Toshiba LF494 - Manual (Page 133)

TOSHIBA
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Empty pipe alarm
If ilic detector pipe is not filled with fluid, the following message appears.
Design piping so that the detector pipe i:; always filled with the fluid to be measured. If the
empty alarm cnable/disable status is set to OFF, this function is disabled. See 8,2.13,
“Empty Pipe Alarms.'’
Alarm message Description Corrective action
EMPTY
Detector pipe is not filled
with fluid. Arrange piping so that the
detector pipe is always
filled wdth fluid.
Precautionary notes on using the empty pipe alarm
(1) The flowmeter delects an empty pipe condition by monitoring the impedance and signal
level between the flow signal lines connected to a pair of electrodes. Therefore, the
following factors may trigger an erroneous empty pipe alarm:
• Opening or loose connection of flow signal lines
• The fluid to be measured carrying a lot of bubbles
• Contamination of the electrode with non-conductivc deposits
(2) If the tlow'meter i,s not grounded properly or if it is in ait environmcni w^herc high
electrical noise exists, the empty pipe alarm may not function properly. Under these
conditions, the reliability of flowmeter accuracy itself is not high. Try to ground the
flowmeter securely to an independent good ground and relocate the cable runs to
prevent noise from entering into the ilow'meier circuit,
(3) If the fluid still remains in the detector pipe or the internal wall of the detector pipe is
contaminated with electrically conductive deposits, the impedance between the signal
lines will not go high and the empty pipe alarm may not work. In this kind of event, try
to use other means to detect an empty pipe condition (such as a pump stop signal or a
signal from a valve).
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