Burkert Type 8712 - Manual (Page 9)

9
Descriptionofthesystem
Type 8626, 8712
5.3.1. control electronics
The control electronics:
• process the mass flow-rate set-point values and measured values,
• control the solenoid valve.
set-point value
The set-point value (w) is transmitted either by an analogue input signal
or digitally via the serial or the field bus interface. If the set-point value
is supplied by analogue transmission, the following assignments are
applied:
signal
range set-point associated
with the range min. set-point associated
with the range max.
4...20 mA 4 mA, w = 0 % 20 mA, w = 100 %
0...20 mA 0 mA, w = 0 % 20 mA, w = 100 %
0...5 V 0 V, w = 0 % 5 V, w = 100 %
0...10 V 0 V, w = 0 % 10 V, w = 100 %
For the control of a system where quick flow-rate changes are not
permitted, a ramp function can be activated. The settings for a raising
and a falling set-point value can be set separately.
More detailed information on the ramp function and on all
other functions can be found in the software documentation
for the MFM / MFC.
control settings
The initial control settings are set at the factory.
• Amplification factors:
After start-up, the controller operates with amplification factors
dependent on the loop properties. When the autotune function runs,
these are determined automatically. This function enables the control
settings to be optimized for the system's actual conditions.
• Control dynamics setting:
The device has a setting which can change the control dynamics
with the aid of the "Mass Flow Communicator" software
(see section „10.1.3“). Its extreme effects are:
1. a very quick adjustment in which overshoots are possible.
This enables the controller to respond immediately to very low
control deviations; which causes the control to be very turbulent,
2. a slower adjustment to the required flow-rate. If the system is less
dynamic, the behaviour of the controller may be damped so that
minor fluctuations in the measured value or set-point value are only
adjusted slowly.
Zero point shut-off
A zero point shut-off is integrated to ensure the sealing function of the
valve. This is activated if the following conditions occur at the same time:
Set-point value < 2 % of
nominal flow-rate Q
nom
(with control range 1:50)
and
Measured value < 2 % of
nominal flow-rate Q
nom
(with control range 1:50)
If the zero point shut-off is active, the PWM signal is set to
0 % so that the valve is completely closed.
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