175
Reference Manual
00809-0300-4750, Rev CA
March 2016
9.6.1
Installed sensor tests
If a problem with an installed sensor is identified, refer to
to assist in
troubleshooting the sensor. Disconnect or turn off power to the transmitter before
performing any of the sensor tests. Always check the operation of test equipment before
each test.
If possible, take all readings from the lead wire clips (removal of terminal block is required
for access). If the lead wire clips are inaccessible, take measurements at the sensor terminal
block or through remote cabling as close to the sensor as possible. Readings taken through
remote cabling that is more than 100-ft. (30 m) in length may provide incorrect or
inconclusive information and should be avoided.
The expected values in the test below assume the measurements have been taken directly
at the clips. Refer to
for electrode and coil wire keyed positions in
the clips.
Table 9-8. Sensor Tests and Expected Values
Test
Sensor
location
Required
equipment
Measuring at
connections
Expected value
Potential cause
Corrective
action
A. Sensor
coil
Installed or
uninstalled
Multimeter
1 and 2 = R
2
Ω
≤
R
≤
18
Ω
•Open or shorted
coil
•Remove and
replace sensor
B. Shields to
case
Installed or
uninstalled
Multimeter
17 and 3
3 and case
ground
17 and case
ground
< 0.3
Ω
•Moisture in
terminal block
•Leaky electrode
•Process behind
liner
•Clean terminal
block
•Remove sensor
C. Coil to
coil shield
Installed or
uninstalled
Multimeter
1 and 3
2 and 3
∞Ω
(< 1nS)
∞Ω
(< 1nS)
•Process behind
liner
•Leaky electrode
•Moisture in
terminal block
•Remove sensor
and dry
•Clean terminal
block
•Confirm with
sensor coil test
D. Electrode
to
electrode
shield
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
•Unstable R
1
or R
2
values confirm
coated electrode
•Shorted
electrode
•Electrode not in
contact with
process
•Empty pipe
•Low conductivity
•Leaky electrode
•Process reference
ground not
connected
properly
•Remove coating
from sensor wall
•Use bullet-nose
electrodes
•Repeat
measurement
•Remove sensor
and complete
tests in
•Connect
process
reference
ground per
“Process
reference
connection” on
page 17
E. Electrode
to
electrode
Installed
LCR (set to
resistance
and 120 Hz)
18 and 19
Should be stable
and same relative
magnitude of R
1
and R
2
from Test D
•See Test D above
•See Test D
above
R
1
R
–
2
300
Ω
≤
Summary of Contents for Rosemount 8750W
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