Leaders in Pipelin
e Survey Systems
C
C
C
-
-
-
S
S
S
C
C
C
A
A
A
N
N
N
2
2
2
0
0
0
1
1
1
0
0
0
SYSTEM MANUAL Version 6.03i
24
4.8. Apparent Problems with Current Value
The maximum signal current achievable will be defined by the resistances in the Signal
Generator–pipeline circuit. The circuit resistances consist of the following components:
1. Pipe to soil resistance
≈
3
Ω
– usually small because of the large area in contact
2. Signal Generator to pipe connection
≈
0
Ω
– should be zero for good connection
3. Signal Generator to earth connection – dependent on earthing system used see
If the user is unable to apply any current at all, i.e. no output from the Signal Generator or
the message ‘Output disconnected high resistance’ displayed, it can often be caused by a
high value for item 3 above, but this must not be assumed and all components of the
circuit need to be checked, including any cables being used. .
Earth spike resistance Vs Current mA
1
10
100
1000
10000
0
200
400
600
800
1000
1200
Current (mA)
R
esi
stan
ce
(o
h
m
s)
The graph above shows the earth contact resistance required for a given current to be
achieved.