ALARM TRIP OUTPUT

An alarm trip provides a contact closure or a conducting open collector transistor output when an input signal exceeds a level determined by the Setpoint of the alarm trip.

DEADBAND

Hysteresis, commonly called "deadband" is usually designed into the product so the product recovers from an alarm condition at a slightly different input level than the input for the alarm condition.

Deadband is desirable so that noise on the input signal will not make the alarm "chatter" when the input is at the alarm level and the noise is riding above and below the alarm level.

Deadband also has functional uses such as level control. An alarm can be made to trip at a high level and recover at a low level. The trip and recovery can be used to control a pump to automatically fill a tank when a minimum level is reached.

Deadband can be fixed at a given percent of the input span or can be made adjustable. Fixed deadband is less expensive.

TRIP LOGIC

The trip's logic can be arranged to make the alarm trip on an increasing or decreasing signal.

A relay contact can be normally open or normally closed and go to the opposite condition on an alarm. This can provide for fail-safe operation so a contact will go to the desired condition if primary power is lost to the product.

LATCHING TRIP

A latching alarm locks up in the alarm condition and must be manually reset after removing the alarm condition on the input.

The reset can be made by switch closure or a logic level input from a computer or PLC.

ALARM TRIP OUTPUT COST FACTORS