Introduction

In order for an alarm to be raised, a track must break a rule a certain number of times, consecutively. The Break Count is the number of times that the rule can be broken before the defined 'Action' - e.g. an alarm - is triggered. The break count is a key setting because it allows you to provide a measure of confidence that an incident is genuine before raising an alarm. This enables you to provide a balance between the speed of detection vs the false alarm rate.

The break count has a number of associated settings which impact the way in which the break count is adjusted and reset. These are all covered on the Advanced page.

Contents

Break Count Examples

The graphs below illustrate the different break count logic depending on whether you are using an Allowance Curve or not. These graphs can be found in Playback when looking at a historic alarm record: ClearWay™ Queries.

This is an example of a simple Break History Graph, whereby the Break Count for a Stopped Vehicle alarm has been met. This is because the Stopped Vehicle rule was broken 8 times, and then the alarm was maintained for two counts, before being cleared. 

Open

Here is an example of a Break History Graph that demonstrates a Break Count without the Allowance Curve enabled. The Break Count cannot fall, only restart, and the break count has been broken twice.

Open

Finally, this is a Break History Graph with the Allowance Curve in use. Note that the Break Count can rise and fall depending on whether the track consecutively breaks the rule.

Allowance Curve

When the Use Allowance Curve option is enabled within a rule, the Break Count (the number of times that the rule has been broken) is permitted to fall as well as rise, in conjunction with the Break Count. This allows some leeway to be built into the rule to avoid unnecessary alarms. The Break Count will be incremented when a target is breaking the rule and then decremented when it is not. Additionally, the Allowance Increment and Allowance Decrement values can be set so that the rate at which a target increases and decreases its Break Count is weighted. The alarm will only be activated once the Break Allowance value is reached. This option is useful in situations where targets are expected to momentarily break rules, but not to to the point of warranting notice. 

In this example, the target is moving along a path through a golf course. However, the target does not stick rigidly to the path and wanders onto the greens. Using the Allowance Curve, the Break Count increases when the target deviates from the track and decreases once the target returns to the track. Using the Break Allowance property, the maximum allowable break count can be determined before an alarm condition is raised. Furthermore, the Allowance Increment and Allowance Decrement properties can be used to determine the size of increment and decrement, thus ‘weighting’ desirable and undesirable behaviour accordingly.

Here, the Allowance Increment and Decrement values are both set to 1 (thus, 1 is added when the rule is broken and 1 is removed every time the target is seen not breaking the rule). The Break Allowance is set to 3.

The result of the example is that although the target occasionally moves off the path, the break count never reaches the Break Allowance value of 3, therefore, no alarm is raised. If the target did stay off the path for 3 consecutive observations or strayed off the path five times out of seven (+2-2+3), then an alarm would be raised.

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