OmniCare EVC System
Installation & Commissioning Manual
90
OmniCare issue 1
C
O
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I
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A
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I O N S
A.3 H
OW
TO
C
ALCULATE
C
ABLE
L
ENGTH
To calculate the approximate length of a single cable run between
two Remote Units use the following procedure:
1. Disconnect both ends of the relevant cable from the Remote
Units.
2. Using an accurate DVM, select the Resistance range.
Connect both probes together and note the resistance
reading shown.
3. Temporarily link two of the conductors together at one end
of the cable.
Measure the resistance between the of the two conductors at
the other of the run and note the reading.
Remove the temporary link.
4. Subtract the resistance of the meter (noted in step 2) from
the resistance of the conductors (noted in step 3).
5. Divide the result by 2 to give the resistance of a single
conductor.
6. Identify the type of cable in use, and refer to Table A.1 to find
the maximum resistance for a single cable run of the stated
cable type. Note the value given.
7. Compare the calculated resistance (gained in step 5) with the
stated maximum.
• If the calculated value is less than the stated maximum
then the cable run is likely to be OK and less than the
maximum distance allowed.
• If the calculated value is close to, or higher than the
stated maximum then it is likely that the cable run is too
long and a Repeater Unit will be required.
N
OTE
: Cable manufacturers state a maximum value for resistance.
In reality the actual resistance of a length of cable may be less.
As a result, calculating cable length using resistance will give the
SHORTEST
distance. If the calculated result is close to the maximum
stated value then it is likely the cable run is longer than permitted.
