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MicroPM™

Continuous Pump Performance Monitoring System for Water Utilities

Benefits
  • Real-time data for the operating points of every pump

      - Select pump combinations which operate close to their Best Efficiency Point (BEP), and within the Preferred Operating Range         (POR)

 

  • Rapid identification of pump system problems, under all operational conditions

      - Without continuous condition monitoring, problems such as excessive wear, operation outside the POR, cavitation, and air                entrainment, can go unnoticed for many months or years

 

  • Preferentially operate the most efficient pumps

      - In a pump station, there is usually a spread of several % in pump efficiency, from one pump to another. The accurate                       efficiency measurements enable preferential selection of the most efficient pumps

 

  • Performance-based maintenance - Payback times for refurbishment easily calculated

 

  • Readily interfaced with PLC / SCADA and/or HMI – expert firmware is included within the MicroPM, so SCADA development and maintenance costs are low

 

  • Flow meters for each pump, with low uncertainty

      - Calibration of sensors can be checked on-site

      - True mass flow rate, independent of velocity profile, pipe configurations, build-up, cavitation, and air entrainment

      - Lower cost than alternatives for retrofitting to existing pump stations

      - Low construction and pipework costs for new pump stations

      - Volume flow rate calculated automatically

 

  • An essential component of pump control systems

Measurement technique

The basis of the technology is the measurement of the differential fluid temperature across each pump to an accuracy of better than one-thousandth of a degree, with long term stability. This information, together with the differential pressure across the pump, enables the pump efficiency to be calculated, from the change in enthalpy. The power supplied to the pump is also known, and the combination of pump efficiency, total head, and pump input power provides accurate flow rates.

The standard MicroPM comprises of:

  • 2 temperature probes, thermowells, fittings, and cables

  • 2 or 3 pressure probes, fittings, and cables (a 3rd pressure probe can check for valve problems, and measure the pressure near the discharge manifold)

  • A microprocessor, for collecting and analysing data. This can be in a separate waterproof enclosure, or in a module for DIN rail mounting

  • Electrical power meter. This can be an existing or new meter

  • Speed information, for pumps with variable speed drives. Speed can be supplied by either existing or new sensors

 

The MicroPM SCADA interface is via MODBUS TCP, MicroPM being a slave device. Information is held in specific registers that SCADA can read from and write to. SCADA then handles the retrieved data as required, presenting the information to operators in the most appropriate way and populating historian databases.

 

In addition to providing thermodynamic data, self-testing of both system level parameters and pump level parameters have been included in MicroPM. All self-test results are available to SCADA which help to minimise the SCADA development required and allows SCADA to promptly flag issues needing operator attention.

 

The MicroPM connects via wired Ethernet, though the subsequent network is not limited in any way, and can be either wired or wireless.

MicroPM also provides an embedded web page interface that is accessible to any suitably networked device that has a browser. This interface is used primarily for initial setup and configuration but also allows for status checking and live data monitoring, via a number of ways including the comparison to pump curve data.

Embedded web pages for easy access to live data, and initial set-up

Here is a web-page display of a data set, in US units (metric units can alternatively be selected). This web-page can be viewed on an HMI.

Typically, 20 samples will be counted over a minute, and then the averages and standard deviations will be calculated.

Standard deviations of data sets assist with the identification of issues such as unstable suction water, cavitation, and air entrainment.

MicroPM is programmed to only provide averaged data if acceptable stability criteria are met (threshold levels are adjustable).

Operate pumps close to the Best Efficiency Point

The data for each pump can be automatically compared with manufacturer’s data, to check that it is operating within expected parameters. For a real-life example, see the above section from an embedded webpage, which provides a graphical ‘at-a-glance’ summary of pump performance. The X-axis is flow rate, and there are 4 parameters displayed on the Y-axis:

 

  • Pump efficiency (blue) – a slight fall here

  • Total dynamic head (pink) – spot on

  • Electrical power (red) – increase due to loss in pump efficiency

  • NPSHa (green) – well above the requirement
     

The curves are manufacturer’s data, and the coloured dots show the current operating point. The two vertical lines define the Preferred Operating Range (POR), which is typically the flow rate at the BEP -20% and +10%. According to ISO/ASME standard 14414-2015 “Pump system energy assessment”, the vertical lines define the points at which the Mean Time Between Failures (MTBF) is cut in half, compared with a maximum value at the BEP. Operating outside of these limits rapidly increases the probability of pump failure, cavitation, and recirculation, and reduces the life of bearings and seals.

The operating point of this pump is close to perfect, it is within the POR, and only -2.8% lower than the Best Efficiency Point (BEP) flow rate.

 

Actual data is also scaled to a manufacturer’s speed, using the affinity laws. Here, the data is for a fixed speed pump and the scaling factors are unity.

 

A cursor can be moved over the graph to obtain real values, in place of the xxxxx shown above.

Expert firmware within the microprocessor

MicroPM provides an embedded webpage interface that is accessible to any suitably networked device with a browser. This interface is also used for initial setup and configuration. It allows for status checking and live data monitoring, via a number of ways, including the comparison to pump curve data shown above. The MicroPM connects via wired Ethernet, though the subsequent network is not limited in any way, and can be either wired or wireless.

 

The MicroPM SCADA interface is via MODBUS TCP, MicroPM being a slave device. Information is held in specific registers that SCADA can read from and write to. SCADA then handles the retrieved data as required, presenting the information to operators in the most appropriate way and populating historian databases.

 

In addition to providing thermodynamic data, self-testing of both system level parameters and pump level parameters have been included in MicroPM. All self-test results are available to help to minimise the SCADA or HMI development required, and promptly flag issues needing operator attention.

Ease of installation and commissioning

-Fit thermowells/ fittings

-Mount microprocessor enclosure (either free-standing or DIN rail) and power supply

-Fit temperature and pressure probes (and tachometers, if required)

-Run probe cables back to enclosure

-Run ethernet cable from enclosure to PLC/ SCADA /HMI

-Mount panel power meters into control console and wire up

 

Interfaces can be developed/ tested in parallel by communicating with a remote MicroPM via the Internet

Extract from ISO/ASME standard 14414-2015 (Pump System Energy Assessment)

© ISO and Standards Australia Limited. Copied by Robertson Technology with the permission of ISO and Standards Australia under Licence 1611-c014

Temperature and pressure probes fitted to the discharge side of a pump

Energy costs and maintenance

There is often a wide discrepancy between what a pump station was designed for, and how it is actually operated. For example, in a large-scale pump performance and efficiency testing program using our equipment, involving more than 150 water pump tests in 8 municipal water supply and distribution systems, the average decrease in pump efficiency between the manufacturer's original Best Efficiency Point (BEP) and actual point of operation in the field was 12.7%.

 

Not only does this raise energy costs, but maintenance costs are also sharply increased, when pumps are operated outside the POR.

 

For minimization of both energy and maintenance costs, pumps should be operated close to the BEP.

Use of low mass thermowells for temperature sensing in pipes

Thermowells are essential for accurate and continuous temperature measurement, to minimise vibration heating, mechanical stress, and stem effect. For a fuller discussion, see the technical paper “IMechE Site Testing June 2013”. 


When testing with portable units, compromises are often made, and immersion temperature probes are inserted into the fluid via gate or ball valves. This method is prone to measurement error due to vibration heating. If used for continuous monitoring, the mechanical stresses may eventually lead to metal fatigue and fracture of the temperature probes.


Immersion temperature probes used for continuous monitoring will also attract mineral deposits, making it difficult to remove the probes.


For wet sump applications, a thermowell is not required for the suction temperature measurement.

Example Configurations

MicroPM has been installed on all pumps in this pump station