Thursday, 6 December 2012

Safe-zone End Cap Good Practice

Greetings, Cronapressman here - Blogging a few tips on good fitment practice of the Safe-zone End Caps.

Pre-fitment  - To achieve successful electrical continuity through the alarm strip the base rail must first have been securely fixed with appropriate fixings (dependent on wall structure) and the Safe-zone insert must have been trimmed accurately and neatly.
Remember that the insert needs to be cut 1-2 mm shorter than the base rail at each end. I find it best to fit the insert from one end and cut to size when within 50 mm of the opposite end.

Let's take a moment to study the Safe-zone End Cap above -
1) 3 x fixing slots to insure sound wall fitment.
2) 2 x Protruding tangs to insure correct position of connector tongue within the insert by locating under the base extrusion.
3) Rebate to accept sealing silicone if requirement to weatherproof.
4) Cover cap fixing pins (not visible) can be super-glued (Cyanoacrylate) to resist un-authorised removal.

Let's do it -
No 1) - Push the Safe-zone End Cap connector tongue fully home inside insert. Double check protruding tangs are under base.
No 2) - Mark 3 slot positions on wall.
No 3) - Drill wall with appropriate masonry drill and insert masonry plugs.
No 4) - Replace Safe-zone End Cap and fix to wall. Pushing firmly into insert as fixing screws are tightened.
No 5) - Test for electrical continuity.
No 6) - Cover cap to be push fit when alarm has passed testing.
NOTE - Further removal and replacing of cover cap will compromise the ability of the fixing pins to maintain a sound hold. The cover cap is designed to aid the electrical connections by applying a slight downwards pressure.

Remember - If it looks right it will be right !   If it doesn't - you guessed it - it won't !

Keep checking the Cronapress blogspot and Cronapress website for more news and tips.

Sunday, 2 December 2012

The advantage of using 1.2kW resistor on Affray/ Panic Strips

Greetings, 'Cronapress Ken' here presenting -  

Technical and R&D Dept. - Bulletin No1

Why should a press strip profile use a 1.2kW resistor rather than a 10kW?

Although terminating the profile with 1.2kW increases the current and power drawn from the supply, there is an advantage gained if the system is used in the real world where interference is present. If the connecting cable between the profile and the sensing electronics is in ducting where other electrical cables are present then the proximity of these can generate interference signals. Cables carrying high frequencies can be troublesome as  can cables carrying  power at mains frequency when switching transients occur. Radio interference is also another source of interference.

In all cases, magnetic and electric screening will reduce the interference but, unfortunately, it may not be be possible and certainly will be prohibitively expensive. So what can be done about it?

The effect of interference can be represented in simple terms by a voltage source and an impedance representing the coupling between source and profile. This impedance will usually be quite high compared with the value of the terminating resistor of the profile e.g. stray capacitance between cable and profile. The interference appearing across the profile is thus determined by the ratio of the terminating resistor to this impedance. Thus the worst case would be with the profile open circuited. But using a 1.2kW resistor rather than a 10kW resistor will thus give a 1.2/10 reduction in interference and hence a significant benefit. It should be remembered that it will not eliminate it and additional protection may be needed in adverse environments. Hardware and software filtering can be effective in screening out  false triggering from interference signals.

 Look out for more Technical Bulletins on the both the Cronapress Blogspot and Cronapress Website.