Blocked Sewer Monitoring

Blocked Sewer Alarms & Sewer Surcharge Monitoring

Affordable, Proven and Simple to use with Real-Rime Radio Telemetry based Data & Control for Event Mitigation … No GSM or SMS after the Event Autopsy Reports!

The award winning BDT & BDT MKII Level Transducer coupled with our Ofcom licenced radio telemetry band and our Gateway receiver has made the dream of a simple to deploy and affordable means of detecting blockages or backup in clogged sewers, sewer monitoring and delivering sewer alarms. This combination permits data delivery both in real-time for real-time control and pollution mitigation and remotely back into existing telemetry and SCADA without the need for any third party software.

BDT blocked sewer system

BDT blocked sewer system

BDT Blocked Sewer Level Transducer

Unlike ultrasonic transducers that need configuration, programming and careful adjustment, the BDT works straight out of the box and the alarm depth is simply sent by curling the transducer cable. This permits in the majority of cases for the BDT to be installed from the surface thus eliminating the need for confined space entry team.

Each BDT level sensor comes complete with a radio telemetry “head unit” that contains a 10-year battery pack, controller and radio uplink that broadcasts the level status every 2.5 seconds. The whole assembly is ATEX certified and fully encapsulated to exceed the IP68 standard. It is also supplied with a stainless steel quick release mounting bracket and 4m of cable.

Wide Area Booster/Repeater

Thanks to our field deployable Booster/Repeaters we can deliver the status of BDT level sensors in real-time from almost anywhere without need for cellular coverage areas of many tens of square km.

Booster/Repeaters are available in a number of housing styles that permit them to be installed in almost any location. For street furniture we have a battery powered strap on pole mounted unit, for kerb side we have a highways approved bollard housing and for areas such as parks there is a covert booster disguised as a bird house.

The operation of the Booster/Repeater is unique, not only does it pickup the message from BDT transducers but unlike cellular sends a reassuring system check health message every 5-minutes.

Typical Gateway Receiver Connected to a Telemetry Outstation

Typical Gateway Receiver Connected to a Telemetry Outstation

Gateway Receivers and Interface to Existing Telemetry

By installing a Gateway receiver at a local pumping station or similar telemetry connected asset, it is possible to relay the status of the BDTs directly to any legacy telemetry system, SCADA or BMS system.

Each Gateway receiver is supplied with card slots that accept digital/relay cards that directly output the status of the associated BDT via its booster. Gateways are available with sufficient slots to service anything from a single BDT to up to 64 units. Spare slots in the Gateway can also accommodate cards associated with other RDN sensors such as our award winning FDT flow detection transducer that is used for CSO event duration monitoring, high wet well level alarms, flap valve position indicators or site security alarms.

Data Concentrators

Where BDT status is to be delivered to the internet or a central SCADA system directly, we offer a range of data concentrators and receivers that can be provided to emulate a wide range of protocols and similarly utilise a number of data transfer protocols from FTP, GPRS, UDP, RS232, RS485, LAN and WiFi.  File formats include CSV and JSON.

Sentinel FM - Blocked Sewer Monitoring Example

Sentinel FM – Blocked Sewer Monitoring Example – Red icons indicate blockages – Green Locations that are OK

Sewer Sentinel Receiver

Sewer Sentinel Blocked Sewer Alarm Receiver

Sewer Sentinel Blocked Sewer Alarm Receiver

Designed for installation in site manager offices or security gate houses the Sewer Sentinel Receiver can display visually the status of up to 4-BDT blocked sewer sensors as 4 distinct zones using colour changing LEDs. The LEDs are green when the level is normal and convert to red whenever the level is high or a surcharge is detected. There is also a mutable audible alarm and the option to connect and external siren or alarm via a relay.

BDTs and Their Role in Real-Time Local Control

It is publically acknowledged that data derived from deployment of BDTs has assisted in the reduction of pollution incidents. However, this is just the beginning as many customers are now using the data as past of their real-time control strategies, where for example high level alarms are used to hold off pumps or to close pollution containment valve.


For More Details please follow the link here Blocked Sewer & Surcharge Monitoring Application Note AN05-01

Simplified System Block Diagrams:

Blocked Sewer Monitoring System with Gateway Receiver

Fig 1: Blocked Sewer Monitoring System with Gateway Receiver


Blocked Sewer Monitoring via Data Concentrator

Fig 2: Blocked Sewer Monitoring via Data Concentrator with Data Via the Internet and/or SMS Text

Blocked sewer alarm system

Fig 3: Blocked Sewer Alarm System for Industrial Site with Alarm Messages Delivered to BMS/SCADA and to Security Office / Lodge


Q. How does the BDT measure the level?

A. It measures 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.

Q. Can a BDT cope with washing machine foam?

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

Q. Does the BDT provide an analogue output?

A. The BDT is a switch device and is intended to replace the countless ultrasonic that are set to just switch and alarm at a set point. Intentionally the BDT is not a level transducer.

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

A. The BDT is ideal for use in shallow drains and sewers as it can be supplied if necessary with reduced length anti-ragging tubes. 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 operated?

A. BDTs are supplied with 4m cable lengths as standard. Extra long cabled versions can be supplied to special order up to 10m 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 or UKEx certified version of the BDT available?

A. BDTs are Intrinsically Safe and available to order for Zone 2 and Zone 0/1/2 operation. Standard BDT are supplied for Zone 2 operation, Zone 1 & 0 BDTs are subject to surcharge.

Q. What is the typical life of a BDT?

A. The typical BDT has a projected battery life of over 10-years which has been verified by the battery manufacturers computations. This assumes normal UK (drainage) ambient conditions and a <2.5 second sampling rate.

Q. Can the BDT cable be cut?

A. We do not recommend cutting the BDT cable. The cable is a special high quality cable that includes a foil EMC screen which makes it difficult to splice. Therefore we state that cable cutting will invalidate the product warranty.