Sensepoint XCD RFD Technical Manual SPXCDHMRFENU Issue 1
18
6.3 Power
The Sensepoint XCD transmitter requires a power supply from the controller of between
16Vdc and 32Vdc. Ensure that a minimum supply of 16Vdc is measured at the sensor,
taking into account the voltage drop due to cable resistance.
The maximum loop resistance in the eld cable is calculated as follows
R
loop
= (V
controller
– V
detector min
) / I
detector
Example;
The controller is supplying a nominal 24Vdc
(V
controller
)
, the detector minimum allowable
voltage is 16Vdc
(V
detector min
)
, therefore the maximum allowable voltage drop between the
controller and detector is 8Vdc; this means a voltage drop of 4V in each core (+ve core
and -ve core).
Power consumption of the detector is 5.0W. The current required to drive the detector at
the minimum voltage is (I = P / V), 5 / 16 = 312.5 mA (I detector).
So, the maximum eldcable loop resistance (R loop) = 8 / 0.31 = 26 Ohms, or 13 Ohms
per core, (allowing for component variations, losses, etc.).
The following tables show the maximum cable distances between the controller and
transmitter assuming a voltage drop of 3V in each core and for different cable parameters.
The tables are examples only and actual cable parameters and source power supply
voltage for the application should be used to calculate the maximum cable distance
allowed at the installation site.
Typical cable data Maximum Cable length (L)
Cable size
(cross sectional area)
Cable resistance
Ω/km (Ω/mi)
Meters Feet
0.5mm2 (20AWG*) 36.8 (59.2) 353 1158
1.0mm2 (17AWG*) 19.5 (31.4) 666 2185
1.5mm2 (16AWG*) 12.7 (20.4) 1023 3356
2.0mm2 (14AWG*) 10.1 (16.3) 1287 4222
2.5mm2 (13AWG*) 8.0 (12.9) 1621 5318
*nearest equivalent
Table 2: Maximum cable distances
+24V
+20V
(wrt Controller 0V)
+4V
(wrt Controller 0V)
0V
4-20mA
Field Cable (L)
Signal
Diagram 7: Power Connection
16V (min)
Controller
XCD
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