Endress+Hauser prolevel FMC 661, Operating Instructions Manual

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1.4 Functional description
Fig. 1.7 is a block diagram of the Prolevel FMC 661. The transmitter supplies the power
to the sensor. The capacitance or pressure measured by the sensor is converted into a
frequency signal by the electronic insert located in its head and transmitted to the Prolevel
over a two-core cable. The signal is then processed to provide six operating modes.
Signal processing By calibrating at two levels, »empty« and »full«, the frequency signal is converted to a
level measurement in the units entered during calibration. In mode 5, the measured value
at channel 1 is then corrected. For non-linear volume/level relationships, volume can be
calculated from level via the vessel characteristic which describes the shape of the
vessel. The signal resulting from the calibration and linearisation provides a standard
0/4...20 mA output, proportional to level or volume. Any portion of the measuring range
can be taken to provide a scaled output. The two sets of two relays can be assigned to
either measuring channel to provide level control by switching pumps on and off.
All measured values and the complete configuration can be accessed via the optional
Rackbus RS-485 interface.
Fail-safe operation If a fault condition is detected, e.g. a break in sensor - transmitter cable, the analogue
signal switches to -10 % or +110 % level or holds the last measured value. The alarm
relay de-energises and the red LED on the front panel lights. In addition, each set of
relays can be set to switch on or off as required.
Hz
cap./press.
electronic
insert
analog
digital
current
sensitivity [Hz/pF]
offset [Hz]
offset [pF] sensitivity [pF/cm]
range upper limit
V2
range lower limit
V1
frequency
volume
V2
V1
level
volume
H2
H1
level
cap./press.
level
zero point shift
level
limit
detection
switch point
hysteresis
min. / max. fail-safe mode
switching delay
frequency
2
relay 1a, 1b
relay 2a, 2b
BA142_08
Channel 1
Channel 2
Fig. 1.7:
Signal processing in the
Prolevel FMC 661 for single
channel operation (level
and/or limit switching)
Mode in V8H0 Function
0 Simultaneous level measurement and limit detection on channels 1 and 2
1 Level measurement on channel 1 only
2 Limit detection on channel 2 only
5 Corrected level measurement — the level measurement at channel 1 is
corrected when the product covers the limit switch at channel 2
6 Simulation of level, volume or current at channel 1
7 Simulation of limit detection at channel 2
Table 1.1:
Prolevel FMC 661 operating
modes
Prolevel FMC 661 Chapter 1: Introduction
Hauser 9