Field equipment photoelectric sensing sensitivity adjustment

• US 8,970,124 B2
• Filed: 10/04/2010
• Issued: 03/03/2015
• Est. Priority Date: 10/10/2009
• Status: Active Grant

• Current Assignee: OVAL Limited (Arthur J Gallagher & Company)
• Original Assignee: OVAL Limited (Arthur J Gallagher & Company)
• Inventors: Kameyama, Tatsumi, Nakayama, Noriaki, Endo, Yoshifumi
• Primary Examiner(s): Tran, Thienvu
• Assistant Examiner(s): LO, CHRISTOPHER KWOK YEUNG
• Application Number:
  US13/376,905
• Publication Number:
  US 20120081031A1
• Time in Patent Office: 1,611 Days
• Field of Search: 315149-151, 315/158, 315291-293, 315/112, 315/224, 315/308, 315312-313, 315/318, 315/362, 250/205, 250/221, 250/222.1, 250/201.4, 340/13.24, 340/539.26
• US Class Current: 315/291
• CPC Class Codes: H03K 17/941 using an optical detector H03K17/968 takes precedence
• CPC Class Codes: H03K 2217/94031 Calibration involving digital processing
• CPC Class Codes: H05B 45/12 using optical feedback

Abstract

A photoelectric sensing sensitivity adjusting device includes: an LED for emitting light by being supplied with energy (current or voltage); a regulator for LED driving for supplying the energy to the LED; a light receiving device for receiving the light emitted from the LED; a digital potentiometer for controlling increase or decrease of the energy to be supplied to the LED; a CPU for digitally controlling, according to a control program, the increase or decrease of the energy to be supplied to the LED; and a photodetection portion for detecting an optical signal, converting the optical signal to an electrical signal, and outputting the electrical signal.

Claims

1. A photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device, capable of performing optimum sensitivity adjustment, wherein:

a switching operation portion (man-machine interface) of the field device is configured so as not to be exposed to external air through provision of a light-emitter-beam transmissive material to a front surface thereof;

the operation portion comprising;

a switching operation portion for turning on/off a photoelectric sensor by bringing a light reflector closer to the front surface formed of the light-emitter-beam transmissive material;

a data display screen for displaying a screen according to a switching mode designated by the switching operation portion, after a switching operation (ON operation) of the switching operation portion is performed by bringing the light reflector closer to the front surface of the operation portion to thereby switch modes of display data including a setting; and

a photoelectric sensing sensitivity adjusting device for adjusting optical detection sensitivity of the photoelectric sensor which is turned on/off by the switching operation portion,

the photoelectric sensing sensitivity adjusting device comprising;

a light emitter including an LED, for emitting light by being supplied with energy (current or voltage);

a regulator for LED driving with an output adjusting function, for supplying the energy (current or voltage) to the LED serving as the light emitter;

a light receiving device for receiving the light which is emitted from the light emitter and reflected by bringing the light reflector closer to the front surface formed of the light-emitter-beam transmissive material;

a digital potentiometer for controlling increase or decrease of the energy (current or voltage) to be supplied to the LED serving as the light emitter from the regulator for LED driving;

a CPU for digitally controlling the increase or the decrease of the energy (current or voltage) to be supplied to the LED serving as the light emitter from the regulator for LED driving, by controlling the digital potentiometer according to a software control program with a control signal;

a personal computer connected via a communication terminal unit, for controlling the CPU; and

a photodetection portion for detecting an optical signal emitted from the LED, converting the optical signal to an electrical signal, and outputting the electrical signal.

2. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 1, wherein the field device is accommodated in a sturdy housing intended for on-site installation in consideration of durability.

3. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 1,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside a photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (up-shifting or down-shifting) a wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via a digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be increased or decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (up-shifted or down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

4. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 1,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

11. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 2,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside a photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (up-shifting or down-shifting) a wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via a digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be increased or decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (up-shifted or down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

12. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 2,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

13. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 3,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

5. A photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device, capable of performing optimum sensitivity adjustment through control of a digital potentiometer by a CPU, wherein:

a switching operation portion (man-machine interface) of the field device is configured so as not to be exposed to external air through provision of a light-emitter-beam transmissive material to a front surface thereof;

the switching operation portion being configured so as not to be exposed to external air with provision of a light-emitter-beam transmissive material to a front surface thereof,

the switching operation portion comprising;

a switching operation portion for turning on/off a photoelectric sensor comprising a light emitter and a photodetector, by bringing a light reflector closer to the light-emitter-beam transmissive material;

a data display screen for displaying, on a screen, according to a designated mode, a mode of display data through a switching operation of the switching operation portion; and

a photoelectric sensing sensitivity adjusting device adjusting optical detection sensitivity of the photoelectric sensor,

the photoelectric sensing sensitivity adjusting device comprising;

an LED;

a photo IC;

a variable output regulator;

a digital potentiometer; and

a CPU,

wherein the LED emits light by being supplied with electrical energy,

wherein the photo IC receives the light which is emitted from the LED and reflected by the light reflector, and outputs a signal,

wherein the variable output regulator has one end connected to the LED via a first resistor and another end connected to the digital potentiometer via a second resistor, and increases or decreases a forward current of the LED by changing an output voltage, to thereby adjust a light emission amount of the LED,

wherein the digital potentiometer controls the output voltage of the variable output regulator, to thereby control energy (voltage or current) to be supplied to the LED from the variable output regulator, and

wherein the CPU transmits a control signal to the digital potentiometer to control the output voltage of the variable output regulator, thereby adjusting the light emission amount of the LED by controlling the energy (voltage or current) to be supplied to the LED from the variable output regulator.

6. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 5,

wherein the photo IC comprises:

a photodetection portion;

a pulse generator;

an AND circuit; and

a transistor,

wherein the photodetection portion detects the light which is emitted from the LED and reflected by the light reflector, and outputs a received optical signal to one terminal of the AND circuit when the light has a given light amount or more,

wherein the pulse generator outputs a given pulse signal to cause the LED to emit the light in synchronization with the given pulse signal by using the given pulse signal, and inputs the given pulse signal to another terminal of the AND circuit,

wherein the AND circuit performs an AND operation between the received optical signal, which is output after the light emitted from the LED is received, and the given pulse signal output from the pulse generator, and outputs a resultant to the CPU, and

wherein the transistor is turned on/off by the given pulse signal output from the pulse generator so as to cause the LED to emit the light in synchronization with the given pulse signal.

7. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 5,

wherein the digital potentiometer comprises a wiper terminal provided with an adjustment level corresponding to 32 bits, and

wherein, by using a CS signal specifying a target device, an UP/DOWN signal for determining whether the adjustment level of the digital potentiometer is to be increased or decreased, and a signal (counter signal) for shifting the adjustment level of the digital potentiometer every time a pulse edge is detected, which are output via digital control lines from a PIO built in the CPU,

the digital potentiometer controls, according to the adjustment level, a connecting location of a wiper terminal of the variable output regulator to change a resistance value of the second resistor connected to the another end of the variable output regulator, and controls a resistance-divided voltage ratio between the second resistor and the first resistor which is connected to the one end of the variable output regulator, thereby controlling the output voltage (or current) to be supplied to the LED from the variable output regulator.

8. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 7, wherein the CPU executes a software program so as to:

determine, based on an input of an output signal output from the AND circuit of the photo IC, whether or not the light has been emitted from the LED;

until the photodetection portion of the photo IC detects reflection light obtained when the light emitted from the LED is reflected by the light reflector, sequentially control, according to the adjustment level corresponding to 32 bits, a connecting location of the wiper terminal of the digital potentiometer by using the CS signal specifying the target device, the UP/DOWN signal for determining whether the adjustment level of the digital potentiometer is to be increased or decreased, and the signal (counter signal) for shifting the adjustment level of the digital potentiometer every time the pulse edge is detected, which are output via the digital control lines from the PIO built in the CPU; and

control the resistance-divided voltage ratio between the first resistor connected to the one end of the variable output regulator and the second resistor connected to the another end of the variable output regulator, thereby controlling the output voltage (or current) to be supplied to the LED from the variable output regulator.

9. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 5,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside the photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (down-shifting) the wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via the digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is decreased or increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

10. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 5,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

14. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 6,

wherein the digital potentiometer comprises a wiper terminal provided with an adjustment level corresponding to 32 bits, and

wherein, by using a CS signal specifying a target device, an UP/DOWN signal for determining whether the adjustment level of the digital potentiometer is to be increased or decreased, and a signal (counter signal) for shifting the adjustment level of the digital potentiometer every time a pulse edge is detected, which are output via digital control lines from a PIO built in the CPU,

the digital potentiometer controls, according to the adjustment level, a connecting location of a wiper terminal of the variable output regulator to change a resistance value of the second resistor connected to the another end of the variable output regulator, and controls a resistance-divided voltage ratio between the second resistor and the first resistor which is connected to the one end of the variable output regulator, thereby controlling the output voltage (or current) to be supplied to the LED from the variable output regulator.

15. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 6,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside the photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (down-shifting) the wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via the digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is decreased or increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

16. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 7,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside the photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (down-shifting) the wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via the digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is decreased or increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

17. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 8,

wherein the CPU executes an automatic sensitivity adjustment function for optical sensing including:

resetting a current adjustment level of the digital potentiometer to set an adjustment level of the digital potentiometer to a maximum sensitivity level;

determining whether or not the light of the LED which is emitting the light under a state of the resetting of the current adjustment level is detected by the photodetection portion provided inside the photodetector;

outputting, when the light of the LED is detected by the photodetection portion, a signal for changing (down-shifting) the wiper terminal of the digital potentiometer to the digital potentiometer from the CPU via the digital control line connecting the digital potentiometer and the CPU, and setting the adjustment level of the digital potentiometer to be decreased by “

1”

(by 1 bit);

determining whether or not sensitivity of the wiper terminal of the digital potentiometer can be adjusted (down-shifted) to fall within an adjustment level range; and

when the sensitivity can be adjusted to fall within the adjustment range, determining whether or not the adjustment level falls within the adjustment level range (=27 to

     5) of the wiper terminal of the digital potentiometer,

wherein the adjusted sensitivity of the photoelectric sensor is decreased or increased in a stepwise manner, and the adjustment is ended at a level at which an output from the photodetector is changed.

18. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 6,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

19. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 7,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.

20. The photoelectric sensing sensitivity adjusting device of an optical-sensing non-contact switching device (SW) for a field device according to claim 8,

wherein the CPU executes an automatic correction function for an optical switch, including:

determining whether or not a long period of time has successively elapsed after a state of output from the photodetector became ON;

determining that there is a malfunction when an ON state has been kept successively for the long period of time after the state of the output from the detector became ON, outputting a signal for changing (down-shifting) the wiper terminal to the digital potentiometer from the CPU, and setting the sensitivity adjustment level of the photodetector to be decreased by “

1”

level;

determining whether or not the state of the output from the photodetector is ON even after the sensitivity adjustment level of the photodetector is set to be decreased by the “

1”

level;

controlling the sensitivity adjustment level of the photodetector until the state of the output from the photodetector becomes OFF after determining that the sensitivity adjustment level of the photodetector is continuously high because the state of the output from the photodetector is ON; and

when the state of the output from the photodetector becomes OFF, determining that the sensitivity adjustment level of the photodetector has become appropriate, and ending controlling of the sensitivity adjustment level of the photodetector,

wherein the adjusted sensitivity of the optical switch is decreased in a stepwise manner, and the adjustment is ended at the level at which the output from the photodetector is changed, thereby automatically correcting the sensitivity adjustment of the optical switch.