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May 28, 2020

Reducing False Alarm Rates in Remote site Management

EXECUTIVE SUMMARY

Remote site management systems are designed to reduce maintenance personnel’s workload and ensure operational efficiency of remote systems. However, if they are not properly set up or versatile enough, they can actually increase workloads by generating an abundance of false, or nuisance alarms. This can lead to increased operating costs and eventually a mistrust of the remote management system by maintenance technicians.

Fine tuning different alarm parameters and applying techniques such as de-glitching delays, signal averaging, hysteresis and intelligent alarm muting can go a long way towards ensuring a system is operating optimally and is trusted and appreciated by site maintenance personnel.

1. INTRODUCTION

Remote site management systems are required by law in certain industries, and not in others. They are nevertheless generally recognized as being essential to the efficient operation of remote communications installations. If not properly installed, or adjusted, or if the right system is not used in a particular installation, these remote management systems can actually reduce operational efficiency by sending false alarms. These false, or nuisance alarms will greatly reduce the usefulness of the remote management system and can eventually instill a mistrust of the system in technical personnel, which could even go as far as alarms being ignored. Having a system that “Cries Wolf” too often can be disastrous when a real alarm or emergency occurs. Nobody likes being awoken needlessly in the middle of the night.

There are ways of ensuring that all alarms sent will be important ones and at severity levels that are proportional to the required remedial action. In this paper, we will present several means of attaining this goal of minimizing false alarms while still maintaining optimal site monitoring and control capabilities.  Techniques like de-glitching delays, hysteresis, software filtering, alarm aggregation, intelligent input qualification and alarm redirection will be explained.

Once you have read this paper, you will be able to recognize sources of false alarms and you will be familiar with methods for minimizing them.

1.1. DE-GLITCHING DELAYS

In many installations, the electrical system may be subject to fast transients and noise caused by switching equipment on and off. A fast-starting electric motor is one example of a device that can cause glitches on the network, and consequently on electronic equipment connected to it. These glitches can cause spurious alarms as shown in the figure below.

Input glitch and corresponding spurious alarm

Adding a 2-second de-glitching delay avoids alarms that could be triggered by electrical motor start-ups, power relay switching etc. as shown below.

Input glitch is ignored if it lasts less than 2 seconds
Input signal is validated since it is present for more than 2 seconds

The delay should be adjustable to minimize glitches while capturing valid alarm conditions that can occur. An adjustment range between 1 second and several minutes, in order to account for various input conditions, will allow for best optimization.

For example, an audio silence of several seconds is probably ok (to account for pauses in speech and/or music), but an alarm is surely warranted after 20 to 30 seconds of silence.

1.2. HYSTERESIS

Monitoring a noisy input signal that varies closely around a trigger level, can cause multiple alarm on-off cycles as shown in the figure below.

Noisy input signal oscillating around alarm threshold causes multiple alarms

Adding Hysteresis creates a dead-zone around the trigger level. This ensures that an input signal must exceed the trigger level to set an alarm, and then it must return below a “reset” level to stop the alarm.

Alarm is set off by exceeding the trigger level and then reset only if the signal falls below the Hysteresis level.

This reduces the number of alarm on-off cycles.

1.3. FILTERING BY AVERAGING

A noisy input signal can lead to multiple alarms as shown below. Using an electronic filter could be one way of reducing these nuisance alarms, but adding a filtering circuit (soldering a capacitor and resistor for example) is not always easy or even possible.  Using a mathematical averaging function is the next best thing. Calculating a running average over a certain number of input samples by adding them together and then dividing the sum by the number of samples will reduce the noise level correspondingly.  If the number of samples in the average is adjustable over a certain range (say 2 samples to 20 samples), the resulting noise reduction can be fine-tuned for different noise and input conditions. Noise can be filtered while not affecting the input signal of interest. The figures below illustrate this averaging operation.

Noisy input signal with multiple alarm outputs.
Averaged input signal and single alarm output.

1.4. ALARM AGGREGATION

Since alarms rarely come alone, and since deglitching delays and filtering may all be set to different values to account for the varied characteristics of the inputs being monitored, a system could make many calls to send multiple alarms.

Say the microwave link went down, this would cause audio to be lost at the site input, which would then produce no audio at the site and finally no output from the transmitter.  Up to 4 different alarm calls to site maintenance personnel could result from this fault.

      Hello, this is your site. I have an alarm.

    Hi again, this is your site. I have another alarm.

Oh, hi there, just another alarm to tell you about.

 Yeah, it’s me again, guess what…another alarm.

Being able to add a delay before actually transmitting the first alarm allows the different alarms to be consolidated into a single call.

Hello, this is your site calling. I have this list of alarms to tell you about.

1.5. ALARM INPUT QUALIFICATION

Say you have a power failure at your site. Depending on how you are set up, several subsystems may stop working. The HVAC, tower lights, GPS time sync receiver, backhaul link, transmitter and battery charger may all stop working and set off an alarm.  This means that your site maintenance people, or Network Operations Center can receive 6 or more different alarms, all caused by the power failure.

Having a smart “mute” function or Input Qualifier on all monitored inputs will allow you to mask this multitude of alarms and to only send one alarm, indicating the single cause that is the power failure.

Qualifiers can be used to mute different alarms

The example above uses the Power Fail alarm to mute other alarms, but any input should be useable to mute other alarms.  Main audio could be used to mute audio sub-channel alarms, and these could then be used to cascade other mute functions. This allows for very flexible and smart alarm muting.

1.6. ALARM REDIRECTION

Depending upon the nature of an alarm, being able to redirect it to the proper resource can be a big time-saver.  For example, if the generator is running out of fuel, why not send the message directly to the fuel supplier instead of to the site technician, who would then have to call the fuel supplier himself? This method doesn’t actually reduce the overall number of alarms, but it does reduce the number of alarms sent to an individual who cannot take direct action on them. The site maintenance technician’s workload is therefore reduced and this frees them up for more important tasks. 

Having a system that can intelligently direct different alarms to different destinations is the key to this method. One way of doing this is by using different alarm-call lists. List 1 can be dedicated to Radio alarms, and be set to call Technician A. List 2 can be dedicated to HVAC alarms and be programmed to call Technician B and so on.

2. Conclusion

Different methods of reducing false alarms and ensuring that a remote site management system is trusted and appreciated by maintenance personnel were presented. De-glitching delays, hysteresis, signal averaging, alarm aggregation, intelligent alarm muting on root-cause and alarm redirection are techniques that are useful to achieve these goals.

3. About Davicom

In the mid 1990’s, Davicom started producing and commercializing the first generation of its Remote Monitoring and Control Systems. From the very beginning, these unique systems were designed, developed and maintained with a single objective in mind: to provide the broadcast and telecommunications industries with an efficient, intelligent and trusted monitoring and control system for their remote transmission sites.

Over the years, new capabilities were added to maintain the product’s position as an industry innovator. From initial VT-100 terminal communications, through the addition of fax & voice capabilities, the units have evolved to the present secure-Internet version with SNMP V3 functionality, iOS/Android App support and smart-functions for reduced false alarm rates. Davicom systems are used worldwide by industry leaders in broadcast, public safety and land mobile radio to help maintain the integrity and operational efficiency of their networks.

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