Hach-Lange WTOS P-RTC - Manual (Page 8)

8
General Information
2.2 Areas of application
The RTC101 P-Module is a universal open-loop control and closed-loop control unit in
waste water treatment plants for automatic precipitant metering for phosphate
precipitation.
Depending on the operating situation, the precipitant dosage can be based on measured
values in the influent or effluent or based on profiles. The system automatically selects the
best possible strategy. The user is able to make restrictions manually.
2.3 Functional principle
In the following, a distinction is made between the open-loop control and the
closed-loop control of the precipitant concentration.
For the open-loop control of the precipitant dosing, the measuring point for the
phosphate concentration is upstream of the precipitant dosing point.
For the closed-loop control of the precipitant dosing, the measuring point for the
phosphate concentration is downstream of the precipitant dosing point.
The measuring point for the flow rate is usually located in the influent of the waste water
treatment plant. At the measuring point, the actual flow rate (influent quantity and
recirculation - e.g. RAS, MLR, etc) is determined via further entries in the RTC module.
If the measured values for the flow rate quantity and/or phosphate concentration are
temporarily not available (e.g. due to a malfunction), the system automatically refers back
to saved profiles.
Connect the following input signals on the control unit in order to make optimum use of all
system functions:
• Flow rate, measurement signal 4–20 mA
• Fault indicator signal of the flow rate measurement (230 V AC or 24 V DC)
In the event that measured value failures are not signaled according to NAMUR 43, as
the values are below the 4 mA threshold.
Note: If these signals are not available, the equipment operates with limited functionality.
• sc1000 controller with PO
4
P PHOSPHAX sc analyzer.
The measured value is adopted directly.
• Dosing pump for the precipitant
The dosing pump is continuously actuated via a 0–20 mA or 4–20 mA current loop
signal as well as via a changeover contact. If the dosing rate is below the minimum
precipitant flow rate of the pump, the system automatically switches to pulse/pause
mode.
N O T I C E
The use of an RTC Module does not release the operator from the duty of care to the system. No
guarantees as to the functionality or operational safety of the system.
In particular, the operator must make sure that instruments connected to the RTC
open/closed-loop controller are always fully functional.
To make sure these instruments supply correct, reliable measurement values, regular
maintenance work (for example, cleaning of the sensor and laboratory comparative
measurements) is essential! (Refer to the user manual for the relevant instrument.)