A protocol defines the rules by which devices talk to each other. DNP3 is a protocol for transmitting data from Point A to Point B via serial and IP communications. Although DNP is most commonly used by electric, gas, water and wastewater utilities, it can be used anywhere a SCADA system is exists.

Why Do Devices Need to Talk to Each Other?
Utility providers commonly have lots of operations they need to monitor. Typically, there is a central operations center plus remote equipment in the field.  The central operations center houses their main computer.  Installations/substations house remote equipment in the field.  DNP is used to facilitate communication between the main computer and remote equipment, enabling the main computer to remotely open/close circuit breakers, measure line voltages, start/stop motors, open/close valves, check for errors, etc.

View Previous Blog Series on DNP3:

DNP3 Part 1 – Date/Time Stamping

DNP3 Part 2 – Communications Options

DNP3 Part 3 – Security

DNP3 Part 4 – Reliability

DNP3 Part 5 – Compliance

The design life of most equipment requires periodic maintenance: adjustments, alignments, lubrication, rotating, parts replacement, etc. Every time we fail to perform routine maintenance, we shorten the equipment’s design life.

Maintenance Approaches

Reactive Maintenance

Defined – Run it until you break it! No effort is made to maintain equipment; manufacturer recommendations are ignored. Also called “Crisis Maintenance” or “Hysterical Maintenance”.

Pros - No manpower hours are expended. No maintenance costs are incurred.

Cons – You may think you’re saving money, but you’re not.  Shortening the equipment’s design life may result in higher replacement costs. You may have an additional expense if you’ve worn down your secondary/backup equipment. Then, there is the element of chance – there is no guarantee that a critical piece of equipment will not fail during peak demand, or during weekend/holiday time.

Preventive Maintenance

Defined - Actions performed on a set schedule that detects, precludes or mitigates degradation of a component or system with the aim of sustaining or extending its design life. Also known as Condition Based Monitoring.

Pros – Although it is not the optimum maintenance program, it is a vast improvement over Reactive Maintenance. Performing manufacturer recommended preventative maintenance will maximize the equipment’s design life. Money will be saved by ensuring the equipment runs as efficiently as possible.

Cons - Risk is increased by human error during the performance of maintenance. You may find yourself conducting unneeded (but scheduled) maintenance. Although the risk of failure is reduced, it will not be eliminated.

Predictive Maintenance

Defined – Actions that detect the onset of failure, thereby allowing causal stressors to be eliminated or controlled prior to deterioration of the equipment. Predictive Maintenance differs from Preventive Maintenance by basing maintenance on need rather than a preset schedule.

Pros – A well-organized Predictive Maintenance program will all but eliminate catastrophic failures. The ability to plan ahead will facilitate inventory/part ordering and avoid overtime cost. Equipment operation can be optimized, energy costs can be reduced and system reliability increased.

Cons – Requires staff training and investment in technology.

MultiTrode Can Help

At MultiTrode, we believe Predictive Maintenance guarantees the best results. Predictive Maintenance, also known as Condition Based Monitoring, is the ideal maintenance strategy because it identifies when assets need to be replaced – allowing the utility to plan cost-effective maintenance.

To ensure that the hydraulic and electrical state of the pump and motor can be clearly monitored, the MultiSmart Pump Station Manager measures the following:

• Flow rates per pump, total volume per pump
• Energy used per pump
• Pup efficiency in gals/kWhr or liters/kWhr
• Insulation resistance per pump
• Supply voltage (all 3-phases)
• Current monitoring (all 3-phases)
• Detailed fault analysis for each pump

For a free MultiSmart demo, email UsSales@multitrode.com.

Learn more about the innovative Level Sensing Probe and intuitive MultiSmart Pump Station Manager at www.multitrode.com.

Part One: Date/Time Stamping – or Less Guessing
Part Two: Communications Options – Polling and Unsolicited Reporting
Part Three: Security

The DNP3 protocol also supports guaranteed delivery. What does this mean?

Suppose you want to send a command to start a pump. How do you know the RTU at site received the command? With some older and simpler protocols the only way to check is to read the status of the pump at a slightly later time – and hope you catch it in the act.

Or suppose you want to ensure that the message High level alarm or All pumps unavailable sent from the RTU was not missed by the master station or SCADA? With some protocols, like Modbus, there isn’t any mechanism for ensuring this.

DNP3 provides message acknowledgements. With unsolicited reporting, the RTU might send all changed data every half hour, or if the event buffer was full. The “message” that the DNP3 protocol sends includes all the tags that have changed with the date/time of each, and also includes a sequence number. The master station would send an acknowledgement to the RTU – or “outstation” – that that sequence number had been received.

In the event that the RTU / outstation didn’t get that confirmation, it would retry. And after a certain time period the site would go into a Comms Fail mode with probably a longer retry delay. I say “probably” because that depends on how the user sets it up, but that would be the sensible approach.

As you can see if you’ve been following this series on DNP3, the creators of DNP3 designed it for the challenging world of telemetry where communications is always suspect and often problematic.

There’s more to configure in the protocol of course, but each element is there to ensure data integrity:

• you know what happened
• exactly when it happened
• you can guarantee that the SCADA system knows about it
• and you can ensure that data is genuine and not from a hacker