short time is mixed, it is possible to prevent the alarm signal from being generated by such noise.

The alarm signal S _AL output from the comparator 26 can of course be used as it is as the alarm signal S _K indicating the presence of an intruder, but in the configuration shown in FIG. 1, the alarm signal S _AL is input to the counter section 27. Has been done. The counter unit 27 realizes the pulse counting function described above, and outputs the alarm signal S _K only when the predetermined number of alarm signals S _AL are counted within a predetermined time. It is possible to arbitrarily set the number of alarm signals, that is, how many alarm signals should be output within a predetermined time period before the alarm signal is output. In addition,
Since the pulse counting function is well known, detailed description will be omitted.

The processing of the AD ₁ signal system has been described above. Next, the processing of the AD ₂ signal system will be described.

The analog signal input to the input terminal AD ₂ is converted into digital data by the A / D conversion section 30, converted into an absolute value by the absolute value conversion section 31, and input to the average value calculation section 32.

The average value calculator 32 collects the data generated by the A / D converter 30 when the data is valid, and when 16 valid data are collected as shown in FIG. 4A, the average value is calculated. The value is obtained and one average value data is generated as shown in FIG. 4B. When one average value data is generated, the average value calculation unit 32 collects 16 valid data again, calculates the average value thereof, and repeats the process of generating the average value data.

Then, as shown in FIG. 4C, the average value calculator 32 generates (n-
3) 4th average value of average value data, (n-2) th average value data, (n-1) th average value data, and nth average value data generated this time The process of obtaining the average value of the data is repeatedly executed. This becomes noise data. The signal level of the signal system of AD ₂ is M of the signal level of the signal system of AD ₁ by the amplifier 21 in advance.
Since the average value calculation unit 32 obtains the average value of four consecutive average value data, the average value calculation unit 32
Double and adjust to the signal level of the signal system of AD ₁ . It will be apparent that this is the finally obtained noise data N, and that this has a value according to the noise level including all noises such as white noise and disturbance noise. That is, the signal system of AD _{2 is} a signal system for detecting the noise level.

Further, when the average value calculator 32 generates the _n-th noise data N _n , it calculates (N _n -N _n-1 ) and generates (n-1) immediately before that. The increase / decrease from the _nth noise data N _n-1 is calculated, and the (N _n −N
The _n-1 value of) notifies the threshold value storage unit 28 repeatedly executes the process of adding the value of the threshold so far (N _n -N _n-1). As a result, the threshold value stored in the threshold value storage unit 28 is adaptively updated according to the noise level. Then, the updated threshold value is held until the next update, and is used as the threshold value of the comparator 26. It should be noted that in the initial state, a predetermined default value is written as a threshold value in the threshold value storage unit 28, but this threshold value is adaptively updated by the processing described above.

Therefore, when the white noise increases or the disturbance noise occurs, the noise level rises, so that the threshold value also rises, and as a result, the false alarm due to the noise is generated. It is possible to avoid it.

By the way, first, the average value calculation unit 32 uses A /
Although it has been stated that only valid data among the data generated by the D conversion unit 30 is collected, this is as follows. That is, when the data generated by the A / D conversion unit 23 exceeds the threshold value V _TH written in the threshold value storage unit 28, this data is highly likely to be a person detection. The data generated by the A / D converter 30 in synchronization with this data is not desirable as data for detecting the noise level.

Therefore, it is necessary to invalidate undesired data as data for detecting such a noise level, and the comparator 29 is provided for that purpose.

Each time the comparator 29 generates data in the A / D converter 23, the value of the data and the threshold storage 2
The threshold value V _TH written in 8 is compared, and if it exceeds the threshold value V _TH , the prohibition pulse P _DE is notified to the average value calculation unit 32.

In response to this, when the average value calculation unit 32 receives the inhibition pulse P _DE , it is synchronized with this and the A / D conversion unit 30.
Invalidates the data generated in and does not collect it. Then, after waiting for the next valid data and collecting 16 valid data, the process of obtaining the average value is performed.

As described above, all the data generated by the A / D conversion unit 30 is not valid, and A / D of the signal system of AD ₁ is not used.
Only when the value of the data generated by the D conversion unit 23 is less than or equal to the threshold value V _TH , the data synchronized with the pulse becomes valid. Therefore, the timings at which the average value data shown in FIG. 4B and the noise data N shown in FIG. 4C are generated are not constant.

By the way, the average value calculation unit 32 is (N _n -N
The value of ( _n-1 ) is also notified to the display control unit 33. Display control unit 33 with respect to which is compared with two thresholds V _UL, V _LL value set in advance the value of _{(N n -N n-1)} . Here, the threshold value V _UL is a value indicating the upper limit of the allowable noise level, and the threshold value V _LL is a value indicating the minimum value of the noise level that at least this level of noise exists.

Then, the display control unit 33 displays (N _n -N
_If the value of ( _n-1 ) exceeds the threshold value V _UL , one display element, for example, the display element 34 is turned on, and (N _n -N
_When the value of ( _n-1 ) is less than the threshold value V _LL , the other display element, for example, the display element 35 is turned on.

Therefore, when the display element 34 is turned on, the user must confirm that the noise level is abnormally high, that is, the environment around the heat ray sensor is deteriorated and the heat ray sensor cannot be used normally. You can know the display element 35
If is lit, it is possible to know that the noise level is abnormally low, that is, there may be an abnormality such as a disconnection in the signal system of the heat ray sensor. It can be performed. Appropriate display elements such as LEDs can be used as the display devices 34 and 35.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. For example, although two display elements are used in the above embodiment, one display element may change the blinking cycle.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining processing in the signal system of AD ₁ in FIG.

FIG. 3 is a diagram for explaining the meaning of processing of the absolute value conversion unit 25 in FIG. 1.

FIG. 4 is a diagram for explaining processing in the AD ₂ signal system of FIG. 1;

FIG. 5 is a diagram showing a configuration example of a conventional heat ray sensor.

FIG. 6 is a diagram showing an example of an output signal waveform of the light receiving means 1.

FIG. 7 is a diagram for explaining conversion of an output signal of the light reception output 1 into an absolute value.

FIG. 8 is a diagram for explaining a problem of a conventional heat ray sensor.

[Explanation of symbols]

20, 21 ... Amplifier, 22 ... Signal processing means, 23 ... A /
D conversion unit, 24 ... Average value calculation unit, 25 ... Absolute value conversion unit, 2
6 ... Comparator part, 27 ... Counter part, 28 ... Threshold value storage part, 29 ... Comparator part, 30 ... A / D conversion part, 3
1 ... Absolute value conversion part, 32 ... Average value calculation part, 33 ... Display control part, 34, 35 ... Display element, S _A ... Alarm signal, S _K
... alarm signal.

Claims (2)

[Claims] 1. A light receiving means including a pyroelectric element, and an output signal of the light receiving means is sampled at a predetermined cycle, and an average value of a first predetermined number of consecutive sample values is obtained for each sampling, and the average thereof is calculated. A heat ray sensor, comprising: signal processing means for generating an alarm signal when the value continuously exceeds a threshold value a predetermined number of times. 2. The signal processing means further samples the output signal of the light receiving means at a predetermined cycle, and obtains an average of absolute values of the sample values for every second predetermined number of sample values, The heat ray sensor according to claim 1, wherein the threshold value is updated based on the average value.