Fire alarm system signal testing

Abstract

A method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprising: generating a string of test bytes; applying the string of test bytes across one end of the loop; and receiving the string of test bytes across the other end of the loop after passing through the loop. The received string of test bytes may be compared with the generated string of test bytes and the quality of the signal communication of the loop determined based on the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes.

Description

[0001] Fire Alarm System Signal Testing

[0002] Field of Invention

[0003] The present invention relates to the installation and commissioning of fire alarm systems on a premises.

[0004] Backg round

[0005] Fire alarm systems are installed in many premises, such as office buildings, factories, homes, and the like, and typically include a fire alarm control panel (often known as control and indicating equipment, CIE), a number of detectors and sounders, and wiring connecting the detectors and sounders to the fire alarm control panel. The system might also include call points and a range of other ancillary modules. In many cases, the wiring which is installed is a 2 wire addressable loop, and the detectors, sounders, call points and other ancillary modules (hereafter called "the devices") are arranged on the loop connected across its 2 wires. Multiple loops are generally installed from the control panel, with each loop typically carrying the devices to a different part of the premises. The loops typically provide power to the devices on the loop, and convey instructions and data from the control panel to the individual devices, such as configuration data to all devices or an alarm signal to the sounders, and convey data from the devices to the control panel, such as an indication that a fire has been detected. The looped arrangement means that there is some resilience to a break in an individual loop occurring during operation and that the voltage level between the wires in the loop are maintained sufficiently high to sustain all of the devices around the complete loop. In one known fire alarm system, a fire alarm control panel can support up to 16 loops, and each loop can support up to 250 devices. In it, communication on the loop uses frequency shift keying (FSK)) with sinusoidal signals on a DC pedestal of 37.6V.

[0006] The installation of a fire alarm system begins with determining where each device in the system is to be located, and laying 2-wire cables in loops from the intended position of the control panel to the location of each intended device on a loop, with the loop ending back at the intended position of the control panel. The devices can then be attached to the cables and secured in position.

[0007] Once the system has been installed, it must be commissioned, which involves testing that everything is operating correctly and configuring all of the devices. This often takes place before the control panel has even been installed. Each loop can be as long as 2000 m, and the cable used to form it might be supplied by different manufacturers, so they have different resistance, capacitance and inductance. Resistance affects the DC voltage level. Capacitance can cause signals to be attenuated as they pass through it. If attenuation is too high, it can negatively affect communication between the control panel and the devices, potentially resulting in false alarms being triggered, or even no alarm being signalled when a fire condition is present. To test the loops, a portable commissioning tool is often used which is connected to the ends of the wires that will form a loop. The portable commissioning tool, such as the MX TrueStart tool, tests the loop by ensuring that each wire has continuity, and by applying a DC voltage across one end of the loop and testing that the voltage at the opposite end of the loop is maintained at a sufficiently high voltage that it is able to operate all of the devices around the loop. The portable commissioning tool also communicates with each device on the loop once they have been installed in order to configure them, as appropriate.

[0008] An aim of the present invention is to improve the testing of the system during commissioning in order to reduce faults which arise later and to measure the quality of signal communication through the cabling so that the quality of cables used is sufficiently high, even if the cables used are sourced from different manufacturers and are made to different specifications.

[0009] Summary of Invention

[0010] According to a first aspect of the invention, a method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprises: generating a string of test bytes; applying the string of test bytes across one end of the loop; receiving the string of test bytes across the other end of the loop after passing through the loop; comparing the received string of test bytes with the generated string of test bytes; and determining the quality of the signal communication of the loop based on the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes.

[0011] The present invention is intended to reduce the number of faults which are found later in the commissioning process and after commissioning of a fire alarm system is complete by determining the quality of signal communication of a two-wire addressable fire alarm loop, especially where the cables used to form the two-wire cabling might be supplied by different manufacturers so they have different electrical properties. This can cause signals to be attenuated as they pass through it. If attenuation is too high, it can negatively affect communication between the control panel and the devices, potentially resulting in false alarms being triggered, or even no alarm being signalled when a fire condition is present.

[0012] According to a second aspect of the invention, a method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprises: generating a string of test bits; applying the string of test bits across one end of the loop; receiving the string of test bits across the other end of the loop after passing through the loop; measuring the pulse width of the test bits in the received string of test bits; and determining a measure of the quality of the signal communication of the loop based on the number of test bits in the received string of test bits which have a pulse width greater than a pulse width error threshold.

[0013] According to a third aspect of the invention, a fire alarm loop tester arranged to test the quality of signal communication of a two-wire addressable fire alarm loop, the tester comprises: a signal generator (11) arranged to generate a loop signal encoded with a string of test bytes; a signal terminal (3) arranged for connection across one end of a loop being tested and arranged to apply the loop signal across that end of the loop (2); a receiver circuit (15) arranged for connection across the other end of the loop and arranged to receive the loop signal across that other end of the loop after passing through the loop, and arranged to decode the received loop signal to give a received string of test bytes; and a processor for outputting the quality of the signal communication of the loop based on the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes.

[0014] Other advantageous features are claimed in the dependent claims.

[0015] Brief Description of the Drawings

[0016] The present invention will now be described by way of example only with reference to the accompanying drawings in which:

[0017] Figure 1 is a schematic diagram of a fire alarm system and a portable commissioning tool which forms part of the present application;

[0018] Figure 2 is a schematic diagram of a fire alarm system and a portable commissioning tool according to the present invention with a part of the commissioning tool being shown in more detail with a receiver circuit;

[0019] Figure 3 is a diagram showing a test byte of a loop signal applied to one end of a loop 5; and

[0020] Figure 4 is a flow diagram showing a method of determining the quality of signal communication of a two-wire addressable fire alarm loop according to the present invention.

[0021] Detailed Description Once a fire alarm system has been installed, it needs to be commissioned as described above, and in this case, a portable commissioning tool according to the present invention is connected to the ends of the loop, as shown in Figure 1. While the portable commissioning tool according to the invention is novel compared with known ones, it is intended that it would retain the functionality to conduct known system testing too. Figure 1 shows a fire alarm system 1 having 2-wire addressable network wiring in the arrangement of a loop 2 with two ends, a number of addressable networked devices 4 attached to the addressable network loop 2, and a portable commissioning tool 5 having four terminals 3 to which the ends of the loop 2 are connected.

[0022] The addressable networked devices 4 can be any of a range of different fire alarm system devices, including : sensors 4a such as smoke detectors, heat detectors, fire detectors and the like; notification devices 4b such as sounders and strobes; and other ancillary modules such as call points 4c which are typically found on the loop of a fire alarm system. The devices 4 are connected across the wires of the loop such that they are powered from the loop and are able to transmit and receive data to and from other devices on the loop, such as the portable commissioning tool 5. Base units are often connected directly to the wires of the loop, and the devices may then be attached to the base units for easy connection to the network loop at a location defined by the position of the base unit (not shown).

[0023] The portable commissioning tool 5 is able to test an addressable network loop 2 and the devices 4 which are positioned on the loop 2. If it detects a fault with the loop 2 or any of the devices 4, the wiring commissioning tool will identify it and indicate the fault in its display 6. The devices can be configured by an installation technician using a user input 7 on the portable commissioning tool 5 in the form of buttons.

[0024] It is advantageous to install the addressable network loop 2 and the devices 4 and test them using the portable commissioning tool 5 before the control panel is fitted.

[0025] Figure 2 shows the fire alarm system of Figure 1 in which a part of the portable commissioning tool 5 is shown in more detail with its electronic components arranged in a block diagram. The tool 5 is connected to the loop 2 with the networked devices 4 located on the loop 2. The loop is a two wire loop having a first wire 21 and a second wire 22, and the loop has a left end 27, 28 and a right end 29, 30 each connected to a terminal 3 of the portable commissioning tool 5.

[0026] The portable commissioning tool 5 includes a signal generator 11 which, during a test, generates a loop signal encoded with a string of test bytes, and that string of test bytes is supplied to one of the terminals 3 which applies the loop signal to the left end 27, 28 of the loop. In this embodiment, the encoding used to modulate the loop signal is frequency shift keying (FSK) using sinusoidal signals on a DC pedestal of 37.6V. The general structure of a data packet under this encoding method is shown in Figure 3 in which the packet comprises: a header; a byte comprising an 8 bit data packet; and a stop bit. The data is encoded such that the frequency of a "0" is much higher than the frequency of a "1". In this case, the frequency of a "0" is 6667Hz, and that of a "1" is 3030Hz, and it is clearly seen from Figure 3 that, when converted to a pulse width modulated signal, a "0" is represented with a much narrower pulse width than a "1". Of course, it is to be understood that FSK encoding could use different frequencies from this embodiment, and could use a different pedestal voltage. Indeed, different encoding systems altogether could be used.

[0027] The opposite, right, end of the loop 29, 30 is connected to the other of the terminals 3 so that the right end of the loop 2 is connected to a receiver circuit 15. This enables the received loop signal to be received and decoded.

[0028] The receiver circuit 15 comprises a first stage, which is a capacitive attenuator circuit 16, followed by a second stage which decodes the bytes and the bits of the received loop signal. The second stage involves parallel circuits : a decoder circuit 17 and an overcurrent detector circuit 18. The attenuator circuit 16 couples the FSK signal to the decoder circuit 17. The decoder circuit receives the attenuated received loop signal in this embodiment. The decoder 17 generates a decoded byte signal in the form of a PWM signal.

[0029] The portable commissioning tool 5 includes a micro-controller unit (MCU) which includes a 16-bit analog to digital converter (ADC) and a processor, neither of which are shown independently in Figure 2. In this embodiment, the micro-controller is a Renesas R5F565NEDDFP.

[0030] The decoded byte signal and the decoded bit signal are directed to the processor which determines the quality of the signal Byte comparison and bit comparison is done by the processor.

[0031] The portable commissioning tool also has a number of other functions which are not described in detail here because they don't impact on the present invention. For example, the tool is able to carry out continuity tests on the individual wires 21 and 22 of the loop 2, and is able to communicate with the networked devices 4 on the loop 2 during configuration, for example to configure and set up the networked devices, and to set their system addresses. Since these different processes require different kinds of connections to the ends of the wires, the portable commissioning tool also includes a switch array 11 containing 5 controllable switches which can be opened and closed on the signal of a switch controller 13. The portable commissioning tool also includes a main circuit breaker control, a voltage discriminator, a current loop amplifier and overcurrent sense circuit, and a control circuit for loop isolator. However, the components described above give a skilled person sufficient information about how to carry out the invention without the need to describe these features in detail.

[0032] The extent to which the test bytes of the decoded loop signal (the decoded byte signal) match the test bytes applied to the loop depends on the transmission quality of the loop itself. The worse the transmission quality, the greater the number of mismatches. The system is able to operate within a transmission quality range, but once the number of mismatches exceeds a certain level, the quality of the transmission through the loop is at a level where the system may not function properly. By measuring the number of mismatches, it is possible to assess whether the transmission quality of the loop is lower than a threshold for reliable data transmission through the loop. This might be done, for example, by comparing the number of mismatches between the test bytes of the decoded loop signal and the test bytes of the loop signal applied to the loop. The extent to which the test bytes of the decoded loop signal match the test bytes applied to the loop depends on the transmission quality of the loop itself. The worse the transmission quality, the greater the number of mismatches.

[0033] The extent to which the test bits of the decoded loop signal (derived from the decoded byte signal) match the test bits applied to the loop also depends on the transmission quality of the loop itself. The worse the transmission quality, the greater the number of mismatches. The system is able to operate within a transmission quality range, but once the number of mismatches exceeds a certain level, the quality of the transmission through the loop is at a level where the system may not function properly. By measuring the number of mismatches, it is possible to assess whether the transmission quality of the loop is lower than a threshold for reliable data transmission through the loop. This might be done, for example, by comparing the number of mismatches between the test bits of the decoded loop signal and the test bits of the loop signal applied to the loop. The extent to which the test bits of the decoded loop signal match the test bits applied to the loop depends on the transmission quality of the loop itself. The worse the transmission quality, the greater the number of mismatches.

[0034] The process of determining the quality of signal communication of the two-wire addressable fire alarm loop 2 will now be described with reference to the flow chart in Figure 4. The first step 71 is to connect the loop 2 to the terminals 3 of the portable commissioning tool 5 with the left end 27, 28 of the wires 21, 22 of the loop connected to one pair of terminals, and the right end 29, 30 of the wires of the loop connected to the other pair of terminals. The words 'left' and 'right' in this context have no technical meaning, but simply indicate that there are two ends which are connected to two different terminals. The loop could, for example, be connected to the terminals the opposite way around. If there is a switch array 12, it is configured using the switch controller 13 such that the signal generator 11 is connected to the terminal 3 to which the left end 27, 28 of the loop is connected, and the receiver circuit 15 is connected to the terminal 3 which is connected to the right end 29, 30 of the loop. The switch controller 13 might be controlled by a main MCU.

[0035] In step 75, the signal generator 11 is activated to generate the loop signal encoded with the string of test bytes described above using FSK encoding. Each test byte includes 8 test bits, and 8 bytes are generated as dummy command data in a pulse lasting for 25ms. The dummy command data in this example is: (0x01, 0x78, 0x99, 0x12, 0x34, 0x82, 0x27, 0xE5). The pulse is paused for 15 ms to allow for the loop signal to be processed in steps 77 to 83 below, and the pulse is repeated. In this example, the pulse of dummy command data is sent 100 times. Of course, the number of bytes transmitted in a pulse can be changed, as appropriate, and it is possible in some instances for the loop signal to have shorter pauses between pulses, and even no pause at all. In step 77, the loop signal is applied to the left end 27, 28 of the loop so that it propagates along the length of the loop.

[0036] Once the loop signal reaches the right end 29, 30 of the loop, it is received in step 79 by the terminal 3 to which the right end 29, 30 of the loop is connected.

[0037] In step 81, since the receiver circuit 15 is connected to the terminal 3, the received loop signal is received by the receiver circuit 15 and is attenuated by the attenuator circuit 16.

[0038] In step 83, the attenuated received loop signal is passed to the decoder circuit 17 and to the overcurrent detector circuit 18. The decoder circuit decodes the received loop signal to produce a decoded byte signal. The byte signal is directed to the micro-controller unit (MCU).

[0039] Step 85 involves comparing the decoded string of test bytes with the string of test bytes applied to the loop using the processor of the micro-controller MCU. It identifies which of the bytes match, and which do not, and generates a byte error signal. In parallel, in step 85, a decoded string of test bits is analyzed by the processor of the micro-controller MCU by measuring the pulse width of every bit. If the width of a bit is between 7 and 23 FW counts of a timer, corresponding to about 37 to 123 microseconds, the bit is determined to be a "1". If the width of a bit is between 24 and 40 counts of the timer corresponding to about 128 to 213 microseconds, it is determined to be a "0". If the width of the bit is more than a pulse width error threshold of 40 counts of the timer, a bit width error is determined to have occurred.

[0040] In this embodiment, each of the pulses of dummy command data is processed through steps 75 to 85 in turn, which allows time for all of these steps to be completed. Once all of the pulses of dummy command data have been received by the processor of the microcontroller and the byte errors and bit width errors have been analyzed, the signal quality can be determined.

[0041] In step 87, the processor of the micro-controller MCU determines the signal quality from the number of byte errors and from the number of bit width errors. The more byte errors and bit errors, the lower the quality of signal communication of the loop. If the number of byte errors and / or bit errors is below a lower threshold, the quality of signal communication of the loop is rated as 'excellent'. If the number of byte errors and / or bit width errors is above the lower threshold but below an upper threshold, the quality of signal communication of the loop is rated as 'good'. If the number of byte errors and / or bit width errors is above the upper threshold, the quality of signal communication of the loop is rated as 'poor'. In this embodiment, the lower byte threshold is 100 and the upper byte error threshold is 1000, the lower bit width error threshold is 1000, and the upper bit threshold is 5000. This gives ranges for the ratings:

[0042] In this embodiment, where the byte error and bit width error have different ratings, the worst of the two ratings is used. However, in other embodiments, it might be appropriate to use the better of the two ratings, or to combine the different results in some way, perhaps also with some other measure of the signal quality to determine the rating.

[0043] It will be appreciated that the number of byte errors or bit width errors which represent excellent, good or poor signal quality will depend on the particular system being tested, and on the number of test bytes and test bits applied to the loop. Furthermore, different ratings might be used instead of 'Excellent', 'Good' and 'Poor', such as a numerical rating.

[0044] Alternatively, the quality might be determined by the proportion of the test bytes or bits which are byte errors or bit width errors. It will be appreciated that using only one of the byte errors or bit width errors might be enough to rate the signal quality, but it is advantageous to use both because it gives more data comparison points for a particular loop signal, either improving accuracy of the assessment of the signal quality, or permitting the signal quality to be assessed more quickly using a shorter loop signal than if only one type of error were used. Various further modifications to the above-described examples, whether by way of addition, deletion or substitution, will be apparent to the skilled person to provide additional examples, any and all of which are intended to be encompassed by the appended claims.

Claims

Claims1. A method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprising : generating a string of test bytes; applying the string of test bytes across one end of the loop; receiving the string of test bytes across the other end of the loop after passing through the loop; comparing the received string of test bytes with the generated string of test bytes; and determining the quality of the signal communication of the loop based on the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes.

2. A method of claim 1, wherein each test byte is composed of 8 test bits, and wherein the method further comprises: measuring the pulse width of the test bits of the test bytes in the received string of test bytes; and determining a second measure of the quality of the signal communication of the loop based on the number of test bits in the received string of test bytes which have a pulse width greater than a pulse width error threshold.

3. A method of claim 2, wherein the determining step includes comparing the number of test bits in the received string of test bytes which have a pulse width greater than a pulse width threshold with a series of ranges to determine which range the quality of the signal falls, each one of the ranges representing a different rating of the second measure of the quality of signal communication.

4. A method of any one of the preceding claims, wherein the determining step includes comparing the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes with a series of ranges to determine which range the quality of the signal falls, each one of the ranges representing a different rating of a first measure of the quality of signal communication.

5. A method of claim 2, wherein the determining step includes determining the proportion of the test bits in the received string of test bytes which have a pulse width greater than a pulse width error threshold, with the proportion giving a value representing the second measure of the quality of signal communication.

6. A method of any one of claims 1, 2 and 5, wherein the determining step includes determining the proportion of the test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes, with the proportion giving a value representing a first measure of the quality of signal communication.

7. A method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprising : generating a string of test bits; applying the string of test bits across one end of the loop; receiving the string of test bits across the other end of the loop after passing through the loop; measuring the pulse width of the test bits in the received string of test bits; and determining a measure of the quality of the signal communication of the loop based on the number of test bits in the received string of test bits which have a pulse width greater than a pulse width error threshold.

8. A fire alarm loop tester arranged to test the quality of signal communication of a two-wire addressable fire alarm loop, the tester comprising : a signal generator (11) arranged to generate a loop signal encoded with a string of test bytes; a signal terminal (3) arranged for connection across one end of a loop being tested and arranged to apply the loop signal across that end of the loop (2); a receiver circuit (15) arranged for connection across the other end of the loop and arranged to receive the loop signal across that other end of the loop after passing through the loop, and arranged to decode the received loop signal to give a received string of test bytes; and a processor for outputting the quality of the signal communication of the loop based on the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes.

9. A fire alarm loop tester according to claim 8, wherein each test byte is composed of 8 test bits, and wherein the processor is further arranged to measure the pulse width of the test bits of the test bytes in the received string of test bytes; and to determine a second measure of the quality of the signal communication of the loop based on the number of test bits in the received string of test bytes which have a pulse width greater than a pulse width error threshold.

10. The fire alarm loop tester according to claim 9, wherein the processor is arranged to compare the number of test bits in the received string of test bytes which have a pulse width greater than a pulse width threshold with a series of ranges to determine which range the quality of the signal falls, each one of the ranges representing a different rating of the second measure of the quality of signal communication.

11. The fire alarm loop tester according to any one of claims 8 to 10, wherein the processor is arranged to compare the number of test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes with a series of ranges to determine which range the quality of the signal falls, each one of the ranges representing a different rating of a first measure of the quality of signal communication.

12. The fire alarm loop tester according to claim 9, wherein the processor is arranged to determine the proportion of the test bits in the received string of test bytes which have a pulse width greater than a pulse width error threshold, with the proportion giving a value representing the second measure of the quality of signal communication.

13. The fire alarm loop tester according to any one of claims 8, 9 and 12, wherein the processor is arranged to determine the proportion of the test bytes in the received string of test bytes which do not match the test bytes in the generated string of test bytes, with the proportion giving a value representing a first measure of the quality of signal communication.

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