Technical / Programming Manual
FT128 Rev 2.2
165
If the temperature was raised to 80C, we would expect that the resistance would also
increase. The relationship between resistance and temperature is given by,
Where,
R = Resistance per unit
R
ref
= Resistance per unit at a reference temperature
Coefficient of copper
T = Actual temperature
T
ref
= Reference temperature
Hence, calculating for this gives:
Therefore, the new distance would be:
Figure 57 COM Loop Current Consumption vs. Cable Length
The total COM loop unit current consumption is increased as the number of units are added
to the loop. Refer to “Current Consumption” page 168 as details are given as to how much
current is consumed by each unit as they are added to the loop. Use the FT128 current
calculation spread sheet to calculate the expected total current consumption before using
this graph in Figure 57.
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