93-520-20 Issue 3.3
Page 6 of 60
CirrusPro Engineer’s Manual
1.0 Introduction
This manual details the methods employed to install, commission and service the CirrusPro Series
Aspirating Fire Detectors.
Background
It is known that particles smaller than the wavelength of visible light occur spontaneously as a material
is overheated, and in numbers far above those present in a normal ambient environment. CirrusPro
Detectors utilise the Wilson Cloud Chamber principle to detect the sub micron particles that are
generated at the incipient, and all other stages of fire.
A filtered air sample is delivered to the detector via a centrifugal blower, a portion of which is diverted
into a humidifier. At approximately 100% relative humidity, the sample is directed to the Cloud
Chamber where, because of cooling, due to rapid vacuum expansion, water condenses onto the small
particles and forms a ‘cloud’.
Consequently, the thermally generated particles cause many droplets to form into the cloud, which is
then detected by the measuring system of the Cloud Chamber. The density of the cloud being
proportional to the number of particles present.
The result is a continuous signal that corresponds to the particle concentration. This signal is used to
provide a staged alarm sequence with four alarm levels.
The CirrusPro Detectors are self-supervised systems that continuously monitor for correct operation.
Any problem is immediately reported with the front panel Fault LED, buzzer and the operation of a
Fault relay.
CirrusPro Series Detectors locally store fault data, background particle concentration and event data.
These can be accessed and plotted with optional Cirrus Windows Software.
An optional panel display can be fitted that allows configuration options and full data to be displayed.
This can be mounted local to the detector or remote and networked to up to 32 devices (detectors or
panel display).
The CirrusPro Cloud Chamber
The diagram above shows the physical details of the CirrusPro Cloud Chamber for reference
throughout this manual.
