Specifications

Siemens Mobility, Traffic Solutions
Sopers Lane, Poole, Dorset
BH17 7ER
Version 10 Page 115 of 120 Status Issued
Last Editor harry.smyth Date 03 November 2014
Document
Name
GENERAL HANDBOOK FOR HEIMDALL
DETECTORS
Doc. No. 667/HB/31900/000
Copyright  Siemens plc 2014 All Rights Reserved
12 CALCULATING PERMISSIBLE DETECTOR SUPPLY
CABLE LENGTHS
This section can be used to calculate the permissible cable lengths for non-standard
installation requirements, for example the ST900 ELV detector supply kits.
12.1 General Considerations
When considering power supply needs for the Heimdall detector, care must be taken to
ensure that all power losses are taken into account. This is particularly true for supply
feeder runs to each detector.
The following rules must be followed for each installation:
 The minimum allowed voltage at any time on any detector is 19.2 volts
 This voltage applies at the minimum mains voltage of 207 volts (which is -10% on
the standard European voltage of 230v or -13.75% on the standard UK voltage of
240v).
 This voltage applies when the transformer is loaded with all the installed
detectors volts (if applicable).
 The detector interface cable resistance must be allowed for in calculating the
maximum permissible cable lengths.
The following fixed parameters will need to be applied to all calculations:
 The supply and return resistance for a 1 mm2 cable is 0.042 ohms per metre.
 Transformer secondary winding resistance
 Worst case no-load voltage
 Maximum supply current.
For the Siemens supplied 24 AC Detector Transformers the following table can be
consulted.
Kit
160VA LV Supply
667/1/20292/008
50VA LV Supply
667/1/27853/000
Transformer Part Number 667/7/15855/005 667/7/00977/007
Resistance Rs 0.309 ohms 1.3 ohms
Worst case no-load
voltage at 207 volts
mains (i.e. 230v -10%)
Vmin 21.26v 23.13v
Maximum current Imax 6.6 A 2 A
Table 12-1 – Siemens AC Detector Supply Specification