Haigh Engineering Streamlines Screening Design with Level Transmitter

June 1, 2007
Haigh Engineering Company Ltd., founded in 1955, designs and manufactures waste disposal systems used by the wastewater industry, hospitals and care homes, catering establishments, shipping and other applications.

UK inventor of the Tweeny incorporates a SITRANS Probe LU level transmitter from Siemens Milltronics to improve performance of more advanced wastewater systems, in which inlet screens require constant monitoring of water levels to ensure proper flow into the plant.

Haigh Engineering Company Ltd., founded in 1955, designs and manufactures waste disposal systems used by the wastewater industry, hospitals and care homes, catering establishments, shipping and other applications.

The company, based at Ross-on-Wye in Herefordshire, made the first British waste disposal unit called the Tweeny. ISO 9001-2000 registered, it’s a technology leader in its field. Haigh uses computerized 3D design modeling and the latest in manufacturing techniques against tight tolerances to ensure consistent performance and reliability. Ease of installation, service and maintenance are all designed into the equipment. It maintains strict control over manufacturing from raw materials to finished product by maintaining a modern machine shop with CNC lathes, laser cutting, fabrication, welding facilities, paint spraying and post-production capabilities - all onsite. Many products are now exported worldwide.

One major product line is inlet screens used in wastewater treatment plants to filter out solid wastes. Haigh manufactures a range of inlet screens and supplies many of the major UK water plants. A key feature of modern designs is streamlining installation by pre-wiring equipment before delivery to a customer’s site.

Inlet screens require constant monitoring of upstream water levels to ensure a proper constant water flow through the screen and into the plant. A rising water level indicates blockage by debris that needs to be raked. Water levels can change rapidly, making accurate, reliable readings of level and rate of change essential. Previous Haigh designs used a transducer and separate pump level controller, but this duplicated functionality Haigh already had incorporated into its control panel. The controller relays were interfaced with slave relays, making the panel more complex and costly than desired.

In 2004, Haigh chose to simplify the design of its inlet screens and wanted a straightforward, compact level device that would connect directly with the central panel.


Working with Siemens, Haigh selected the SITRANS® Probe LU transmitter to complement the new design philosophy. The unit is a 2-wire, loop powered ultrasonic transmitter introduced by Siemens in June 2004.

Space is tight in these new streamlined screen designs. This probe has a compact design, with sensor and electronics in the same small enclosure. It’s easy to install, with a swivel head that aligns with conduit for easy wiring and adjusts for optimal visibility. The 4-20 mA signal feeds directly into the main panel. It offers a high signal-to-noise ratio and patented Sonic Intelligence® signal processing for superior reliability.

The level transmitter’s narrow beam angle allows Haigh to position the sensor exactly where it’s needed for the customer’s particular application. ATEX Intrinsically Safe approved units are available to meet customer requirements.

The probe is easy to set up on site with as few as two parameters. And an infrared handheld programmer makes it easy to program from up to a meter away. This is a big advantage over a fixed keypad that may be difficult to access. A built-in alphanumeric display is visible through the transparent lid. For the operator, this convenience means no need to open the lid and expose electronics to the application environment.

Cheriton Fitzpaine Sewage Treatment Works in Devon, England
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Inlet screens are outdoor installations, so weatherproof equipment is essential. The probe is weatherproof IP68 and has a UV-protected display suitable for operation in direct sunlight. It also features built-in temperature sensor to compensate for temperature swings in the application.


“Using the Probe LU, we simplified our design and wiring in a way that reduces cost but also improves value to our customers,” said Bob Dean, Haigh contracts engineer. “This new panel has no complicated wiring loops and no interposing slave relays, just a simple 4-20 mA fed into a small PLC and an HMI screen on the panel. It meets our customers’ need for compact design and reliable measurement, as well as the need for reduced production cost. We have now standardised on Siemens Milltronics level instruments for these applications.”

Author’s Note: Melissa Moroney is a marketing communications specialist at Siemens Milltronics Process Instruments Inc. in Petersborough, Ontario, Canada. Specializing in ultrasonic, radar, capacitance and electro-mechanical level measurement devices, it’s a unit of Siemens Automation & Drives. Contact: 705-740-7016 or www.siemens.com/level