The filter monitoring function can handle up to 5 filters:

  • Supply air pre-filter
  • Supply air filter
  • Supply air end-filter
  • Extract air pre-filter
  • Extract air filter

The intended filter placement in the AHU is as follows:

Filter condition can be monitored either by guard or sensor. In both cases the filter alarm is triggered when over pressure is detected.

The Guard uses a digital pressure switch. The switch activates if pressure drop across the filter is higher then manually preset limit.


The Sensor uses a differential pressure transmitter. Filter monitoring is made air flow dependent. This means that a higher pressure drop is permitted across a filter at a higher air flow.
The linear dependency of flow-pressure drop can be adjusted manually or set via calibration.

Each of the filter monitors has a dedicated alarm to point out the dirty filter.

Filter sensors or guards are also being monitored for valid readings - malfunction (e.g. wire break) triggers a sensor error alarm.

Filter type

Related filter alarm

Related sensor error alarm

Supply air pre filter

AL242 Pre-filter alarm supply air

AL245 Sensor error pressure pre-filter supply

Supply air filter

AL53 Filter alarm supply air

AL177 Sensor error pressure filter supply air

Supply air end filter

AL243 End filter alarm supply air

AL246 Sensor error pressure end-filter supply

Extract air pre filter

AL244 Pre-filter alarm extract air

AL247 Sensor error pressure pre-filter extract

Extract air filter

AL54 Filter alarm extract air

AL178 Sensor error pressure filter extract air

Periodic filter replacement can be set in addition to or instead of pressure drop monitoring. Upon the end of the period, the service interval alarm will be triggered.

Chapter info                              

Last reviewed: 09/14/2021

Access version: 4.6-1-00 (3068)