An indicator has a permanent magnet and a coil rotatably supported on the permanent magnet and wound so as to form a surface that is parallel to and disposed at a preselected distance from a bottom surface of the permanent magnet. The coil generates a torque by interaction with a magnetic field of the permanent magnet upon supply of a current to the coil. An indicator needle is mounted to undergo rotation with the coil through a range of angles corresponding to indicator angles of the indicator needle. A pair of spiral springs urge the indicator needle in a direction opposite to a direction of the torque to undergo rotation through the range of indicator angles. The pair of spiral springs comprise a first spiral spring connected at one end thereof to one end of the coil and a second spiral spring connected at one end thereof to another end of the coil. The first spiral spring is larger than the second spiral spring and is arranged on an outer peripheral side of and coaxially with the second spiral spring so that the first and second spiral springs lie on a common plane.
1. An indicator comprising:
a fixing member having two connection terminals formed thereon;
a permanent magnet fixed to the fixing member;
a coil rotatably supported on the fixing member for generating a torque by interacting with a magnetic field of the permanent magnet;
an indicator needle mounted to undergo rotation with the coil;
a first spiral spring connected at one end thereof to one of the connection terminals of the fixing member and connected at another end thereof to one end of the coil for urging the indicator needle in a direction opposite to a direction of the torque generated by the interaction between the coil and the magnetic field of the permanent magnet; and
a second spiral spring disposed on the same plane as the first spiral spring and connected at one end thereof to the other one of the connection terminals of the fixing member and connected at another end thereof to another end of the coil for urging the indicator needle in the direction opposite to the direction of the torque generated by the interaction between the coil and the magnetic field of the permanent magnet, the first spiral spring being larger than the second spiral spring and being arranged on an outer peripheral side of and coaxially with the second spiral spring.
2. An indicator according to claim 1 ; wherein each of the first spiral spring and the second spiral spring is fixed to the fixing member and the coil so that an inner diameter of the first spiral spring increases and an outer diameter of the second spiral spring decreases in a case where the indicator needle rotates in the direction of the torque.
3. An indicator according to claim 1 ; wherein the permanent magnet has magnetic domains of different polarities magnetized in an axial direction and formed alternately to each other; and wherein the coil is wound to form a surface parallel to and disposed at a predetermined distance from a bottom surface of the permanent magnet.
4. An indicator according to claim 1 ; wherein the indicator needle undergoes rotation through a range of angles corresponding to indicator angles of the indicator needle; wherein the coil generates the torque by interacting with a magnetic field of the permanent magnet upon supply of a current to the coil; and wherein a spring constant of each of the first and second spiral springs remains constant regardless of the indicator angle of the indicator needle so that the current supplied to the coil and the indicator angle are proportional to each other.
5. An indicator according to claim 1 ; wherein the permanent magnet is cylindrical-shaped.
6. An indicator according to claim 1 ; wherein the permanent magnet comprises a disk-shaped body having magnetic domains of different polarities magnetized in an axial direction and formed alternately to each other.
7. An indicator according to claim 1 ; wherein the coil is rotatably supported on a center line of the permanent magnet by the fixing member and is wound so as to form a surface that is parallel to and disposed at a preselected distance from a bottom surface of the permanent magnet.
8. A measuring device comprising:
a detecting portion that detects a sound generated by an instrument and that outputs the detected sound as a first analogue value;
an A/D converter portion that converts the analogue value to a digital value;
a control unit that analyzes a frequency of the digital value and outputs a pitch signal corresponding to a pitch of the frequency of the digital value;
an indicator according to claim 1 ; and
a drive portion that converts the pitch signal into a second analogue value and that supplies a current corresponding to the second analogue value to the coil of the indicator to generate the torque by interaction with the magnetic field of the permanent magnet to thereby rotate the indicator needle in the direction of the torque to indicate the pitch.
9. A measuring device according to claim 8 ; wherein each of the first spiral spring and the second spiral spring of the indicator is fixed to the fixing member and the coil of the indicator so that an inner diameter of the first spiral spring increases and an outer diameter of the second spiral spring decreases when the indicator needle rotates in the direction of the torque to indicate the pitch.
10. A measuring device according to claim 8 ; wherein the indicator needle undergoes rotation through a range of angles corresponding to indicator angles of the indicator needle that indicate the pitch; wherein the coil generates the torque by interacting with a magnetic field of the permanent magnet upon supply of a current to the coil; and wherein a spring constant of each of the first and second spiral springs remains constant regardless of the indicator angle of the indicator needle so that the current supplied to the coil and the indicator angle are proportional to each other.
11. A measuring device according to claim 8 ; wherein each of the first spiral spring and the second spiral spring is fixed to the fixing member and the coil so that an inner diameter of the first spiral spring increases and an outer diameter of the second spiral spring decreases in a case where the indicator needle rotates in the direction of the torque.
12. An indicator comprising:
a permanent magnet;
a coil rotatably supported on the permanent magnet and wound so as to form a surface that is parallel to and disposed at a preselected distance from a bottom surface of the permanent magnet, the coil generating a torque by interaction with a magnetic field of the permanent magnet upon supply of a current to the coil;
an indicator needle mounted to undergo rotation with the coil through a range of angles corresponding to indicator angles of the indicator needle; and
a pair of spiral springs that urge the indicator needle in a direction opposite to a direction of the torque to undergo rotation through the range of indicator angles, the pair of spiral springs comprising a first spiral spring connected at one end thereof to one end of the coil and a second spiral spring connected at one end thereof to another end of the coil, the first spiral spring being larger than the second spiral spring and being arranged on an outer peripheral side of and coaxially with the second spiral spring so that the first and second spiral springs lie on a common plane.
13. An indicator according to claim 12 ; wherein the first and second spiral springs are connected to the coil so that during rotation of the indicator needle through the range of indicator angles, an inner diameter of the first spiral spring increases and an outer diameter of the second spiral spring decreases.
14. An indicator according to claim 12 ; wherein the permanent magnet has magnetic domains of different polarities magnetized in an axial direction and formed alternately to each other.
15. An indicator according to claim 12 ; wherein a spring constant of each of the first and second spiral springs remains constant regardless of the indicator angle indicated by the indicator needle so that the current supplied to the coil and the indicator angle are proportional to each other.
16. An indicator according to claim 12 ; wherein the permanent magnet is cylindrical-shaped.
17. An indicator according to claim 12 ; wherein the permanent magnet comprises a disk-shaped body having magnetic domains of different polarities magnetized in an axial direction and formed alternately to each other.
18. An indicator according to claim 12 ; wherein the coil is rotatably supported on a center line of the permanent magnet.
19. A measuring device comprising:
a detecting portion that detects a sound generated by an instrument and that outputs the detected sound as a first analogue value;
an A/D converter portion that converts the analogue value to a digital value;
a control unit that analyzes a frequency of the digital value and outputs a pitch signal corresponding to a pitch of the frequency of the digital value;
an indicator according to claim 12 ; and
a drive portion that converts the pitch signal into a second analogue value and that supplies a current corresponding to the second analogue value to the coil of the indicator to generate the torque by interaction with the magnetic field of the permanent magnet to thereby rotate the indicator needle to one of the indicator angles to indicate the pitch.