Electricity Monitoring Issues: ModBus/RTU from Serial to Ethernet

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Thread Starter

Mario Berges

I'm currently involved in a project for the development of an Electricity Monitoring system for an old campus building. The device we are using for the metering is the EnerSure (http://www.trendpoint.com/EnerSure.html) from Trendpoint Systems. This unit has a serial port ans uses the Modbus/RTU protocol for communication.

Modbus is completely new for me and the team, but nevertheless we have made some progress. We have a few issues/questions on which we would like to receive feedback from this community.

Our ideal setup is as follows:

- Each circuit panel (about seven in total) will be monitored by one EnerSure unit.
- The readings from all the devices will be polled and stored in a database (single database preferably) at a frequency close to 1 reding/second, conserving the data from all the devices.
- We will later parse the data and make it available to different computers in the building (by having them query the main DB) and probably online for remote access.

Our current questions/issues:

- Using a serial connection for each device seems improper or inefficient for the proposed goals, since we would need 1 PC per EnerSure unit, or some kind of hub which would limit our sampling frequency.

- We've seen some Ethernet to Serial converters, but don't know about their efficiency for this kind of use. We would like to have each unit connected to the Ethernet/LAN which is spread all over campus.

- For logging the data to the computer, we are currently using a software called Modscan (http://www.win-tech.com/html/demos.htm) which only seems to support logging into a text file, making it impossible to read and write to it at the same time. Is there any other software out there which could do similar things but with a DataBase dumping capability?
 
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Mario,

Assuming you wanted to stay with the current mfg:

On that same webpage, It looks like the metering manufacturer also makes a software which will help with historical database needs. It also looks like they have a serial to ethernet converter option (which is good because that means testing they've done and can support you which can be an issue if you go 3rd party). However I don't see a web based product for sharing with your coworkers. You can use something like Remote Desktop sharing in Windows XP or a Remote Terminal Services Setup with a Windows Server. The question therein is do you really want other people having access to that PC and database? How protected do you want it to be?

Modbus is an open protocol so you could also use something 3rd party with some custom drivers that is already a web based product that supports, trending, reporting, and the web for sharing (which would also mean keeping the main dataserver safe from others). Powerlogic makes such a software. Here is a link: http://www.powerlogic.com/products.cfm?id=7

Depending on the size of your system and what your future upgrade needs are you may want to stay with the current manufacturer or consider upgrading to something else if your Power/metering info is now becomming more of a critical need. Powerlogic makes meters with built in Ethernet and onboard webpages... just depends on how high tech you want to go.
 
Some idea for your question:
If you wish to use 7 different energy meters to monitor your 7 circuit panel (DB panel), then you can use RS485 multidrop instead of using RS232 serial. However, I don't think so you can use 1 energy meter to monitor 7 circuit panel. :)

Serial to Ethernet converter is widely use in automation industry. The reliability is based on the brand. I used a lot of different brands before, I did not encounter any problem. :)

Actually ModScan is a very basic software for integrator to test the established communication between hardware and software. If you need a better GUI to show your energy reading, you need a SCADA software which can take in Modbus value and present it into HMI. :) Or does this EnerSure provide any free software?
 
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Mario Berges

Thank you both for your responses.

The project, besides aiming at solving a specific problem, is meant to become an educational opportunity as well. We are a team of engineering graduate students, and as engineers, we fell that even if we acquire off-the-shelf solutions, we need to understand the workings.

Trendpoint offers a software for polling the EnerSure and storing the data, but we are considering finding another solution to that part, besides of the above reasons, also because of budget limitations.

We have found a nice open source software piece developed by Daniel Klein: http://www.klein.com/thermd/ that supports EnerSure units. It is very possible that we will be using this one.

We also found that Trendpoint is starting to provide for their new units the option of having factory installed Serial-to-Ethernet converters. We are ordering a few of those to install them by ourselves here.

What we haven't resolved yet are issues related to database design, polling frequency, multiple/simultaneous/continuous polling, etc.
If anyone has experience in these areas using the Modbus over Ethernet protocol, please comment.

Thanks again for the responses.
 
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