Tuning Installation and Operation Handbook
4.4.1
Commissioning the Motorised Valve Controller
The commissioning procedure for bounded control mode is as follows:
1. Measure the time taken for the valve to be raised from its fully closed to its fully open position and enter this
as the value in seconds into the ‘
tm
’ parameter.
2. Set all the other parameters to the default values shown in Table 4-3.
The controller can then be tuned using any of the automatic, or manual, tuning procedures described earlier in this
chapter. As before, the tuning process, either automatic or manual, involves setting the values of the parameters
in Table 4-1.
4.4.2
Adjusting the minimum on-time
‘
mp.t
’
The default value of 0.2 seconds is satisfactory for most processes. If, however, after tuning the process, the
valve activity is excessively high, with constant oscillation between raise and lower pulses, the minimum on-time
can be increased.
The minimum on-time determines how accurately the valve can be positioned and therefore the control accuracy.
The shorter the time, the more precise the control. However, if the time is set too short, process noise will cause
an excessively busy valve.
4.4.3
Inertia and backlash settings
The default values are satisfactory for most processes, i.e. ‘
OFF
’.
Inertia
is the time taken for the valve to stop after the output pulse is turned off. f this causes a control problem,
the inertia time needs to be determined and then entered into the parameter, ‘
In.t
’. The inertia time is subtracted
from the raise and lower output pulse times, so that the valve moves the correct distance for each pulse.
Backlash
is the output pulse time required to reverse the direction of the valve, i.e. the time taken to overcome the
mechanical backlash of the linkages. If the backlash is sufficient to cause a control problem, then the backlash
time needs to be determined and then entered into the parameter, ‘
bac.t
’.
The above two values are not part of the automatic tuning procedure and must be entered manually.
4-6 HA025041 issue 12 Aug 14
Summary of Contents for XST-2-0-12-1V1-E28
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