JP3957209B2 - Electromagnetic characteristic detector - Google Patents

Description

  The present invention relates to an electromagnetic detection device that detects the electromagnetic characteristics of a subject, and in particular, compensates for variations in the electrical characteristics of electrical components used for electromagnetic detection of the subject and detects the electromagnetic characteristics of the subject. The present invention relates to a detection device.

An object of the present invention will be described only for an image forming apparatus. In an image forming apparatus such as a PPC (Plain Paper Coupler) or LBC (Laser Beam Printer), an electrostatic latent image corresponding to image information is formed on a photoconductor. Then, the formed electrostatic latent image is developed with a developer, and toner is selectively attached to the electrostatic latent image on the photosensitive member with a paddle roller, whereby a toner image of image information is developed and formed on the photosensitive member. .
In this case, as the development proceeds, the toner in the developing unit decreases, but the magnetic carrier only decreases slightly. Therefore, a toner hopper is provided, and the reduced toner is replenished to the developing unit from the toner hopper. ing.
By the way, when the mixing ratio of the toner with respect to the magnetic carrier is decreased, the density of the developed toner image is decreased, and when the mixing ratio of the toner with respect to the magnetic carrier is increased, the density of the developed toner image is increased. In order to perform the image formation, it is necessary to always maintain the mixing ratio of the toner contained in the developing unit to the magnetic carrier within an appropriate range. Therefore, the image forming apparatus includes a toner concentration in the developer. A toner density detection sensor (T sensor) is provided for detecting the toner.

In the image forming apparatus, in order to detect the toner density in the developer, Japanese Patent Application Laid-Open No. 2004-228620 describes a detection coil disposed adjacent to the developer and a reference disposed away from the developer. The coil is connected to each other in series and driven by an AC power supply, and the toner concentration in the developer is detected by detecting the phase difference between the AC power supply voltage and the output voltage at the connection point of the detection coil and the reference coil. A magnetic sensing device is disclosed.
Further, in Patent Document 2 described later, a developing unit is disposed in the vicinity of the coil L1 and the coil L2 that are magnetically coupled to each other, and a capacitor C1 is connected in parallel to the coil L1 to form a first resonance circuit. The capacitor C2 is connected in parallel to the coil L2 to form a second resonance circuit to constitute a tuning circuit as a whole, and this tuning circuit is connected to the solid-state oscillation circuit, and the output signal of the tuning circuit is the detection circuit. A magnetic level detecting device for detecting that the toner level in the developer has reached the reference level by comparing the level with a reference voltage in a comparison circuit via the circuit is disclosed.
JP-A-6-289717 JP 2000-131120 A

It is possible to detect the toner concentration in the developer by the magnetic detection device disclosed in Patent Document 1 or the magnetic material level detection device disclosed in Patent Document 2. When manufacturing this detection device, it is necessary to make adjustments due to variations in the electrical characteristics of the coil and capacitor mounted on the device and used for detection.
Strictly speaking, there are variations in the electrical characteristics among individual products in the coils and capacitors on the market, and the electrical characteristics of the coils and capacitors used in the resonance circuit of this type of detector are different. As the signal level of the toner density detected by this type of detection device fluctuates due to variations, accurate detection cannot be performed. Therefore, this type of detection device detects variations in the electrical characteristics of the coil and capacitor used in the resonance circuit. it is necessary to remove the adverse effects on the.

An example of a conventional magnetic permeability detector has a configuration as shown in FIG. 3, and a resonance circuit including a coil L1 and a capacitor C2 of the phase comparison circuit 5A, and a resonance circuit including a coil L4 and a capacitor C3 constitute a tuning circuit. The developer 6 whose toner density is detected is arranged in the vicinity of the coils L1 and L4 so that the toner density changes the inductance value of the coils L1 and L4.
In this case, a sine wave signal having an oscillation frequency corresponding to the toner concentration of the developer 6 is output as a detection signal from the tuning circuit, converted into a rectangular wave by the exclusive OR circuit 7B, and one of the exclusive OR circuits 7A. Input to the input terminal.
On the other hand, since the output signal of the oscillation circuit 3 is converted into a rectangular wave by the exclusive OR circuit 7C and input to the other input terminal of the exclusive OR circuit 7A, in the exclusive 0R circuit 7A, the oscillation of the oscillation circuit 3 is performed. A phase difference between the output signal V1 and the detection signal V2 corresponding to the toner density of the developer 6 is detected and input to the second circuit 2 as a detection signal.

The detection signal input to the second circuit 2 is input to the inverting input terminal of the differential amplifier 8A via the differential amplifier 8B and is input to the non-inverting input terminal of the differential amplifier 8A by the resistors R8 and R9. A difference value between the resistance-divided power supply voltage and the detection signal is output as a magnetic permeability detection characteristic signal from the output terminal L13 of the differential amplifier 8A.
In this case, in order to compensate for variations in the electrical characteristics of the coils L1 and L4 and the capacitors C2 and C3 constituting the tuning circuit, a control signal is applied from the terminal L11 to the variable capacitance diode D via the resistor R5. The frequency of the detection signal output from is adjusted and controlled, and a characteristic signal having a signal level that has been controlled and adjusted is output from the differential amplifier 8A of the second circuit.

However, the signal level of the output signal of the differential amplifier 8A corresponding to the control signal from the terminal L11 has a characteristic as shown in FIG. 4, and the output signal of the differential amplifier 8A with respect to the control voltage range of approximately 11V. Can be adjusted by about 5V, and the adjustment control is not performed linearly.
For this reason, the conventional magnetic permeability detector 12A requires a final manual adjustment process using a trimmer capacitor or core as necessary, which adds labor and adjustment time, and increases the manufacturing cost. However, problems arise, and the use of moving parts causes problems in reliability in operation.

The present invention has been made in view of the current state of the manufacturing process of this kind of detection device as described above, and its purpose is to detect variations in the electrical characteristics of components used in the detection operation, and to output the output signal voltage of the device. An object of the present invention is to provide an electromagnetic characteristic detection device for a subject that compensates for a level accurately by correcting and adjusting and constantly outputs a highly accurate detection characteristic signal voltage .

In order to achieve the above object, a first invention according to claim 1 detects the electromagnetic characteristics of a subject, compensates for variations in the electrical characteristics of electrical components used for the detection, and responds to the compensation. An electromagnetic characteristic detecting device that outputs a detection characteristic signal voltage whose signal voltage level is adjusted and corrected, and a resonance circuit comprising a coil and a capacitor is disposed in the vicinity of the subject to detect the electromagnetic characteristic of the subject. A first circuit that outputs a corresponding detection signal voltage , a second circuit that amplifies the detection signal voltage output from the first circuit and outputs the detection signal voltage as a detection characteristic signal voltage , and the second circuit Te, the detection characteristic signal corrected adjusting signal voltage level change of the voltage, the signal voltage for controlling so as to output a detection characteristic signal voltage signal voltage level is corrected adjusted due to variation in electrical characteristics of the electrical components Les It is characterized in that it has a Le adjustment means.

According to the first invention, the resonance circuit, which is disposed in the vicinity of the subject in the first circuit and includes a coil and a capacitor, outputs a signal whose phase is shifted in accordance with the electromagnetic characteristics of the subject. by the circuit, based on the detection of the phase difference between the drive signal of the signal and the resonant circuit to be outputted from the resonance circuit, is output detection signal voltage corresponding to the detected electromagnetic properties of the object, the detection signal voltage of the second In the second circuit, the detection signal voltage is amplified and output as the detection characteristic signal voltage in the second circuit. However, the signal voltage level adjusting means causes variations in the electric characteristics of the electrical components used for detection of the object. be compensated, the signal voltage level change of the detection characteristic signal voltage caused by the variation is corrected adjusted, the signal voltage level is sensed characteristic signal voltage adjusted corrected output, electromagnetic JP The production of the sensing device, the variation automatically compensate the electrical characteristics of the electrical components used in the detection, manual adjustment is not necessary, the manufacture of high-performance magnetic properties detection device is carried out by reducing the manufacturing cost.

Similarly, in order to achieve the object, according to a second aspect of the present invention, the signal voltage level adjusting means is adjusted and adjusted from the second circuit by adjusting the operating point of the second circuit. The detection characteristic signal voltage is controlled so as to be output.

According to the second invention, the signal voltage level adjusting means performs control so that the detection characteristic signal voltage corrected and adjusted is output from the second circuit by adjusting the operating point of the second circuit. Thus, the operation of the first invention is executed.

Similarly, in order to achieve the above object, according to a third aspect of the present invention, in the first aspect, the signal voltage level adjusting means includes the detection signal voltage from the first circuit and the signal voltage level adjusting means. A control is performed such that a difference signal voltage with respect to a control signal voltage set by the step is input to a second circuit, and the difference signal voltage is amplified by the second circuit and output as a detection characteristic signal voltage. To do.

According to the third invention, the signal voltage level adjusting means inputs the difference signal voltage between the detection signal voltage from the first circuit and the control signal voltage set by the signal voltage level adjusting means to the second circuit, By performing the control so that the difference signal voltage is amplified by the second circuit and output as the detection characteristic signal voltage , the operation of the first invention is executed.

Similarly, to achieve the above object, according to a fourth aspect of the present invention, in the third aspect, the signal voltage level adjusting means sets the DC voltage signal voltage as the control signal voltage and is divided by resistance. A difference signal voltage between the DC voltage signal voltage and the detection signal voltage from the first circuit is input to the second circuit.

According to the fourth invention, in addition to the operation of the third invention, the signal voltage level adjusting means sets the DC voltage signal voltage as the control signal voltage , and the DC voltage signal voltage divided by the resistance and the first circuit By inputting the difference signal voltage with respect to the detection signal voltage from the second circuit to the second circuit, the control signal voltage control is set in fine steps, and highly accurate and stable control is performed.

Similarly, in order to achieve the above object, a fifth invention according to claim 5 is the developer used in the electrophotographic system according to any one of the first invention to the fourth invention, wherein the subject is an electromagnetic The characteristic is a change in magnetic permeability.

According to the fifth invention , any one of the actions of the first invention to the action of the fourth invention is executed with the subject used as the developer used in the electrophotographic system and the electromagnetic characteristics as the permeability change.

1st invention, that is, a detection characteristic signal in which an electromagnetic characteristic of a subject is detected, a variation in an electric characteristic of an electric component used for the detection is compensated, and a signal voltage level is adjusted and corrected corresponding to the compensation A first electromagnetic characteristic detection apparatus that outputs a voltage , wherein a resonance circuit including a coil and a capacitor is disposed in the vicinity of the subject, detects an electromagnetic property of the subject, and outputs a corresponding detection signal voltage . Circuit, a second circuit that amplifies the detection signal voltage output from the first circuit and outputs the detection signal voltage as a detection characteristic signal voltage , and a variation in the electrical characteristics of the electrical components relative to the second circuit. the signal voltage level change of the detection characteristic signal voltage due to correction adjustment, and characterized in that the signal voltage level and a signal voltage level adjusting means for controlling to output a detection characteristic signal voltage correction adjustment That the effect of the invention is as follows.

According to the first invention, the resonance circuit, which is disposed in the vicinity of the subject in the first circuit and includes a coil and a capacitor, outputs a signal whose phase is shifted in accordance with the electromagnetic characteristics of the subject. by the circuit, based on the detection of the phase difference between the drive signal of the signal and the resonant circuit to be outputted from the resonance circuit, is output detection signal voltage corresponding to the detected electromagnetic properties of the object, the detection signal voltage of the second In the second circuit, the detection signal voltage is amplified and output as the detection characteristic signal voltage in the second circuit. However, the signal voltage level adjusting means causes variations in the electric characteristics of the electrical components used for detection of the object. be compensated, because the signal voltage level change of the detection characteristic signal voltage caused by the variation is corrected adjusted signal level is adjusted corrected sensed characteristic signal is outputted, the electromagnetic characteristic detection instrumentation When manufacturing the sensor, it is possible to automatically compensate for variations in the electrical characteristics of the electrical components used for detection, eliminating the need for manual adjustment, and reducing the manufacturing cost to produce a high-performance electromagnetic characteristic detection device Is possible.

According to the second invention, the signal voltage level adjusting means performs control so that the detection characteristic signal voltage corrected and adjusted is output from the second circuit by adjusting the operating point of the second circuit. As a result, the effect obtained by the first invention can be realized.

According to the third invention, the signal voltage level adjusting means inputs the difference signal voltage between the detection signal voltage from the first circuit and the control signal voltage set by the signal voltage level adjusting means to the second circuit, By performing control so that the difference signal voltage is amplified by the second circuit and output as the detection characteristic signal voltage , the effect obtained by the first invention can be realized.

According to the fourth invention, in addition to the effect obtained by the third invention, the signal voltage level adjusting means sets the DC voltage signal voltage as the control signal voltage , and the resistance-divided DC voltage signal voltage and the first voltage signal voltage are adjusted . By inputting the difference signal voltage with respect to the detection signal voltage from the circuit to the second circuit, it is possible to finely set the step by the control signal voltage and perform highly accurate and stable control.

According to the fifth invention , any one of the effects of the first invention or the effect of the fourth invention can be realized by setting the subject to be a developer used in the electrophotographic system and changing the magnetic characteristics of the electromagnetic characteristics. .

"Embodiment"
One embodiment of the present invention will be described below with reference to FIGS. 1 and 2 in the case where the subject is a developer of an image forming apparatus and the detected electromagnetic characteristic is a change in magnetic permeability.
As shown in FIG. 1, the magnetic permeability detection device 12 according to the present embodiment includes a first circuit 1 and a second circuit. The first circuit 1 includes an oscillation element OSC, a resistor R1, and a resistor. An oscillation circuit 3 including R2, a capacitor Co1, a capacitor Co2, and an exclusive OR circuit 7D is provided, and is further connected to the oscillation circuit 3 via an exclusive OR circuit 7C. The oscillation signal of the oscillation circuit 3 is exclusive OR A phase comparison circuit 5 that is input as an oscillation output signal voltage V1 via a circuit 7C is provided.
In this phase comparison circuit 5, a resonance circuit composed of a coil L1 and a capacitor C3 and a resonance circuit composed of a coil L4 and a capacitor TC are arranged to constitute a tuning circuit, and an output signal of this tuning circuit The voltage is input to one input terminal of the exclusive OR circuit 7A via the exclusive OR circuit 7B, and the oscillation signal of the oscillation circuit 3 is input to the other input terminal of the exclusive OR circuit 7A. The oscillation output signal voltage V1 is input via 7C.
In this embodiment, a developer 6 in which a magnetic carrier and a nonmagnetic toner are mixed is disposed in a non-contact state in the vicinity of the coils L1 and L4 constituting the respective resonance circuits of the phase comparison circuit 5. The coils L1 and L4 are magnetically joined to each other so that the toner concentration of the developer 6 changes the inductance values of the coils L1 and L4.

The detection signal voltage output from the exclusive OR circuit 7A of the phase comparison circuit 5 of the first circuit 1 is input to the non-inverting input terminal of the differential amplifier 8B of the second circuit 2 via the resistor R7. The differential voltage from the input signal voltage at the inverting input terminal of the differential amplifier 8B is amplified by the differential amplifier 8B and input to the inverting input terminal of the differential amplifier 8A. The control signal voltage output from the control signal voltage generating circuit of the signal voltage level adjusting means is applied to the non-inverting input terminal of 8A by a resistor R8 and a resistor R9 in response to a command from the microcomputer of the signal level adjusting means (not shown). It is configured to be divided and input.
In this embodiment, although not shown, a signal voltage level adjusting means including a microcomputer and a control signal voltage output circuit is provided, and an output terminal of the control signal voltage output circuit is connected to the terminal L11.

The operation of the present embodiment having such a configuration will be described.
In the phase comparison circuit 5 of the first circuit 1, the detection signal voltage V2 of the toner density of the developer 6 converted into a rectangular wave by the exclusive OR circuit 7B by the exclusive OR circuit 7A and the exclusive OR circuit 7C A phase difference from the oscillation output signal voltage V1 of the oscillation circuit 3 converted into a rectangular wave is detected and input to the second circuit 2 as a detection signal voltage .
The detection signal voltage input to the second circuit 2 is input to the inverting input terminal of the differential amplifier 8A via the differential amplifier 8B, and the control signal voltage input to the terminal L11 is resistance-divided by the resistors R8 and R9. The differential voltage from the input signal voltage to the non-inverting input terminal of the differential amplifier 8A thus amplified is amplified by the differential amplifier 8A and output from the output terminal L13 as a characteristic signal voltage for magnetic permeability detection.

Hereinafter, a case will be described in which it is detected that the toner density of the developer 6 in the developing unit is at a preset reference amount Ps.
In general, the phase difference output voltage of the exclusive OR circuit 7A, the frequency of the output signal voltage V2 of the tuning circuit of the phase comparator 5 and coincides with the frequency of the oscillation output signal voltage V1 from the oscillation circuit 3, position The phase difference output voltage tends to fluctuate greatly.
For this reason, when the toner density is the reference amount Ps, if the frequency of the oscillation output signal voltage V1 from the oscillation circuit 3 and the frequency of the output signal voltage V2 of the tuning circuit coincide with each other, the toner concentration becomes the reference amount. When falling from Ps, the phase difference changes, and a detection signal voltage having a sufficient phase difference is output from the exclusive OR circuit 7A.

Here, the operation of storing the adjustment control data in the microcomputer of the signal voltage level adjusting means will be described.
When storing the adjustment control data, the permeability of the reference control signal voltage including the reference control signal voltage is obtained by using a reference model permeability detector that has normal characteristics of coils and capacitors constituting the tuning circuit and does not vary beyond the allowable range. Various adjustment control data necessary for adjustment control of the magnetic susceptibility detection device are stored in the microcomputer of the signal voltage level adjustment means .
When the magnetic permeability detection device of the reference model is used, as described above, the detection signal voltage output from the exclusive OR circuit 7A in the first circuit 1 is input to the second circuit 2 and the differential amplifier 8B. Is input to the inverting input terminal of the differential amplifier 8A, but the toner density is set to the reference amount Ps. In this state, for example, the signal at the output terminal L13 of the differential amplifier 8A is inverted, and the signal The control signal voltage input from the terminal L11 is adjusted under the control of the microcomputer so that the logical value of the signal becomes “0”, and the signal at the output terminal L13 of the differential amplifier 8A is in a state where the toner density is the reference amount Ps. There inverts the control signal voltage which satisfies the condition that the logical value of the signal becomes "0" is selected as the reference control signal voltage, signal voltage level adjustment with its various adjustment control data necessary data for other adjustment control It is stored in the microcomputer means.

In the present embodiment, a signal voltage level adjusting means including a microcomputer storing various adjustment control data obtained in this way and a control signal voltage output circuit is attached to the magnetic permeability detecting device 12 according to manufacturing. Yes.
Therefore, in this magnetic permeability detecting device, when the toner concentration of the developer 6 decreases beyond the allowable range of the reference amount Ps, the polarity of the signal at the output terminal L13 of the differential amplifier 8A of the second circuit 2 is inverted. The logical value is not “0”, the toner density drop of the developer 6 is detected, and a toner replenishment notification is issued.
In this embodiment, when manufacturing the magnetic permeability detecting device, as described above, various drive adjustment data including the reference control signal voltage data are stored in the microcomputer of the signal voltage level adjusting means, and the assembly is completed and adjusted. The control signal voltage output circuit starts with a reference control signal from the control signal voltage output circuit to the magnetic permeability detecting device in which the toner concentration of the developer 6 is set to the reference amount Ps in response to a command from the microcomputer of the signal voltage level adjusting means. When the voltage is input to the terminal L11 and the microcomputer confirms that the logical value of the signal at the output terminal L13 of the differential amplifier 8A is “0”, the electrical characteristics of the coil and capacitor of the tuning circuit are within the specified characteristics. Therefore, it is determined that the magnetic permeability detection device 12 that has completed the assembly process can operate normally.

On the other hand, in a state where the reference control signal voltage is inputted from the control signal voltage output circuit to the terminal L11, the signal of the output terminal L13 of the differential amplifier 8A is at a predetermined level voltage , and the logical value of the signal is “0” If it is determined that the electrical characteristics of the coil and capacitor of the tuning circuit of the phase comparison circuit 5 are not within the specified characteristics,
In this case, the control of the microcomputer of the signal voltage level adjusting means, the control signal voltage control signal voltage input from the output circuit to the terminal L11 is divided by the resistances in the resistor R8 and the resistor R9 by the differential amplifier 8A non of The control signal is input to the inverting input terminal, and in this state, the control signal is compensated for variations in the characteristics of the coil and capacitor of the tuning circuit and the logical value of the signal at the output terminal L13 of the differential amplifier 8A becomes “0”. By adjusting the voltage , correction adjustment of the output signal voltage level of the differential amplifier 8A of the second circuit 2 is performed.
In this case, the characteristics shown in FIG. 2 are obtained between the control signal voltage supplied from the terminal L11 and the output signal voltage of the differential amplifier 8A to be corrected and adjusted . With the control signal voltage in the range of about 9V, the output signal voltage can be corrected and adjusted linearly with high accuracy over a wide range of 7.5V.
Therefore, according to the present embodiment, the output signal level of the differential amplifier 8A of the second circuit 2 is automatically finely corrected and adjusted, and variations in the characteristics of the coil and capacitor of the tuning circuit are reduced. It is possible to compensate accurately.

Further, in the present embodiment, the signal level correction and adjustment operation of the output terminal L13 of the differential amplifier 8A by the input of the control signal voltage from the terminal L11 according to the command of the microcomputer is performed by the output signal voltage of the first circuit 1. The maximum value exceeds the maximum signal voltage level that can be input to the second circuit 2, so that no peaking or signal jump occurs, and the toner density changes from the minimum value to the maximum value. Sometimes, the change width of the output signal voltage of the first circuit 1 is ½ or less of the power supply voltage, the input signal voltage of the non-inverting input terminal of the differential amplifier 8A based on the control signal voltage and the output of the first circuit 1 The difference value with the signal voltage is amplified twice or more, and stable operation is maintained.
In this way, in order to compensate for variations in the electrical characteristics of the coil and capacitor of the tuning circuit of the phase comparison circuit 5 based on the instruction of the microcomputer while the toner density of the developer 6 is the reference amount Ps, The magnetic permeability detecting device 12 in which the output signal level is corrected and adjusted so that the logical value of the signal at the output terminal L13 of the differential amplifier 8A of the circuit 2 of FIG. It is possible to perform normal permeability detection operation by completely compensating for the variation in electrical characteristics.

Thus, according to the present embodiment, the electrical characteristics of the coil and capacitor of the tuning circuit provided in the phase comparison circuit 5 of the first circuit 1 with the toner density of the developer 6 being the reference amount Ps at the time of manufacture. And the signal voltage level of the signal at the output terminal L13 of the differential amplifier 8A of the second circuit 2 is determined not to be a preset level, for example, the logical value “0”. , on the basis of a command of the microcomputer of the signal voltage level adjusting means, the control signal from the voltage output circuit, the output logic value of the signal at the terminal L13 is "0" the control signal voltage to be inputted, the signal level of the output terminal L13 Therefore, variations in the electrical characteristics of the tuning circuit coils and capacitors are automatically compensated, eliminating the need for manual adjustment processes and the use of moving parts, resulting in high performance and high operational reliability. It is possible to manufacture the magnetic permeability detecting device agent to reduce the manufacturing cost.

In the above embodiment, the case where the change in the magnetic permeability of the developer used in the image forming apparatus is detected has been described. However, the present invention is not limited to this embodiment. It is also possible to detect the filling concentration in a predetermined space.
Further, in the present embodiment, the case where the change in the magnetic permeability of the developer is detected based on the case where the toner density is the reference amount has been described. However, the present invention is not limited to this embodiment. It is also possible to detect the change in the magnetic permeability of the developer on the basis of the case where the toner density is the minimum allowable amount.

It is circuit explanatory drawing which shows the structure of one embodiment of this invention. It is a characteristic view which shows the operation | movement of the embodiment. It is circuit explanatory drawing which shows the structure of the conventional magnetic permeability detection apparatus. It is a characteristic view which shows operation | movement of the conventional magnetic permeability detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st circuit 2 ... 2nd circuit 3 ... Oscillation circuit 5 ... Phase comparison circuit 6 ... Developer 7A-7D ... Exclusive OR circuit 8A, 8B ... Differential amplifier 12 ... Magnetic permeability detection apparatus

Claims (5)

Electromagnetic characteristic detection that detects the electromagnetic characteristics of the subject, compensates for variations in the electrical characteristics of the electrical components used for the detection, and outputs a detection characteristic signal voltage in which the signal voltage level is adjusted and corrected in accordance with the compensation Device,
A first circuit that is disposed in the vicinity of the subject and that detects an electromagnetic characteristic of the subject and outputs a corresponding detection signal voltage ;
A second circuit that amplifies the detection signal voltage output from the first circuit and outputs the detection signal voltage as a detection characteristic signal voltage ;
The second circuit corrects and adjusts a change in the signal voltage level of the detection characteristic signal voltage caused by variations in the electric characteristics of the electric components, and outputs a detection characteristic signal voltage in which the signal voltage level is corrected and adjusted. And a signal voltage level adjusting means for performing control as described above. The signal voltage level adjusting means adjusts the operating point of the second circuit and performs control so that a corrected characteristic signal voltage is output from the second circuit. The electromagnetic characteristic detection apparatus according to 1. The signal voltage level adjusting means inputs the difference signal voltage between the detection signal voltage from the first circuit and the control signal voltage set by the signal voltage level adjusting means to the second circuit, and the difference signal voltage is 2. The electromagnetic characteristic detecting apparatus according to claim 1, wherein control is performed so that the signal is amplified by the circuit of No. 2 and output as a detection characteristic signal voltage . The signal voltage level adjusting means sets the DC voltage signal voltage as the control signal voltage , and inputs the difference signal voltage between the resistance-divided DC voltage signal voltage and the detection signal voltage from the first circuit to the second circuit. The electromagnetic characteristic detecting device according to claim 3, wherein 5. The electromagnetic property detection apparatus according to claim 1 , wherein the subject is a developer used in an electrophotographic system, and the electromagnetic property is a change in magnetic permeability.

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