VEGA WEIGHTRAC 31 Foundation Fieldbus - Manual (Page 30)

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5 Connecting to power supply
WEIGHTRAC 31 • Foundation Fieldbus
42375-EN-131120
5.4 Connection - Tachometer
The speed of the conveyor belt, the chain conveyor or the feed screw
are absolutely necessary for mass flow determination.
There are three different possibilities:
•
Entering a constant speed
•
Accepting a speed value from the plant control system (e.g. PLC)
•
Connecting a tachometer (analogue or digital)
If a constant speed is entered, fluctuations in the speed are not taken
into account. This can cause measurement errors. We recommend
using a real value from the plant control system or the optional
tachometer.
See "Parameter adjustment - Mass flow detection".
If you have entered a constant belt speed, we recommend using a
belt stop signal.
If the belt stops, measurement is also halted for this period. Without
a belt stop signal, WEIGHTRAC 31 would continue summing the
delivery rate.
You can implement the belt stop signal with a switching relay or a
signal from the plant control system (PLC).
Connect a switching relay to terminals 14 and 16.
Connect the digital output signal (open collector) from the plant con-
trol system (PLC) to terminals 14 and 15.
Belt speed - PLC
The shown diode should have a blocking voltage of > 50 V, any type
of diode can be used.
If the output of the PLC is an "open collector", then the diode is not
required.
Tachometer - analogue
Connect the analogue tachometer according to the following illustra-
tion.
Constant belt speed
Belt speed (PLC), ta-
chometer (analogue)