I've extended an existing alarm system using the obsolete Scantronic 9452 control panel - originally installed 1994 - that had 3 of 4 zones used.

The system has now been extened onto the spare 4th zone, using 1 x Everspring S230 (http://www.everspring.com/cgi-bin/Look.cgi?Security^^Pid=EEEEE20000626104820&way=query) and 1 x Melcom Micron (http://www.lynteck.co.uk/pdf/LY99-083-00_Micron.pdf) pulse count PIRs, both star-wired back to the control panel. However in walk testing the panel is not responding (yes, the new zone has been programmed)! The test LEDs on the detectors are lighting correctly, their tamper switches are working OK, and I've replaced the Melcom detector, but still get the same response. The other 3 zones and EE are testing fine.

Is there a known incompatibility beteen the 9452 panel and recent PIRs, or some other possible explanation? Incidentally, the PIRs in use on the other zones are by Rokonet of similar vintage to the control panel (http://www.rokonet.com) - perhaps these are not of the pulse-count variety and the panel is too old to handle pulse count detectors, for example?

Suggestions would be very welcome! Thanks

Sounds that way to me too?

me too, you need to wire your PIR's in series so that when either opens it breaks the circuit. this applys to both the alarm circuit (Z4) and the anti-tamper circuits, only the DC connections supplying the PIR's with power should be parallel.

Your analysis was spot on! It was so obvious I'm still kicking myself for not spotting it! Thanks to you all for putting me straight...

Max