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Use for MR sensor

Fig.1	Reading of the magnetic pattern of the bill The most useful use of the MR sensor is reading of the magnetic pattern. Magnetic printing is to print it in ink which magnetic powder was combined with. The bill of each country of the world is one of the familiar things in the magnetic printing.
But, there are a few magnetic bodies contained in the magnetic printing very much. Therefore, a bill never sticks to the magnet 1000 yen. Generally that existence isn't known. Do you know how a MR sensor reacts with the magnetic printing and it is detected? The character which shows it in the above is the example of the character made for the information processing. This character was prescribed by JIS X9002. (Type E13B) JIS X9002 is the standard of "the typeface for reading of the character for the magnetic ink and the specifications of the printing". A signal like a photograph of the Fig. 2 appears in the output terminal of the MR sensor when the E13B pattern character that magnetism was printed with this standard is passed through the detection side of the MR sensor.	Fig.2
Fig.3	A MR sensor is detected clearly though there are a few magnetic changes very much. A used circuit diagram is shown in the Fig. 3. Furthermore, the example which is easy to understand is shown.

The magnetic pattern of the bill

Fig.4

Next, let's observe a bill with a MR sensor. The 1$ bill of the United States is used.
All magnetic patterns can't be shown to everyone. Therefore, a real photograph (left) and the image of the magnetic pattern(right) are divided with a diagonal. You will be able to recognize that the signal which is the same as the pattern being printed is detected. A MR sensor is used in the machine which handles a bill such as a vending machine, and the truth of the bill is judged from that signal.

A magnetic encoder

A MR sensor can be used as an encoder which detects rotation and a position, too.
For this use, four MR elements are arranged in the interval and they have bridge connection. This MR sensor is drawn to the rotating gear near. See a Fig. 5.

Fig.5

Then, a signal like the next image can get it from two output terminals(Fig. 6).

Fig.6

You can see two signals Va and Vb that a phase is different. This signal is a sine wave. One period copes with one tooth of the gear. In other words, the number of rotation is calculated when the number of peaks which could get it is divided by the number of teeth. And, a difference in the phase between Va and Vb shows rotating direction. You can know the direction which a gear turns around by examining the phase of two signals. This encoder is useful when you want to control the rotation of the motor precisely. You can't control that precisely if the rotation speed of the motor shaft and a position of rotation aren't known. Because of that, a MR sensor, speed of response is fast and resistant to the dirt such as oil as well, is adopted in the servomotor for the main shaft of the precise machine tool.

Potentiometer

A usual potential meter has the part which touches each other. Because of that, it has the possibility that resistance value changes discontinuously by the abrasion and the dust. Because resistance value changes due to a change in a magnetic field, there is no contact point in a potential meter which a MR element was used for.
It is useful as a variable resistance for the adjustment which a change in continuance should be necessary.