by David Baginski, Telog Instruments, Inc.
December 17, 2011

Lift stations can be difficult and costly to monitor, especially when the stations are located in remote areas.

Despite the challenge, collection system operators need to monitor lift stations to track performance and obtain real-time alarms on a long list of potential problems: pump failures, wet well overflow, energy consumption, vandalism, power failures or exceeding pump temperature or vibration specifications.

An ideal system should provide real-time alarm and flow data to operations, maintenance and collections, so operators can ensure that the pumps are functioning properly and address issues as soon as they arise. In addition, an effective monitoring system should provide historic trend data to engineering and modelers, to help them understand the variables that affect station performance.

Such a system provides time-stamped event data, trend data, station flow history, pump cycle data and historical data on pumping rates and energy efficiency. Site diagnostics are also a key element in an effective lift station monitoring strategy.

With so much valuable data required to keep lift stations in top working order, an economical solution is needed to this monitoring problem. Water utilities can indeed obtain a cost-effective remote monitoring system that collects information on station operation, and provides real-time alarms and historic data on pump activity and performance.

This system shares data with interested parties over a web server or through email and SMS messages, as each recipient prefers. Operators can generate daily, weekly or monthly reports, and share longer blocks of data with third-party software including SCADA or modeling programs.


A unit monitoring a lift station
A unit monitoring a lift station

 

Remote Telemetry Units Collect and Send Data

This lift station monitoring solution uses remote telemetry units (RTUs), which collect station data automatically at intervals set by the operator. The collected data are sent over standard wireless networks to the information management system at the wastewater utility's central server.

The best RTUs for this application allow users to choose the communications technology each RTU employs to send the data to the host server: packet switched cellular, landline telephone, radio or Ethernet. The RTUs should transmit the data either at regular intervals or on detection of a station alarm, which informs central operations of a problem the moment the issue begins.

When the data reaches the information management system on the host server, it can be made available to operators in a report format or graphical presentation on a designated website. This makes the information easy to access, providing operators with the data needed to make informed decisions about troubleshooting before a malfunction leads to a flooded neighborhood or rural area. Alarm notifications can be forwarded by email or SMS, as the recipient prefers.

This application can be implemented at relatively low cost. Expenses include the price of the RTUs and installation of dedicated telephone landlines, if required; the use of cellular phone technology is significantly less expensive. Choose RTUs that run on long-lasting batteries, to limit routine site visits to once a year or less.

Event and Trend Data

Pump run times are key parameters for water utilities. Knowing the frequency and duration of each pump cycle can help engineers see changes in the lift station's operability, alerting utilities to potential wastewater increases or lift station malfunctions.

The existing SCADA methodology for monitoring pump run times polls the pump's on/off intervals once per minute or even less frequently, limiting the usefulness of the information it gathers. A one-minute variance at the beginning and end of every cycle can skew the results significantly, misleading operators into a false sense of security about the cycle's regularity.

Choose RTUs that can record and time stamp each pump's on/off event with one second resolution. Using this information, operators can compute cumulative run times and cycle times with greater accuracy, revealing issues quickly when conditions change.

Charting pump flow rate on a daily basis

Other Useful Measurements

The best RTUs monitor three types of inputs:

  • Analog signals including wet well level, temperature and vibration
  • Digital alarm inputs when generators fail or water levels exceed pre-set limits
  • Digital pulse inputs including rain gauge tip, flowmeter frequency and similar measurements

Installing sensors at the lift station for these inputs will maximize the usefulness of information gathered by the RTUs. Consider adding sensors for wet well level, pump on/off status, pump current draw, line pressure, temperature, vibration and rain levels. The RTUs can collect measurement and alarm data from installed programmable logic controllers (PLCs) as well.

Lift Station Flow Algorithm

Water utilities in hilly terrain know the challenges of monitoring their lift stations-especially those with forced mains-for potential overloads and breakdown situations. Flow measurement methods have been restricted to the use of expensive magmeters, or to complex computations using the lift station algorithm to approximate the flow without a flowmeter. Most utilities forego the calculations altogether.

Pages