4
MAN3037-2
XP95 PRODUCT GUIDE
Figure 2 – Diagram Showing Lines of Equipotential for the XP95 Ionisation Smoke Monitor
5.2
Electrical Description:
The detector is designed to be connected to a two wire loop circuit carrying both data and a 17V to 28V dc
supply. The detector is connected to the incoming and outgoing supply via terminals L1 and L2 in the
mounting base. A remote LED indicator requiring not more than 4mA at 5V may be connected bR
and -R terminals. An earth connection terminal is also provided, although this is not required for the
functioning of the detector.
When the device is energised the ASICs regulate the flow of power and control the data processing. The
ionisation chambers are energised and the ultra low leakage sensor ASIC provides a conditioned analogue
signal to the analogue to digital (A/D) converter within the communications and processing ASIC. When
smoke enters the ionisation chambers through the integral gauze, the voltage at the sensing electrode
increases to produce an analogue signal. An A/D conversion of the signal from the ionisation chambers is
carried out once per second or when either the detector or preceding address is being interrogated.
Whenever the device is interrogated this data is sent to the control equipment. EN54 threshold alarm levels
are calibrated within the processing ASIC. If the device is not addressed within 1 second of its last polling
and the analogue value is greater than 55 the alarm flag is initiated and the device address is added to the
data stream every 32 polling cycles from its last polling for the duration of the alarm level condition, except
when the alarming device is being interrogated. This can provide a location identified alarm from any device
on the loop in approximately two seconds.
The detector is calibrated to give an analogue value of 25±7 counts in clean air. This value increases with
smoke density. A count of 55 corresponds to the EN54 alarm sensitivity level. See Fig 3. Counts of 8 or less
indicate fault conditions. Count levels between 45 counts and 55 counts can be used to provide an early
warning of fire.
Figure 3 – Typical Response Characteristics – XP95 Ionisation Detector