JPS599866B2 - How to detect minute magnetic field changes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of detecting minute changes in magnetic field using a Hall element.

In order to control a certain physical state to keep it within a certain range, we focus on the magnetic properties of that state, detect changes in the state based on magnetic changes, and respond according to the amount of change. In some cases, control may be performed by specific operations.

For example, in the magnetic development method used in electrophotography, a constant magnetic field is applied to the developer by utilizing the fact that the magnetic permeability of the developer changes as the mixing ratio of toner and carrier changes.
This is the case when the mixing ratio is controlled within a certain range by detecting the change in the leakage magnetic flux. In such a case, a means for detecting minute deviations of the magnetic field from the reference state is required. A Hall element is well known as a magnetic field detection element.

Hall elements have excellent sensitivity and can detect even extremely weak magnetic fields. In particular, Hall elements made of indium antimonide are known for their extremely high sensitivity. However, in general, Hall elements have a remarkable temperature characteristic, that is, the dependence of the output on temperature for a constant input, and therefore measures such as special temperature correction or constant temperature measurement are required. I needed it. The purpose of the present invention is to consider the function of the output of the Hall element as a two-variable function with magnetic flux density as the input quantity and temperature as variables, and further, to finally obtain the output by using the characteristic relationship between the control current terminal voltage and temperature. The above two-variable function is approximated by a two-variable linear function with magnetic flux density and control current terminal voltage as variables, and based on the approximation function, the minute change in magnetic flux density from the reference value is calculated. An object of the present invention is to provide a detection method.

According to the detection method of the present invention, there is no need for temperature correction or constant temperature measurement of the measurement space as described above. The present invention will be described below with reference to the drawings. As is well known, detection of a magnetic field by a Hall element is
As shown in FIG. 1, a control current 1 is applied between control current terminals that are input terminals of a Hall element 1 installed at a position where a magnetic field is to be detected. , the Hall effect due to the magnetic flux density B of the magnetic field to be detected is detected as a Hall voltage VN between the output terminal provided perpendicularly to the control current terminal, and the magnetic flux density B
This is done by determining the magnitude of the magnetic flux density B based on the detected Hall voltage VH based on the correspondence between the magnetic flux density B and the Hall voltage VH. Generally, in a Hall element, as mentioned above, the output VH is determined not only by the magnetic flux density B but also by the temperature T.
It also depends on. Therefore, the control current is 1. When VH is kept constant, the function of the Hall element with respect to Hall voltage VH can be regarded as a two-variable function with magnetic flux density B and temperature T as variables. That is, Vll=f(B,T)(1). The function f is determined as a characteristic depending on each Hall element. Even if it is difficult to express its specific form using a known function, it is possible to approximate it with arbitrary precision using a known function. Now, when trying to detect a magnetic field using a Hall element, the variation range of the magnetic field to be detected is a relatively narrow range near the reference value, that is, the variation is minute and temperature If it is known that the range of change is comparatively narrow, the function f in equation (1) can be approximated by a linear equation. Hereinafter, explanation will be given based on a specific example. That is, this is a case where a magnetic field having a magnetic flux density of about 50 to 150 Gauss is detected at room temperature by using a Hall 5 element made of indium antimonide vapor. It is assumed that the Hall element 1 shown in FIG. 1 is a Hall element formed by vapor deposition of indium antimonide. Reference value B of magnetic flux density. is 100 Gauss, and the temperature reference value T. is 20° C., and an attempt is made to detect the deviation of the magnetic flux density 4B from the reference value, regardless of minute temperature changes. At this time, the control current is 1. is kept at 5 mA in this example, depending on the characteristics of the Hall element 1. Therefore, first, it can be said that equation (1) is expanded by Taylor in the vicinity of the reference value.

f(BO, TO) is a control current 1 to the Hall element 1. This is the value of the Hall voltage when a magnetic field with a magnetic flux density of 100 Gauss is applied at a temperature of 20° C. through a current (5m1f). If this is written as VHO, equation (2) becomes as follows. To obtain the constant If (BO, TO), the temperature is maintained at 20°C, and the magnitude of the magnetic flux density B of the magnetic field acting on the Hall element 1 through which a control current of 5 mA is passed is varied in the vicinity of 100 Gauss. The resulting change in Hall voltage may be differentiated with respect to the magnetic flux density B at a point of 100 Gauss.
That is, FIG. 2 shows the relationship between the magnetic flux density B and the Hall voltage VH of the Hall element 1 at 20°C, and from this figure, VH0 = -37.0 mV,
)=-0.287 is determined. Constant Ding Ding f (BO, TO)
In order to obtain , a similar operation can be performed for temperature T and Hall voltage VH. In Figure 3, the Hall element 1 is 5m7.
V7) This shows how the Hall voltage changes in response to temperature changes when a magnetic field with a magnetic flux density of 100 Gauss is applied through a control current. Based on this figure, the constant f(BO, TO) was determined to be 0.6. Therefore, equation (3) is Vll+37=-0.287(B-BO)
+0.6(T-TO)(4).

On the other hand, the control current terminal voltage V not only of the Hall element 1 but also of the Hall element in general.

It is known that a constant characteristic relationship holds between the temperature T and the temperature T regardless of changes in the magnetic field in the practical range. FIG. 4 shows this characteristic relationship for the Hall element 1.
The curve of FIG. 4 does not substantially change even if the magnetic flux density B is changed in the range of 0 to 200 Gauss. Therefore, if the relationship shown in FIG. 4 is expressed as T=9(VO) using function 9, equation (4) can be expressed as υυ'5.

V here. O is T. 1.7 for control element 1 for
It is 5V. Therefore, the relationship T=l(VO) is approximated by the linear equation υ-υ near T=20°C, and the constant d is based on Figure 4, d=-? It was determined that

As a result, equation (5) becomes 0.0341th 1.

Now, since the deviation from the reference magnetic flux density is (B-BO), this can be given from equation (7).

Therefore, an analog calculation circuit corresponding to the right side of equation (8) is set to calculate the Hall voltage VH generated in the Hall element 1 and the control current terminal voltage V.

If this is input as an electrical signal to the analog calculation circuit, the output will be a minute change in the magnetic flux density in the magnetic flux to be detected, B-BO force. FIG. 5 schematically shows only the essential parts of an example of an apparatus for carrying out the present invention. That is, the main parts of the device include a Hall element 1, an ammeter 2, a variable resistor 3, operational amplifiers 4, 5,
6, 7, resistors 8, 9, display device 8, DC power supplies El, E2
It is made up of.

A DC voltage is applied to the control current terminal of the Hall element 1 by the DC power supply E1, and when the switch S is closed, the control current is 1. However, in the control current circuit, an ammeter 2 and a variable resistor 3 are arranged in series, and the variable resistor 3 is controlled by the ammeter 2, and once the control current 1c is In this device example, when the setting is 5m1V, from then on, the resistance position of the variable resistor 3 is changed in response to changes in the internal resistance of the Hall element 1, so that a control current of 5mA is always passed through the Hall element 1. There is. The Hall voltage terminal is connected to the operational amplifier 5, and the control current terminal is connected to the operational amplifier 4), so that the voltages generated at these terminals are input to the respective operational amplifiers as electrical signals. Operational amplifiers 4 and 5 are differential amplifiers,
The potential difference between the terminals as an input signal is amplified by a respective magnification factor. The magnification of the operational amplifier is -61.32 times, and the magnification of the operational amplifier 5 is -3.48 times. operational amplifier 4
and 5 are both input to an operational amplifier 6.
The operational amplifier 6 is a summing amplifier and outputs the sum of the signal values of the input signals. The output of the operational amplifier 6 is input to an operational amplifier 7 which is a summing amplifier, and a constant DC voltage set by resistors 8 and 9 is also input to the operational amplifier 7 from the DC power supply E2. There is. This DC voltage signal corresponds to the constant term -21.6 in equation (8). Therefore, operational amplifiers 4, 5, 6, 7, resistors 8 and 9, and DC power supply E2 constitute an analog calculation circuit corresponding to the right side of equation (8). Therefore, if the Hall element 1 is installed in the magnetic field to be detected, the switch S is turned on, and the necessary equipment is activated, the second term of equation (8) at the operational amplifier 4VC is changed to the operational amplifier 5. Yotsute (8)
The first term of the equation is calculated, the operational amplifier 6 subtracts these terms, and the operational amplifier 7 further calculates (8
B-BO, which is the result of adding the constant term of the equation ), is displayed on the display device 10.

That is, a change in magnetic flux density from a reference magnetic flux density of 100 Gauss is detected. Now, it goes without saying that the change in the magnetic field detected by this device can be considered valid only if the approximation of equation (8) holds; In the vicinity, there is a temperature range in which the curves shown in FIGS. 3 and 4 can be regarded as straight lines, and this is a temperature range approximately from T=10° C. to 40° C.
This substantially matches the actual room temperature fluctuation range, so it matches well with the detection situation. Therefore, the detection accuracy of this device was examined by installing the Hall element 1 in a magnetic field whose magnetic flux density was maintained at 100 Gauss, and varying the temperature T in the range of 10°C to 40°C, and examining its output value. As a result, it was confirmed that 100±1 Gauss was always displayed within the above temperature range. Therefore, according to this device, when detecting minute changes in magnetic flux density on the order of 10 Gauss, very accurate detection results can be obtained within the above temperature range regardless of the temperature. As described above, according to the present invention, it is possible to provide a method for detecting minute magnetic field changes that is accurate and sensitive, can follow temperature changes, and does not require special correction for temperature changes.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining magnetic field detection by a Hall element, Fig. 2 is a diagram showing an example of the relationship between changes in magnetic flux density and changes in Hall voltage at 20°C, and Fig. 3 is a diagram illustrating magnetic field detection at 20°C.
FIG. 4 is a diagram showing an example of the characteristic relationship between temperature and control current terminal voltage in a Hall element; FIG. 5 is a diagram showing the relationship between Hall voltage and temperature when maintained at Gaussian; 1 is a diagram schematically showing only the main parts of an example of a device for implementing the method. 1...Hall element, 2...Ammeter, 3
・・・・・・Variable resistor, 4, 5, 6, 7...
operational amplifier.

Claims (1)

[Claims] 1. In a magnetic field detection method using a Hall element, the control current is kept at a constant value, and the function of the Hall element with respect to the Hall voltage V_H is determined by a two-variable function V_H with magnetic flux density B and temperature T as variables. = f(B, T), and furthermore, the characteristic relationship between the control current terminal voltage V_C and the temperature T in the Hall element is expressed as T by the function g.
=g(V_C), and using this relationship, set V_H to V_H=f(B, g{V_C}), and set the function f to the control current terminal voltage V_C_o corresponding to the reference temperature T_O and the standard of the magnetic flux density. A linear function V_H_O+a(B-B
_O) + b(V_C-V_C_O), and the equation V
_H-V_H_O=a(B-B_O)+b(V_C-V
_C_O) is determined and this is solved for (B-B_O) to create an equation B-B_O=1/a(V_H-V_H_O)-
An analog calculation circuit corresponding to the right side of b/a (V_C - V_C_O) is set, and the Hall voltage V_H generated in the Hall element and the control terminal voltage V_C are directly input to the analog calculation circuit as electric signals, and the analog calculation circuit A method for detecting minute magnetic field changes, characterized in that (BB_O) is calculated as the corresponding function value.