Technical Terms - ProMinent DULCOMETER D2C Operating Instructions Manual

9

Technical Terms

Calibration:
Solenoid valve:
Zero point:
Slope:
Set point:
Regulated value:
Control parameter: The control parameters (xp, Ti, Td) determine the control characteristic (PID).
Manual control:
xp value:
Ti (integral
action time):
Td (differential
action time):
Metering direction: This value determines in which direction the controller is active. In case of the
Additive base load: This results in the fact that the controller always generates a manipulated value
Relay:
22
By calibrating (adjusting), the measuring value readout will be adjusted to the actual
probe signal. Without calibration, a correct measurement is not possible. A calibration
should be performed regularly (depending on application).
Activation of solenoid valves (motor-driven pumps) is defined by the cycle time and
the minimum on-state interval (minimum time) (pulse length control). The on-state
interval always corresponds to at least the minimum time. However, it is increased up
to the cycle time at a maximum depending on the control deviation and the control
response. The cycle time itself defines the maximum possible on-state operations.
For instance, an actuator is switched on a maximum of 60 times per hour when the
cycle time is at 60 seconds. The minimum time defines the minimum on-state interval
duration. It should be selected as small as possible while, however, ensuring that
metering is still possible within this time.
The zero point of pH probes is theoretically 0 mV. In practice, for a good probe
function a zero point of ± 25 mV is acceptable.
The zero point of chlorine probes is 4 mA. A calibration is not necessary.
The slope of pH probes should always be ≥ 50 (better: ≥ 55) mV/pH. The slope of the
chlorine measuring cell is given in mA/ppm. For a good probe function, the values
accepted by the controller are sufficient.
The set point is the value which is to be continuously maintained stable throughout
the process via controlling.
The regulated value is the value (e.g. frequency, mA signal) the controller sends to the
final controlling element (e.g. metering pump) to reach again the set point.
In this setting, the controller produces a controlled variable corresponding to the
entry. It is retained up to the next change. It is independent of the measured variable
and the set control parameters. This setting can be used for determining the time
response (e.g. dead time...) of the controlled system.
This value influences the proportional control behaviour. In case of a deviation of 1.4
pH (=10 % of 14 pH) or 0.2 ppm (=10 % of 2 ppm), a xp value of 10 %, for example,
leads to a regulated value of 100 %. If the xp value has to be increased to 20 %, the
deviation must be double the value in order to reach a regulated value of 100 %. In
case of control overshooting, the set xp value must be doubled.
This value defines the integral (I) control behaviour. The greater Ti, the lower the
I proportion.
This value defines the differential (D) control behaviour. The lower Ti, the lower the
D proportion.
metering direction "acid", the controller generates a manipulated value when the
specified value for pH is exceeded.
corresponding to the additive base load. This load may only be reset to 0 using the
stop button. This function should not be activated when using PI or PID controllers.
The relay (alarm, limit relay) switch when the corresponding prerequisites (e.g. alarm
condition, limit violation) are given. The relay function can be set either as make
contact (active closed) or break contact (active open). The relay may be reset pressing
the stop button. (Exception: limit value).