16
3.2.7 Measuring unit for control value
Operation with PFU 2000 RAM / PMU 2000 settings:
If the signal transmitter used features a measuring unit different
from the one in the presetting, an alternative measuring unit can
be selected (display 213). The measuring unit selected will auto-
matically be changed in the relevant displays, but the measuring
range of the signal transmitter will not be converted automatically.
It is also important to convert and set the output signal as well as
minimum and maximum values of the signal transmitter operating
range (displays 219 and 220).
The following measuring units can be selected:
1. Differential pressure:
m, Pa, ft, kPa.
2. Differential temperature:
K, °F.
3. Temperature:
°C, °F.
4. Flow:
m
3
/h, l/h, l/s, gpm.
5. Level:
m, cm, ft, in.
6. Open loop:
%.
7. Pressure:
bar, mbar, psi, kPa.
8. Pressure with pre-pressure
measuring:
bar, mbar, psi, kPa.
Operation with PFU 2000 EPROM settings:
See section 6.3.1 PFU 2000 DIP switch settings.
3.2.8 System time
System time is an adjustable parameter to adapt the behaviour of
the controller to the hydraulic system (display 204). System time
is defined as the time that passes from a change in pump speed
is made until the measured value reaches approx. 70% of the cor-
responding final change.
Operation with PFU 2000 RAM / PMU 2000 settings:
With the control parameter “pressure”, the recommended setting
is 2 secs.
A lower setting involves the risk of hunting.
A higher setting causes delays in reaching the setpoint.
The setting range is 0.4 to 800 secs.
Operation with PFU 2000 EPROM settings:
The default setting is 2 secs.
Fig. 18
1. Final value after a jump in speed.
2. Actual value.
3. System time.
Time
H
3.
70%
100%
1.
2.
System time
TM
00 79
92 229
6
3.2.9 Minimum switching sequence
Minimum switching sequence is the time between two switchings
(on/off of pumps).
Operation with PFU 2000 RAM / PMU 2000 settings:
To prevent hunting in the system and to limit pressure and current
surges, a minimum time between switching the individual pumps
on and off can be set (display 205).
The higher the set value (sec.), the bigger the risk of differences
between setpoint and actual value.
In order to avoid that the “actual value” exceeds “max. limit”, the
minimum switching time is temporarily set to 1 sec. if the actual
value exceeds the mean value between “setpoint max.” and
“max. limit”.
The setting range is 2 to 300 secs.
For further information, see section
3.1.4 Cascade control.
Operation with PFU 2000 EPROM settings:
The default setting is 5 secs.
3.2.10 Medium switching sequence
Medium switching sequence is the time that describes the maxi-
mum number of switchings (on/off of pumps) per hour under nor-
mal conditions.
Operation with PFU 2000 RAM / PMU 2000 settings:
This setting is only possible on service code level.
In case of frequent starts and stops, this function prolongs the op-
erating time of the pump in order not to exceed the permissible
number of switchings.
The medium switching time (sec.) to be set is calculated as
3600 s/permissible maximum number of switchings per hour.
Unnecessarily high settings may result in differences between
setpoint and actual value. This can be avoided by accepting more
frequent pump changes.
In order to avoid that the “actual value” exceeds “max. limit”, the
medium switching time is temporarily set to 1 sec. if the actual
value exceeds the mean value between “setpoint max.” and
“max. limit”.
If the medium switching time is effective with a mains-operated
pump in operation, the actual value may exceed the setpoint set.
In addition, the medium switching sequence influences the
changeover to on/off mode at low flows.
The setting range is 2 to 300 secs.
For further information, see section
3.1.4 Cascade control.
Operation with PFU 2000 EPROM settings:
The default setting is 5 secs.
