Tech Note

A problem has been experienced in the field by HU-961 users with regard to Pin 2 (Alert Out) use as a signaling source.

Pin 2 is normally an open contact output with a maximum rating of 24 VDC at 0.5 amps.   This programmable signal is active low (ground) from the receipt of the EAS header "HOT MESSAGE" to the receipt of a front panel or host PC command.

The problem is experienced when the user exceeds the rating of the internal relay on board the HU-961 - connected to Pin 2 internally.  This relay is a "reed" type with a maximum rating of 24 volt - 500mA.  This rating can easily be exceeded upon "turn-on" of the user's external circuit/light that is connected to Pin 2 because of the initial current required to start a standard light, strobe light or other device.

The symptom of the problem will show as a "sticky" relay  i.e. ... the relay can become intermittent or will activate and not deactivate properly.  Tapping on the HU-961 case or relay will normally correct the problem temporarily.  A fix of the problem can only be accomplished by a change out of the relay on the HU-961 circuit board.  The problem will occur again if the operating parameters of the new relay are not adhered to.

We recommend that this Pin 2 be tied only to a "Logic Low" circuit or circuits such as the coil of another relay.  A typical application is shown below.

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