Smart Waste Water Treatment with MultiSmart’s PLC Extension

Praveen Karunambaran — Sun, 15 Feb 2009 06:59:14 +0000

Recently, we have received a purchase order from a customer regarding a lift station (pump station) application for odor reduction for their sewage treatment plant. The sewage pit, as you all might know, fills up very quick during the morning as well as in the evening and is very slow during the late nights. For odor control the customers are dosing SulfaLock into the waste water pit depending on the flow rate. After observation of the pit for a few weeks the customers came up with a diurnal curve, which is to be followed to control the dosing. They also wanted the ability to change the data values for the diurnal curve, as and when the statistical data corresponding to the flow in the sewage pit in a day changes.

The diurnal curve is shown in the figure below. The output rate required is plotted against the time of the day in minutes.

Diurnal Curve - Waste Water Treatment

This unique RTU application requires custom programming which can become quite cumbersome when having to start from scratch. MultiSmart, having most advanced pump station management technology and the PLC extension built in, made this custom application development look very simple. With support for DNP and MODBUS communication, which are the popular communication protocols used in Water and Waste Water Treatment Telemetry, and the integrated 1000 plus tags related to Pump Station Management statistics it was extremely easy to configure the communication.

The functionality is programmed into the MultiSmart with the help of the PLC extension. More information about the PLC programming within MultiSmart is described towards the end of this blog. Data points at every hour mark is identified from the diurnal curve and saved to the parameter profile of the PLC program. This has the added advantage that the data values can be changed at any time without any change to the program whenever desired. However there are security measures in MultiSmart which will restrict any unauthorised access and modification to these parameter values which can affect its operation.

The PLC program looks at the current system time, calculates the value of the data point with respect to the diurnal curve and generates a corresponding output to the Analog output of the MultiSmart which is driving the dosing pump. The Analog output events were logged against the time using the built in Event Logger functionality in MultiSmart and we got the following result (graph plotted in Excel) when operated for nearly 20 hours.

MultiSmart Analog Output

The output stayed well within the expected range and was steady. The whole application was developed and the initial test was carried out successfully in less than 7 hours.

Brief Overview of MultiSmart’s PLC extension, ISaGRAF

ISAGRAF is a control software environment which supports all of the internationally recognized IEC61131-3 control languages and offers a combination of highly portable and robust control engine. Support for the latest release, version 5, of the ISaGRAF is available in MultiSmart.

This PLC extension of MultiSmart allows system integrators and end-users to further enhance or adapt the capability of MultiSmart. The product has enormous amount functionalities built in, but there are always customers or applications that push the envelope. The product has 1000s of tags, and System Integrator’s or End-Users can now interface to these with the PLC engine. This means they can extend the capability without having to rewrite existing functions.

The ISaGRAF implementation of IEC61131-3 is added because it is the most proven platform and v5 is chosen as it offers a number of advantages over v3. One example is the ability in v5 to run different ‘resources’, or applications, at different rates to allow more critical applications to run more frequently.

A sample ISaGRAF program using function block diagram is shown below. The capability to show the run time statistics, including the values of variables, in the MultiSmart faceplate helps immensely in the development of the PLC program and in troubleshooting.

Example of ISaGRAF PLC Program with Fucntion Block Diagram for MultiSmart

The ISaGRAF TIC code can be dumped straight into the MultiSmart directory structure, which enhances the easiness in portability.

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Smart Waste Water Treatment with MultiSmart’s PLC Extension