1. Field of the Invention
The present invention relates to a radio communication system of a water heater including a slave set which remotely operates a water heater main body by radio communication, and a master set which continuously communicates with the water heater main body by wired communication and which intermittently communicates with the slave set by radio communication to relay communication between the water heater main body and the slave set.
2. Description of the Related Art
As a conventional water heater, since an indoor wiring operation of a remote control unit is unnecessary and installation is easy, and besides a remote control unit can easily be provided for an already installed water heater, there is known a radio communication system in which the outdoor water heater main body is remotely operated by radio communication using an indoor slave set (radio remote control unit) while relaying the master set of the outdoor water heater.
For example, as shown in FIG. 5, the radio communication system of this kind includes a master set 103 which is connected with a wire communication line 106 to an electronic unit 102 of the water heater main body 101 and which communicates with the water heater main body 101 by wired communication, and a slave set 105 which communicates with the master set 103. Wire communication is continuously performed between the master set 103 by radio communication and the water heater main body 101, and radio intermittent communication is performed between the master set 103 and the slave set 105. The intermittent communication between the master set 103 and the slave set 105 is kept in timing-synchronization on the side of the slave set 105 based on a transmission-start time point information included in radio data from the master set 103, indicative of the start time point of the next data transmission (e.g., Japanese Patent Application Laid-open No. 2005-328296).
Therefore, when operation information given by switching operation of the slave set 105 is transmitted to the master set 103 by radio intermittent communication, an operation instruction from the master set 103 is immediately transmitted to the water heater main body 101 by full-time wire communication. Then, the water heater main body 101 performs an operation according to the operation instruction. The monitor information (such as combustion operation state, stoppage state of combustion, and hot water supply temperature) of the water heater main body 101 is continuously received by full-time wire communication with by the master set 103, and is transmitted to the slave set 105 by radio intermittent communication from the master set 103. With this configuration, the slave set 105 can periodically obtain the latest monitor information of the water heater main body 101, and the monitor information is displayed on the display section of the slave set 105. In this manner, the master set 103 operates to relay the communication such that the outdoor water heater main body 101 is remotely operated by the slave set 105, i.e. the radio remote control unit, and that the monitor information of the water heater main body 101 is displayed on the slave set 105, in the above-mentioned radio communication system.
Some kinds of the water heater main body can change the setting of the hot water supply temperature only by 1° C. Also, it is desired to suppress the abrupt change in temperature of outgoing hot water by finely controlling the combustion in the water heater main body 101 even if the setting of the hot water temperature is changed during the supply of hot water. In response thereto, as shown FIG. 5, there is known a water heater main body 101 which operates such that if the hot water supply temperature is changed by the slave set 105, the master set 103 instructs the water heater main body 101 to change the hot water supply temperature of the water heater main body 101 little by little (e.g., by 1° C.). In this kinds of the water heater, since the master set 103 continuously communicates with the water heater main body 101, the master set 103 continuously receives the monitor information from the water heater main body 101 even while the master set 103 is transmitting data to the water heater main body 101. The master set 103 transmits the monitor information of the water heater main body 101 of the transmission timing to the slave set 105 at the transmission timing of the radio intermittent communication with the slave set 105. Therefore, depending on the transmission timing of the master set 103, monitor information of the water heater main body 101 can be transmitted to the slave set 105 from the master set 103 in a state where the change of the hot water supply temperature in the water heater main body 101 has not yet been completed.
For example, if the hot water supply temperature of the water heater main body 101 is changed from the current value of 40° C. to 50° C. in the slave set 105, the master set 103 automatically transmits an operation instruction to change the hot water supply temperature by “+1° C.” to the water heater main body 101 ten times successively so that the hot water supply temperature of the water heater main body 101 is changed from 40° C. to 50° C. Even when the hot water supply temperature of the water heater main body 101 has been changed only to 43° C. at the intermittent communication timing, the master set 103 transmits monitor information indicating that “hot water supply temperature is 43° C.” to the slave set 105. However, the slave set 105 displays setting information in the slave set 105 and monitor information transmitted from the master set 103 on the same display section. Thus, in the display section of the slave set 105, since the hot water supply temperature is changed to 50° C. first, displayed contents indicating that “hot water supply temperature is 50° C.” is rewritten to “hot water supply temperature is 43° C.” by the monitor information received from the master set 103. Therefore, when a user sees the displayed contents, in which the hot water supply temperature should have been set to 50° C. by the slave set 105, is changed to 43° C., the user feels suspicious or uncomfortable and may mistakenly believe that the slave set 105 is out of order.
To avoid such a problem, it can be considered that the slave set 105 does not receive radio data from the master set 103 for certain period. However, in this case, the slave set 105 does not also receive transmission-start time point information indicative of a next data transmission time point from the master set 103. Thus, there arises a problem that communication timing of the intermittent communication between the slave set 105 and the master set 103 cannot be in synchronization with each other.