Power Supply; Example Cable Length Calculation; Cabling Recommendation - Honeywell OELD Operating Instructions Manual

OELD User Manual (3018M5000_1-3) Revision 1, Issue 3

4.1 Power Supply

OELD requires an isolated voltage supply of 18 - 32 Vdc (nominal 24 Vdc), which is suitably approved
for the region (for example, UL approved). 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.
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The maximum loop resistance in the field cable is calculated as follows:
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4.1.1 Example Cable Length Calculation

Example – OELD with Searchpoint Optima Plus:
Searchpoint Optima Plus requires a voltage supply of 18 – 32 Vdc. Its power consumption is 5 W.
Therefore total power consumption including OELD is 7 W maximum.
The controller is supplying a nominal 24 Vdc (V controller) and the detector minimum allowable volt-
age is 18 Vdc (V detector min), therefore the maximum allowable voltage drop between the controller
and detector is 6 Vdc; this means a voltage drop of 3 V in each core (+ve core and -ve core).
Power consumption of the detector is 7 W. The current required to drive the detector at the minimum
voltage is (I = P / V), 7 / 18 = 388 mA (I detector).
So, the maximum field cable loop resistance (R loop) = 6 / 0.388 = 15.4 Ω, or 7.7 Ω per core.
The following tables show the maximum cable distances between the controller and OELD with
Searchpoint Optima Plus for different cable options, assuming a voltage drop of 3 V in each core. The
tables are examples only and actual cable parameters and source power supply voltage for the appli-
cation should be used to calculate the maximum cable distance allowed at the installation site.
Note: Sufficient operational margins should be allowed

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.