16
OELD Operating Instructions
4.1 Power Supply
The OELD requires a voltage supply of 18 - 32 Vdc (nominal 24 Vdc). Power consumption is 2 W maximum.
Refer to individual sensor manuals for sensor specific limits and power consumption.
Ensure that the minimum required supply voltage is present at the sensor, taking into account the voltage drop due to cable
resistance.
Note
Make allowance for the insertion loss resistance.
The maximum loop resistance in the field cable is calculated as follows:
R
loop
V
controller
I
detector
—
V
detector min
―
―
4.2 Cabling Recommendation
The cable used must be appropriate for the hazardous area classification and meet local, national and/or company regulations. The
use of industrial grade, screened field cable is recommended.
An example would be 3-core copper cable with screen (minimum 90% coverage) and suitable mechanical protection (e.g. steel wire
armor) to suit an M25 or 3/4”NPT gland entry or conduit.
The allowable conductor size for the terminals is 0.2 – 2.5 mm² (24 - 12 AWG). The OELD terminals will accept only wire sizes(solid-
core or stranded) in this range. The temperature rating of the conductors should be greater than 80°C. The terminals should be
torqued between 0.5 Nm to 0.6 Nm.
Ensure the cable gland is installed correctly and fully tightened. All unused cable/conduit entries must be sealed with a suitable
certified blanking plug.
4.3 Earth Regimes
Caution
Any earthing regime employed must avoid earth loops.
The following information is provided to assist with proper earthing of the OELD:
•
The OELD has two internal earth points provided (see Electrical Connections). This is to facilitate connection of the sensor to
protective earth.
•
Field cable screens should be connected to instrument earth at the control room. The other end of the field cable screen should
be suitably terminated or isolated. It should not be connected to internal earth point.
4 Electrical Connections
