ABB CM30 - Page 24

ControlMaster CM30 and CM50
Universal process controllers,
1
/4 and
1
/2 DIN 6 Basic Level
22 IM/CM/ED–EN Rev. B
…Basic / …Loop 1 (2) Mot Valve
Calculation for Control Pulses (Boundless Control)
The following calculations are for guidance when setting deadband, proportional and integral values:
Ratio 
Bias
The required valve position = (Ratio x PID O/P) + Bias.
Note. Applicable only for motorized valve with feedback – see page 21.
Deadband Example: If the valve is set to be driven to the 50 % open position and the deadband is set
to 4 %, the motor stops driving when the position feedback is 48 %. The deadband is
between 48 % and 52 %.
Travel Time For motorized valve without feedback (see page 21), this parameter is used to control the
valve movement.
For motorized valve with feedback, the time entered is compared with the actual valve
movement. If the valve is sticking, a diagnostic message is generated (set Travel Time to 0
s
to disable this feature).
SP  PV
(Eng Hi  Eng Lo)
Db (Eng Units)
(Eng Hi  Eng Lo)
Tt x Db
PB x (Eng Hi  Eng Lo)
Ti x Db
2 x (PV  SP)
= 2 x
SP  PV
(Eng Hi  Eng Lo) x PB
Minimum 'On' time of integral action pulses (for a fixed control deviation):
Minimum (approximate) time between integral action
pulses (for a fixed control deviation):
Duration of the proportional step
% Control Deviation =
% Deadband =
Key:
Tt = Travel Time
Ti = Integral Time
Db = Deadband
PB = Proportional Band
Pv = Process Variable
SP = Control Setpoint
Position %
Deadband 
(centred around 
required position)
Required Valve Position