23
ENG
“EVD ice” +0300038EN - rel. 1.1 - 23.04.2018
proportion to how much the cooling capacity of the unit has increased or
decreased in percentage terms. When the calculated position has been
reached, regardless of the time taken, there is a constant 5 second delay
before the actual control phase starts.
Note:
if information is not available on the variation in unit cooling
capacity, this will always be considered as operating at 100% and therefore
the procedure will never be used. In this case, the PID control must be
more reactive (see the chapter on Control) so as to react promptly to
variations in load that are not communicated to the driver.
t
t
t
t
OFF
ON
R
OFF
ON
NP
OFF
ON
C
OFF
ON
A
T3
W
Fig. 8.p
Key:
A Control request
R
Control
C Change in capacity
T3 Repositioning time
NP Repositioning
t
Time
W Wait
Stop/end control
The stop procedure involves closing the valve from the current position
until reaching 0 steps, plus a further number of steps so as to guarantee
complete closing. Following the stop phase, the valve returns to standby.
t
t
t
t
OFF
ON
R
OFF
ON
ST
OFF
ON
S
OFF
ON
A
T4
Fig. 8.q
Key:
A Control request
R
Control
S
Standby
T4 Stop position time
ST Stop
t
Time
8.10 Special control states
As well as normal control status, the driver can have three special states
related to specific functions:
•
manual positioning: this is used to interrupt control so as to move the
valve, setting the desired position;
•
recover physical valve position: recover physical valve steps when fully
opened or closed;
•
unblock valve: forced valve movement if the driver considers it to be
blocked.
Manual positioning
Manual positioning can be activated at any time during the standby or
control phase. Manual positioning, once enabled, is used to freely set
the position of the valve using the corresponding parameter. Control is
placed on hold, all the system and control alarms are enabled, however
neither control nor the protectors can be activated. Manual positioning
thus has priority over any driver state/protector.
Par. Description
Def. Min. Max. UoM
U1 Enable manual valve posit. 0/1=yes/no
0
0
1
-
U2 Manual valve position
0
0
999
step
Notes:
1.
the manual positioning status is NOT saved when restarting after a
power failure.
2.
in for any reason the valve needs to be kept stationary after a power
failure, proceed as follows:
•
remove the valve stator;
•
set the PID proportional gain =0. The valve will remain stopped at
the initial opening position, set by corresponding parameter
Retrieve physical valve position
This procedure is necessary as the stepper motor intrinsically tends to lose
steps during movement. Given that the control phase may last continuously
for several hours, it is probable that from a certain time on the estimated
position sent by the valve driver does not correspond exactly to the physical
position of the movable element. This means that when the driver reaches the
estimated fully closed or fully open position, the valve may physically not be in
that position. The “Synchronisation” procedure allows the driver to perform a
certain number of steps in the suitable direction to realign the valve.
Note:
realignment is in intrinsic part of the forced closing procedure and
is activated whenever the driver is stopped/started and in the standby phase.
Unblock valve
This procedure is only valid when the driver is performing superheat
control. Unblock valve is an automatic safety procedure that attempts
to unblock a valve that is supposedly blocked based on the control
variables (superheat, valve position). The unblock procedure may or may
not succeed depending on the extent of the mechanical problem with
the valve. If for 10 minutes the conditions are such as to assume the valve
is blocked, the procedure is run a maximum of 5 times. The symptoms of
a blocked valve do not necessarily mean a mechanical blockage. They
may also represent other situations:
•
mechanical blockage of the solenoid valve upstream of the electronic
valve (if installed);
•
electrical damage to the solenoid valve upstream of the electronic valve;
•
blockage of the filter upstream of the electronic valve (if installed);
•
electrical problems with the electronic valve motor;
•
electrical problems in the driver-valve connection cables;
•
incorrect driver-valve electrical connection;
•
electronic problems with the valve control driver;
•
secondary fluid evaporator fan/pump malfunction;
•
insufficient refrigerant in the refrigerant circuit;
•
refrigerant leaks;
•
lack of subcooling in the condenser;
•
electrical/mechanical problems with the compressor;
•
processing residues or moisture in the refrigerant circuit.
Note:
the valve unblock procedure is nonetheless performed in each
of these cases, given that it does not cause mechanical or control problems.
Therefore, also check these possible causes before replacing the valve.