Watermanagement System for Combustion Engine Test Stands

Introduction
Due to the high utilization of the existing coolant facility, the Austrian Magna subsidiary company 'Engineering Center Steyr GmbH & Co KG' decided on a new water management system. In test benches for combustion engines, cooling water is essential for, e.g., operating the heat exchanger of the main cooling system and the eddy current brake. Closed or semi-closed cooling cycles reduce water consumption and increase economic efficiency. Concerning semi-closed systems, additives and particles evaporate less than water; the impurity of water and hence the electrical conductivity increase. Some water has to be replaced by conditioned water ('desalination') at certain levels of conductivity. Cooling systems, like micro controller equipped units for softening or conductivity control, are widely spread. However, these stand-alone solutions will not act together sufficiently. Therefore, an innovative overall control setup was designed, which meets the given demands.

System Description
FieldPoint 2000 RT was selected to ensure high reliability and expandability of the controlling unit as well as short code development time. Each bank consists of one dual channel terminal base with 4xPT100, 4x4-20mA, 2x0-10V input channels and one 16x digital output module. The control unit allows saving data locally, providing an easy data upload to a local server. A user interface is running at the local server to give information about the current and historical status or to request up/down load of data. Figure 1 shows the block diagram of the setup.

The developed control unit performs several tasks (monitoring of water level, temperature, pump pressure, conductivity, further the supply of softened water, water hardness control, regeneration of the softening unit). No further nod is required. The same master unit controls both of the independent cooling cycles. In case of emergency, each water treatment unit can supply both cooling systems. All relevant measurement data are logged automatically what enables the deduction of important trends, like the connection between water consumption and temperature.

Figure 1 Block Diagram of the Water Management System

Each cooling unit is equipped with sensors for:
· Conductivity
· Water consumption
· Water level (ultrasonic)
· Temperature
· Pressure
Additional sensors (hardness, pH-value) can be embedded easily.

To guarantee high quality refill water, each facility uses a twin tank alternating softening system. If one tank is run-down after draining the specified water volume, it is switched to a regeneration status while the other tank continues the supply. Since the required amount of refill water varies with cooling power, temperature, etc., the capacity of the softening unit usually must consider even peak requirements. By using a new innovative controlling system the unit can be scaled down just to cover the average need. Unlike many of the conventional controlling units, the developed system enables subsequent regeneration only if the brine is ready. If no sufficient time span for regeneration of the brine is provided, hard water will enter the system causing fatal consequences like calcification of the pipes and of hot surfaces of breaks and heat exchangers. Settings for either one or two brine barrels provide the fastest regeneration without any risk of overrunning the system. Through calculating the overall water hardness and operating a bypass valve accordingly, the required hardness of feed-water can be achieved.

Software Features
A watchdog function is periodically checking the regeneration process and valves. If a measurement channel provides out-of-range data a warning or error condition arises. In such case, a snapshot of all parameters is stored and an alarm (flashlight/horn) is activated. However, the internal error is cleared after each software cycle. The optical/acoustical signal is latched until it is acknowledged. To prevent loss of information due to a power failure, important data like regeneration phase or valve positions are periodically being stored at a temporary file on the flash RAM of the controller. After the device has been rebooted, the temporary file supplies all information to the controller, which continues operation at the point of interruption.

The on-line user interface (Figure 2) enables monitoring of data, which are provided by the controller via DataSocket™. They return the actual status of all channels, error messages, regeneration information, and valve status. The off-line mode displays charts and trends of historical data stored in the database. A request-for-data uploads the latest data from the FieldPoint 2000 flash RAM to the database. Through LabVIEW HTTP-Server and CGI, both interfaces can be operated by a Web browser at any workstation



Figure 2 Screen Capture of the User Interface

Several calibration parameters and limits are stored in an initialisation file. Changes of settings are made at the local server. Thereafter, the user requests a download of the new file to the controller. The controller sends a request-for-file with local and remote file name to the server, which transfers the file via FTP followed by an OK tag. The controller checks the file for validation and replaces the old initialisation file. This allows a safe update without interrupting the controller. The upload of measurement data is done similarly. For convenience, a new file is created each month; data compression and automatic size check prevent an out-of-memory of the controller.

Conclusion
This new network-based water management system is successfully in use and provides an innovative overall solution replacing the previous non-interacting controllers. The reliability of the FieldPoint RT controller together with software safety features prevents system crashes that can cause a considerable loss of production time. Fully automated measurements make the operation much more convenient, as well as time- and cost-effective by lowering personnel costs and down time. The new system supports higher water capacity at a good quality, reducing shut downs and above-mentioned fatal consequences caused by high water hardness. It enhances flexibility as each water treatment unit can supply both cooling systems by cross switching. As just one economic result, preventing complete draining of the cooling basins saves water. Furthermore, the modular setup of the system allows future extension in a low-cost manner and adaptation with regard to other facilities. Considering all these factors, up to 10% of total costs can be saved.