In the water and wastewater industry in the US, Modbus is the most common telemetry protocol. Its great benefit is its simplicity – and almost everyone in automation and process control is familiar with it.

For a few years now, we’ve been promoting DNP3 for telemetry instead of Modbus. Why? What’s the benefit? For people new to protocols and telemetry it’s hard to know where to start. 

Today, we’ll cover the first benefit:

Date/Time Stamping – or Less Guessing

DNP3 adds a date/time stamp to every event when it occurs. Each event is added to the “event buffer” in the RTU with its own date/time stamp. Then when the RTU communicates with the SCADA, or “master station”, the data can be stored in a Historian (database) or displayed on the HMI with the actual time the event took place – not the time that the master station received the data.

I mention that point because a lot of SCADA systems, most of them, were so orientated around process plants with hard-wired high speed data connections (like ethernet or high speed serial) that the normal mode of operation was to log the data with the date/time that it was received by the SCADA (and ignore any date/time stamp from the field if one existed). It doesn’t matter too much in a process plant – the comms is almost instantaneous – and if any comms outage occur they are quickly fixed.

DNP3 tells you when the event occurred – not when the SCADA system found out about it! 

In wastewater collection and water supply systems almost all of the assets are distributed in the field. And communications are often disrupted. Even when they are not disrupted, you don’t want every event to be communicated when it occurs.

Here’s how a typical Modbus network works – the master station (typically the master PLC) “polls” each site in turn to get all of the current data.

“Get the current data” means read a snapshot of all of the Modbus “registers” or data points. Most of them won’t have changed, so you are using precious bandwidth to capture lots of unchanged data. What about the data that has changed? Unfortunately, you don’t find out when it changed. You can just see that a different value is there now.

Modbus fills up the bandwidth with data that hasn’t changed. DNP3 only captures the data that has changed. So it can communicate a lot more useful data in the same bandwidth.

Let’s use the example of an analog process value. The value that the SCADA last captured from the field was 6.8, this time around – 10 minutes later – it is 6.9. So when the SCADA trending client displays this value – or you produce some kind of report, the process shows 6.8 moving to 6.9. Is that what happened? Or did it go to 7.1 and then back down? You’ll never know. You might know your own process really well, or you might be guessing.

You might know your own process really well, or you might be guessing. Using DNP3 avoids the kind of detective work that often goes on, where the operations and engineering staff try to fill in the gaps!

And then lastly, what if comms to that site – or a number of sites – is down for 24 hours? With DNP3, when comms is restored, all of the events during that period will be communicated to the SCADA (check out the technical note below).
 

Do I need this?

Whe you build a house, if you have the right foundations and structure you can add another floor. If not, you have to knock it down and start again.

To begin with, just getting reliable data out of a SCADA system is a great relief. But once it’s working and providing data you start to ask more questions – because you want to make the system work better.

Did both pumps run together in Pump Station 18?
What’s the hydraulic delay between Station 19 and 18?
I know the radio failed but do we know how high the level got at Station 12? And so on.  

A Quick Technical Note

Designing your comms system always takes some work and this isn’t aimed to be a technical workshop. But one important point with your field device is to ensure that the event buffer has been configured with enough memory to capture all the data that you might need in an outage. And the other important point is to ensure that the DNP3 configuration is for SOE (sequence of events) – as it is possible to configure last event only.

I mention these points because it is often only when you really want the data that you find out it wasn’t configured to capture that data that you wanted. Best to check when starting out.

Learn More

There are two whitepapers about DNP3  on the main site. One covers DNP3 Security – “Keeping SCADA systems open and secure from cyber-attack” and the other is more general – “Benefits of DNP3″.

To access the whitepapers you do need to complete a short registration form.



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SCADA & Telemetry

A few years ago, we found that operators in a few wastewater utilities in one state were visiting their lift stations regularly – some once a week, others once a month, to pump the station right down to the snore point of the pump. It was an important maintenance task because pumping the well down as far as possible was a great way to clean out as much of the build up as possible.

The operators here found that the result was more reliable operation of level devices, less pump blockages and less need for frequent visits from the cleaning crew.

That insight led to a simple well clean out function in the MT2PC, and then in a more advanced form in MultiSmart. The MT2PC version just allowed for a periodic pump down, every so many cycles for so many seconds. Customer feedback from the MT2PC feature was that some improvements could be made -which we couldn’t put into the MT2PC - but of course we did implement these improvements in MultiSmart.

How does it work?

The idea is that periodically, when the well level reaches the normal lead pump (duty pump) OFF point the pump down cycle is extended a little.

Optimize Station - MultiSmart

The MultiSmart feature allows the choice of how to initiate this extra pump down – after a set number of cycles (e.g. every 100 cycles), or on a timer. If you choose timers for the well clean out you might set Monday between 8am and 1pm. If it was a very slow moving well and the OFF point wasn’t reached within this time, the well cleanout wouldn’t happen. Normally of course the OFF point would be reached within this time window and so the cleanout would take place - but only once. The advantage of the timer over using number of cycles is that you can make sure it takes place when people are at work – in case there’s a problem.

Should we introduce “Stop on under-current”?

There was a third choice for the well clean out that we think is a good idea but it hasn’t gone into the product yet (as of writing this post) – run the pump on until under-current - i.e. until the pump starts to snore. In a way you can use this already, but you’ll get an under-current alarm!

If you think that this would be a useful feature for you – or you have any other comments about this feature or the practice of cleaning out wells – please comment (below)!

How is it setup?

From the Settings menu, on the first screen you see Station Optimization, select that and  Optimize and you’ll find the well clean out function with all the parameters. You’ll find some other useful features there as well.

Disabling the low level alarm is managed from the level alarms in the advanced menu:  Advanced – Pump control – Well – Well 01 -Level alarm -Low level – Well clean out disabled (check the box). You might have a low low level alarm as well, if you do you should do the same for that alarm.



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In the well

If you’ve visited our site before, welcome back, and if you’re a first time visitor to multitrode.com, thanks for stopping by.

Why do we have a new site?

The previous site was running since 2002 and was on a technology platform (for the techies – Cold Fusion) that made it hard to do some new things we wanted to do.

Just about everyone’s familiar with that problem – usually not with running a website – but having an out-dated system slow us down or increase our workload. Most of our customer base has the frustration of large parts of their infrastructure being old and out-dated – sometimes all of it. In a recent survey we did of Florida utilities, ageing of existing infratructure was considered much more of a problem than managing any growth of the system. And across our major markets of the water & wastewater utilities in the US, UK and Australia it’s something we see every day.

The Blog

The Blog is something new for us as a company. A lot of people are very familiar with blogs, and for them blogs can often be their main source of information. For many others, the response is more “what’s a blog?”

Blog stands for – is short for – “Web log” – but really is a more informal way of communicating with the outside world.

Press releases, by their nature, tend to be fairly formal exercises and only communicate a small subset of what we would like to be saying to our customers and partners around the world.

So the idea behind us starting a blog is to have more frequent and richer communication with all the people we work with.

There’s two more great advantages of a blog – they allow and encourage responses; and it’s easy to subscribe to a blog so you can read updates, without getting your email box full of stuff you haven’t got time to read.

Let me explain a little more

If you’re like me, you use your email inbox as a tool for managing a lot of your action items. People you work with, inside and outside your company, email you and expect responses. If your inbox fills up with possibly interesting news from outside companies you get frustrated and start deleting it – even though you might want to read it if you just had a few minutes.

So getting too much email is one of the frustrations of modern working life. We’ll try not to send too much to your inbox!

Another way of keeping track of what’s going on is visiting a supplier or partner’s website every once in a while to see what’s new. It’s hard to remember what was there last time. How do you find the new content? Maybe there’s a press release about a new product or an update or a new service or a case study – but maybe there isn’t. There’s a great tool for keeping track of news, and the techies amongst you will have been using it for years. I only really started using it about 12 months ago – a news feed program.

Google Reader is what I found so easy to use, and now I can’t understand why I didn’t use newsfeeds long before. What does Google Reader do?

Basically it takes all the new content from all the websites and blogs that you subscribe to and puts it all into one place. So instead of you visiting the websites of 5 newspapers, and trawling around looking for interesting stuff, instead you can just get all of the news stories you want delivered to the reader. Maybe it doesn’t sound that great, but what you find when you start using it, is you can keep up to date with information from 50 sources very quickly. I’m currently subscribed to over 40 feeds, some of them work related, some are personal interests, and the new stuff just arrives. Some of the feeds I hardly look at, others I read most of the posts and sometimes follow all the discussions that follow if I have time. When you realise you aren’t interested in a news source any more, you just click “Unsubscribe” and it’s gone.

You can check out Google Reader very easily – at www.google.com/reader – all you need to do it create a Google account if you don’t have one, and then search for some news feeds. There’s lots of other readers around, for more on the subject take a look at the Wikipedia article: http://en.wikipedia.org/wiki/Aggregator

How do you subscribe to a news source?

Usually you look for RSS (Really Simply Syndication) or a feed symbol on a webpage (see the top right of this page) – or you can simply search for the site from Google reader. When you see the RSS or feed symbol on a site you click on it and it usually offers to add the newsfeed for that site to a number of readers, including Google Reader.

Click on the +Google button..

Once you click on the Google Reader button on the right, you’ll be subscribed to that newsfeed or blog.

Try it, or any other news feed “aggregator”, and you’ll start to find that it’s the place you go to get the information you want.

Hope to see you back at the MultiTrode blog soon, there’s plenty going on that we want to share with everyone. Read more…

General News