GB2271453A - Controlling a plurality of devices - Google Patents

Abstract

Apparatus for controlling a plurality of dampers in an air conditioning system comprises a plurality of damper control stations (7) connected in a serial network loop (10) controlled by a network controller (15). Initially the network controller (15) transmits a global poll message around the network loop through the station controllers (7) each of which attaches its address to the message so the global poll message received by the network controller comprises the station addresses in the sequence in which the station controllers are connected in the network (10). A break in the loop and its location are detected by transmitting a global poll message. Each controller acknowledges receipt of the message to the preceding controller. If this does not receive the acknowledgement it sends the message back to the network controller (15) which then sends a global poll message the other way round the loop. A station controller (7) can be by-passed and operate under its own local control. <IMAGE>

Description

"Method and apparatus for controlling a plurality of devices" The present invention relates to a method and apparatus for controlling a plurality of devices located at respective remote locations, and in particular, though not limited to a method and apparatus for controlling a plurality of remotely located dampers in a duct or ducts of an air conditioning system.

Dampers in a duct or ducts of an air conditioning system are typically controlled by servomotors. In general, the servomotors are controlled by station controllers which operate under the control of a master controller. In general, the station controllers are connected directly to the master controller by a plurality of parallel connections.

This is a relatively expensive and cumbersome way of connecting station controllers to the master controller, and also requires relatively large quantities of cabling which also adds to the expense of the system as well as being unsightly.

There is therefore a need for a method and apparatus for controlling a plurality of devices located at respective remote locations which overcomes these problems.

The present invention is directed towards providing such a method and apparatus.

According to the invention there is provided apparatus for controlling a plurality of devices located at respective remote locations, the apparatus comprising a plurality of station controllers associated with the respective devices for controlling and monitoring the respective devices, the station controllers being connected in a serial network loop, and a network controller connected into the network loop for controlling communications in the network loop, the network controller comprising first and second main ports for connecting into respective ends of the network loop, each main port having transmitting means and receiving means for respectively transmitting and receiving a message onto or from the network loop, main control means in the network controller for controlling transmission and reception of a message through the first and second main ports and for monitoring the first and second ports to determine if the message is received by either the first or second main port, the control means transmitting the message through the second main port if the message transmitted through the first main port is not received by the second main port, and a main storing means for storing the received message, each station controller comprising first and second secondary ports for connecting into the network loop, and each secondary port having transmission and receiving means for respectively transmitting and receiving the message, and secondary control means for receiving the message through one of the secondary ports and attaching a station address of the said station controller to the message and transmitting the received message with the station address attached thereto to the next adjacent station controller in the network loop through the other of said secondary ports, the secondary control means of each station controller transmitting the message with the station address attached thereto to the station controller from which the message was received for return to the main port of the network controller from which the message was transmitted in the event that the next adjacent station controller to which the message had first been transmitted fails to acknowledge receipt of the said message.

In one embodiment of the invention the station address of each station controller is attached to the end of the received message. Preferably, the secondary control means of each station controller attaches the status of the associated device to the message after the station address of the station controller.

Advantageously, the station controllers are assigned respective unique predetermined station addresses.

In one embodiment of the invention the message is a global poll message for determining the status of the network loop.

Preferably, each station controller is operable in two modes, namely, a central control mode in which the station controller operates under an instruction contained in a message transmitted by the network controller and a local control mode in which the station controller operates under the control of its secondary control means.

Advantageously, each station controller comprises bypass means for permitting communications between the next adjacent station controllers on opposite sides of the said station controller in the network loop in the event of power loss in the said station controller.

Preferably, each bypass means comprises a line through relay.

In one embodiment of the invention the main control means of the network controller comprises means for down loading data from the main storing means.

Preferably, the apparatus comprises a master controller connected to the network controller for receiving down loaded data from the network controller and for delivering messages to the network controller for transmission to the station controllers.

In one embodiment of the invention each device is a damper in a duct of an air conditioning system.

Additionally the invention provides a method for controlling a plurality of devices located at respective remote locations using the apparatus according to the invention, each device being controlled by a respective station controller, the method comprising the steps of transmitting a message through the first main port of the network controller for transmission through the network loop to the second main port of the network controller, transmitting another message through the second main port should the message transmitted through the first main port not be received by the second main port, monitoring the first and second main ports of the network controller to determine reception of each message, reading each received message from the main ports on which the message is received, and storing each received message, the method further comprising the steps of sequentially attaching station addresses of the station controllers to the message on receipt of the message by the respective station controllers, transmitting the received message with the station address attached thereto to the next adjacent station controller in the network loop, and transmitting the message with the station address attached thereto to the station controller from which the message was received for return to the main port of the network controller from which the message was transmitted should the next adjacent station controller to which the message had first been transmitted fail to acknowledge receipt of the said message.

In one embodiment on the invention the method comprises the step of reading the stored received message and the sequence of station addresses stored in the main storing means for determining the sequence within which the station controllers are connected in the network loop.

Preferably, each station controller attaches its station address at the end of the received message.

In another embodiment of the invention the method comprises the step of reading the last station address of the message received by the main ports for determining if a break exists in the network loop and for determining the position of the break. In a further embodiment of the invention the method comprises the step of bypassing a station controller in the event that the said station controller has lost power.

Preferably, the method comprises a step of checking for the absence of station addresses in the message received by the main ports to establish if a station controller has lost power. Advantageously, each station controller reverts to local control mode should that station controller fail to receive a message from the network loop at predetermined time intervals.

Preferably, the method further comprises the step of attaching the status of each device to the message.

Ideally, the status of each device is attached to the message after the station address of the said station controller has been attached to the message.

In one embodiment of the invention the message is a global poll message for determining the status of the network loop. In one embodiment of the invention each device is a damper in a duct of an air conditioning system.

Further the invention provides an air conditioning system comprising at least one duct having a plurality of remotely located dampers mounted therein and apparatus according to the invention for controlling the dampers.

The invention will be more clearly understood from the following description of a preferred embodiment thereof given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of apparatus according to the invention for controlling a plurality of remotely located devices, Fig. 2 is a circuit diagram of portion of the apparatus of Fig. 1, Fig. 3 is a circuit diagram of another portion of the apparatus of Fig. 1, Fig. 4 is a flow chart of a computer programme for use with the apparatus of Fig. 1, Fig. 5 is a flow chart of another computer programme for use with the apparatus of Fig. 1, and Fig. 6 is a flow chart of a further computer programme for use with the apparatus of Fig. 1.

Referring to the drawings and initially to Figs. 1 to 3 there is illustrated apparatus according to the invention indicated generally by the reference numeral 1 for controlling a plurality of devices, namely, dampers 2 of an air conditioning system (not shown).

For convenience only one of the dampers is schematically illustrated in Fig. 2 in a duct 3, a portion only of which is illustrated in Fig. 2. Such air conditioning systems will be well known to those skilled in the art. Such air conditioning systems, in general, comprise one or more ducts for delivering air of controlled temperature and humidity into a plurality of locations in a building. A plurality of dampers similar to the dampers 2 are located in the ducts for controlling the flow of air through the ducts.

The apparatus 1 comprises a plurality of station controllers 7 for controlling respective dampers 2.

Each station controller 7 operates a servomotor 8 for operating the damper 2. A sensor 9 associated with each damper 2 monitors the status, in other words, the position of the damper 2, which is relayed back to the station controller 7. The station controllers 7 are connected in a serial network loop 10 by a cable 11.

Communications through the serial network loop 10 are controlled by a network controller 15 connected to respective ends 16 and 17 of the network loop 10. The station controllers 7 operate under the control of a master controller 20 which communicates with the station controllers 7 through the network controller 15. The master controller 20 is described below.

Referring to Fig. 3, the network controller 15 comprises a main control means, in this case, a microprocessor 22 for controlling the operation of the network controller 15, communicating with the master controller 20 and for controlling communications on the network loop 10. Communications between the microprocessor 22 and the master controller 20 are through communication ports 24 and 25 in the network controller 15 and the master controller 20, respectively. First and second main ports 27 and 28 in the network controller 15 couple the network controller 15 with the ends 16 and 17, respectively, of the network loop 10. The first and second main ports 27 and 28 of the network controller 15 comprise transmitting means and receiving means, namely, transmitters 29 and receivers 30, respectively, for transmitting and receiving messages onto and from the network loop 10.A read only memory 31 stores a computer programme described below for controlling the operation of the network controller 15 and communications on the network loop 10. A main storing means, namely, a random access memory 32 stores messages for transmission onto the network loop 10 and received from the network loop 10.

Referring to Fig. 2, each station controller 7 comprises a secondary control means, namely, a microprocessor 35 for communicating with the network loop 10 and for controlling the station controller 7, and the servomotor 8. An output port 36 in each station controller 7 couples the servomotor 8 to the station controller 7. The servomotors 8 are driven by the respective motor driver 37 under the control of the microprocessor 35. An input port 38 in each station controller 7 couples the sensor 9 to the microprocessor 35 through an opto isolator 39 in the station controller 7 for relaying the status of the damper to the microprocessor 35. First and second secondary ports 40 and 41 in each station controller 7 connect the station controllers 7 into the network loop 10 serially.Transmitting and receiving means, namely, transmitters 42 and receivers 43, respectively, are provided in the first and second secondary ports 40 and 41 for transmitting messages onto and receiving messages from the network loop 10.

A read only memory 45 in each station controller 7 stores a computer programme described below for controlling the station controller 7 and for communicating the station controller 7 with the network loop 10 and for controlling the servomotor 8.

An accessible switch array 47 connected to the microprocessor 35 of each station controller 7 allows a predetermined station address unique to each station controller 7 to be selected and assigned to that station controllers 7 for enabling each station controller 7 to be identified and also for enabling its position in the network loop 10 to be identified as will be described below. A secondary storing means, namely, a random access memory 46 stores the station address of the station controller 7, the status of the damper for transmission onto the network loop 10, and data received from the network loop 10.

Bypass means comprising a line through relay 48 in each station controller 7 permits a station controller to be bypassed in the event of power being lost or removed from the station controller 7.

Referring again to Fig. 3, the master controller 20 comprises a microprocessor 55 which controls the operation of the master controller 20 and the station controllers 7 through the network controller 15. A read only memory 56 in the master controller 20 stores computer programmes for controlling the operation of the master controller 20 and for controlling the servomotors 8 of the air conditioning system in response to external inputs from a control panel (not shown) of the air conditioning system. Such external inputs may be data entered in the control panel, or it may be an input from a feed back from a temperature sensor, humidity sensor or the like in the air conditioning system. Such external inputs will be well known to those skilled in the art.Such computer programmes which interpret such external inputs will also be well known to those skilled in the art, and it is not intended to describe them in further detail. A random access memory 57 stores the addresses of the station controllers 7 in the sequence in which the station controllers 7 are connected in the network loop 10 to facilitate identifying a faulty station controller 7 or a break in the network loop 10 between adjacent station controllers 7 as will be described below. A random access memory 58 stores data received from the station controllers 7 through the network controller 15 relating to the status of the network loop 10 and the status of the dampers 2. A display 59 in the master controller 20 displays the status of the network loop 10, and indicates if a break occurs in the loop as will be described below.A serial interface port 54 is provided in the master controller 20 for connection of a personal computer (not shown) or other computer into the master controller 20 during commissioning of the apparatus or diagnostic operations. By the use of a suitable computer programme not described in the personal computer (not shown) the sequence in which the station controllers 7 are connected in the network loop 10 may be displayed on the personal computer display.

Before describing the computer programmes which control the network controller 15 and the station controllers 7 in detail, the main operating features of the apparatus 1 will first be described. The network controller 15 under the control of the microprocessor 22 controls all communications on the network loop 10. Messages containing instructions to the respective station controllers 7 from the master controller 20 to be transmitted to the station controllers 7 are transmitted onto the network loop 10 by the network controller 15. At predetermined intervals the network controller 15 transmits a global poll message in order to check the status of the network loop 10 and to check the status of the dampers 2.Messages from the master controller 20 are communicated to the microprocessor 22 of the network controller 15 and stored in the random access memory 32 for transmission onto the network loop 10. All messages including global poll messages are transmitted from the network controller 15 through the first main port 27 onto the network loop 10. The messages are passed in the direction of the arrows A around the network loop 10 sequentially through the station controllers 7 and returned to the second main port 28 of the network controller 15 assuming there is no break in the network loop 10. Each station controller 7 acknowledges a received valid message to its adjacent station controller 7 from which the message was received or the network controller 15 if the message was received directly from the network controller 15.Further, the network controller 15 acknowledges all valid messages received from the station controller 7 adjacent to it from which it has received a message. Failure to receive an acknowledgement of a transmitted message is assumed by the station controller 7 or network controller 15 as the case may be which transmitted the message to indicate a break in the network loop 10 between the station controller 7 and/or network controller 15 which sent the message and the controller 7 or 15 which should have received the message. On such a break being found the message is returned by the station controller 7 to its next adjacent controller 7 or the network controller 15 from which the message was received. The message is then returned to the main port 27 or 28 from which it was sent through the leg of the network loop 10 through which it was originally sent.This indicates to the network controller that a break in the network loop 10 has occurred, and the location of the break can be determined as will be described below. On a message being transmitted through the main port 27 the microprocessor 22 in the network controller 15 monitors the main ports 27 and 28 for receipt of the message. Should the message be received by the second main port 28 the network loop 10 is intact. Should the message be received on the first main port 27 a break in the network loop 10 is assumed. The network controller 15 under the controlof the microprocessor 22 then transmits the message from the second main port 28 onto the network loop 10. The message is passed around the network 10 in the direction of the arrows B in sequence through the station controllers 7.The microprocessor 22 monitors the main ports 27 and 28 for receipt of the message. Should the message be received on the main port 27 it is assumed that continuity in the network loop 10 has been restored.

Should the message be received on the second main port 28 the break in the network loop 10 is confirmed.

Each message containing an instruction to a station controller 7 from the master controller 20 for transmission to a station controller 7 contains the station address of that station controller 7. As the message is passed through the network loop 10 and the station controllers 7 each station controller 7 checks the station address to ascertain if the address is for that station controller 7. The station controller 7 whose address corresponds to the station address of the message seizes the message and passes the message on to the next station controller 7 for transmission around the network loop 10 back to the network controller 15. The message seized by the station controller 7 is stored in the random access memory 46 and is subsequently processed by the microprocessor 35 of the station controller 7.In the event that the message is an instruction to operate the servomotor 8, the servomotor 8 is operated under the control of the microprocessor 35 in response to the instruction in stored message.

Each global poll message comprises three main instructions to the station controllers 7. The first instruction instructs the station controllers 7 to attach their respective station addresses at the end of the received global poll message. The second instruction instructs the station controllers 7 to attach the status of their associated dampers 2 at the end of the global poll message immediately after its station address. The third instruction instructs the station controllers 7 to pass on the message to their next adjacent station controller 7 in the network loop 10. Accordingly, as the global poll message is passed through the network loop 10 and the station controllers 7, the global poll message acquires a string of station addresses and damper statuses in the sequence in which the station controllers 7 are connected into the network loop 10. The global poll message on passing through the network loop 10 is received by the network controller 15 and stored in the random access memory 32 of the network controller 15 for subsequent down loading to the master controller 20 to enable the master controller 20 to check the status of the network loop 10, and the status of the dampers 2.

On installation of the apparatus 1 the sequence in which the station controllers 7 are connected in the network loop 10 is first determined. This is determined with a personal computer (not shown) connected into the interface port 54 as follows. Under the control of the personal computer, through the master controller 20, the microprocessor 22 and the network controller 15 transmits a global poll message through the first main port 27 onto the network loop 10. The global poll message is transmitted to the first station controller 7 in the network 10 adjacent the first main port 27. For convenience, this first station controller 7 is identified as station controller 7a. The remaining station controllers are identified as station controllers 7b to 7h in sequence around the network loop 10.The station controller 7a receives the global poll message through the first secondary port 40, and acknowledges receipt to the network controller 15. The station controller 7a attaches its station address stored in the random access memory 46 of the station controller 7a onto the end of the global poll message. The status of the damper 2 associated with the station controller 7a is also attached onto the global poll message after the station address. The station controller 7a then transmits the global poll message with its station address and status report attached thereto through the second secondary port 41 to the next station controller 7b in the network loop 10.The station controller 7b receives the global poll message, acknowledges receipt to the station controller 7a, and attaches its station address and the status of its associated damper 2 to the end of the received global poll message. The station controller 7b then transmits the global poll message to the station controller 7c and so on until the global poll message is received on the second main port 28 of the network controller 15. The received global poll message on the second main port 28 is read by the microprocessor 22 and stored in the random access memory 32 for subsequent down loading to the master controller 20.

The master controller 20 on receiving the global poll message stores the sequence of the station addresses in the random access memory 57 for further reference.

Under the control of the personal computer (not shown) the sequence of the station addresses is down loaded into the personal computer and displayed on the visual display of the personal computer thereby enabling one to see the sequence in which the station controllers 7 are connected in the network loop 10. Once the apparatus has been commissioned the personal computer (not shown) is disconnected from the port 54 and the apparatus operates under the control of the master controller 20.

A break in the network loop 10 and its location is identified by transmitting a global poll message through the first and second main ports 27 and 28 of the network controller 15 onto the network loop 10.

The received global poll messages which are received on the first and second main ports 27 and 28 are read and stored in the random access memory 32, and are subsequently down loaded to the master controller 20.

The sequence of station addresses on the two received messages are compared against the sequence in the random access memory 57 and the location of the break can readily be identified and displayed on the display 59. In the event of two breaks occurring in the network loop 10, the location of the two breaks can likewise be determined. In the event of a single break, the network loop 10 is fully functional since all messages from the network controller 15 can be passed through all station controllers 7 using the two main ports 27 and 28 for transmitting and receiving the messages. In the event of two breaks occurring, the station controller or controllers 7 intermediate the two breaks are isolated from the network loop 10.

In the event that power is lost to any station controller 7, the appropriate line through relay 48 automatically connects the network loop 10 to bypass that station controller 7. On power being restored to that station controller 7, the appropriate line through relay 48 is opened thereby bringing that station controller 7 back into the network loop 10.

Additionally, to ensure that a break, or any other failure in the network loop 10 does not result in loss of control of a damper, each station controller 7 is operable in two modes, namely, a central control mode and a local control mode. When operating under the central control mode the station controller 7 operates under the control of the master controller 20 through the network controller 15. In the local control mode each station controller 7 operates under the control of a suitable computer programme which is not described and which is stored in the read only memory 31. The microprocessor 35 of each station controller 7 when operating in local control mode controls the servomotor 8 in response to the sensor 9 under the control of a computer programme (not described) in the read only memory 31.

The status of the dampers 2 are read by the microprocessor 55 of the master controller 20. Should adjustment to the position of any of the dampers 2 be required, an appropriate message containing an instruction to the relevant station controller 7 for transmission around the network loop 10 to the appropriate station controller 7 is prepared by the microprocessor 55 and delivered to the network controller 15 for transmission onto the network loop 10.

Referring now to Fig. 4 the computer programme in the read only memory 31 which controls the network controller 15 will now be described. Block 60 of the computer programme starts the computer programme and moves the computer programme to block 61. Block 61 checks if a message to be transmitted onto the network loop 10 has been received from the master controller 20. If no message has been received for transmission from the master controller 20 the computer programme moves to block 62. Block 62 checks if it is time to transmit a global poll message onto the network loop 10. In this embodiment of the invention the network controller 15 is set to transmit a global poll message every ten seconds. If block 62 determines that it is not yet time to transmit a global poll message, the computer programme returns to block 61. If block 62 does determine that it is time to transmit a global poll message, the computer programme moves to block 63. Block 63 sets up the global poll message for transmission onto the network loop 10, and the computer programme moves to block 64. Block 64 calls up a computer programme in the read only memory 31 for transmitting the message onto the network loop 10 which will be described with reference to Fig. 5 below. In the event that block 61 determines that a message has been received from the master controller 20 for transmission onto the network loop 10, the computer programme moves to block 65. Block 65 sets up the message received from the master controller 20 for transmission onto the network loop 10 and the computer programme then moves to block 64 which calls up the computer programme of Fig. 5 for transmitting the message onto the network loop 10.

Referring now to Fig. 5 the computer programme for controlling the transmission and receipt of messages by the network controller 15 onto the network loop 10 will now be described. The computer programme transmits global poll messages or messages received from the master controller 20 for transmission onto the network loop 10 for one or more station controllers 7.

Block 70 initiates the programme for transmitting a message onto the network loop 10 and the programme moves to block 71. Block 71 transmits the message through the first main port 27 onto the network loop 10 to the first station controller 7a in the network loop 10. Block 72 checks if the message has been acknowledged by the first station controller 7a. If the message has been acknowledged by the first station controller 7a the computer programme moves on to block 73. In the event that the message is not acknowledged by the first station controller -7a, the computer programme moves to block 74 which is described below.

Block 73 monitors the second main port 28 and checks if the message has yet been received on the second main port 28. If the message has been received by the second main port 28 the computer programme moves to block 75. Block 75 records the fact that there is no loop break since the message passed around the network loop 10 to the second main port 28. If the message is a global poll message, the received global poll message including the station addresses and the status of the respective dampers is stored in the random access memory 32 for subsequent down loading to the master controller 20. The computer programme then moves to block 76 which ends the computer programme.

Should block 73 determine that the message has not been received by the second main port 28, the computer programme moves to block 77. Block 77 monitors the first main port 27 and checks if the message has been received back on the first main port 27. If the message has not yet been received back on the first main port 27 the programme moves to block 78 which checks if the actual time elapsed since the message was transmitted through the first main port 27 is greater than the normal time which the message should have taken to travel through the network loop 10.

Should block 78 determine that the actual elapsed time is less than the normal time the computer programme returns to block 73. In the event that the actual elapsed time is greater than the normal time the computer programme moves to block 79. Block 79 checks if the message was transmitted three times through the first main port 27. If the message has not yet been transmitted three times, the computer programme returns to block 71 and the message is retransmitted through the first main port 27 again.

In the event that the message was transmitted three times, the computer programme moves to block 74. This block 74 assumes that a loop break exists between the first main port 27 and the first of the station controller 7a in the network loop 10, and writes the loop status in the random access memory 32 if the message being transmitted is a global poll message.

The computer programme then moves to block 80. Before proceeding to describe block 80, it is necessary to return to block 77.

In the event that block 77 determines that the message has been received back on the first main port 27, the computer programme moves to block 81. Block 81 determines that a break in the network loop 10 has been detected and stores the received global poll message including the station addresses and the status of the respective dampers in the random access memory 32 for subsequent down loading to the master controller 20 on demand if the message was a global poll message. The programme then moves to block 80.

Block 80 transmits the message onto the network loop 10 through the second main port 28 and the computer programme moves to block 82. Block 82 monitors the second main port 28, and checks if the message has been acknowledged by the control station 7h immediately adjacent the second main port 28. If the message is not acknowledged by the station controller 7h the computer programme moves to block 83. Block 83 determines that a break exists in the network loop 10 between the second main port 28 and the station controller 7h. If the message is a global poll message the status of the network loop 10 is stored in the random access memory 32 for subsequent down loading to the master controller 20. The computer programme then moves to block 76 which ends the programme.Should block 82 determine that the message has been acknowledged by the station controller 7h the computer moves to block 84 which checks if the message has been received by the second main port 28. If the message is received by the second main port 28 the computer programme moves to block 85 which determines that the message has been received by all station controllers 7 between the second port 28 and the break in the loop. If the message is a global poll message, the received global poll message including the station addresses and the status of the respective dampers 2 are stored in the random access memory 32 for subsequent down loading to the master controller 20.

Needless to say, if there is more than one break in the network loop 10, block 85 determines that the message has been received only by those station controllers 7 between the second main port 28 and the break in the network loop 10 nearest the second main port 28.

Should block 84 determine that the message has not been received by the second main port 28, the computer programme moves onto block 86 which checks if the message has been received by the first main port 27.

If the message has been received by the first main port 27 the computer programme moves to block 87.

Block 87 determines that continuity in the network loop 10 has been restored since the message has passed through the entire network loop 10 from the second main port 28 to the first main port 27. If the message is a global poll message, the received global poll message including the station addresses and the status of the respective dampers 2 are stored in the random access memory 32 for subsequent down loading to the master controller 20. Should block 86 determine that the message has not been received at the first main port 27, the computer programme moves to block 88. Block 88 checks if the actual elapsed time since the message was transmitted through the second main port 28 is greater than the normal time which the message should have taken to travel through the network loop 10. If the actual elapsed time is less than the normal time the computer programme returns to block 84.On the other hand, should block 88 determine that the actual elapsed time is greater than the normal time the computer programme moves to block 89, which checks if the message was transmitted three times through the second main port 28. If the message has not been transmitted three times through the second main port 28, the computer programme returns to block 80. If block 89 determines that the message has been transmitted three times through the second main port 28, the computer programme moves to block 90.

Block 90 determines that a loop break exists. If the message is a global poll message, the status of the network 10 is stored in the random access memory 32 for subsequent down loading to the master controller 20, and the computer programme moves onto block 76 and ends.

Referring now to Fig. 6 a computer programme stored in the read only memory 45 of each station controller 7 which controls communications between the network loop 10 and the respective station controllers 7 will now be described. Block 100 of the computer programme starts the programme and moves the programme to block 101. Block 101 checks if a message has been received from the network loop 10 by the station controller 7.

If block 101 determines that no message has been received the computer programme moves to block 102.

Block 102 determines if the elapsed time period since the last message was received by the station controller 7 is greater than the normal time interval between the transmission of global poll messages by the network controller 15. If the elapsed time period is less than the normal time interval the computer programme returns to block 101. On the other hand, should block 102 determine that the elapsed time period is greater than the normal time interval, the computer programme moves to block 103. Block 103 determines that the network loop 10 connecting the station controller 7 to the network controller 15 is broken and switches the station controller 7 to the local control mode. In other words, the station controller 7 controls its associated damper 2 without the intervention of the master controller 20.The computer programme remains in this mode until corrective action has been taken.

In the event that block 101 determines that a message has been received, the computer programme moves to block 104 which checks if the received message is a valid message. If the received message is not a valid message the computer programme moves to block 105 which transmits a negative acknowledgement to the adjacent station controllers 7 which transmitted the message, and the computer programme returns to block 101. If block 104 determines that the received message is a valid message the computer programme moves to block 106 which transmits a positive acknowledgement to the adjacent control station 7 which transmitted the message. The computer programme then moves to block 107 which checks if the message is a message being returned as a result of a break in the network loop 10.If block 107 determines that the message is a message being returned as a result of a break in the network loop 10 the computer programme moves to block 108 which is described below. If block 107 determines that the message is not a message being returned as a result of a break in the network loop 10 the computer programme moves to block 109. Block 109 checks if the message is a global poll message. If the message is a global poll message the computer programme moves to block 110 which adds the station address and the status of the damper 2 to the end of the global poll message. Should the global poll message already have station addresses and status reports attached in sequence to the end of the global poll message, the station address of the station controller 7 and the status of the damper 2 are added in sequence at the end of the last station address and damper status.The computer programme then moves to block 108. In the event that block 109 determines that the message is not a global poll message the computer programme moves to block 111 which checks if the message is for that particular station controller 7. If the message is for that station controller 7 the computer programme moves to block 112 which executes the message. The computer programme then moves to block 108. If block 111 determines that the message is not for that particular station controller 7, the computer programme moves to block 108.

Block 108 transmits the message to the next adjacent station controller 7 in the network loop 10. The computer programme then moves to block 113 which checks if an acknowledgement has been received from the station controller 7 to which the message has been transmitted. If an acknowledgement has been received, and the message has been transmitted the computer programme returns to block 101. If an acknowledgement has not been received or if the message has not been transmitted, the computer programme moves to block 114. Block 114 checks if the message is being returned as a result of the break in the network 10.

If the message is being returned the computer programme moves to block 115 which is described below.

If the message is not being returned, the computer programme moves to block 116 which transmits the message back to the station controller 7 from which the message has been received and the computer programme moves to block 117. Block 117 checks if the message has been acknowledged by the sending station controller 7 as having been received. If so the computer programme returns to block 101. If not the computer programme moves to block 115. Block 115 ignores the message and returns the computer programme to block 101.

Returning now to Fig. 3 the operation of the master controller 20 will be described. The master controller 20 receives stored data from the random access memory 32 of the network controller 15 on demand. This data includes the sequence of station addresses and the status of the respective dampers 2 stored with the received global poll messages. The master controller 20 compares the sequence of the station addresses received from the random access memory 32 with the reference sequence of station addresses originally stored in the random access memory 57. Provided thereceived sequence of station addresses from the random access memory 32 compares with the reference sequence of random access memory 57, the master controller 20 determines that the network loop 10 and station controllers 7 are fully functional.In the event that the received sequence from the random access memory 32 does not compare with the reference sequence in the random access memory 57, the master controller 20 determines where the break or breaks in the network occur by making appropriate comparisons between the station address sequence from the random access memory 32 and the reference sequence of station addresses. An alarm is then initiated and details of where the break or breaks occur in the network 10 are displayed on the display 59.

The microprocessor 55 of the master controller 20 reads the status of the dampers 2 down loaded from the random access memory 32 of the network controller 15 and checks if the dampers 2 are correctly positioned.

If it is determined that a damper 2 is not correctly positioned, a message with an appropriate instruction to the relevant station controller 7 is transmitted from the master controller 20 to the network controller 15 for transmission onto the network loop 10 to the appropriate station controller 7. The message to be transmitted is detected by the computer programme comprising blocks 60 to 65 of the network controller 15 and the message is transmitted by the computer programme comprising blocks 70 to 90 in the network controller 15.

Transmission through the network loop 10 may be by RS 232, RS 485, or RS 422 communication systems. Where the length of the cables 11 between adjacent station controllers 7 or between the network controller 15 and the adjacent station controllers 7 is relatively long, RS 485 data communication systems may be used. In such cases, it is envisaged that cabling distances between adjacent station controllers 7 and between the network controller 15 and adjacent station controllers 7 may be up to 1,200 M.

While the apparatus has been described as comprising a network having eight station controllers, it will be appreciated that the network loop may comprise any number of station controllers depending on the number of dampers to be controlled. Each damper will be provided with a station controller. In certain cases, it is envisaged that a network may comprise as low as two station controllers.

While the apparatus has been described for controlling dampers of an air conditioning system, the apparatus may be used for controlling any system which comprises devices which are located at remote locations and require controlling from a central master controller.

Claims (5)

CLAIMS:

1. Apparatus for controlling a-plurality of devices located at respective remote locations, the apparatus comprising a plurality of station controllers associated with the respective devices for controlling and monitoring the respective devices, the station controllers being connected in a serial network loop, and a network controller connected into the network loop for controlling communications in the network loop, the network controller comprising first and second main ports for connecting into respective ends of the network loop, each main port having transmitting means and receiving means for respectively transmitting and receiving a message onto or from the network loop, main control means in the network controller for controlling transmission and reception of a message through the first and second main ports and for monitoring the first and second ports to determine if the message is received by either the first or second main port, the control means transmitting the message through the second main port if the message transmitted through the first main port is not received by the second main port, and a main storing means for storing the received message, each station controller comprising first and second secondary ports for connecting into the network loop, and each secondary port having transmission and receiving means for respectively transmitting and receiving the message, and secondary control means for receiving the message through one of the secondary ports and attaching a station address of the said station controller to the message and transmitting the received message with the station address attached thereto to the next adjacent station controller in the network loop through the other of said secondary ports, the secondary control means of each station controller transmitting the message with the station address attached thereto to the station controller from which the message was received for return to the main port of the network controller from which the message was transmitted in the event that the next adjacent station controller to which the message had first been transmitted fails to acknowledge receipt of the said message.

2. Apparatus as claimed in Claim 1 in which the station controllers are assigned respective unique predetermined station addresses, the station address of each station controller being attached to the end of the received message, and the secondary control means of each station controller attaches the status of the associated device to the message after the station address of the station controller.

3. A method for controlling a plurality of devices located at respective remote locations using the apparatus of any preceding claim in which each device is controlled by a respective station controller, the method comprising the steps of transmitting a message through the first main port of the network controller for transmission through the network loop to the second main port of the network controller, transmitting another message through the second main port should the message transmitted through the first main port not be received by the second main port, monitoring the first and second main ports of the network controller to determine reception of each message, reading each received message from the main ports on which the message is received, and storing each received message, the method further comprising the steps of sequentially attaching station addresses of the station controllers to the message on receipt of the message by the respective station controllers, transmitting the received message with the station address attached thereto to the next adjacent station controller in the network loop, and transmitting the message with the station address attached thereto to the station controller from which the message was received for return to the main port of the network controller from which the message was transmitted should the next adjacent station controller to which the message had first been transmitted fail to acknowledge receipt of the said message.

4. A method as claimed in Claim 3 in which the method comprises the step of reading the stored received message and the sequence of station addresses stored in the main storing means for determining the sequence within which the station controllers are connected in the network loop, and the method further comprises the step of reading the last station address of the message received by the main ports for determining if a break exists in the network loop and for determining the position of the break.

5. A method as claimed in Claim 3 or 4 in which the station address of the respective station controllers are attached at the end of the received message, and the status of the devices is attached to the message after the corresponding station addresses of the respective station controllers.