Endress+Hauser Mycom S CLM 153 Operating Instructions Manual page 53

Mycom S CLM 153
!
Endress+Hauser
2. PFM (pulse-frequency modulation; "pulse-frequency controller")
Pulse-frequency modulated outputs aid control e.g.of solenoid dosing pumps. As with
PWM, PFM is output as a rhythmic signal by the relay.
The greater the calculated actuating variable, the higher the frequency of the related
contact. The maximum settable frequency 1/T is 120 min
a constant factor of the entered frequency (s. fig. 19).
Here too, two PFM relays are required for a two-sided process.
contact
t
ON
t
OFF
on
off
period T
Fig. 19: left: pulse-width modulation (PWM)
Right: pulse-frequency modulation (PFM)
3. Three-point step controller
With Mycom S, this type of control is only possible for one process side ("Up" or "Down").
With two-sided processes, either PWM or PFM must be used for the other process side.
Select this type of control for actuator drives (e.g. valves, butterfly valves etc.), which
must be controlled by means of two relays and which have position feedback. Only
actuator drives with position feedback are supported. If the "+relay" picks up, the valve
opens (flow increases) until the "+relay" drops out again. The "–relay" closes the valve in
a similar way.
The Mycom S has an internal position controller which compares the set and actual
positions of the valve, (set position from the primary controller and actual position from
the position feedback). The relay in question picks up as soon as the position error
exceeds the set switching differential X
frequently and more precisely, the smaller the X
accurate overall control. However, if the switching differential is too small, there is the
risk that the position control starts to oscillate.
For your process, you must find the optimum value between a large switching
differential which protects the actuators and a small switching differential which ensures
better control quality.
The set motor run time aids valve monitoring.
Note!
If using a driven valve, gate valve orsimilar, you must determine this motor run time
before starting with the menu settings.
4. Analogue (via current output 2, 20 mA)
The current output can be used to output the analogue actuating variable for one or two-
sided processes and cannot be combined with the method described above.
• With one-sided processes, the actuating variable range 0% ... 100%
(or –100% ... 0%) is represented on the selected current range (0 ... 20 mA or
4 ... 20 mA). The output current is proportional to the actuating variable.
• With a two-sided process, the complete actuating variable range from
–100% ... +100% is represented on the given current range. An actuating variable of
0% leads to a current of 10 mA (at 0 ... 20 mA) or 12 mA (at 4 .. 20 mA), (see fig. 20).
contact
t
ON
on
off
time [s]
. The actuator drive is controlled more
SD
selected. This also results in a more
SD
6 Commissioning
-1
. The switch-on period t
time [s]
is
ON
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