Addressing method for slave units in fire detection system

A method and system for assigning working addresses to slave units in a vehicle fire system. Slave units responding to a default address are identified along with available working addresses. Individual slave units are isolated at the default address by instructing the slaves to compare their serial numbers to a broadcast serial number until only a single slave responds, wherein bits in the serial numbers are reversed to create a more sparse distribution of the serial numbers of the slave units, and assigning the slave units, which responded to the default address, to the available working addresses.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 15/095,680, filed on Apr. 11, 2016, entitled “Fire detection system with automatic firmware updating”, now U.S. Patent Publication No.: 2017/0293478, and U.S. application Ser. No. 15/095,691, filed on Apr. 11, 2016, entitled “Fire detection system with distributed file system”, now U.S. Patent Publication No.: 2017/0293630, both of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Fire systems, such as fire detection systems, fire suppression systems or combination fire detection and suppression systems, typically comprise a master module and a series of slave units. Slave units have elements that are designed to perform specific tasks related to fire detection, notification, and suppression, such as detecting information about the environment and communicating the information to the master module, or, upon receiving instructions from the master module, performing a fire suppression function or generating an audible and/or visual alert to occupants.

Different types of slave units or combinations of slave units are typically deployed based on the specific application. Fire systems for premises typically include fire sensors, pull stations, and alarms. On the other hand, fire systems for vehicles typically include a variety of sensors, release modules, annunciators, and manual override switches.

Fire systems are installed on large vehicles such as those used in the mining, forestry, landfill and mass transit industries to prevent or mitigate damage to complex and expensive equipment. For example, a mining dump truck could feature a reciprocating engine driving a generator, which in turn provides power to electric motors that drive the wheels. Any one of these components can overheat and catch on fire, causing extensive damage to complex and expensive equipment. The fire systems are employed to minimize such losses.

The master modules and slave units of fire systems are typically installed on a common bus. As a result, they need to have unique working addresses so that the master module can communicate with individual slave units. Slave units typically also have a serial number or unique identification number programmed into their read-only (ROM) memory. Serial numbers are generally large (typically 8 or more bytes). By contrast, working addresses need to be small (typically a single byte) in order to facilitate efficient communication between the master module and slave units.

In some systems, the slave units are assigned working addresses at installation. These addresses are commonly indicated by setting dual in-line package (DIP) or rotary switches. Assigning or changing the address of a slave module requires physical access to the above mentioned switches.

Other systems employ the serial numbers to dynamically assign working addresses. The system described in “Identifying a Plurality of Devices,” U.S. Pat. No. 8,232,869 B2 to Bennett, which is incorporated herein by this reference, scans for matching serial numbers at varying levels. The master module determines that there are slave units that have not been assigned a working address. The master module broadcasts only a portion of the serial number (i.e. the portion of the serial number containing a certain number of the least significant bits) with instructions for the slave units that have not been assigned working addresses to compare the portion of the serial number to the corresponding portion of their own serial numbers and respond if they match. If a match is found, the slave unit with the matching serial number is assigned a working address.

In this system, the possibility exists for data collisions to occur. When the portion of the serial number for more than one slave unit matches the serial number portion broadcast by the master module, each matching slave unit sends a response message simultaneously. Because the master and slaves are installed on a common bus, the transmissions collide, resulting in corrupted data. Collisions are detected by the master module through the use of checksum or CRC values contained in the transmissions. In the event of a collision, the master module initiates a second level scan that broadcasts a larger portion of the serial number (i.e. a greater number of bits) than the first level scan in order to differentiate between the two or more slave units that responded.

SUMMARY OF THE INVENTION

The problem with assigning addresses through the setting of DIP or rotary switches is that modules in fire systems, especially vehicle fire systems, often need to be potted, or submerged in a gel or solid to protect them from the harsh environments typical of fire systems. As a result, DIP or rotary switches cannot be used.

One problem with the dynamic addressing method is the imprecise detection of collisions. Statistically, using checksum values to validate data transmissions can result in undetected collisions, which could result in problems such as two slaves being assigned a single working address, or a working address being assigned (via a corrupted serial number) to a slave unit that does not exist. Consequences could range from inefficient communication to system malfunction or having to re-initialize the system.

Another problem with these existing dynamic addressing methods is the presumption that serial numbers are evenly distributed across the possible serial number space. In fact, this is often not the case, as different units of fire systems are often manufactured in the same facility, within a very narrow timeframe. Units belonging to a single fire system can be manufactured on the same day in the same manufacturing facility, resulting in serial numbers that differ by only a few bits, because the date and place of manufacture form part of these numbers. This clumping in serial number space of similar serial numbers by units in the same system cancels out the beneficial effect of scanning for only the least significant bits of the serial number, as most serial numbers in fact differ only in the portion of the serial number scanned for in the first level scan. As a result, the method requires a large number of iterations of the scanning process in order to identify all of the slave units that are not assigned working addresses. A larger number of search iterations results in inefficiency.

In implementations, the present invention features a process of creating a more sparse distribution of serial numbers across the serial number space and a more robust system for detecting collisions. Slave units that are not assigned working addresses are isolated using bit reversal in the broadcast serial numbers in order to create a more sparse distribution of serial numbers across the serial number space.

In general, according to one aspect, the invention features a method for assigning working addresses to slave units in a vehicle fire system. The method comprise identifying slave units responding to a default address, determining available working addresses, isolating individual slave units at the default address by instructing the slaves to compare their serial numbers to a broadcast serial number until only a single slave responds, wherein bits in the serial numbers are reversed to create a more sparse distribution of the serial numbers of the slave units, and assigning the slave units, which responded to the default address, to the available working addresses.

In a current embodiment, identifying slave units responding to the default address comprises sending a message to the default address and determining if any slave units reply. Further, determining available working addresses comprises incrementing through working addresses until no slave units respond to a current address, which is then determined to be an available address. Slaves respond with their newly assigned working address and at least part of their serial number.

In general, according to another aspect, the invention features a method for assigning working addresses to slave units in a vehicle fire system. The method comprises determining available working addresses, isolating individual slave units at a default address by instructing the slaves to compare their serial numbers to a broadcast serial number until only a single slave responds, confirming that individual slave units have been isolated by responding with a potentially corrupt serial number and confirming whether a slave unit responded, and assigning the slave units, which responded to the default address, to the available working addresses.

In general, according to another aspect, the invention features a vehicle fire system, comprising slave units and a master module for assigning working addresses to the slave units by identifying slave units responding to a default address. This master determines available working addresses, and assigns the slave units, which responded to the default address, to the available working addresses. This assignment is performed by isolating individual slave units at the default address by instructing the slaves to compare their serial numbers to broadcast serial numbers broadcast by the master module until only a single slave unit responds and choosing the broadcast serial numbers by reversing bits in the broadcast serial numbers to create a more sparse distribution of the serial numbers of the slave units at the default address.

In general, according to another aspect, the invention features vehicle fire system, comprising slave units and a master module for assigning working addresses to the slave units by identifying slave units responding to a default address, determining available working addresses, and assigning the slave units, which responded to the default address, to the available working addresses, by isolating individual slave units at the default address by instructing the slaves to compare their serial numbers to broadcast serial numbers broadcast by the master module until only a single slave unit responds, and confirming that individual slave units have been isolated by responding with a potentially corrupt serial number and confirming whether a slave unit responded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a block diagram of a fire system100, such as a fire detection system, a fire suppression system or a combination fire detection and suppression system, installed on a vehicle108, to which the present invention is applicable.

The system100comprises a master module102and a series of slave units106installed on a common bus104. The master module102sends instructions to and receives information from the slave units106, and the slave units106receive instructions from the master module102and send information (for example, information about the environment detected by a slave unit106) to the master module102.

The data bus104is preferably common from a logical perspective. The master module102preferably uses a common address space to communicate with the various slave units106using the data bus104. That said, the bus104is currently implemented as several physical data buses/wiring interfaces (ports) on the master module102. This helps to ensure proper and repeatable installation by having specific units be connected to specific wiring interfaces or ports on the master module102.

In the illustrated example, the installed slave units include a display unit106-1, which displays information about the state of the fire system100, a battery unit106-2, which supplies power to the fire system100, two linear heat detector units106-3, which detect heat and communicate information to the master module102, two manual activation switch units106-4, which, when activated by an operator (for example, a driver of the vehicle) trigger a fire suppression function, two IR detector units106-5, which detect infrared radiation and communicate information to the master module102, two fire sensor units106-6, which detect the presence of fire and communicate information to the master module102, and two release units106-7, which perform a fire suppression function.

In one example, the fire sensor unit106-6could detect that a fire is present through the operation of its fire sensor slave element and send the information to the master module102. The master module102, in turn, could then send instructions to the release module106-7to perform a fire suppression function, and/or instructions to the display106-1to display an alert.

FIGS. 2A-2Bare schematic diagrams of a master module and a generic slave unit of the fire system100. Each unit similarly includes a controller202,214, a transceiver204,216, volatile random access memory (RAM)206,218, nonvolatile memory208,220, and read only memory (ROM)210,222. Each unit106,102connects to the common bus104through its transceiver204,216.

FIG. 2Ais a schematic diagram of a generic slave unit106. Examples include fire sensor units106-6, release units106-7, IR detector units106-5, manual activation switch units106-4, and battery units106-2. The slave ROM210stores the slave unit's serial number212, which is a unique identification number assigned to the slave unit when it is manufactured. Each of the slave units typically includes a slave element205, which is typically different for each type of slave. For example, for a smoke detector slave unit, the slave element205is a smoke sensor that detects smoke, with the slave controller monitoring the detected smoke levels by the element and communicating those levels to the master module. In another example, for a fire detector slave unit, the slave element205might be a thermistor that detects ambient temperature with the slave controller monitoring the detected temperatures levels and communicating those levels to the master module or triggering an alarm condition itself. In the case of a release unit, the slave element205might be a relay that controls the release of fire suppressant. The slave controller in this case waits for a release instruction from the master module102and then operates the relay accordingly.

FIG. 2Bis a schematic diagram of the master module102. The master nonvolatile memory220stores an address space224, which is information about each slave unit106, including the slave unit's assigned address, serial number, and the type of module.

FIG. 3is a flow diagram showing the method for assigning working addresses to slave units106by the master module102.

Steps302through308illustrate the process of determining whether there are any unaddressed slave units106installed on the fire system100. Unaddressed slave units106are listed in the address space224under the default address “120”.

In one example intended to illustrate the operation, a fire system100includes a master module102, two fire sensors106-6, a release unit106-7, an IR detector unit106-5, a manual activation switch unit106-4, and a battery unit106-2, of which the second fire sensor unit106-6-2, the IR detector unit106-5, the manual activation switch unit106-4, and the battery unit106-2are unaddressed slave units106.

Illustrating this example,FIG. 4is a diagram of an address space224, which lists addresses from 0 through 120 inclusive, where address “0” is always assigned to the master module102, and address “120” is always the default address. In this example, address “1” is assigned to the first fire sensor unit106-6-1, which has a serial number of “0100”. Address “2” is not assigned to any slave units106. Address “3” is assigned to the release unit106-7, which has a serial number of “0101”. Addresses “4” through “119” are not assigned to any slave units106. Finally, address “120” lists the second fire sensor unit106-6-2, which has a serial number of “0102”, the IR detector unit106-5, which has a serial number of “0103”, the manual activation switch unit106-4, which has a serial number of “0104”, and the battery unit106-2, which has a serial number of “0105”, indicating that these four unaddressed slave units106respond to the default address “120”.

As the unaddressed slave units106respond to the default address, the master module102determines whether there are any unaddressed slave units106by sending instructions to the default address and determining whether a response is received.

FIG. 5illustrates the vacant slave address inquiry502, which is an instruction sent by the master module102to a slave unit106at an address in the address space224. The vacant slave address inquiry502includes a header with a format code, which is a unique code specifying the instruction given. Slave units106that receive the vacant slave address inquiry502must send a response to the master module102with an acknowledgment.

Returning toFIG. 3, in step302, the master module102starts with address120, which is the default address. In step304, the master module102then sends a vacant slave address inquiry502to the default, and in step306it is determined whether a response is received. If there is no response, the addressing process ends in step350. If there is a response, it is determined that at least one unaddressed slave unit106exists on the fire system100.

Steps310through318illustrate the process of determining the next available address in the address space224. In step310, the master module102sets a current address to 1, the current address being the address to which the master module102sends instructions to determine the next available address. In step312, the master module102sends a vacant slave address inquiry502to the current address. In step314, a slave unit106assigned to the current address potentially sends a response to the master module102. In step316, it is determined whether a response is received by the master module102from a slave unit106at the current address. If a response is received, it can be concluded that a slave unit106is already assigned to the address. In this case, in step318, the current address is incremented, and another vacant slave address inquiry502is sent to the current address. Steps312through318repeat until no response is received in step316, at which point the current address is determined to be the next available address in the address space224.

In general, steps320through346illustrate the process of targeting a single unaddressed slave unit106in order to assign it an address. Throughout the process, the master module102sends messages to the default address. Because the possibility exists for multiple slave units106to respond to the default address, a binary search of the serial numbers212of the slave units106is used to isolate the slave units106.

FIG. 6is a diagram of the serial number212of a module installed on a fire system100. The serial number212includes a four digit decimal number assigned sequentially to the module upon its manufacture, the year, month and day of manufacture, a code indicating the module type, and a code indicating the location of manufacture. In the illustrated example, only the sequential four digit decimal number is depicted for the purpose of clarity. However, it should be noted that the method described can include the full serial number212or any portion thereof.

As it is not uncommon for slave units106manufactured in close succession to be installed on the same fire system100, it is possible for serial numbers212on one system100to differ by only a few bits. For instance, in the illustrated example, the serial numbers212listed in the address space224are “0099”, “0100”, “0101”, “0102”, “0103”, “0104”, and “0105”. In order to make the binary search more efficient, the bits in the serial numbers are reversed, creating a more sparse distribution of serial numbers across the serial number space.

FIG. 7illustrates one example of bit reversal in a serial number212. In the illustrated embodiment, the bits of the serial number are reversed such that the first bit is swapped with the last bit, the second bit is swapped with the second to last bit, and so on for all bits of the serial number. After the bit reversal process, the serial number “0104” has been changed to serial number “0088”.

FIG. 8illustrates an example of bit reversal for a series of sequential serial numbers212. In the illustrated example, the number “0100” becomes “0152”, “0101” becomes “0664”, “0102” becomes “0408”, “0103” becomes “0920”, “0104” becomes “0088”, and “0105” becomes “0600”. As a result of bit reversal, the group of sequential numbers has become more sparsely distributed.

Returning toFIG. 3, the search for an isolated slave unit106responding to the default address begins in step320, in which a broadcast serial number, which is a potential serial number sent from the master module102to the slave units106responding to the default address, is set to 50% of the highest possible serial number. An adjust number, which is a value by which the broadcast serial number is either increased or decreased throughout the search, is set to the same value as the broadcast serial number.

The master module102communicates the broadcast serial number to the slave units106using a particular instruction.FIG. 9illustrates the automated address acquisition instruction504, which is an instruction sent by the master module102to a slave unit106at an address in the address space224. The automated address acquisition instruction504includes a header with a format code, and each of the eight bytes of the broadcast serial number. Slave units106that receive the automated address acquisition instruction504must send a response to the master module102if the serial number212of the slave unit106is larger than or equal to the broadcast serial number.

FIG. 10illustrates the my serial number packet506, which is sent by a slave unit106to the master module102in response to an automated address acquisition instruction504. The my serial number packet506includes a header with a format code, and each of the eight bytes of the serial number212of the slave unit106.

Returning toFIG. 3, in step322, the master module100sends an automated address acquisition instruction504to the default address including the broadcast serial number. In step324, slave units106responding to the default address compare the broadcast serial number to their own serial numbers212. In step326, it is determined by each slave unit106responding to the default address whether their own serial number212is larger than or equal to the broadcast serial number.

In step328, if it is determined that none of the slave units106responding to the default address has a serial number212that is larger than or equal to the broadcast serial number, no reply is received by the master module102. In step330, the adjust number is decreased by half, and the broadcast serial number is then decreased by the value of the adjust number. In step332it is determined whether the adjust number is greater than the lowest possible serial number. If it is, step322is repeated. In this way, the broadcast serial number is adjusted downward and sent again by the master module102to the slave units106until either the adjust number becomes less than or equal to the lowest possible serial number, or until one or more slave units106respond to the master module102.

If, on the other hand, it is determined in step326that one or more slave units106responding to the default address have a serial number212that is larger than or equal to the broadcast serial number, a my serial number packet506is sent from each slave unit106with a serial number212greater than or equal to the broadcast serial number to the master module102.

If more than one slave unit106responds to the master module102in step334, a data collision occurs. As a result, in step336, the master module102receives a my serial number packet506which includes a serial number212that is potentially corrupt. Steps338through342illustrate the process of determining whether or not the serial number212received by the master module102in step336is corrupt.

The master module102confirms the integrity of the serial number212received using a particular instruction.FIG. 11illustrates the “I heard this serial number” instruction508, which is an instruction sent by the master module102to a slave unit106at an address in the address space224, in response to a my serial number packet506. The “I heard this serial number” instruction508includes a header with a format code, each of the eight bytes of the serial number212received with the my serial number packet506, and an address to be assigned to the slave unit106whose serial number212matches the serial number212included in the instruction. Slave units106that receive the “I heard this serial number” instruction508must send a response to the master module102if the serial number212of the slave unit106matches the serial number included in the instruction.

FIG. 12illustrates the address transmission success packet510, which is sent by a slave unit106to the master module102in response to the “I heard this serial number” instruction508. The address transmission success packet510includes a header with a format code, a card address, and a module ID.

Returning toFIG. 3, upon receipt of a my serial number packet506, the master module102sends an “I heard this serial number” instruction508to the default address including the serial number received and the next available address. In step340, each slave unit106responding to the default address compares the serial number212included in the “I heard this serial number” instruction508to their own serial number212. In step342, it is determined whether the serial numbers are the same for any of the slave units106.

If a match is found, in step348, the slave unit106with the matching serial number212stores the address and sends an address transmission success packet510to the master module102. The master module102then updates the address space224to list the slave unit106with the matching serial number under the next available address. The next available address is then determined and the search process starts over at step320.

If, on the other hand, none of the serial numbers212of the slave units106responding to the default address matches the serial number212included in the “I heard this serial number” instruction508sent by the master module102in step338, no response is received by the master module102in step344, and it is determined that a data collision has occurred. In step346, the adjust number is reduced by half, and the broadcast serial number is increased by the value of the adjust number. The search process then repeats in step322, with the adjusted broadcast number. In this way, the broadcast serial number is adjusted upward and sent again by the master module102to the slave units106until a valid serial number212in step342.

The search process continues until each slave unit106responding to the default address is isolated and assigned an address. When there are no slave units106responding to the default address (for example, when all of them have been assigned addresses), the broadcast serial number is adjusted downward and sent again in steps322through332until the adjust number is less than or equal to the lowest possible serial number, in which case the addressing process ends in step350.

Returning to the illustrated example, at the start of the addressing process, a vacant slave address inquiry502is sent by the master module102to the default address. The second fire sensor unit106-6-2, the IR detector unit106-5, the manual activation switch unit106-4, and the battery unit106-2all send a response to the master module102. As a result, it is determined that there are unaddressed slave units106responding to the default address.

Next, the current address is set to “1”. The master module102sends a vacant slave address inquiry502to the current address and receives a response from the first fire sensor unit106-6-1. The current address is incremented to “2”, and another inquiry is sent. This time, no response is received, and it is determined that address “2” is the next available address.

Assuming, for the purposes of this example, that the serial number space ranges from 1-999, the broadcast serial number is then set to “499”, and the adjust number is set to “499”.

Next, an automated address acquisition instruction504is sent to the default address with the broadcast serial number. The IR detector unit106-5, whose serial number after bit reversal is “920”, and the battery unit106-2, whose serial number after bit reversal is “600”, both respond with a my serial number packet506, because both of their serial numbers are greater than the broadcast serial number. Because both slave units106respond simultaneously, there is a collision. The master responds with an “I heard this serial number” instruction508, including a corrupted serial number.

Because the corrupted serial number does not match any of the serial numbers of the slave units106responding to the default address, the search is repeated with a broadcast serial number adjusted upward to “749”. This time, only the IR detector unit106-5responds, and the IR detector unit106-5is assigned the next available address “2”. An address transmission success packet510is sent to the master module102confirming that the address “2” was assigned to the IR detector unit106-5.

FIG. 13shows the address space224after the first slave unit106responding to the default address is assigned an address. The IR detector unit106-5is now assigned address “2”, while the second fire sensor unit106-6-2, the manual activation switch unit106-4, and the battery unit106-2are all listed under the default address.

The addressing process then continues by determining the next available address “4” and restarting the search process with a broadcast serial number of “499” and an adjust number of “499”. This time, only the battery unit106-2responds, and it is assigned address “3”.

FIG. 14shows the address space224after the second slave unit106responding to the default address is assigned an address. The battery unit106-2is now assigned to address “4”, and the second fire sensor106-6-2and manual activation switch unit106-4are listed under the default address.

The addressing process then continues by determining the next available address “5” and restarting the search process with a broadcast serial number of “499” and an adjust number of “499”. After bit reversal, the serial number212for the second fire sensor unit106-6-2is “408”, and the serial number212for the manual activation switch unit106-4is “88”. Since neither serial number is greater than “499”, the broadcast serial number is adjusted downward to “249”. This time, the second fire detector unit106-6-2responds and is assigned address “5”.

FIG. 15shows the address space224after the third slave unit106responding to the default address is assigned an address. The second fire sensor unit106-6-2is now assigned to address “5”, and only the manual activation switch unit106-4is listed under the default address.

The addressing process continues by determining the next available address “6” and restarting the search process with a broadcast serial number of “499” and an adjust number of “499”. After bit reversal, the serial number212for the manual activation switch unit106-4is “88”. Since it is not greater than “499”, the broadcast serial number is adjusted to “249” and sent again. This process repeats with broadcast serial numbers of “124” and “62” being sent. In response to the broadcast serial number of “62”, the manual activation switch106-4responds and is assigned address “6”.

FIG. 16shows the address space224after the fourth and final slave unit106responding to the default address is assigned an address. The manual activation switch106-4is now assigned to address “6”, and no slave units106are listed under the default address.