| ||
| ||
Case Study: Tank Level and MODBUS
IntroductionAt Anasazi Trails Water Plant (New Mexico), an industrial PLC is controlling the water plant and collecting instrumentation reading. A third party data logger was used to monitor the water level in two tanks near by but it has been burned out by the electrical surcharge. Anyway, the third party logger had some limitations so now was the time to upgrade. The plant is often left unattended, so there is a need to send real-time alarms to an operator in case of emergency. There is also a need to pro-actively monitor the tank levels as well as the operations of the plant. ObjectivesReplace the old logger with new one that will perform following operations: Monitor the water level in two tanks as the old unit used to do. The wires and transmitters were still in order. Interface the PLC to get critical data and signal values. Perform historical logging of data that can be used reports and analysis. Issue an alarm in case of emergency. Solution
A Borynet Data Control Server (DCS) has been chosen to for a logger with support of U3 DAQ and MODBUS module. The 4-20 mA tank level signals from the old unit was fed to the U3 data acquisition unit. Another two digital signals representing working states of two well pumps were also connected to U3. Additionally, the water plant PLC has been connected directly to the DCS with a null modem serial cable. The PLC has been setup as MODBUS Slave (server) to respond to new data logger requests. The data logger, on the other hand, has been configured to query around 50 most critical signals (coils and registers) from the PLC: such as pressure, flow, turbidity, chlorine level, process states, valve states, exceptions codes etc. With a total of around 60 signals, the DCS Server was configured to save data in two archive logs: the hourly averages and summaries were saved in the daily files and the daily averages and summaries in monthly files. A consumer type of Internet Service (DSL) with one static IP was ordered for the site with a local ISP. Borynet company has helped to configure the provided router such as firewall and forwarding services to allow for reliable and secure access to the DCS. As a result, the operator and administrators of the facility were able to access the DCS services remotely . The built-in web site provided window on day-to-day status operations. Additionally, it allows for easy download of data log files to a PC. Several signals have been configured for real-time email emergency alarms. Among email addresses used where included some cell phone numbers. When tested, it took only several seconds for an alarm message to reach the cell phone. ConclusionsA modern solution reaching to older PLC and traditional electrical signals was an instant success. The BORYNET DCS acts like true modern gateway to existing infrastructure. Note, that the access to the PLC is extremly save due to the fact that the DCS acts as a sencondary firewall and read-only MODBUS over a serial cable. In summary, the users benefit from interactive information. The real-time alarms
protect the plant and minimize its down time and save the maintenance costs.
As one of the user said pulling the DCS status web site in his I-Phone:
| ||
|
