UFC 3-570-06
JANUARY 31 2003
Figure 7-34. Calibration of an IR Drop Test Span
A m m eter
D C Po wer S up ply
A dj ust ab le
A
Sw itch
R esis to r
-
+
+-
V oltm et er
mV
IR D rop
-+
T est St at io n
P ip elin e or c ab le
7-13.1
measurement circuits. The outside circuit comprises an ammeter to measure the
current, a DC power supply, an on/off switch and some means of adjustment. A
portable rectifier may be used as the current source, switch, and the means of
adjustment. The inside circuit is a high input resistance voltmeter (minimum of 10
megaohms), set to the millivolt scale.
Pipelines and cables inherently will have current flowing at all times.
Therefore, a change in voltage drop measurement is compared to the amount of test
current applied.
Following all polarities in Figure 7-34, connect all circuit components.
Polarity is important for correct determination of the direction of the current
flow in the pipeline or cable during subsequent test procedures.
With the outside circuit switch off, record the mV measurement of the
inside circuit.
Starting at a low current level, turn the outside circuit switch on and adjust
current up to the desired test current. Record the measurement of the test
current.
7-50
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