Metrohm viva 1.1 (ProLab) - Manual (Page 947)

￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
7 Devices
viva 1.1 (for process analysis)
￭￭￭￭￭￭￭￭ 935
Description of the mode of operation
The controller uses internally a PWM block, which is used to drive the
actuator. The mark-to-space (pulse-pause) ratio is adjusted adaptively to
the behavior of the controlled system. The PWM output is switched on as
soon as the control deviation E (setpoint value minus actual value) is
greater than zero and switches off when the control deviation is less than
zero. As long as the control deviation is within the interval ( -tolerance
range - tolerance range), the pulse-pause ratio will not be changed. If E is
larger than the tolerance range, then the pulse-pause ratio will be
increased by one step. After this increase, the system will wait for the con-
trol delay time to elapse before the pulse-pause ratio is possibly altered
once again. In the event that the level falls below the -tolerance range,
the pulse-pause ratio will be reduced by one step. The pulse-pause ratio is
varied only within the interval [fMinLimit - fMaxLimit]. The cycle period of
the PWM signal can be specified.
E Control deviation; difference of setpoint value minus actual value
Tolerance range Range of fE in which the pulse-pause ratio is not changed.
Working range If fE is exceeded in this range, then the output signal will be set perma-
nently to active.
Cycle period Cycle period of the PWM signal. For technical reasons, this should be at
least one order of magnitude over the PLC cycle time of 30 ms. Values
below 30 ms are invalid.
minimum pulse ratio Minimum pulse-pause ratio in percent (0% - 100%).
maximum pulse ratio Maximum pulse-pause ratio in percent (0% - 100%).
Step size Value by which the pulse-pause ratio is varied with each adaptation (0% -
100%). Excessively large values lead to very few possible pulse-pause
ratios. Smaller values cause the controller to react with finer gradations,
but also more slowly.
Control delay: Waiting time between the individual variations of the pulse-pause ratio.
Normally these should correspond to at least the cycle period. Values
under 30 ms are invalid.
7.10.8.1.8 Properties - PWM controller
Dialog window Configuration ▶ Devices ▶ [Edit] ▶ Properties... ▶ Properties - 'De-
vice type' - 'Device name' ▶ Controller ▶ [Edit] ▶ Properties - 'Controller type'
Control variable
Selection of the controlled variable from all analog inputs or selection of a
calculated value.