Zero - Zero Point Switch-Off - Burkert 8625-2 Manuel D'utilisation

6.6.7 ZERO - zero point switch-off

Zero point switch-off enables the proportional valve to assume a tight-closing
function in addition to the control function.To obtain tight closure when the set point
is 0, at set points below 2% of the overall range, no signal is sent to the valve, so
that the entire spring force is available for tight closure. The lower 2% of the set
point range is hence not available for control purposes.
Without zero point switch-off, a signal is sent to the valve also when the set point
is 0. This signal generates just enough magnetic force for the start of opening. This
acts in opposition to the spring force, so that the valve is not perfectly tight in most
cases.
(works setting: NO)
Fig.: Zero point switch-off
Preconditions for zero
• Zero point switch-off (YES) has been selected;
• The setpoint is less than 2 %;
• Non-inverted control.
32 - 8625-2 Standard
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No zero point switch-off ( NO ):
The control is continuous down to the lower limit, i.e. until the
minimum pulse-duty ratio set in the menu item „VALC" is
reached. The valve is closed but usually not leak-free.
Zero point switch-off ( YES ):
The control is continuous until the input signal has reached a
value of less than 2%, then the valve will be closed.