Tech Tips

Outdoor applications of fiber-optic perimeter intrusion detection systems expose the sensor cable to a wide variety of stimuli ranging from high winds, rain, and in some cases even the signals associated with trains, trucks and other vehicles.

 

For a fence mounted Fiber SenSys installation to achieve its highest operational potential, there are several important details ranging from fence quality to the sensor installation techniques that must be considered. 

This document will cover the most effective way to fasten sensing cable (in conduit) to chain link fences using stainless steel wire ties.

Some of the factors that influence how well wire ties are installed include the manner in which the ties are routed as well as the frequency and placement of ties along the run of sensing cable in conduit.  First and foremost, it is important to install the sensor to the inside of the protected barrier in all cases.  This document will first outline the preferred method for applying wire ties and then discuss the recommended frequency and placement for the wire ties.

High Security Tie Installation

Stainless steel wire ties offer the highest security method for attaching the FSI conduit to chain link fences because of their extreme durability.  Some of our competitors recommend using plastic ties but we have found that synthetic materials tend to degrade over time due to UV radiation exposure.  The simplest process for attaching a wire tie is as follows:

  1. Bend the tie at the midpoint so there is roughly a 45° fold
  2. Rout the tie through horizontally adjacent fence diamonds
  3. Squeeze the circular ends together and insert the hook of the twist tool
  4. Pull the tool towards your body for approximately 3½ pulls
  5. Secure the tie so that it is snug yet not digging into the conduit

Logically, one would assume that the best way to apply wire ties to a horizontal run of conduit would be to route the ties vertically between adjacent fence diamonds.  However, the highest security method of routing ties on both vertical and horizontal conduit runs is by routing the tie through horizontally adjacent fence diamonds.  When ties are routed through horizontally adjacent diamonds, the ties burrow tightly within the framework of the fence (see Figure 1).  If the ties are strung through vertically they do not conform to the fence, which leaves small gaps that can be cut from the non-secure side of the fence (see Figure 2).

Frequency of Ties and Pull Tension

The disadvantages associated with not adding the proper amount of ties include increased ease of sensor removal and various aesthetic drawbacks.  For the best results, add ties every 12 inches (30cm) and as close-fitting as possible on either side of each fence post. Removing the sensor undetected becomes nearly impossible if enough ties are added and attached in a high security fashion.  Additionally, adding the correct amount of ties and applying approximately 25lb (11Kg) of tension to the conduit during install helps to prevent hot and cold expansion, which results from the conduit expanding during higher temperatures.  The tail end of the twist ties may either be left pointing horizontally or bent in a direction of the installer's choosing.

Conclusion

Fiber SenSys has exhaustively tested countless wire ties and application techniques for installing our perimeter security products and give our recommendations based on proven test data.  Incorrectly installed wire ties are a very common mistake found in the field. Fastening stainless steel wire ties correctly goes a long way towards making an installation more secure and aesthetically pleasing.  We recommend that you meet with your installation team and go over these simple, yet important details before every installation.

Fiber SenSys Fiber Defender® Alarm Processors

You can download the side-by-side comparison of our alarm processor units here:

 

Fiber Defender 300 Series Comparison Chart 1

Fiber Defender Series Comparison Chart 2

To properly install the FSI sensor on a fence, simulations of actual intruders in a cut and a climb scenario are necessary.  Two technicians are required to configure the system; one must be in charge of operating the FSI AutoTune® software or making manual changes using the FSI configuration software while the other conducts actual intrusion simulations.  By default, virtual processor 1 (on-board the APU) is configured to detect climbing intrusions and virtual processor 2 is configured to detect cutting intrusions.  The purpose of this installment of Tech Tips is to provide detailed instructions on how to properly simulate cut and climb intrusions on a chain-link perimeter fence.