Endress+Hauser Mycom S CLM 153 Operating Instructions Manual page 52

6 Commissioning
Actuators:
Upward/
downward controller:
Process:
Direction of action, one
or two-sided:
Batch or inline process
arrangement:
Look-ahead control
Controlling the actuators
52
Definition of terms
Valves, gate valves, pumps and similar
The terms "up" (=upward controller) and "down" (=downward controller) used in the
menu are used in relation to the direction of action:
Down = The control doses only if the measured value is greater than the setpoint.
Up = The control doses only if the measured value is smaller than the setpoint.
The controller or the process (to simplify matters this will, from henceforth, be referred
to as the "process") can be differentiated on account of their different features:
One-sided control only works in one of two directions. It influences the process in such
a way that the measured value either rises (upward controller) or drops (downward
controller).
With a two-sided process, control can generally work in both directions, ("up" and
"down"). This means that you can both increase and decrease the value of the controlled
variable (here = measured value).
With active control, the batch and inline processes are different in their relationship to
the medium current:
Pure batch process: The batch container is filled with the medium. During the
subsequent batch process, no additional medium is fed in. The change in the measured
value is caused only by the control. To be able to compensate for possible so-called
"overshoots", use a two-sided control (see above). For as long as the actual value is
within the neutral zone, no additional dosing agent is added.
Pure inline process: Here, the control works with the medium flowing past. The
measured value of the medium in the inflow may be subject to strong deviations for
which the control should compensate. The volume of medium which has already flowed
past can no longer be influenced by the controller. For as long as the actual value
corresponds to the setpoint, the actuating variable has a constant value.
The Mycom S controller takes this differing behaviour into account. It is the internal
handling of the integral part of the PI or PID controller which is different for these
settings.
In practice, the most common option is the semi-batch process. Depending on the ratio
of inflow to tank size, this process shows the behaviour of an inline or a batch process.
To be able to optimally resolve the general problems of a purely inline process, the
CLM 153 is able to "look into the future" using a second sensor and a flowmeter. This
means that the controller can react to strong variations in the inflow at an early stage.
The CLM 153 has four different methods for controlling the actuators (seeabove.)
1. PWM (Pulse-width modulation, "pulse-length controller")
Pulse-width modulated outputs aid control e.g.of solenoid valves. With PWM, one side
(i.e. "up" or "down") of the internal, analog actuating variable is output to a relay as a
rhythmic signal.
The larger the calculated actuating variable, the longer the appropriate contact remains
picked up (i.e. the longer the switch-on period t
length freely between 1 and 999.9 seconds. The minimum switch-on period is
0.4 seconds.
A two-sided process requires two PWM relays or one PWM and a three-point step
controller (seebelow.) One PWM relay on its own can only output an actuating variable
of
• –100% ... 0% or
• of 0% .... +100%.
To avoid pulses which are too short, enter a minimum switch-on period. Pulses which
are too short are not given to the relay/or the actuators. This benefits the actuator.
Mycom S CLM 153
; s. fig. 19 is). You can set the period
ON
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