KROHNE IFC 110 Converter - Manual (Page 65)

Part C Special applications, functional checks, service, and order numbers Sect. 6.9
05/2003 IFC 110 F 65
6.9 Empty pipe detection EPD
The signal converter is equipped as standard with an EPD (Empty Pipe Detection)
which only needs to be activated as and when required.
To ensure proper functioning, the following requirements need to be met:
Type
of signal cable
Electrical conductivity
of process liquid Nominal size
of flow sensor Max. length
of signal cable
A = Type DS > 200 µS/cm ≥ DN 25 / ≥ 1“ < 20 m / 65 ft
B = Type BTS > 50 µS/cm ≥ DN 25 / ≥ 1“ < 20 m / 65 ft
Settings for empty pipe detection (EPD)
• Fct. 3.06 APPLICATION • EMPTY PIPE • YES (switched on) • NO (switched off)
The calibration mode must be run through during initial start-up!
• If“YES“ selected, the impedances for EMPTY and FULL PIPE need to be determined.
• Select subfunction VALUE FULL and CALIB. YES (determine impedance for “full pipe“)
WAIT (approx. 20 s)
• Select subfunction VALUE EMPTY and CALIB. YES (determine impedance for “empty pipe“)
WAIT (approx. 20 s)
• Store values after completion of calibration for “Full” and “Empty” values; quit operator control
after the second calibration.
When the electrodes are not wetted (= empty pipe), typically a response time of approx. 20
seconds is required before “empty pipe“ is indicated. In this time undefined display values and
output signals are possible.
Functional description
A high-resistance AC voltage is applied
to the electrodes. The process liquid in
the measuring tube forms a voltage
divider together with the internal
resistance of the circuit. The voltage
ratio is measured and weighted (see
figure on right). Impedance and length
of electrode cable will also affect the
result.
The result is a numerical value
proportional to the impedance at the
input. The switching point of the Empty
Pipe Detector is defined when the
system is calibrated for “full pipe“ and
“empty pipe“(at approx. 2/3 of the range
between the two calibration points). In
order to function properly there must be
a difference of at least “10“ between the
two calibration points. In operation, the
display indicates in the range between
0 and 150 (non-dimensional). The value
for “FULL PIPE“ must be lower than that
for “EMPTY PIPE“.
Display
Switching point
Impedance
EMPTY
PIPE
FULL
PIPE
Process
liquid