model 2704 controller installation and operation handbook - Soliton

Loop Set Up
2704 Controller
9.7.2. Commissioning the Motorised Valve Controller
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 ‘Travel Time’ parameter.
2. Set all the other parameters to the default values shown in 9.7.1.
The controller can then be tuned using any of the automatic, or manual, tuning procedures
described in Chapter 8. As before, the tuning process, either automatic or manual, involves
setting the values of the parameters in Table 9.7.1. The only difference with boundless
control is that the derivative term, although present, will have no effect.
9.7.2.1. Adjusting the minimum pulse-time
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.
9.7.2.2. 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. If this
causes a control problem, the inertia time needs to be determined and then entered into the
‘Inertia’ parameter. 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 ‘Backlash’ parameter.
The above two values are not part of the automatic tuning procedure and must be entered
manually.
9-16 Installation and Operation Handbook. Part No HA026502 Issue 1.0 Apr-00