Fire alarm system signal testing

Abstract

A method of determining the quality of signal communication of a two-wire addressable fire alarm loop, comprises: generating a loop signal waveform having a first amplitude; applying the loop signal waveform across one end of the loop; receiving the loop signal waveform across the other end of the loop after passing through the loop; measuring the amplitude of the received loop signal to give a second amplitude; and determining the quality of the signal communication of the loop based on the magnitude of the second amplitude of the loop signal waveform.

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 with each end of the loop terminating at the control panel. 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.

[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 and capacitance. 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 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, the method being carried out by a fire alarm loop tester and comprising : generating a loop signal waveform having a first amplitude; applying the loop signal waveform across one end of the loop; receiving the loop signal waveform across the other end of the loop after passing through the loop; measuring the amplitude of the received loop signal to give a second amplitude; and determining the quality of the signal communication of the loop based on the magnitude of the second amplitude of the loop signal waveform.

[0011] The present invention is intended to reduce the number of faults which are found during and after commissioning of a fire alarm system 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 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 waveform generator arranged to generate a loop signal waveform having a first amplitude; a terminal arranged for connection across one end of a loop being tested and arranged to apply the loop signal waveform across that end of the loop; an amplitude measurement circuit 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 measure the amplitude of the received loop signal to give a second amplitude; and a processor for determining and outputting the quality of the signal communication of the loop based on the magnitude of the second amplitude.

[0013] Preferably, the tester includes terminals 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, wherein the amplitude measurement circuit is arranged for connection to the terminals to receive the loop signal across that other end of the loop after passing through the loop. The terminals have a separate terminal for the end of each wire in the loop, four in total for a loop.

[0014] Brief Description of the Drawings

[0015] The present invention will now be described by way of example only with reference to the accompanying drawings in which:

[0016] Figure 1 is a schematic diagram of a fire alarm system and a portable commissioning tool which forms part of the present application;

[0017] Figure 2 is a schematic diagram of a fire alarm system and a portable commissioning tool with a part of the commissioning tool being shown in more detail with an amplitude measurement circuit;

[0018] Figure 3 is a schematic diagram of the amplitude measurement circuit of Figure 2;

[0019] Figure 4 is a chart showing various waveforms where the cable loop of the fire alarm system has no capacitance;

[0020] Figure 5 is a chart showing various waveforms where the cable loop of the fire alarm system has a capacitance of lpF;

[0021] Figure 6 is a chart showing various waveforms of a part of the waveform shown in Figure 5; and

[0022] Figure 7 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.

[0023] Detailed Description

[0024] 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 wires in the loop 2 are connected.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] Figure 2 shows a 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.

[0029] The portable commissioning tool 5 includes a signal waveform generator 11 which, during a test, generates a waveform having a first amplitude. The waveform might be a regular sine wave, or the waveform might vary in its frequency. In this embodiment, the waveform is a 6.66kHz sine wave having constant amplitude of 6.2 V peak to peak with a duration of 20ms, and is supplied to one of the terminals 3 which applies the waveform to the left end 27,28 of the loop. 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 an amplitude measurement circuit 15. This enables the amplitude of the signal waveform that has passed through the length of the loop to be measured.

[0030] The amplitude of the waveform that has passed through the loop 2 depends on the capacitance of the loop. The system is able to operate within a range of capacitance, but once the capacitance exceeds a certain level, the quality of the signals transmitted through the loop will be reduced to a level where the system may not function properly. By measuring the amplitude of the waveform that has passed through the loop, it is possible to identify whether the capacitance is higher than a threshold for reliable data transmission through the system

[0031] The amplitude measurement circuit 15 comprises a first stage of a bandpass filter 16, a second stage of a peak detector 17 and a third stage of a buffer 18. More details of the amplitude measurement circuit 15 is described below with respect to Figure 3.

[0032] The portable commissioning tool 5 includes a micro-controller unit (MCU) which includes a 16-bit analogue 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.

[0033] 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.

[0034] 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.

[0035] Figure 3 shows the amplitude measurement circuit 15 in which the filtering circuit 16 includes a bandpass filter which, in this case, has a gain of 0.5 and is arranged to filter the 6.66kHz signal waveform that has passed through the loop and attenuate the signal by 2. In this case, it also applies a DC offset of approximately 1.6 V.

[0036] The peak detector 17 is an amplifier circuit which measures the signal waveform once it has passed through the filtering circuit 16 in order to determine the second amplitude. The second amplitude measurement obtained passes through the buffer 18 from which the second amplitude measurement FSK_AMP in the form of an output voltage is output to one input of the analogue to digital converter of the micro-controller unit (MCU). The output voltage FSK_AMP is sampled by the analogue-to-digital converter ADC of the microcontroller (MCU). It generates counts corresponding to the DC voltage level. The microcontroller (MCU) converts the counts representing the DC voltage level to determine the quality of signal communication.

[0037] The quality of signal communication might be determined, for example, by applying a signal with a first amplitude of a predefined magnitude to the loop, and then assessing the magnitude of the second amplitude of the signal after it has passed through the loop against predefined thresholds.

[0038] Alternatively, it might be determined by comparing the second amplitude of the signal after it has passed through the loop with the first amplitude of the signal that is applied to the loop. .

[0039] 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 7.

[0040] 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

[0041] In step 73, the switch array 12 is then configured by the switch controller 13 such that the signal waveform generator 11 is connected to the terminals 3 to which the left end 27, 28 of the loop are connected, and the amplitude measurement circuit 15 is connected to the terminals 3 which are connected to the right end 29, 30 of the loop. The switch controller 13 might be controlled by a main MCU. In step 75, the signal waveform generator 11 is activated to generate a loop signal waveform having a first amplitude of 6.2v peak to peak. The waveform is a 6.66kHz sine wave having a duration of 20ms in this embodiment, but different frequencies and durations, and waveforms with frequencies that change over time, can be used. However, in this case, the frequency remains constant.

[0042] In step 77, the loop signal waveform is applied to the left end 27, 28 of the loop so that it propagates along the length of the loop.

[0043] Once the loop signal waveform reaches the right end 29, 30 of the loop, it is received in step 79 by the terminals 3 to which the right end 29, 30 of the loop is connected.

[0044] In step 81, since the amplitude measurement circuit 15 is connected to the terminals 3, the received loop signal waveform is received by the amplitude measurement circuit 15 which, in step 83, measures the amplitude of the received loop signal to give a second amplitude in the form of a de voltage. This step involves a first stage of filtering the signal and attenuating it by 2, a second stage of measuring the second amplitude and a third stage of buffering the amplitude measured by the peak detector 17. In this step, it should be appreciated that the essential part is to measure the second amplitude. Attenuation is done to keep the voltage level below 3.3 V as this micro-controller operates on a 3.3 V supply and the FSK waveform has a peak-to-peak voltage of up to 6.2 V. Attenuation and buffering are features which each have their own advantages independent of the others.

[0045] With regard to step 83, four worked examples of received loop signal waveforms where the capacitance of the loop 2 is at four different levels will now be described.

[0046] In the first worked example, the capacitance of the loop is zero. Figure 4 shows graphs of the loop signal waveform generated by the loop signal waveform generator 11 (top line), the received loop signal waveform as it reaches the peak detector 17 of the amplitude measurement circuit 15 (middle line), and the measured amplitude which is the output of the amplitude measurement circuit 15 (bottom line). It is notable that the line representing the measured amplitude decays over time after the loop signal waveform has been received by the peak detector 17 of the amplitude measurement circuit 15 (the initial part), is then substantially flat, and then decays again after the loop signal waveform received by the amplitude measurement circuit 15 ends (final part). The part of the measured amplitude that we are interested in occurs after the initial part after the initial decay has subsided, but before the final part of the measured amplitude is reached where it decays again. In this example, the measured amplitude is 2.25 V. In the second worked example, the capacitance of the loop is 0.25 pF. Graphs (not shown) of the loop signal waveform and the measured amplitude would appear quite similar to the graph in Figure 4, but the measured amplitude is 2.0 V.

[0047] In the third worked example, the capacitance of the loop is 0.5 pF. Graphs (not shown) of the loop signal waveform and the measured amplitude would appear quite similar to the graph in Figure 4, but the measured amplitude is 1.9 V.

[0048] In the fourth worked example, the capacitance of the loop is 1 pF. Figures 5 and 6 show graphs of the loop signal waveform and the measured amplitude of the received loop signal in this example. Figure 5 shows these things over a longer time period so that the entire 20 ms waveform is included, but Figure 6 shows just a part of the waveform once the measured amplitude has stabilized after its initial decay at the beginning of the waveform. In this example, the measured amplitude is 1.7 V.

[0049] In this embodiment, as part of step 87, the quality of the signal communication of the loop is determined by the processor of the micro-controller MCU based on the magnitude of the second amplitude of the loop signal waveform.

[0050] There are a number of ways of doing this determination. In one arrangement, the first amplitude has a predefined magnitude, and the magnitude of the second amplitude is compared against a lookup table to determine the quality of the signal communication. The lookup table might give a rating which is a numerical value, or it might give a classification into categories such as 'EXCELLENT', 'GOOD' and 'POOR'. In this embodiment, it is determined that the capacitance of the loop should not exceed just over 0.5 pF. The threshold for the measured amplitude between what is acceptable and what is not acceptable is 1.9 V. During this test, if the measured voltage is less than 1.9 V, the loop is considered to have poor signal quality. If the voltage is above 2.1 V, the quality of the signal is considered to be Excellent. Anything in-between is considered to be Good.

[0051] In another arrangement, it is done by comparing the magnitude of the second amplitude with the magnitude of the first amplitude and generating a rating based on the result of that comparison. This rating might be a numerical value, or it might be classified into categories such as 'EXCELLENT', 'GOOD' and 'POOR'.

[0052] 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, the method being carried out by a fire alarm loop tester and comprising : generating a loop signal waveform having a first amplitude; applying the loop signal waveform across one end of the loop; receiving the loop signal waveform across the other end of the loop after passing through the loop; measuring the amplitude of the received loop signal to give a second amplitude; and determining the quality of the signal communication of the loop based on the magnitude of the second amplitude of the loop signal waveform.

2. A method of claim 1, wherein the second amplitude is measured using a peak detector amplifier circuit.

3. A method of claim 1 or 2, wherein the measuring of the second amplitude excludes an initial part of the received signal waveform.

4. A method of any one of claims 1 to 3, wherein the measuring of the second amplitude excludes a final part of the received signal waveform.

5. A method of any one of the preceding claims, wherein the measuring of the second amplitude includes filtering the received loop signal waveform to attenuate it.

6. A method of any one of the preceding claims, wherein the determining step includes comparing the magnitude of the second amplitude with a series of ranges to determine which range the attenuation falls, each one of the ranges representing a different rating of the quality of signal communication.

7. A method of any one of claims 1 to 5, wherein the determining step includes comparing the magnitude of the second amplitude with the magnitude of the first amplitude to give a value representing the quality of signal communication.

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 waveform generator (11) arranged to generate a loop signal waveform having a first amplitude; terminals (3) arranged for connection across one end of a loop being tested and arranged to apply the loop signal waveform across that end of the loop (2); an amplitude measurement 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 measure the amplitude of the received loop signal to give a second amplitude; and a processor for determining and outputting the quality of the signal communication of the loop based on the magnitude of the second amplitude.

9. The fire alarm loop tester according to claim 8, wherein the amplitude measurement circuit includes a peak detector amplifier circuit (17).

10. The fire alarm loop tester according to claim 8 or 9, wherein the amplitude measurement circuit is arranged to measure the amplitude of the received waveform excluding an initial part of the received signal waveform.

11. The fire alarm loop tester according to any one of claims 8 to 10, wherein the amplitude measurement circuit is arranged to measure the amplitude of the received waveform excluding a final part of the received signal waveform.

12. The fire alarm loop tester according to any one of claims 8 to 11, wherein the amplitude measurement circuit (15) includes a filtering circuit (16) arranged to filter the received loop signal waveform to attenuate it.

13. The fire alarm loop tester according to any one of claims 8 to 12, wherein the processor is arranged to compare the magnitude of the second amplitude with a series of ranges to determine which range the attenuation falls, each one of the ranges representing a different rating of the quality of signal communication.

14. The fire alarm loop tester according to any one of claims 8 to 12, wherein the processor is arranged to compare the magnitude of the second amplitude with the magnitude of the first amplitude to give a value representing the quality of signal communication.

15. The fire alarm loop tester according to any one of claims 8 to 14, further comprising terminals (3) arranged for connection across the other end of the loop and arranged toreceive the loop signal across that other end of the loop after passing through the loop, wherein the amplitude measurement circuit (15) is arranged for connection to the terminals to receive the loop signal across that other end of the loop after passing through the loop.

Images