BDT Drainage Alarm Sensor

Smart Sensor – Sewer and Drain Solutions

Sewers & Drains

Increasing regulations around sewer overflow and extreme weather push the need for remote monitoring of sewer networks. By monitoring your wastewater and stormwater networks with RDN’s range of Sewer, Drain, Culvert, and Stack alarms you can reduce your problems related to overflow, inflow, and infiltration.


The Challenge

Sewers and drains block for a variety of reasons ranging from sewer collapse, tree roots through to the build-up of FOG and wet wipes, etc. sewers and drains in critical locations require monitoring 24/7. The frequency of blockages tends to increase significantly where there are kitchens, public toilets, and in particular baby change facilities. Early warnings of a blockage can be invaluable to businesses as they permit them to avoid spills and contamination. It also allows them to plan maintenance out of hours, in private, and out of sight of customers.

With a high population density, there is huge pressure on our sewerage networks, especially those that date back to the Victorian era. For many water utility companies, up to two-thirds of treated wastewater is inflow from combined sewers. This significantly increases operating costs and capital expenditures for new treatment works to keep up with capacity demand. As a result, many utilities release large quantities of untreated wastewater into our rivers and oceans, increasing the vicious cycle of water pollutants and contributing to more plastics in the oceans affecting nature and also us.

BDT Drainage Alarm Sensor

BDT Drainage Alarm Sensor

Our Solution

With a proven 10-year successful track record, our award-winning in-house designed and manufactured water level sensor, known as the “BDT” is a device that has been specifically designed for sewer and drain monitoring.  The BDT is a great energy-saving and sustainable alternative to ultrasonic transducers; no programming is required and the energy required is just 1/50,000 compared to a typical ultrasonic or its modern microwave radar counterpart.

The Bulk Dielectric Transducer [BDT] Technology has no moving parts and is easy to install often without the need for confined space entry teams. Normally supplied with a wireless transmitting head unit the BDT plus its radio can enjoy a battery life of up 10 years in spite of broadcasting data every 2.5 seconds. The BDT is ideal for drive-by monitoring or fixed networks where messages can be delivered to existing SCADA, remote data servers or interfaced with BMS/telemetry over distances of many km using our Network Boosters, Gateway Receivers, or Cellular Data Concentrators.

Blocked Sewer Alarm Installed

Blocked Sewer Alarm Transmitter Installed

Further, our IoT+ Dashboard provides you with a real-time visual display of live data feed which is formulated into a graph for analysis and remote monitoring.

Sentinel Receiver  Sewer Sentinel 4-Zone Receiver Data Sheet


Q. How does the BDT measure the level?

A. It measures the level of the sewage/water through analysis of the dielectric constant of the media that surrounds its body.

Q. Is the BDT immune from ragging?

A. Yes due to its ability to swing in the flow it generally de-rags naturally. Further, the active area of the BDT is kept well away from the cable using extension tubes. Because the BDT acts on the “bulk dielectric principle” it also can ignore the presence of stuck leaves and tissue on its surface. The MKII BDT introduced in the summer of 2014 has a significantly improved immunity to FOG,

Q. Is the BDT technology proven?

A. The underlying dielectric measurement principle has been around for over 80 years, the BDT however has brought the technology into the 21stCentury. Currently, there are many hundreds of BDT units in service, and thanks to the hard work of our R&D department we now have the MKII BDT, which has been in service since 2013.

Q. Can a BDT cope with washing machine foam?

A. Yes, unlike ultrasonics which can fail miserably, the BDT is designed to ignore foam and will not give false alarms.

Q. Can I use a BDT in shallow sewers/drains?

A. The BDT  is ideal for use in shallow drains as shallow as 250mm deep. The BDT doesn’t suffer from “near field dead zones” that prohibit the use of ultrasonics.

Q. Does a BDT require calibration?

A. No calibration is required the trip point is set at the receiver which operates using a “fuzzy logic” control strategy.

Q. How do we set up a BDT?

A. Setting up a BDT is very simple, in fact even simpler than a float switch. The BDT simply has to be hung at the desired trip level point. The BDT has the major advantage that unlike an ultrasonic where the beam is invisible, the BDT is clearly visible and hence can be set to a particular level simply by adjusting /coiling the support cable, etc.

Q. What software do I require?

A. Nothing at all, no field programming is required to install a BDT system they simply work out of the box.

Q. What about steps and other protrusions?

A. Unlike an ultrasonic the BDT will not give false alarms due to reflections from steps and shelves.

Q. What depth can a BDT operate?

A. BDT Lite is supplied with 4m cable lengths as standard. Extra long cabled versions can be supplied to special orders up to 6m long.

Q. Do we need to enter the sewer/drain to fit a BDT?

A. The whole concept of the BDT was to avoid confined space entry. The whole BDT can be fitted from the surface providing standard precautions are taken concerning safety restraints for personnel, tools and gas detection, etc.

Q. Is an ATEX-certified version of the BDT available?

A. The BDT  is Intrinsically Safe by design and available to order for Zone 2. Standard BDT is supplied for Zone 2 operation.

A. The typical BDT  has a projected battery life of over 10 years which has been verified by the battery manufacturer’s computations. This assumes normal UK (drainage) ambient conditions and a 2.5-second sampling rate. To date in 2017, we have not received a report of premature battery failure.

Q. Can the BDT cable be cut and re-joined?

A. Unfortunately not as it includes a foil barrier that cannot be easily re-joined.


Sales & orders

Please call your local distributor for prices on products, systems and solutions. Spares and accessories may also be purchased through our online web portal