0191 5131313 | hello@siris.co.uk
0191 5131313 | hello@siris.co.uk

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Use of Contact and Non-Contact EDMs (Event Duration Monitors)

The subject of Event Duration Monitoring has gained prominence over the last few years, with water companies investing in new and improved monitoring in response to changing legislative requirements – often referred to as U_MON3.


Working to support our clients with event duration monitoring is just one of our daily services – and one of the questions we are often asked is why contact EDM solutions are not our first choice or preference. 



Given the often inexpensive outlay and historic role in the industry, they can appear an attractive choice.  However, there are a number of issues when using contact EDM devices that can impact both the accuracy and consistency of the data, as well as the ongoing operation of the device itself.



In this article, we explain the typical shortfalls seen with contact probes and how EDM systems can be better built to ensure reliable data is provided to the regulator.

What is Event Duration Monitoring?

An “event” in the world of flow measurement means an “adverse weather event” (most commonly a storm), which has the impact of increasing flow through a Sewage Treatment Works (STW).

All STWs have a maximum limit of flow that they are permitted to treat. This is known as Flow to Full Treatment (FFT) or Flow Pass Forward (FPF). If the flow within an STW exceeds this limit during a storm event then it is allowed to overflow into a storm management system and/or discharge straight into a river.

However, there are instances where an STW may discharge to a storm management system/river before the maximum limit is reached, or even for a reason not related to a storm event – for example, as the population and communities that they serve grow, STWs may increasingly find excess demand on their original flow capacities – risking more frequent breaches of their permitted FFT.

Event Duration Monitoring (EDM) enables the water utility provider to keep a reliable record of all instances of overflows spilling.  Combined with other data (such as weather conditions and the volume of flow going forward to treatment at the time of the event), this can be presented to the regulator as evidence of a storm event being within the site’s permit condition.  If it is outside the permit condition, then the water utility provider has the benefit of better quality data to make changes to the site and prevent further early spills.

In 2018, the Environment Agency announced a series of measures designed to better monitor Flow to Full Treatment, which included the requirement for water companies to install EDM monitoring by 2025. The Government also announced further measures to ensure STWs are not relying on storm overflows outside of storm events.

EDM probes - non-contact ultrasonic EDM probe above single storm weir.
Non-contact ultrasonic EDM probe above single storm weir.
Contact probes missing storm event.
Contact probes missing storm event.

Fluid Contact or Non-Contact Probes for EDM?

Any EDM system used at an STW or pumping station must be able to accurately recognise when an overflow is taking place and an “event” is being triggered.

The vast majority of typical Event Duration Monitors can be classified as either contact or non-contact (which can use an ultrasonic or radar sensor.) 

The Event Duration Monitor’s job is simply to record an “event” when the fluid level begins to pass to storm management overflow, typically over a storm overspill weir.  The setting of the “event” requires precise calibration and adjustment in terms of both the physical installation and the the Event Duration Monitor’s programmed settings.

How a Contact EDM Works

A contact EDM typically consists of two probes that provide a switched status output to an external system when the fluid level reaches the overflow point.

Issues When Using Contact Probes for EDM

It is difficult to set the probes to the required uncertainty level of +/- 5mm

Often on sewage treatment works it is physically difficult to set the probes to the required ±5mm uncertainty level, which could likely result in a confined space entry and/or isolation of a live sewer channel.  The use of a non-contact EDM device eliminates these safety risks.

Contact Probes are Susceptible to Damage in this Application

The nature of wastewater flow means that objects in the stream can hit and damage the probes, potentially bending them so that they are no longer correctly positioned.   


False alarms can also be triggered by objects such as rags becoming entangled in the probes.

Calibration is not Possible

It is difficult to find any reliable reference point for the calibration of the system given the way it is set up, bringing doubts to the accuracy and reliability of the data during analysis and inspections. 

Furthermore, any checks of of a system using contact probes would require a live event to be triggered, meaning effluent water would be discharged into the overflow system/river.  

The verification of an EDM system using contact probes typically also means entering a confined space and creating a more dangerous environment for those working.  HSE dictates within the hierarchy of safety that this risk should be removed if possible. 

How a Non-Contact EDM Works

Non-contact EDMs are mounted above a channel or wet well – without any contact to the fluid being measured.  The two main types of non-contact EDMs used on the market are ultra-sonic or radar.  Although different technologies, they both operate by sending a signal down to the fluid, which then reflects back to the sensor. 

By knowing the distance to the fluid these devices can then accurately determine the fluid depth at any given moment. 

Advantages of a Non-Contact EDM
Easy to Install

Non Contact EDM sensors can be installed above the channel or wet well with a clear view of the fluid or flow.  There is often no need to then enter the channel to set-up or reference.

Low Maintenance

Given the non-contact nature of the probe, it is not susceptible to the risk of damage or fouling from objects and debris, as with contact-type probes.

Easy to Calibrate

Following initial installation, non-Contact EDMs are easy and safe to validate through accurate pre-set reference points.

In the vast majority of cases everything can be done without the need to enter a confined space or live sewer channel/wet well.  A calibration certificate can then be provided.

Non Contact EDMs can follow the same proven methodology as calibration used for regulatory open channel flow measurement flumes and weirs.


How We Can Help with Event Duration Monitoring

Our team is experienced in all scenarios of EDM system implementation, calibration and ongoing support.




The Client Needs

Our food factory client required two new flow system installations for their site in South West England.

Work Completed

The first install was for a full new flow system, comprising of:


– Flow meter

– Ultrasonic transducer and bracket

– A new primary device of a rectangular weir on a SIRIS carrier board (suitable for flows up to 50 l/s


The second install was also for a flow system as per the above specification but did not require a new primary device as the current one met MCERTS standards.




The Outcome

The client now has confidence in a system that will not only meet their internal reporting and monitoring needs but will also ensure they meet compliance standards for MCERTS inspections and any associated audits.



Require a new flow system?

Our team has the solution for you. Talk to us today.


A full range of flumes for your needs

Our SIRIS flumes come in a range of sizes and capacities.

Including two new additions to the range, we’re sure to have the solution for your needs.


£20,374 - £24,000

Join a team where you will smile every day. From our close-knit collaborative community to the fulfilling work that we do, we can offer you a learning and supportive structure. We are hiring for trainee MCERTS Inspectors and are looking for can-do people with positive attitudes. A technical and inquisitive mind are key.

About us:

Siris Environmental is a Washington-based company providing our industrial and water utility customers with the best possible effluent flow monitoring solutions.


We work with private organisations and water companies across the UK, ranging from small trade effluent customers to large-scale factories and water companies, and have built a reputation for providing high quality service, delivered by a passionate team. 


Now has never been a more exciting time to join us. We are growing rapidly and have plenty of exciting opportunities for the right person to join our team. If you are energetic, hands-on, innovative, and professional, this is the environment for you.

What will you be doing?

  • You will be carrying out calibration of flow meters and service and testing of equipment in the field such as pH, temperature and water samplers
  • You will also be required to support the Inspection Teams on various sewage treatment works across the UK
  • The role requires keeping all equipment clean and tidy, in both the workshop and the vans and ensuring everything is within inspection date and calibration date
  • You will support with equipment sales and projects, which can be as straightforward as packaging up equipment and delivering to site or helping order in parts and ensure enough stock is available
  • You will work both at our Sunderland site and also at customer sites across the UK, likely working away 2-3 days every few weeks, with all hotel and travel expenses covered
wastewater effluent flow meters

Training and Support

  • You will work closely with an experienced service engineer for the first 6-12 months as your mentor, providing support and on-the-spot training during your duties
  • You will also receive various formal training at key points within your role, working towards the end role of qualified MCERTS Inspector
  • Long-term career progression with continuous support and training is naturally part of the culture here at SIRIS

Your Skills and Qualifications

  • The role requires good organisational skills as you will be expected to organise inspection and service visits via calendar planning as well as get confirmation from clients via email or telephone.
  • You will be naturally technically-minded, wanting to find the solutions to problems and help clients and colleagues
  • A can-do, positive attitude is essential for working within SIRIS


  • Flexitime
  • Family-run business feel with big business opportunities
  • Work from home as role allows
  • Ongoing training and development
  • Prospects for career advancements


  • 10 hour shift
  • 8 hour shift
  • 37.5 hours per week

Supplemental pay types:

  • Loyalty bonus
  • Performance bonus

COVID-19 considerations:

SIRIS adhere to all government guidelines in respect of COVID-19

Ability to commute/relocate:

Washington: reliably commute or plan to relocate before starting work (required)


  • GCSE or equivalent (required)


  • Driver’s licence (preferred)

Apply now

Click here to email your CV and contact details.




An end user client was experiencing issues with data accuracy after the installation of a flow meter by a third-party contractor. Our team was able to swiftly identify and adjust set-up to ensure the data they received was correct.

The Client Needs

It was identified that an end user dairy producer was experiencing issues with accuracy of data outputs from their newly-installed electromagnetic flow meter.  It was important that the cause was identified and rectified so that their data was correct, particularly as this was used for charging purposes. 

Our Response

During a routine post-installation verification check, one of our experienced project engineers quickly identified issues within this flow meter installation. It rapidly became apparent that the third-party contractor had not installed the meter correctly, meaning that incorrect measurements were pulling through to the data feed.

Our engineer was able to recognise that the Sensorprom (the part of the flow meter sensor that carries the unit calibration value) had not been installed correctly and had defaulted to factory settings. This included the incorrect bore size, the calibration (cal) factor and the excitation value.

During our initial response our engineer was able to adjust and reset the flow meter to the unique original Sensorprom characteristics. On adjustment the meter significantly changed its flow reading and this was checked against a secondary time of flight reference.



The Outcome

The end user now has confidence that their flow data being recorded and subsequently billed against is correct.

Lee, Project Engineer

“It is critical that any flow meter installation is carried out in line with the manufacturer’s recommendations and industry best practice, and that an independent verification process takes place. Flow monitoring systems are complex and in the case of electromagnetic flow meters there are often issues that would only be obvious to an experienced user. We would advise any end users using contractors to carry out appropriate due diligence on the experience and knowledge of a potential flow monitoring system installer. We are always here to provide advice and support.”

Require flow meter calibration?

Our team has the solution for you. Talk to us today.





Our client, a chemical ingredients manufacturer, recently required a trade effluent flow & monitoring system in order to comply fully with regulatory discharge requirements.

Specification & Installation

To specify the correct system our team confirmed detailed information unique to the site. This included land layout and location, flow volumes and discharge limits, the nature of discharge and upstream hydraulic levels. This information is critical and helps ensure the “correct” system is specified in the first instance.

Our from-scratch solution included:


• Full flow monitoring system comprising: small weir tank with 28º4′ V-Notch thin plate weir and ultrasonic open channel flow meter

• Partech 7300w2 ph and temperature monitor

• Point orange cloud-based data logger

• SIRIS 4-bottle vacuum sampler


Production is now complete and the entire system is ready to ship to the customer. Once installed on site by the client, SIRIS engineers can attend to check the calibration and ensure everything is operating correctly. This would include site calibration of all the instrumentation.

Require a flow monitoring system?

Talk to the team today about your requirements.

SIRIS supports Yorkshire Water and BarhaleDoosan JV in trial of first nature-based wastewater treatment plant.

 A trial of a sustainable wastewater treatment system is underway at the Yorkshire Water Clifton works, where over 20,000 wetland plants utilising the natural clay are being used to remove phosphorous from the wastewater as a natural alternative to traditional, energy-heavy chemical treatment.

The successful trial of the project will pave the way for further low-carbon, sustainable clay and wetland treatment plants, which aim to reduce energy and chemical usage, as well as create wildlife diversity including bees, breeding birds, amphibians and reptiles.
Further sites have already been identified across the Yorkshire region and results will be closely monitored for potential roll-out.

Flow Monitoring Solutions Provided by SIRIS


Working alongside design partner Stantec, BarhaleDoosan JV was the project partner tasked with construction of the site and engaged SIRIS to provide monitoring solutions to deliver key data on the flow of wastewater through the plant. 


With the trial being closely monitored by both project partners and the Environmental Agency, the MCERTS-approved, wastewater flowmeters are providing important data to gauge wastewater evaporation and flow leakage rates between inlet and outlet points at each end of the 5x 800m3 plant cells.  The flow meter system includes a battery powered cloud-based telemetry, meaning information is accessible for project stakeholders.



A high level of evaporation or flow leakage would mean that plants within the marshland would not receive the required nutrients required for their long-term survival and lead to unacceptable levels of phosphorous and BOD in the final wastewater output.


Important to the project for BarhaleDoosan JV was to maintain a low carbon footprint across the whole project, including design and build processes.  The easy-to-maintain open channel flow meters were designed to include a solar panel, which not only makes them highly energy-efficient, but removed the need for installation of over 200m of cable ducts and electric cables, concrete-heavy draw pits and associated deliveries of materials.  





The level of support from the team at SIRIS was outstanding.  They were very approachable, knowledgeable and fully engaged when considering all options to meet our project aims, coming back with well-thought-out and cost-efficient solutions.

Mollie Geoghegan
Engineering Design Manager, Barhale Doosan JV



The team at SIRIS is also excited to see the results from the trial.  General Manager Karl Bambynek said,



“The project is a milestone in bringing sustainability within the wastewater treatment industry and we are proud to be involved in its delivery. If successful we could see significant roll-out and an important positive impact on the environment and its levels of biodiversity.  We are pleased that our flowmeter systems can play a part and look forward to following the project’s progress.”



Guide to: getting ready for your MCERTS inspection

Preparing for your MCERTS inspection might seem daunting – even if you’re used to the process. In this guide, we’ll be explaining the steps you need to take to get your site ready for a successful MCERTS inspection. 


What are the steps to obtaining MCERTS compliance?


The first step to achieving MCERTS compliance is obtaining a consent to discharge permit. This is a legal requirement for most businesses discharging trade effluent to a public waterway or sewage system – although there are some exceptions.


You can learn more about obtaining a consent to discharge permit here.


There are then three stages to getting certified:


1. Inspection: A certified MCERTS inspector will visit your site to inspect your flow measurement system. Provided the installation meets the standards, the inspector will issue a conformance report.


2. Audit: An independant auditor will inspect your QMS (Quality Management System) to make sure it meets performance requirements. If it does, you will be issued with a conformance report.


3. Certification: Provided you have passed the inspection and audit, you will be issued with an MCERTS certificate. Certification is valid for five years after which the installation is re-inspected. The QMS is subject to periodic surveillance audits during the five-year period.

MCERTS certification process


You can view the status of your MCERTS certification through the CSA Group’s Certificate Database, which shows whether a certificate is still current or has been withdrawn or suspended.



Getting ready for your MCERTS inspection

The following steps are our recommendations for preparing for your MCERTS inspection. Whether it’s your first inspection or a re-inspection, it’s a good idea to go through these steps to give your site the best chance of a positive outcome.


1.Familiarise yourself with the latest MCERTS compliance guidance. It’s a good idea to get up-to-date with the Environment Agency’s latest MCERTS performance standards and conduct an internal audit to highlight any areas of concern ahead of the inspection.


2. Make sure the inspector will be able to access the site. Please ensure any necessary paperwork to allow our team access has been completed ahead our visit and let us know about any training or ID requirements, as well as any site-specific risks.


3. Ensure there will be a qualified team member on site. It’s a good idea to make sure that whoever is on site to welcome the inspector has a good working knowledge of the system and is able to answer any questions.


4. Get your paperwork ready. The inspector will need to see a copy of your Consent to Discharge and/or permit, along with maintenance and calibration records.


5. Collate any representative flow data you have to hand, or make Cloud data available to the inspector. The inspector will typically need to see a 15 minute spot average and daily volumes. This will help them understand the site’s discharge pattern and any variations in flow rate and will be useful if there are unusual flow levels on the day of inspection.


6. Check your maintenance programme. Poorly maintained equipment can cause flow meters to give incorrect readings. Your flow system should be in good condition and well maintained and we will need to check maintenance records to asses how effective your maintenance programme is.


7. Make sure the flow meter display unit is accessible. The inspector will need to see the make/model, connect a laptop to download the data, and possibly interrogate settings to ensure correct set-up.


8. Check the location of the flow meter. Our inspector will need to carry out detailed checks, a flow test. Please make us aware in plenty of time if there are any specialist requirements such as confined space entry. Remember, we may need to access the flow channel and/or isolate the flow.


You can download a printable copy of these steps here.


How Cloud data can help

Our remote data monitoring system makes it much simpler to prepare for your MCERTS inspection. Using our specialist specialist remote telemetry unit and data visualisation software, our inspectors can quickly access real-time data from your monitoring system. With 24/7 remote access to your data, investing in a data monitoring component for your flow measurement system saves time and money. What’s more, you can focus on getting ready for inspection without panicking about paperwork!


Find out more about how data monitoring can help your business.


Get in touch to talk about your MCERTS inspection


Our MCERTS inspection team

At SIRIS, our team of MCERTS experts are always on hand to offer support and guidance.


Get in touch to find out more about MCERTS or preparing your site ready for inspection.


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