Stormwater treatment: Flow, Level and Pressure Measurement

Published: 12 February 2020 - 10:30 a.m.
By: Baset Asaba

Level and pressure applications in storm water treatment may look simple but do have some challenging cases where traditional sensors like ultrasonic sensors for measuring the level can be unreliable. Users managing such plants would prefer to have one simple and reliable technology to cover most measurements

Typical applications in storm water treatment where the level is measured are usually storm water retention basin and open channel flow measurements. In case of heavy precipitation, excess rainwater is temporarily stored in open, artificial reservoirs. The water reservoir buffers the drainage and the water is pre-cleaned through natural settlement. Continuous level data are the basis for calculating the flow through the sewer system and thus protecting against flooding. Further, if combined sewer systems are used for both sewer and rain water, the measurement can face some tricky limitations due to foam, debris and hazardous gases

Newer technologies can improve the reliability of these measurements and how the latest features can bring value to newer designs.

Improvements in measurement:

Traditional instruments offered are ultrasonic, bubblers or hydrostatic level transmitters for measuring level. Radars are definitely the best solution in the market, and it has just started to gain its appeal in the water industry.

Level transmitters signalling erratic readings or providing unreliable measurements both causes an alarm in measurement. It not only needs to work perfectly throughout its lifetime but also should gain confidence of the operators to make sure the right decisions are made for control.

Such is the case in detention tanks and other similar applications. Ultrasonic level transmitters have been occupying their fair share of the market over the years, but as other technologies have been evolving ultrasonic sensors are slowing losing their preference. This has been mainly due to performance issues in certain conditions that pose in front of the sensor.

Not every installation can be made ideal for ultrasonic sensors since the ambient environment cannot be controlled. Pressure and temperature variation create a deviation in its measurement. Condensation on the transducer or foam fail disturb the perfect condition this technology demands for measurement.

Being blinded by the condensation or by seeing no reflection from the foamy surface, would just make the sensor fail. Hydrostatic level transmitters which convert the water head into level, offer a better performance as long as the density remains the same.

Dangers of Overfilling

The lack of dead zones in hydrostatic sensors makes it an obvious choice for reliable measurement, but a non-contact instrument is more appealing due to the convenience of having a single stock item. Ultrasonic sensors have a definite dead band which under certain conditions like flooding, would pose a serious threat. For ultrasonic technology , as the water level comes close to the sensor, the processing power of the electronic will not keep up to analyse the transmitted and received signal.

This creates a dead zone in the near range. Hence, when the product reaches this area the values are driven to a fault, making the operations blind. The effects could be even more adverse, when the sensor misunderstands a far-off false reflection as a product and considers this as a measured value. This means when the tanks are overflowing, the sensor would be showing an empty tank. Only after experiencing the outcomes of such a situation could we comprehend how dead zones makes a huge deal in the safety of such applications. Non-contact radars on the other hand have almost no dead zones and have overcome the issues from condensation and foam. Radar waves unlike ultrasonic frequencies have the capability to penetrate through any material except metal.

Radar level technology has been there since the 80s. But due to the price and size it was not widely used in water applications. This technology was previously sought for demanding applications with higher pressure and temperature.

However, as the installed volume of this technology had increased, it became feasible to drive down manufacturing costs and improve the performance-to-size ratio.

The breakthrough for radar to measure all applications was to develop VEGA’s 80Ghz radar in 2014. Combined with a fast paced evolution in electronic development, VEGA has been able to downsize the whole electronic to a small chip. This helped VEGA to bring the powerful performance of its radar to its newer compact designs launched in 2020.

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Compact VEGAPuls 80 ghz radars with controllers

Narrow spaces and water resistance

Take for instance, manholes where the flow rates are measured. On an event of heavy rains, as the flow rates increase the water level in the channels increases as well. Level transmitters are installed to measure this change in water level to determine the flow rates.

Ultrasonic sensors with its broad beam angle have to be carefully installed to avoid internals like ladders and internals. Being closer to the channel would be preferred here.

On an event where the manholes flood, if the sensors are not waterproofed they would easily be damaged. Being an 80 Ghz radar, the VEGAPuls C11,21 and 23 are available with a beam angle as low as 4 degree and have been designed with a IP68(3bar) rating with such applications well in mind.

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Flow measurement in Open Channels using the Puls C23

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Battery powered dataloggers measuring level using the VEGAPuls C21

Bluetooth for Wireless Adjustments:

Such measurement locations are mostly inaccessible; making device maintenance and configuration difficult. Bulky field communicator or laptops are now a thing of the past, as every VEGA sensor is enabled with Bluetooth.

Since 2016, VEGA has been innovating in Bluetooth connectivity. With measured values and configuration parameters made available wirelessly through a secure app, users can easily troubleshoot and maintain devices in any inaccessible location. Bluetooth in combination with the low powered electronics makes these devices ideal for IIOT solutions.

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Wireless Configuration using VEGATools App

The foray into IIOT

Remote measurements where no infrastructure is available pose a challenge of having no power nearby. Instruments can be battery powered, but then the lifetime would be limited according to the number of measurements needed per day. If the sampling time is high, the battery life would shorten drastically. This depends on what the application demands.

What we often overlook is the start-up time the measuring technology has. If sensors have a long start-up time, the power consumption would increase as the battery needs to maintain the supply during the entire start-up and measurement cycle.

With the newer 80 Ghz possible to start and measure within 10 seconds, the demand on power have drastically reduced making them ideal for any data loggers or remote terminal systems. VEGA’s famously designed CERTEC pressure transmitters are available in the same designs with the same features of low power and Bluetooth connectivity for IIOT implementation.

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VEGABar 38 with abrasion-proof Ceramic measuring cell

With reliable radar level and pressure transmitter, now made available in compact and lower priced versions, it has become affordable for users to deploy smart instrumentation very easily on any point of interest.

All it takes today is to get a radar which doesn’t burden the budget, setup the device using a smart phone and have the measurement right away on the SCADA. For remote sites, VEGA can also assist in getting the devices connected to the control centre using VEGA’s Data server capabilities

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