4 Function description
4.1 Functional principle
4.1.5
Temperature compensation
If the flowmeter is additionally equipped with a temperature sensor, the current density of the flowing li-
quid can be calculated from this measured value by means of a stored density table.
o
With the option
Volume at X°
a normalized volume measurement is then possible at which the dis-
played values are converted to a reference temperature that can be selected freely. This ensures
that measuring errors caused by changes in the density due to temperature variations are avoided.
o
The option
Volume at TempA
calculates the volume back to the temperature flowmeter A. This op-
tion allows the comparison with a reservoir level.
o
Measurement errors are also reduced for the
Mass calculation
option since the electronic unit now
processes the actual density and not a stored mean value during the mass calculation. For the case
of operation with diesel and heavy fuel oil the density calculation should be used since the density
for heavy fuel oil is automatically calculated as of a liquid temperature of 70 °C. Below 70 °C the
density calculation takes place for diesel. The changeover temperature of 70 °C was selected since
the flash point of diesel lies at 60 °C.
4.1.6
Differential measurement
The electronic unit can process the signals of two flowmeters and determine and display the links pos-
sible with it.
o
The option
A-B
allows the subtraction of the values of both channels, e.g. supply and return line of
a consumer supplied with a ring line. This allows differential measurement and the direct display of
the consumption.
o
The option
A+B
allows an addition of the values of both channels and with that, for example, the
display of the total consumption of two consumers.
4.1.7
Circulation ratio and threshold value
The ratio A/(A-B) is called the circulation ratio. On the basis of the laws of error propagation, a strongly
rising error of the displayed differential value results at differential measurement with the option
A-B
for
values A/(A-B) >> 1 so that the value A/(A-B) can also be used to judge the reliability of a differential
measurement. For the case A/(A-B) >> 1, for example in the case of a deactivated consumer but with a
circulation pump that continues to be operated, a threshold value can be specified for A-B below which
the measured values are not taken into consideration for the sum calculation.
4.1.8
Averaging
A strongly fluctuating flow rate causes a jumping display or as a result a fluctuating analog output. The
averaging function reduces this effect by generating a averaging across several measured values. The
number of measured values for averaging can be set. See
3.06 Setting Averaging Analog Average
and see
2.16 Setting Averaging Display Rate Average
.
4.1.9
Limit value bypass
The Limit value bypass function allows the automatic activation of a bypass valve when a flowmeter
blocks. The bypass valve is actuated via Relay output 1. See
3.13 Setting Function Relay 1
.
4.1.10
Group error message
When an error message occurs, Relay output 2 is switched for the group error.
4.1.11
Flow direction detection
In extreme cases the flow direction can change through pulsations, meaning through liquid waves in
the pipe system. Through the use of two pick ups that supply signals out of phase by 90° (square wave
encoder signals), a reversal in the flow direction is recognized by means of the flow direction sensor
and taken into account when calculating the total value. The electronic unit offers incremental encoding
inputs for each flowmeter. This means that the flow direction can be determined without additional
components and taken into account in the calculation at any time.
4.1.12
Filling
A simple filling function can be implemented with the KRAL electronic unit, see
1.07 Filling volume
.
After the filling function has been started, Relay output 1 is activated when the specified quantity is
reached in order, for example, to close a valve that interrupts the filling process, see
3.13 Setting
Function Relay 1
. The filling process can also be interrupted or aborted.
Operating instructions
OIE 12en-GB Edition 2020-03
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