Endress+Hauser Silometer FMC 672 Z, Инструкция по установке и эксплуатации

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1.4 Functional description
The capacitance or pressure measured by the sensor is converted into a frequency
signal by the electronic insert located in its head. The Silometer FMC 672 Z/677 Z
supplies the power and receives a level-proportional frequency signal over a two-core
cable. The signal is then processed to provide the following functions:
Silometer functions
•
Level measurement
By calibrating at two levels, »empty« and »full«, level measurement can be made in
the units entered during calibration.
•
Volume or weight measurement
For non-linear volume/level relationships, volume can be calculated from level via
the vessel characteristic which describes the shape of the vessel. This function is
described under »Linearization« in Chapter 5. If this function is invoked, volume is
indicated at field V0H0 on the LC-display and level at V0H9.
•
Differential level measurement
By using two probes and subtracting the measured levels, the Silometer can
provide a differential level measurement.
•
Level measurement with reference probe
When the dielectric constant of the liquid changes or is unknown, the Silometer can
be configured to provide a corrected level measurement on channel 1 by using a
reference probe connected to channel 2.
•
Analogue output
The signal resulting from the calibration and linearisation provides a standard
0/4...20 mA and 0/2...10 V output, proportional to level or volume. Any portion of the
measuring range can be taken to provide a scaled output.
•
Relay control
The two relays can be assigned to either measuring channel to provide level control
by switching pumps on and off.
•
Rackbus signal
The measured values and complete configuration can be read by the ZA 672
Modbus Gateway (and ZA 67
…
computer interface) for integration into process
control systems and visualisation on personal computers.
•
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.
In addition, each relay can be individually set to switch on or off as required.
frequency
analog
digital
current
voltage
sens. [Hz/pF] offset [Hz]
offset [pF] sens. [pF/cm]
range upper limit
V2
range lower limit
V1
frequency
electronic-
insert
electronic-
insert
capacit.
volume
V2
V1
level
volume
H2
H1
level
capacit.
level
zero point shift
BA064E07
Fig. 1.6
Signal processing in the
Silometer FMC 672 Z/677 Z
for single channel operation
Silometer FMC 672 Z/677 Z Chapter 1: Introduction
9