Vibration Sensor Issues On A Shared Zone Loop.
Vibration Sensor Issues — Recently we were looking at an alarm system that was having issues. It was installed in the 90s, and along with 2 hardwired PIRs it had 2 vibration sensors installed on a single zone loop made it very difficult to tell where the intermittent problem was.
Because the client wanted to keep the perimeter protection, we took out the old vibration sensors and replaced them. What might have been the issue with the original sensors?
A: The issue could have been several things, but it’s most likely that one or more of the sensitivity screws had shifted over time through ambient vibration or thermal expansion and was too sensitive for the environment.
Something to bear in mind is that environmental vibrations evolve. Trucks get larger. Traffic gets heavier. New plant equipment is installed. Window seals shrink. Road surfaces wear.
Key issues with vibration sensors are that they need to be installed the right way up and that sensitivity needs to be correctly adjusted using the sensitivity screw. The idea is to set the sensor’s sensitivity based on the ambient vibration in the area in which the sensor is installed.
If your site is beside a busy road, a low setting will act as a filter to protect the system from alarms generated by B-Doubles or short wheel-based trucks drumming over potholes. Should the site be in a quiet area, you can set the sensitivity higher.
There might also have been some termination or internal corrosion causing resistance and breaking the circuit periodically, though this is less likely in a dry environment away from the ocean. If you have the old sensors, it might be worth popping one to see how clean the circuit is.
Vibration Sensor Issues On A Shared Zone Loop
For techs working in residential and smaller commercial applications shared zone loops might seem anachronistic but when you’re securing multiple large structures from a single centralised controller with non-addressable zone cabling there are times it makes sense to share a zone loop rather than employ star config.
But there are inherent electrical issues to consider. Unless monster AWG was employed, there are times cabling would be towards the outer edge of its voltage carrying capacity even when new.
Alongside this challenge multiple sensors on a legacy loop will always create some voltage drop. And any decades old loop with multiple terminations is going suffer increasing resistance over time.
Voltage drop might impact on all sensors in a loop or it might lead to faults in sensors furthest down-circuit. We’d have been interested to measure the input voltages of all sensors in this loop starting at the farthest end.
You can learn more about fence detection sensors here, or read more SEN news here.
“Vibration Sensor Issues On A Shared Zone Loop.”
