JP3416840B2 - Iron piece detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron piece detecting device,
, Various textile products, sewing clothing, carpets, textiles
Il, felt, non-woven fabric, food, medical products, packed products
Detector for detecting iron pieces mixed in steel etc.
Container). [0002] For example, a sewing needle breaks during a sewing operation.
Is not unusual, and also used during sewing work
Sometimes he forgets to pull the waiting hand. But garment clothing
If there is a remaining needle such as a broken needle or
May cause harm to the user of the garment.
For garment items, iron detection equipment
Inspection of the remaining needle is often performed by a (needle detector)
Various textile products, carpets, textiles, textiles
Lts, non-woven fabrics, food products, medical products, packed products, etc.
Also, iron that is mixed in the product by the iron piece detection device
Often pieces are detected. [0003] By the way, the above-mentioned detection of the iron piece is a conventional method.
Mainly focus on the detection of so-called metal detectors and members made of ferromagnetic materials.
Performed using an iron piece detector etc. configured for the purpose
The iron piece detector described above, for example,
A member for generating a DC magnetic field using a permanent magnet;
DC magnetic field generated by the DC magnetic field
With the detection coil configured with the windings where the bundles interlink
Sensor section (needle section) and the sensor section described above.
The detection signal voltage generated in the output coil is amplified and
Increase when the detection signal voltage exceeds a predetermined threshold
Depending on the output of the instrument, a visual indicator or an audible
In general, those with a configuration mode in which the expression means are operated
Had been used. That is, as described above, the permanent magnet and the
And the detection coil where the magnetic flux generated by the permanent magnet
And the object to be detected
The two are relatively displaced with the person approaching.
Then, an object made of a ferromagnetic material is formed on the object to be detected.
If included, it is generated by the permanent magnet in the sensor
The number of magnetic fluxes linked to the detection coil
Object made of ferromagnetic material and the sensor
The detection coil detects the change in response to the displacement.
Since the output signal voltage is generated, the
The detected signal voltage is higher than a predetermined value
If the object to be detected contains an object made of a ferromagnetic material,
Then, the indicator light and the sounding device are driven. As described above, in the conventional iron piece detecting device,
The sensor part of the iron piece detection device and the detected object move relatively
Is generated in the detection coil in the sensor
Detection signal voltage in the form of an analog signal
Depending on the condition exceeding the threshold value, iron pieces of a predetermined size or more are detected.
Although it was said that it was in a known state, the conventional iron piece detection device
Is used to detect the presence of a steel ball with a diameter of, for example, 1.2 mm
To be able to do so, a strong magnetic field
With a DC magnetic field of
In addition, a steel ball having a diameter of 1.2 mm is applied to a DC magnetic field.
Detection signal generated in the detection coil when moving
Has a high degree of amplification to amplify the voltage to a predetermined voltage value.
Using an iron piece detection device that is configured using an amplifier
Is required. Therefore, the conventional iron piece detector
Detection coil picks up a small external noise magnetic field and malfunctions.
The problem is that it is easy to make crops. [0006] The sensor part of the iron piece detecting device and the test object
Set the relative speed of movement with the body to a predetermined constant speed
The detection signal voltage generated in the detection coil
Prescribed relative movement speed between the sensor unit and the object to be detected
Since it has a frequency component corresponding to the degree,
The detected signal voltage generated in the detected coil is
Corresponds to the specified relative movement speed between the sensor part and the object to be detected
Through a filter that can pass the filtered frequency components.
To prevent malfunction due to external noise magnetic field.
available. However, it is detected by the external noise magnetic field described above.
The noise voltage generated in the coil is connected to the sensor unit described above.
A frequency component corresponding to a predetermined moving speed relative to the sensing object
If it is in the same frequency band as the
Malfunction due to the magnetic field cannot be prevented. By the way, various textile products and sewing clothing are manufactured.
Apparel manufacturers and apparel accessories manufacturers
There are cases where various accessories are used in the product.
Various textile products with sewing accessories attached, sewing
Detect iron pieces using the iron piece detection device for clothing
The above accessories were attached
Iron pieces are present in various textile products and sewing clothing
Even without metal clothing accessories (buttons, fasteners)
Used in magnetic fields.
Eddy currents flow through metal accessories that have been moved
A detection signal voltage is generated in the coil, and the iron piece detection device malfunctions
May cause cropping. Therefore, the above problem does not occur.
In order to make sure that
Manufacturers, apparel manufacturers, etc.
The needle is converted by a steel ball with a diameter of 1.2 mm.
Apparel accessories are calculated using steel balls with a maximum diameter of 0.8 mm
Make it possible to make the iron piece detection device detect
As a reference for setting the degree, for example, the diameter is 1.2 mm.
The detection signal voltage generated in the detection coil corresponding to the steel ball
The state exceeds a predetermined threshold, and
Iron pieces larger than the size are detected, and
Generated on the detection coil corresponding to a steel ball with a diameter of 0.8 mm
The detected signal voltage is below a predetermined threshold
In a state where iron pieces smaller than the specified size are not detected
So that However, the detection sensitivity is not set as described above.
Of iron contained in the object to be detected using the
When detecting a piece, the sensor of the iron piece detection device
Assume that the target is moved at a relatively constant speed.
Even when the DC magnetic field generating member and the position where the
When the distance changes, the detection coil in the sensor
The magnitude of the detection signal voltage in the form of an analog signal to be generated,
Changes in frequency components change iron piece detection sensitivity
I do. So you can determine the size of the iron piece
Absent. [0010] In order to solve the above-mentioned problem, the present applicants' association
First, the members that generate the DC magnetic field H (see FIG. 2)
For example, the direct current in the DC magnetic field generated by the permanent magnet 1) in FIG.
Transfer means (for example, transfer zone 5) in a direction intersecting with the magnetic flux.
The object to be detected Dx (see FIG. 2) is determined by
Moving at the speed shown in FIG.
Is a predetermined distance in the moving direction of the detection target Dx.
The first detection command set at a distance L (see FIG. 2)
2 (see FIG. 2) and a second detection coil 4 (see FIG. 2).
) And the first and second detection cores.
The first and second detection signals generated in the files 3 and 4 are individually A
Each of the AD converters is converted into a digital signal by a D converter.
The cross-correlation of the two digital signals output from
When it is determined that both signals are the same
Only to generate an iron detection output signal
An intelligent device was proposed. By the way, a proposal already made by the applicant company mentioned above.
In the iron piece detecting device, the detected object Dx is transferred by the transfer means.
By moving at a predetermined constant speed, a predetermined distance L
First and second detection coils that are arranged only apart from each other
AD conversion of the first and second detection signals generated in
After the conversion into a digital signal by the converter,
Of the cross-correlation of the two digital signals output from the
The operation is performed, and in this regard, referring to FIG.
The description is as follows. In FIG. 3, x1
(T) is the first piece described above by the iron piece in the detection object Dx.
Modeling the signal generated in the detection coil 3 as a function
And n1 (t) is the detection target Dx
The first detection coil 3 is emitted by means other than the iron piece inside.
The generated signal (noise) is modeled and shown as a function
Y1 (t) is the first detection coil 3
[Sum signal of x1 (t) and n1 (t)]
Is modeled as a function. In FIG. 3, x2 (t) is the detected
The iron piece in the body Dx causes the second detection coil 4 to
The generated signal is modeled and shown as a function.
And n2 (t) is due to other than iron pieces in the detection target Dx.
(The noise generated in the second detection coil 4)
) Is modeled and shown as a function.
And Y2 (t) is an output signal from the second detection coil 4.
[Sum signal of x2 (t) and n2 (t)] as a function
This is shown in the form of Dell. Note that τ in FIG.
The body Dx has a first detection coil 3 and a second detection coil 4
Shows the time required to move the interval L between. That is, as described above, the first detection coil
Output signal Y1 (t) from the second detection coil 4
And the output signal Y2 (t) from the following equation (1), (2), Y1 (t) = x1 (t) + n1 (t) (1) Y2 (t) = x2 (t) + n2 (t) ) ... when expressed by (2), the output from the first detection coil 3
The force signal Y1 (t) and the output signal from the second detection coil 4
The cross-correlation function with the signal Y2 (t) is given by the following equation (3).
Is defined as ## EQU1 ## The first following the integral symbol in the above equation (3)
Focusing on the term, the iron piece in the object Dx
Function x corresponding to the signal generated in the first detection coil 3
1 (t) and the iron piece in the detection target Dx.
Function x2 corresponding to the signal generated in the second detection coil 4
Does (t) have the largest correlation with the delay time τ?
From the above, the first term is the other term in the previous equation, that is, the noise
If the term is sufficiently larger than the term containing
Term can be neglected and, therefore,
Iron pieces in the detection body Dx can be detected. The first detection in the iron piece detecting device
The output signal Y1 (t) from the coil 3 and the second detection coil
The cross-correlation function with the output signal Y2 (t) from
All the actual arithmetic processing is performed by the first detection in the iron piece detection device.
On the time axis indicating the output signal Y1 (t) from the output coil 3
Digital value (discrete value) corresponding to N consecutive sample values
And an output signal Y2 (t) from the second detection coil 4.
Digital values corresponding to N consecutive sample values on the time axis
Value (discrete value) and the first detection coil described above.
The distance of the distance L between the sensor 3 and the second detection coil 4 is
Clock pulse generated during the time when Dx moves (sample
And the number j of pulses having the same period as the
This is performed according to equation (4). In addition, the above-mentioned arithmetic processing
Is performed after the above data is temporarily stored in the memory.
Therefore, a negative sign is added to k and j in the equation. [Equation 2] The problem to be solved by the present invention has been described so far.
In the iron piece detector already proposed by the applicant company,
The object Dx to be detected is determined in advance by the transfer means.
At a predetermined constant speed, separated by a predetermined distance L
Generated by the first and second detection coils 3 and 4
The first and second detection signals are individually digitally converted by an AD converter.
After being converted to a signal, it is output from each of the AD converters.
Calculation of the cross-correlation of the two digital signals
The iron piece detection output signal based on the calculation result.
Because of the iron piece in the object to be detected Dx.
Signal generated in the first and second detection coils 3 and 4 described above.
Signal correlation value (product-sum operation value)
If the value (the product-sum value) is not small enough,
In addition to the problem that it is difficult to obtain good iron detection results,
The detection object Dx is moved by the first detection coil 3
Limited to movement from the side to the second detection coil 4
Therefore, for example, in a state where the detection target Dx is reciprocated,
Even if it is desired to perform an iron piece detection operation,
Cannot detect iron pieces in such a detection mode
Became a problem, and a solution was sought. The present invention provides a method for generating a DC magnetic field.
Generated by the member and the DC magnetic field generating member described above.
In a direction that interlinks with the DC magnetic flux in the DC magnetic field,
Means for moving the object to be detected at a constant speed,
Detection with a winding that can interlink with the magnetic flux that has passed through the object
The coil is moved a predetermined distance in the direction in which the object to be detected moves.
Are individually arranged at the first position and the second position set at a distance from each other.
Means for positioning, and a first detection means provided at the first position.
A first detection signal detected by the output coil;
Digitizing the second detection signal detected by the detection coil
Means for converting the first detection signal into
The detected object is in the first position as described above.
From the second position to the second position
The difference from the digital signal due to the second detection signal
Computing means for computing the autocorrelation by means of
Means for generating an iron piece detection output signal based on the output.
Provided is an iron piece detecting device provided. The present invention will be described below with reference to the accompanying drawings.
The concrete contents of the iron piece detecting device of the above will be described in detail. FIG.
Is a block diagram showing a schematic configuration of the iron piece detecting device of the present invention.
FIG. 1 shows a member 1 for generating a DC magnetic field.
Thus, the DC magnetic field generating member 1 moves the detection target Dx.
A DC magnetic field H of a predetermined magnetic field strength
It is configured as a configuration that can be
And replace it with permanent magnets or electromagnets
It can be configured using Iron piece detection shown in Fig. 1
In the configuration example of the device, as the DC magnetic field generating member 1
FIG. 1 shows a case where a permanent magnet is used.
In the following description, it is described as a permanent magnet 1.
Sometimes. A permanent magnet used as a DC magnetic field generating member 1
Hismagnet is an integral block-shaped permanent magnet
Even if it is composed, or many small
It has a configuration that combines block-shaped permanent magnets.
You may. In FIG. 1, a DC magnetic field generating member 1 is used.
In the example shown in FIG. 1, the permanent magnets
(Up and down direction in the figure)
A predetermined magnetic field strength is applied to the space facing the pole (N pole in FIG. 1).
So that a DC magnetic field H having
The part of one magnetic pole and a part of the side surface
Except for the part except for the side shown in
You. It is formed in the space on the N pole side of the permanent magnet 1 described above.
In the DC magnetic field H, the moving direction of the object Dx
(In the direction of arrow X) at a predetermined distance L
The detection coils 3 and 4 are provided in parallel. Two of the above
Transfer to the space between the detection coils 3 and 4 and the permanent magnet 1
A band 5 is provided. The transfer zone 5 is provided with a drive motor (for example,
Drive motor driven by the output shaft of
Roller 7 and the driven roller 8,
Drive motor is driven and rotated at a predetermined speed.
At a predetermined speed V (for example, 20 meters per minute)
The arrow X direction in FIG. 1 (or the direction opposite to the arrow X direction)
Direction). In the following description, the transfer zone 5 is illustrated in FIG.
The case of transfer in the direction of arrow X is described.
You. By the way, in the iron piece detecting device, at least
A DC magnetic field generator is provided in the entire space including the trajectory of Dx.
It is necessary to generate a DC magnetic field H by the material 1.
In addition, a change in the magnetic flux density in the DC magnetic field described above can be detected.
It is possible to arrange the detection coils 3 and 4 in such a manner
Since it is required, the above-described permanent magnet 1 and detection coil
3, 4 and the like have a configuration mode that satisfies the above requirements.
It goes without saying that is used. FIG.
Inside the rotating shaft of the driving roller 7 and the driven roller 8
Bearing for rotating shaft, etc., means for fixing permanent magnet 1, detection
The illustration of the fixing means of the coils 3 and 4 is shown in the drawings.
Are omitted to avoid complications. In the iron piece detecting device shown in FIG.
The detection coil 3 is made of a ferromagnetic material having a high magnetic permeability.
Using a configuration in which a winding 3b is wound around a core 3a
The detection coil 4 has a high magnetic permeability.
Configuration in which a winding 4b is wound around a core 4a made of a magnetic material
I'm using Each of the detection coils 3 and 4 described above
Needless to say, an air-core configuration may be used.
It is a theory. At a predetermined constant speed V in the direction of arrow X in FIG.
When the detected object Dx is placed on the traveling transfer zone 5,
The detected object Dx has the same moving speed V as the transfer
It passes through the DC magnetic field H generated by the stone 1. The detection target Dx contains an iron piece.
Then, the DC magnetic field H generated by the permanent magnet 1 is
When the detection object Dx moves, the aforementioned DC magnetic field H
The state of the magnetic flux distribution in the inside of the moving detection object Dx
Of the iron pieces, thereby causing the detection coils 3 and 4
Corresponds to the state of change in the distribution of magnetic flux in the DC magnetic field H described above.
A detection signal having a corresponding waveform is generated. By the way,
The two detection coils 3 and 4 are connected to the detection target Dx as described above.
A predetermined distance L in the moving direction (direction of arrow X)
The object to be detected Dx is arranged in advance.
Same as transfer zone 5 running at a fixed moving speed V
Since the vehicle is traveling at one moving speed V, the above two detections
The coils 3 and 4 are present in the object Dx described above.
The detection signal generated by the same iron piece is
Distance L between the two detection coils 3 and 4 and the two detection coils described above.
And the speed V of the object Dx passing between the output coils 3 and 4.
Thus, the time difference T is determined. The first detection generated in the detection coil 3 described above.
The output signal is supplied to the amplifier 9 and the detection coil
4 is supplied to the amplifier 10
You. Amplified by the corresponding amplifiers 9 and 10 described above.
The first and second detection signals are provided individually.
A predetermined frequency by the low-pass filters 11 and 12
Only the signals in the band are extracted and the
It is provided to the analog digital converters 13 and 14. Said
Corresponding to the speed V of the detected object Dx,
The frequency component of the detection signal generated in
And the cut-off frequency of the low-pass filters 11 and 12 described above.
Is the frequency component of the detection signal generated in the detection coils 3 and 4.
Determine according to minutes. For example, the speed V of the detection target Dx is
Generated in detection coils 3 and 4 at 20 meters per minute
If the fundamental wave component of the detected signal to be detected is 9 Hz, for example,
The cut-off frequency of the low-pass filters 11 and 12 described above
Is 20 Hz to 30 Hz, for example. As described above
The use of the cut-off low-pass filters 11, 12 provides
Influence of magnetic field generated from power supply does not appear in detection results
I can do it. Output from the analog-to-digital converter 13
The digital signal based on the first detection signal is stored in the memory 15.
And output from the analog-to-digital converter 14.
The digital signal obtained by the second detection signal is stored in the memory 16.
Is stored. 17 is, for example, a microprocessor and a lander.
Access memory (RAM) and read-only memory
(ROM) and the like.
Reference numeral 18 denotes an operation unit, and 19 denotes one of an indicator lamp and a sound generator.
Or an output unit configured with both. Said
The operation unit 18 described above under the control of the control unit 17
The first detection signal read from the memories 15 and 16
Signal and a digital signal based on the second detection signal.
After calculating the difference between the two signals,
Is calculated for the difference value of. Arithmetic unit
As a digital signal processor (DSP)
Can be used. Next, with respect to the contents of the above-mentioned operation (5)
This will be described with reference to equations (9) to (9). The iron piece detection device described above
In the first, the second
1, the first and second detection coils generated from the second detection coils 3 and 4
In the detection signal, a constant predetermined by the transfer means
Contained in the detected object Dx moving at the speed of
In addition to the signal (detection target signal) generated by the
Due to various factors such as vibration of the sensor, external electromagnetic field, external magnetic field, etc.
Undesired signals (noise) generated by the above-described method are also included.
The aforementioned noise is applied to the first and second detection coils 3 and 4.
A (i) generated at the time and noise B
(I). Now, due to the iron piece in the detection object Dx,
The detection target signal generated in the first detection coil 3
The signal is x1 (i), and the iron piece in the object Dx is
The detection target signal generated in the second detection coil 4
If the signal is x2 (i), the first and second detection
Signals Y1 (i) and Y2 (i) generated in files 3 and 4 are
It is represented by the following equations (5) and (6). (Equation 3) The first and second detection coils described above
The difference signal between the signals Y1 (i) and Y2 (i) generated in 3, 4
Z (i) is represented by the following equation (7). [Equation 4] The first and second detections represented by the above equation (7)
Signals Y1 (i) and Y2 (i) generated by output coils 3 and 4
The autocorrelation of the difference signal (difference value) Z (i) of
(8). ## EQU5 ## In the above equation (8), the noise B in the equation
Assuming that (i) is white noise, the above equation (8) becomes
It is represented by equation (9). (Equation 6) The above equation (9) indicates that the noises B1 (i), B
2 (i) is considered to be white noise as described above.
In the state, the first and second detection coils 3 and 4 are
The noise of a frequency similar to the signal to be detected
Noise correlation value can be ignored, and the
This indicates that the value is represented only by the correlation value. However,
The aforementioned noise B1 generated during the actual iron piece detecting operation
(I) and B2 (i) are not white noises. But detect
The autocorrelation value of the difference value of the target signal is the noise B1 described above.
(I), a value sufficiently larger than the correlation value of B2 (i).
You. Therefore, the arithmetic unit in the iron piece detecting device of the present invention
The following operation performed in step 18, ie, the first check
Digital signal based on the output signal and digital signal based on the second detection signal.
The difference value from the total signal is calculated, and the difference value
Based on the calculation result obtained by the correlation calculation,
The signal to be detected can be detected well.
You. A digital signal based on the first detection signal;
And the difference value between the digital signal and the second detection signal.
, The difference value obtained by the calculation of (Y1-Y2)
Auto-correlation value and (Y2-Y1)
Is the same as the autocorrelation value for
First and second spaced apart by a predetermined distance L
The moving direction of the detection target Dx with respect to the detection coils 3 and 4 is
Whatever the case, the detection of iron pieces contained in the detection target Dx is performed.
The output operation can be performed well. In the operation unit 18, the first detection
And a digital signal based on the second detection signal.
Of the autocorrelation performed on the difference value
The calculation result is compared with a predetermined threshold value, and
When the calculation result of the autocorrelation is larger than the above threshold value
To the output part 19 from the arithmetic part 18 to the iron piece detection output signal.
You. The above-mentioned threshold value is the noise B1 (i) and B2 (i).
From the correlation value and the correlation value of the noises B1 (i) and B2 (i)
And the autocorrelation value of the difference value of the detection target signal is sufficiently large.
It is set to a value that can be determined. In setting the above threshold
Is, for example, when an iron piece of a known size is
Based on the calculation result obtained by the calculation unit 18 of the iron piece detecting device
Can be determined. Iron piece detection output signal from arithmetic unit 18
In the output unit 19 to which the signal is supplied, the iron piece detection output signal is output.
Lights the indicator light provided on the output unit 19
Or sound the sounder provided in the output unit 19.
To detect that iron pieces are present in the detected object Dx.
Let The present invention has been described above in detail.
Thus, the iron piece detection device of the present invention
Belt conveyor in the direction interlinking the DC magnetic flux in the
The object to be detected can be pre-
Generated from permanent magnets by moving at a fixed speed
The magnetic flux passing through the object to be detected moves the object to be detected.
First position set at a predetermined distance in the direction
The first detection coil separately disposed at the first position and the second position.
Interlinking the windings in the coil and the second detection coil,
A first detection signal detected by the first detection coil described above;
Between the second detection signal detected by the second detection coil and the second detection signal
After amplifying the signal component in the specified frequency band,
A digital signal by a digital-to-digital converter,
The digital signal based on the first detection signal
Required to move from the first position to the second position
Digital by the second detection signal delayed by the time
A difference value from the signal is obtained, and the self phase of the difference value is determined.
The correlation is calculated, and the calculation result of the autocorrelation is calculated in advance.
Signal detection output signal when it is greater than the specified threshold
The detection coil generates an external magnetic field.
Even if it detects and generates a signal, the first and second detection coils
At the same time, a frequency similar to the signal to be detected
The signal to be detected must be
Good detection, and therefore an iron piece detection device
Can be detected even if the
Can detect the presence of iron pieces
It is also possible to place them at a predetermined distance L apart.
Of the object to be detected with respect to the first and second detection coils
Regardless of the direction of motion, the iron contained in the object to be detected
According to the present invention, the detection operation of the pieces is performed well.
Excellent performance that solves the conventional problems described above
An iron piece detection device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a schematic configuration of an iron piece detecting device of the present invention. FIG. 2 is a side view of a main part of the iron piece detecting device of the present invention. FIG. 3 is a diagram for explaining a signal detection state in first and second detection coils. [Description of Signs] 1 DC magnetic field generating member (permanent magnet), 2 magnetic paths, 3
4 detection coil, 5 transfer zone, 6 drive motor, 7 drive roller, 8 driven roller, 9, 10 amplifier, 11,
12 low-pass filter, 13, 14 analog-to-digital converter, 15, 16 memory, 17 control unit, 18 operation unit, 19 output unit, Dx object to be detected, H: DC magnetic field,

──────────────────────────────────────────────────続 き Continuing on the front page (72) Michio Nakano 35-35, Sumiyoshidai, Aoba-ku, Yokohama-shi, Kanagawa 34 (72) Inventor Bichai Sachau 1-36-10 Kita-senzuku, Ota-ku, Tokyo Kita-senzuku lodgings RA35 Room (56 References JP-A-7-260943 (JP, A) JP-A-8-233946 (JP, A) JP-A-60-173486 (JP, A) JP-A-58-177873 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01V 3/10 D06H 3/14 G01R 33/00 G01N 27/90

Claims (1)

(1) A DC magnetic field generating member, and a predetermined constant in a direction intersecting with the DC magnetic flux in the DC magnetic field generated by the DC magnetic field generating member. Means for moving the object to be detected at a speed of, and a detection coil provided with a winding capable of interlinking with the magnetic flux passing through the object to be detected, at a predetermined distance in a direction in which the object to be detected moves. Means for individually arranging the first and second positions, a first detection signal detected by a first detection coil provided at the first position, and a second detection Means for converting the second detection signal detected by the coil into a digital signal; the digital signal based on the first detection signal; and the object moving from the first position to the second position. Detection signal delayed by the time required for Difference iron piece detection device including a calculating means for calculating an autocorrelation, and means for generating the iron detection output signal based on the output of the the calculation means for the digital signal by.