Wireless options for WwTWs

Yorkshire Water has trialled a new system for the remote monitoring of filter arm rotation at its WwTWs

Southampton-based Pacscom, a specialist in wireless solutions, has been working with Yorkshire Water to improve efficiency in the operation of the company's WwTWs. Following a period of research and development, the water company has recently undertaken trials at a number of its sites to assess the suitability of a newly designed filter rotation monitoring device.

The initial Hetton Project used low-cost sensors and wireless technology to minimise the risk of compliance failure and achieved a high level of success in terms of proving the application for this technology. This success prompted the business to implement a large-scale pilot programme on eight WwTWs in the York area.

The aim was not just to minimise the risk of compliance failure but also to improve efficiency in ways of working, for example, significant reductions in site visits throughout the region by making better use of its telemetry equipment. It has been calculated site operators currently spend around 40% of their working time in their vehicles travelling to site. A 10% reduction in site visits to WwTWs across the region would result in a potential annual Opex saving of £500,000.

The Hetton Project, which has also involved WRc, has resulted in Pacscom producing a new technology for monitoring filter rotation in a totally non-mechanical contact manner. The monitor lets operators know if the filter arms are rotating properly at any time, thereby reducing the need for regular visits to more remote sites to check the functionality of equipment (Figure 1).

The existing filter rotation systems used by Yorkshire Water had proved unreliable and at the onset of the programme 74 filter monitors were already broken and required refurbishment. In the past, refurbishing conventional filter rotation monitors had met with variable success, but the wastewater business unit did not want to continue using the old technology. Proximity switches at the end of filter arms fail due to arm movement, thermal expansion and contraction and speed. Proximity switches in the centre of filters are expensive to install and require cable trenching through the filter media, reducing filter capacity which in turn could put a site at risk. As a result, they are not seen as a viable solution.

The Pacscom monitor sits on the filter arm and sends a message via radio every time the filter arm rotates. The local telemetry station broadcasts an alarm to Yorkshire Water's Regional Operation Control Centre (ROCC) when the filter arm stops rotating (Figure 2). The Pacscom 200T RM is based on an integrated magnetic sensor and a low-power radio module that reports to a receiver unit via a wireless link. The magnetic sensor is a two-axis magneto resistive device that is capable of measuring the earth's magnetic field and detecting the rotation of moving equipment on which it is mounted.

To protect against false alarms, the 200T RM utilises the standard PacsNet radio protocol. This has the additional advantage of being compatible with the current range of Pacscom's radio telemetry products. The system also supports communications healthy status and battery monitoring as standard (Figure 3). To ensure installation is quick, easy and totally wireless, the rotation monitor comes with an internal primary battery capable of powering the unit in normal operation for a minimum of three years and typically five-seven years.

Designed to operate at temperatures ranging between -15°C and +60°C, the unit is housed in an MUPVC tubular enclosure that has a solvent-bonded top cap and a removable bottom cap sealed with an O-ring to provide protection to IP68. The 173MHz VHF low-power deregulated band is used for these units. The performance of these radios in small utility plants is well proven and distances up to 1km to the receiver may be accommodated even when line of sight is not available. In order to achieve minimal overall product cost for maximum range and reliability, the 200T RM uses an integrated antenna that is tracked directly onto the PCB. The unit, which is normally in power save mode, will wake from its low-power mode every 10sec. On each wake up it will determine its current heading. Using this and previous heading data it will maintain the total number of revolutions, the current heading and the number of degrees of movement since the last reading. On the detection of each new revolution, the unit will transmit a signal to the receiver hub.

The wireless protocol uses FFSK modulation to transmit data at a raw rate of 1,200bps. The protocol incorporates a number of security functions and also includes both error detection and error correction coding to ensure reliable data transfer. There are two receiver options available, the first being a low-cost receiver designed for replacing monitoring products on existing sites. In this application the receiver outputs a pulse for each rotation, which emulates traditional methods and can be fed into existing PLC or RTU control logic.

The second option is a small works monitoring package, which offers simple logic functionality to analyse rotation and all other alarms on a site and create intelligent alarms based on site operational characteristics. This package can be configured by the user in IEC 61131 Graphical Format and is ideal where existing small works have either very basic telemetry or no telemetry at all.

David Fearnside, Yorkshire Water's project engineer, said: "Our operations team sees this as reasonably cost-effective technology to address the continual operational headache of getting reliable alarm information from filter rotation. This should provide a quick hit at improving compliance risk and also have the added benefit of reducing unnecessary call-outs." Around 25 units are currently in use on Yorkshire Water sites with the programme progressing positively - another 100 units have already been ordered by the water company.

"Although originally developed in collaboration with Yorkshire Water and WRc our company believes this device could lead to improved efficiencies not just in the water industry but within other sectors of industry," commented Mike Knights, Pacscom sales and marketing manager.


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