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Movement principle of MR sensor


Fig.A
We will explain how the MR sensor detects a magnetic body like magnetic ink, and what kind of output.
First, As for the Magnetoresistance, called a MR element from now on, that resistance value changes by increasing a magnetic field. This is called magnetic resistance effect.
The state that the resistance value of the MR element changes by the magnetic field is shown to the graph of the Fig.A.
Resistance value depends on the strength of the magnetic field, and not concerned with the direction of the magnetic field.
Select the elements (MR1 and MR2) which characters are equal, and connect those in parallel.
Add equality magnetic fields to two MR elements with a magnet. An output terminal is put on the connection part of two MR elements. The voltage that it is shown in this terminal is called with the output voltage.
Refer to Fig.B.
Output voltages become about halves of the voltages V when a voltage V is increased to both ends of the MR element.
This voltage is called with the middle point voltage.

Fig.B

Fig.C
But, when a magnetic field of the respectively different strength is given to two MR elements, an output voltage is different from the middle point voltage, because the resistance value of the element is different
For example, in the Fig. B, when registant magnetic field add to MR1, an output voltage becomes smaller than a middle point voltage, because resistance value increases more than MR2. And, those output voltages increase more than half when registant magnetic fields add to MR2.
In the same way, think about the case of the detection of the magnetic substance.
A line of magnetic force leans toward the iron settlement, and MR2 gains a bigger magnetic field than MR1 if a magnetic body like iron settlement approaches in one (this case, MR2) of two MR elements.
The resistance value of MR2 increases, and it will be able to be understood by this that an output voltage grows big.
Refer to a Fig. C.
The next figure shows what continued.
The state that a magnetic body is moved through the front of the MR sensor from Fig.1 to Fig.3 is shown.
It was the next figure that showed how the output of the MR sensor changed.
The change in output when a magnetic body crosses the front of the MR sensor is shown.
The arrows of Fig.1 to 3 cope with the magnetic body of the upper figure and the one related to the position of the MR sensor.
Attention
The state of the change in this output voltage is a little different when a magnetic body extends in two MR elements because it is in case of a slight magnetic body.
A MR sensor detects a magnetic body like magnetic ink, and the structure which makes an output voltage change is explained easily here.

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