UFC 3-570-06
JANUARY 31 2003
With outside circuit remaining on, record the mV measurement of the
inside circuit.
Apply this data to the following formulas:
Voltage On - Voltage Off*
Test Current Applied
Test Current Applied
Factor =
Voltage Change*
*Voltage change must consider polarity. For example: 4.1 mV ON minus 1.3 mV OFF
yields a voltage change of 2.8 mV; whereas 4.1 mV ON minus -1.3 mV OFF yields a
voltage change of 5.4 mV (+ mV ON - -mV OFF = +mV ON + mV OFF = Voltage
Change).
Record the resistance of the test span and the calibration factor
established. If the temperature of the pipeline or cable remains constant,
this calibration factor can be stenciled on the IR drop test station and used
for future measurements. If doubt exists or temperatures change, perform
the calibration steps each time measurements are taken.
7-13.2
Direction of Current Flow. Direction of current flow is determined by the
polarity of the mV reading taken on the inside circuit. For example, using Figure 7-35, a
positive IR drop indicates current flow from right to left, while a negative IR drop would
indicate current flow from left to right.
7-51
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