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SENSEPOINT RFD OPERATING MANUAL
RFDMAN MAN0843 Issue 3
6.3 Power
The Sensepoint RFD transmitter requires a power supply from the controller of
between 12Vdc and 30Vdc. Ensure that a minimum supply of 12Vdc is measured at
the sensor, taking into account the voltage drop due to cable resistance.
The maximum loop resistance is calculated as follows:
Rloop = (Vcontroller - Vdetector min) / Idetector
For example, with the controller supplying a steady 16Vdc, then, for a detector
minimum voltage of 12Vdc, the loop voltage drop is 4Vdc.
Power consumption for the transmitter and a flammable sensor is 300mA maximum.
So maximum loop resistance is 12 Ohm (allowing for component variations, losses,
etc.).
Maximum distance between the transmitter and remotely mounted sensor is 45m
2
(147ft) using 1mm
wire (17AWG).
The following tables show the maximum cable distances between the controller and
transmitter assuming a voltage drop of 4V and for different cable parameters.
The tables are examples only and actual cable parameters for the application should
be used to calculate the maximum cable distance allowed at the installation site.
Table 3: Maximum cable distances
6.4 Cabling
We recommend the use of screened 3-core (plus screen 90% coverage), suitably
mechanically protected copper cable with a suitable M20 explosion-proof gland, or
2
¾" NPT steel conduit, with 0.5 to 2.5mm
(20 to 14 AWG) conductors. Ensure the
cable gland is installed correctly and fully tightened.
The following diagrams show examples of how to earth/ground bond the cable at
enclosures. The same principles apply to conduit installations. These bonding
techniques provide good RFI/EMC performance. Earth/ground loops must be
avoided to prevent false alarms.
15
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