What is Persistence?

Persistence is a technique used in remote monitoring units' analog inputs to filter out false alarms, which can avoid unnecessary transmissions as well as the costs associated with those transmissions. When a high or low alarm value is set, the channel can be configured with an optional Persistence value. The Persistence value represents how long the input must remain in the alarm condition before it is considered a true alarm.

Example1: If an input channel is configured with a high alarm and a Persistence value of five (5), the input channel must complete six (6) samples in a high state before the unit will transmit the high alarm. If at any time during the six (6) samples the value becomes less than the specified high alarm value, the process starts over with the next high state. Valid entries are any number from zero (0) to 65535 with each sample cycle being approximately 16 seconds. To disable the Persistence feature, enter a zero (0) in the field.

Example 2: If the Persistence field is set to 50, the unit does not transmit the low alarm unless the alarm condition persists for 13.3 minutes (50 x 16=800 seconds=13.3 min). The unit has to take 50 more samples and see a low state on all of them. If at any time the value goes back above the low state value, then the alarm state is cleared. This technique allows the user to prevent false alarms from being transmitted. It also allows the flexibility to control the repeat of legitimate alarms, such as power outages, from transmitting too often.

Persistence can be found in the Universal Configuration Tool on any of the analog channels after you have checked either the Transmit Low Alarm or Transmit High Alarm check box when configuring the channel.

It is highly recommended that Persistence be set whenever an analog alarm is set on a remote monitoring unit.