900 Series V5.1: Installation Guide, February 2000 35
5. MARINE PRODUCTS – 950M SERIES
The Series 950 Marine range of analogue-addressable marine fire monitors offers the
following:
• A low-profile design
• A high environmental performance
• Ease of installation
• Ease of cleaning and maintenance
• A continuous reporting of smoke/heat level
• Pre-alarm facility
• Alarm flag and address for fast alarm reporting
• Ease of addressing
These detectors are entirely based on the Series 950 Series fire monitors, and are
installed in a similar fashion as described in the Series 950/990 installation.
6. LOOP LOAD CALCULATIONS
6.1. General
When designing a Series 900 system, it is important to ensure that the designed loop
configuration continues to work within the minimum and maximum voltage parameters
under worst case voltage and current conditions.
The low voltage limit is normally 20 VDC for systems that include zone monitoring units,
and 17 VDC for systems without such units.
The voltages mentioned only refer to the minimum DC voltage level. The AC voltage level
must be maintained at 5 V to 9 V above the DC level.
The calculation procedure and expressions shown in the following paragraphs give a
rough method of checking whether the DC conditions are satisfied.
The calculations are for DC voltages only. It cannot be assumed that AC voltage levels
are acceptable if the calculated DC voltage level is within specification. The attenuation of
the AC voltage signals is theoretically proportional to that of the DC voltage and would in
most cases be within the specification when the DC voltages are within specification
limits — provided that the AC voltage levels are well above the minimum level (5 V) to
begin with.
6.2. Calculation procedure for DC voltages
1. Calculate the total quiescent (standby) current for the loop devices, using Table 5:
Device quiescent current.
2. Calculate the worst case condition for additional alarm and LED current, using Table
6: Device alarm current.
3. Determine the total loop resistance, using Table 7: Resistance.
• The cable values given are "per core". For a two-core cable, multiply the
resistance by two.
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