Sewage treatment plants are used to collect and clean wastewater from households and from municipal industrial enterprises. This wastewater is usually supplied via conduits. If the existing topography does not provide a continuous natural gradient, it may be necessary to use pumps to overcome existing height differences in several places. The proper functioning of these pumping stations must be monitored. Pump failure and blocked outgoing conduits can lead to an increase in the sewage level in the pumping station. Upstream conduit breaks result in a decrease. Continuous level measurement is necessary to detect these faults in time.
The level measurement must detect whether the amount of wastewater in the pumping station is within specified limits. If an upper value is exceeded or a minimum value is not met, there are faults in the inlet or outlet, or in the pumping station itself. Deviation from permissible levels must be reported to the control panel so that countermeasures can be taken or alarms triggered.
Pressure transmitters, e. g., type LHCR-51 or LHCS-51, are an optimal way to monitor collecting-tank levels. This sensor technology can use a 4 mA … 20 mA interface to communicate with transmitter power supplies. These trigger certain functions when a previously set limit value is reached. Typical transmitter power supplies are the compact components in the Pepperl+Fuchs STC series.
These transmitter power supplies can be used to trigger an alarm if a critical situation is detected so that appropriate measures can be taken. If the overflow of a wastewater storage tank is imminent, additional pumps can be activated automatically.
Transmitter power supplies and pressure transmitters are available for use in hazardous areas and have the relevant international approvals. Both device types are designed for safety applications according to SIL 2 as per IEC / EN 61508. Transmitter power supplies are also available for SIL 3 circuits. All devices support the 4 mA … 20 mA interface and are HART-transparent so that the field device can be parameterized via the isolated barrier.
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