Communication system and communication apparatus

A communication system comprising:

• a first communication device;
• and
• one or more second communication devices connected to the first communication device by a signal line, a common line and a power line, the one or more second communication devices being connected in parallel with each other with respect to the first communication device when a number of the one or more second communication devices is two or more,
• wherein
• the first communication device comprises
• a direct current power supply configured to generate a direct current for serial communication from alternating current power supplied from an alternating current power supply through the power line and the common line, and pass the generated direct current through a current loop comprising the signal line and the common line that are connected in series, and
• a transmitter configured to transmit data by control of a current flowing through the current loop,
• the one or more second communication devices each comprise a receiver configured to receive data by detection of the current flowing through the current loop,
• at least one device among the first communication device and the one or more second communication devices further comprises an adjuster configured to adjust impedance between the signal line and the common line based on the number of the one or more second communication devices,
• the adjuster comprises a switcher configured to switch, based on the number of the one or more second communication devices, a state between the signal line and the common line between (i) a state of connection via a first load resistor and (ii) a state of disconnection via the first load resistor,
• the adjuster further comprises a determiner configured to determine the number of the one or more second communication devices based on a voltage between the signal line and the common line,
• the switcher is configured to switch, based on the number determined by the determiner, the state between the signal line and the common line between (i) the state of connection via the first load resistor and (ii) the state of disconnection via the first load resistor,
• the determiner comprises a Zener diode and a first photocoupler that are connected in series between the signal line and the common line,
• the determiner is configured to determine that the number of the one or more second communication devices is equal to or less than a reference number when the first photocoupler is conductive and determine that the number of the one or more second communication devices exceeds the reference number when the first photocoupler is non-conductive, and
• the switcher is configured to
• switch the state between the signal line and the common line to the state of connection via the first load resistor when the number of the one or more second communication devices is determined to be equal to or less than the reference number by the determiner, and
• switch the state between the signal line and the common line to the state of disconnection via the first load resistor when the number of the one or more second communication devices is determined to exceed the reference number.

A communication system comprising:

• a first communication device;
• and
• one or more second communication devices connected to the first communication device by a signal line, a common line and a power line, the one or more second communication devices being connected in parallel with each other with respect to the first communication device when a number of the one or more second communication devices is two or more,
• wherein
• the first communication device comprises
• a direct current power supply configured to generate a direct current for serial communication from alternating current power supplied from an alternating current power supply through the power line and the common line, and pass the generated direct current through a current loop comprising the signal line and the common line that are connected in series, and
• a transmitter configured to transmit data by control of a current flowing through the current loop,
• the one or more second communication devices each comprise a receiver configured to receive data by detection of the current flowing through the current loop,
• at least one device among the first communication device and the one or more second communication devices further comprises an adjuster configured to adjust impedance between the signal line and the common line based on the number of the one or more second communication devices,
• the adjuster is configured to adjust the impedance between the signal line and the common line so that the impedance between the signal line and the common line is within a preset range regardless of the number of the one or more second communication devices,
• the adjuster comprises a plurality of series circuits each comprising a second load resistor and a second photocoupler that are connected in series between the signal line and the common line, and
• the adjuster is configured to allow the second photocoupler of a series circuit of the plurality of series circuits to be conductive, the second photocoupler being selected based on the number of the one or more second communication devices.

A first communication device for serial communication with one or more second communication devices, the first communication device comprising:

• a direct current power supply configured to generate a direct current for serial communication from alternating current power supplied from an alternating current power supply through a power line and a common line, and pass the generated direct current through a current loop comprising a signal line and the common line that are connected in series;
• a transmitter configured to transmit data by control of a current flowing through the current loop;
• and
• an adjuster configured to adjust impedance between the signal line and the common line based on a number of the one or more second communication devices,
• wherein the one or more second communication devices are connected in parallel to the first communication device by the signal line, the common line and the power line,
• wherein the one or more second communication devices are connected in parallel with each other with respect to the first communication device when the number of the one or more second communication devices is two or more, and
• wherein the adjuster comprises a switcher configured to switch, in a case in which data is transmitted from the first communication device to the one or more second communication devices, based on the number of the one or more second communication devices, a state between the signal line and the common line to (i) a state of connection via a first load resistor when the number of the one or more second communication devices is equal to or less than a reference number and (ii) a state of disconnection via the first load resistor when the number of the one or more second communication devices exceeds the reference number.

A second communication device that is any of one or more second communication devices connected to a first communication device by a signal line, a common line and a power line, the one or more second communication devices being connected in parallel with each other with respect to the first communication device when a number of the one or more second communication devices is two or more, the first communication device including a direct current power supply configured to generate direct current power for serial communication from alternating current power supplied from an alternating current power supply, the second communication device comprising:

• a receiver configured to receive data by detection of a current flowing through a current loop comprising the signal line and the common line that are connected in series;
• and
• an adjuster configured to adjust impedance between the signal line and the common line based on the number of the one or more second communication devices,
• wherein the adjuster comprises a switcher configured to switch, in a case in which data is transmitted from the first communication device to the one or more second communication devices, based on the number of the one or more second communication devices, a state between the signal line and the common line to (i) a state of connection via a first load resistor when the number of the one or more second communication devices is equal to or less than a reference number and (ii) a state of disconnection via the first load resistor when the number of the one or more second communication devices exceeds the reference number.

A first communication device for serial communication with one or more second communication devices, the first communication device comprising:

• a direct current power supply configured to generate a direct current for serial communication from alternating current power supplied from an alternating current power supply through a power line and a common line, and pass the generated direct current through a current loop comprising a signal line and the common line that are connected in series;
• a transmitter configured to transmit data by control of a current flowing through the current loop;
• and
• an adjuster configured to adjust impedance between the signal line and the common line based on a number of the one or more second communication devices,
• wherein
• the one or more second communication devices are connected to the first communication device by the signal line, the common line and the power line,
• the one or more second communication devices are connected in parallel with each other with respect to the first communication device when the number of the one or more second communication devices is two or more,
• the adjuster is configured to adjust the impedance between the signal line and the common line so that the impedance between the signal line and the common line is within a preset range regardless of the number of the one or more second communication devices,
• the adjuster comprises a plurality of series circuits each comprising a second load resistor and a second photocoupler that are connected in series between the signal line and the common line, and
• the adjuster is configured to allow the second photocoupler of a series circuit of the plurality of series circuits to be conductive, the second photocoupler being selected based on the number of the one or more second communication devices.

A second communication device that is any of one or more second communication devices connected to a first communication device by a signal line, a common line and a power line, the one or more second communication devices being connected in parallel with each other with respect to the first communication device when a number of the one or more second communication devices is two or more, the first communication device including a direct current power supply configured to generate direct current power for serial communication from alternating current power supplied from an alternating current power supply, the second communication device comprising:

• a receiver configured to receive data by detection of a current flowing through a current loop comprising the signal line and the common line that are connected in series;
• and
• an adjuster configured to adjust impedance between the signal line and the common line based on the number of the one or more second communication devices,
• wherein
• the adjuster is configured to adjust the impedance between the signal line and the common line so that the impedance between the signal line and the common line is within a preset range regardless of the number of the one or more second communication devices,
• the adjuster comprises a plurality of series circuits each comprising a second load resistor and a second photocoupler that are connected in series between the signal line and the common line, and
• the adjuster is configured to allow the second photocoupler of a series circuit of the plurality of series circuits to be conductive, the second photocoupler being selected based on the number of the one or more second communication devices.