4 Function description
4.1 Functional principle
Either NPN or PNP can be selected for push-pull pick ups. In addition the flowmeter can also be
equipped with pick ups for flow direction detection. The electronic unit is supplied with settings in ac-
cordance with the customer requirements.
4.1.2
Volume measurement
Each positive edge of the pulse signal starts a period measurement and at the same time stops the
previous measurement. The flow rate is then calculated via the frequency (= inverse of the period dura-
tion) and the K-factor. The inverse of the K-factor is the pulse value in I/P. This is retroactively added to
the total sums for each positive edge of the signal.
4.1.3
Mass calculation
The volume can be converted into mass via a configurable fixed density value (menu 4).
4.1.4
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
2.07 Averaging analog output
and see
2.12 Averaging display rate
.
4.1.5
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.
4.1.6
Electronic evaluation
The electronic unit receives signals from the pick ups and calculates the measured values which are in-
dicated in the display unit and which can be called up at the analog output or at the Modbus interface.
Possibilities of the electronic unit:
o
Language selection
o
Display of the measured values in different units (volumes, masses and temperatures)
o
Averaged display values
o
A density for conversion to mass
o
Information message at faults or invalid inputs
o
1 scalable and assignable analog output 0 - 10 V or 4 - 20 mA
o
1 scalable and assignable pulse output
o
1 analog input 0 – 10 V for background illumination
4.1.7
Modbus connection
The electronic unit can be connected to the system by means of a Modbus interface and can thus be
integrated into existing systems. This ensures simple, reliable and rapid data exchange.
4.1.8
Applications
Different extension stages of the electronic unit are presented on the basis of the following examples.
This allows the required functional scope to be selected in accordance with the requirements.
Single-line measurement
Extension stage
Components
Functions
000135
Basic
o
1 flowmeter
o
1 pick up
o
1 BEM 300 electronic unit
o
Electronic evaluation
o
Volume measurement
o
1 analog output
o
1 pulse output
Operating instructions
OIE 15en-GB Edition 2020-03
9