2000 SERIES SENSORS INSTALLATION GUIDE Revision 3.1 June 1997
3. LOOP LOAD CALCULATIONS
3.1 GENERAL
When designing a Series 2000 system it is important to calculate the designed loop
configuration to ensure that it operates within the minimum and maximum voltage parameters
under worst case voltage and current conditions.
The low voltage limit is normally 20 volt DC for systems that include Zone Monitoring Units and
for systems without such units it is 17 volt DC.
The voltages mentioned only refer to the minimum DC voltage level, the AC voltage level must
be maintained at 5 to 9 volt 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 based on the DC voltage only and the attenuation of the AC voltage
signals is theoretically relative to that of the DC voltage. In most cases, the AC voltage will be
within specification when the DC voltage is within specification limits, provided that the AC
voltage level is well above the minimum DC level (5 volt) to begin with.
3.2 CALCULATION PROCEDURE
1. Calculate the total quiescent (standby) current for the loop devices using Table 2.
2. Calculate the worst case condition for additional alarm and LED current using Table
3.
Notes :
• The ‘worst case’ condition should still be considered as a ‘realistic’ condition,
taking into account the physical location of the sensor, remote indicators and
so on. In most of the applications, 10 sensors in alarm at the same moment
(per loop) is a good indication.
• In some panels (like FP2000), the max. number of LED’s in alarm per loop at
the same time can be programmed.
3. Determine the total loop resistance, using Table 4.
• The cable values given are "per core", therefore for a two core cable the
resistance must be multiplied by two.
• The 10 ohm source impedance is related to the FP2000.
4. Multiply the total current and the total resistance and subtract the result from the
central control equipment loop voltage. This will give the minimum voltage that a
device in the worst possible position on the loop can experience under power fail
conditions.
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