Tyco MX4428 Isolator Base Loading, Example, Calculate DC Load, Ii Calculate AC Load

Document: LT0273	MX4428 MXP Engineering / Technical Manual
	Device Information and Programming

3.2.4ISOLATOR BASE LOADING

If isolator bases are being used, calculate the sum of the “IB Units” from Table 3-2for each section of cable between isolator bases (or between the last isolator base and the end of a cable spur). Include only one of the detectors at the ends of the section. The sum for any section must not exceed 100.

See also section 4.1.3 for details of AS1670 requirements and section 4.1.4 for details of NZS4512 requirements.

3.2.5EXAMPLE

Consider an MXP monitoring 200 * 814PH detectors with 10 814SB Sounder Bases set to High, on a 1300 metre long loop, using 1.5mm2 wire. The cable is divided (with 9 Isolator Bases) into 10 segments with 1 Sounder Base and 20 detectors on each segment.

(i)Calculate DC Load

IA = 195 x 275uA (No. of detectors in NORMAL)

+5 x 3.0mA (No. of detectors with Alarm LEDs turned on, assume limited to 5 max by MXP)

+10 x 15mA (Number of 814SB Sounder Bases)

+9 x 80uA (Number of Isolator Bases)

(Ref Table 3-2.Note 1mA = 1000uA) = 220mA which is well under 400mA

For the voltage drop calculation, assume the worst case in the first instance, i.e. that all devices are at the far end of 1300 metres. The loop resistance of 1.5mm2 wire is 25Ω per 1000m and the isolator base resistance is 0.25Ω.

Total R = 25Ω x 1.3 + 9 x 0.25Ω

= 34.75Ω.

Voltage drop = 34.75 x 0.220 = 7.7V, which is well under the maximum allowable of 16V.

(ii)Calculate AC Load

	AC Units	=	200 x 1 (detectors)
			+ 10 x 2.4		(Sounder Bases)
			+ 10 x 0.1		(Isolator Bases)
		=	225 which is less than the maximum allowable of 250.
	Cable length is well under the limits specified in Table 3-3.
(iii)	Calculate IB Load
	IB Units for each section			= 20 * 1.2 (814PH) + 1 * 2.5 (814SB)
				=	26.5 which is less than 100.

As all parameters are within the specified limits, the design is satisfactory.

Issue 1.5 24 March 2006 Page 3-9