Alarm Latch Relay

Austdac Alarm Latch Relay ALR2


  • Alarm status unaffected by power cycling or power outages
  • DIN rail mounting – compact size
  • Low current consumption
  • Individual ‘set’ and ‘reset’ inputs
  • Wide operating voltage range
  • Power up timer eliminates logic race conditions
  • 2 change over and one normally open output contact sets

The Alarm Latch Relay type ALR2 is a compact DIN rail mounting bi-polar latching relay capable of maintaining its state through power outages. The ALR2 is particularly useful in gas monitoring systems where the gas alarm status must be maintained through a power outage for safety reasons. In this role the ALR2 prevents inadvertent dangerous gas alarm resets.

The Alarm Latch Relay has three sets of voltage free latching output contacts for use in alarm circuits. The relay state is controlled by two momentary inputs, one to set or latch the relay, the second to reset or unlatch the relay.

The ‘set’ input is typically connected to the gas alarm signal, while the ‘reset’ input is typically connected to a deputy key operated switch, allowing alarms to be acknowledged and reset under controlled conditions.

The ALR2 is fitted with front panel state indication LEDs, a green ‘armed’ LED which is illuminated when the ALR2 relay is in the reset state and a red ‘unacknowledged alarm’ LED which is illuminated when the ALR2 relay is in the latched state. Indication outputs are provided to drive external remote mounted LEDs.

The ALR2 is provided with a power up delay to ensure that the inputs are stable before power is applied to the latch relay, this prevents logic-race conditions from producing false alarms during gas monitoring system power up.

The ALR2 voltage free relay output contacts are Exi segregated from the power and input circuits to a value of 30 volts allowing easy integration of the ALR2 output contacts into alarm circuits that are separate intrinsically safe circuits.

The ALR2 is available in a monostable configuration where it operates as a conventional intrinsically safe relay with three sets of voltage free output contacts.