Reference Manual
00809-0100-4793, Rev CA
August 2004
Rosemount 8742C
6-4
Test equipment (such as Fluke Model 25, 27, 83, 85, 87, or 8060A multimeter
and a B&K Model 878 LCR meter or equivalent) is needed to conduct these
tests. Same of the tests will require measuring conductance (nS,
nanosiemens), the reciprocal of resistance. It is possible to test a LCR meter
by selecting the units nS and holding the leads apart. The value should be
less than one, while touching the leads together should result in an overload
value. The LCR meter may be used with flow in the flowtube.
Test
Flowtube
Location
Required
Equipment
Measuring at
Connections
Expected Value
Potential Cause
Corrective Action
A. Flowtube
Coil
Installed or
Uninstalled
Multimeter
1 and 2 = R
• Open or
Shorted Coil
• Remove and
replace flowtube
B. Shields to
Case
Installed or
Uninstalled
Multimeter
17 and
and case
ground
17 and case
ground
• Moisture in
terminal block
• Leaky electrode
• Process behind
liner
• Clean terminal
block
• Remove
flowtube
C. Coil Shield
to Coil
Installed or
Uninstalled
Multimeter
1 and
2 and
(< 1nS)
(< 1nS)
• Process behind
liner
• Leaky electrode
• Moisture in
terminal block
• Remove
flowtube and dry
• Clean terminal
block
• Confirm with
flowtube coil
test
D. Electrode
Shield to
Electrode
Installed
LCR (Set to
Resistance
and 120 Hz)
18 and 17 = R
1
19 and 17 = R
2
R
1
and R
2
should be stable
NO:
N5, E5, CD,
ED:
• Unstable R
1
or
R
2
values
confirm coated
electrode
• Shorted
electrode
• Electrode not in
contact with
process
• Empty Pipe
• Low conductivity
• Remove coating
from flowtube
wall
• Use bulletnose
electrodes
• Repeat
measurement
2
Ω
R
18
Ω
≤ ≤
0.2
Ω
<
∞Ω
∞Ω
R
1
R
–
2
300
Ω
≤
R
1
R
–
2
1500
Ω
≤
Summary of Contents for 8700 Series
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