RTU Communication For Remote I/O

http://cr4.globalspec.com/thread/77981/Modem-Loopback-Unit

A loopback unit is a test mechanism that returns a sent signal to the original xmtr. RTU or Remote Terminal Units communicate serially via the Ethernet protocol if and when that particular protocol is supported, selected and equipped. Select the link in the post above and read more. Mail me personally and I'll shoot you some links to some comms info.

HI Sir ,

Thanks for your apt response , but the above link does not contain any information.

Give me your email id please !

If the backbone for communication is fiber optic cable can we use loopback unit for testing , if not how can we diagnost the communication loop.Please advice.

Not sure what system and equipment you are using.

OPTIC Portion

There are several communication equipment vendors that sell "in-line" fiber-optic loopback monitoring systems that measure the transmitted signal db magnitude, then measure the received signal db magnitude and provide a display of the difference as "db Loss".

With the gathered information it is easy to see when/if there are any failures in the optic generators/receivers and if there are any failures or transmission signal degradation caused by fiber optic conductor damage and/or connection oxidation or poor/loose terminator contact.

COMMUNICATION PACKET MONITORING

Simple pinging of the network device-by-device using IP address, MAC, or ESN (method depending on how you set up your system) will reveal response time and/or lack of response time.

There is software available that will provide this basic monitoring however, you must be absolutely sure that the OS software you are currently using is compatible with whatever software you purchase. Contact the OEM supplier of you communication software to obtain a list of compatible programs.

We are using new RTU (Remote terminal Unit ) to connect remote (control /status) signals to main DCS through fiber optic cable & ethernet switches. For monitoring & control the MOV , Feild Instruments etc

Also upgrading existing RTU by adding new i/o module which is connected through copper cable .

Now the existing RTU is already having modem & loopback unit .

Did modem & loopback unit required for new RTU (FOC Connectivity) ?Please confirm

Yes. The new RTU unit must be compatible with the existing RTU system communications.

Without compatibility the communications cannot establish "handshake" and therefore there will not be any communication nor monitoring.

Whatever is in the existing RTU must be mimicked in the the new RTU unit.

MODEM => MODEM OR LOOPBACK => LOOPBACK

You must also be sure that the Communications Protocol is identical in both RTU's.

If configurable, all baud rate, parity, system polling rate, and watchdog communications "timeout" timer settings must match.

If there is a mismatch on any of these, the communications will experince severe collision incidents with intermittent operations and/or shutdown isolation of the new RTU by your DCS system protection. (Invoked by NIM or NSM)

You should be able to contact the OEM for complete,accurate detailed instructions on how to interface the new RTU with your existing system.

But as per earlier discussions modem & loopback unit is not compatible when we use fiber optic cable connectivity, it is only compatibile with copper cable connectivity.

Then how can we mimick the same unit when the media for communication is different, one RTU is connected to DCS through fiber optic cable the other is by copper cable .Right

Purchase Media convertors from Black Box, 3-COM or one of the other many manufacturers that provide these devices.

Make sure to specify:

1. Type of fiber; "Single-Mode" or Multi-Lode" being used in your application when you order the units.

2. Speed and packet size of DCS communications; This is very critical as most DCS systems operate at a much slower baud rate than SCADA however the word size is usually much larger so the "Polling-Rate" and "Watch-Dog" timer settings will have to match otherwise your system will experience a high collision rate and most likely it will be faulting out as "Message Timeout" and/or "Loss of Communication".

The Media Conveters are specifically designed to address the task of facilitating copper to fiber communications and work well if configured correctly.

Pay careful attention to the temperature rating of the Media Converters.

Know that if you install a converter in a location where the ambient temperature is higher than the device rating, it will fail to operate correctly as they are very temperature sensitive.

Please share if you have any link or some notes which is good to understand the RTU communication using loopback module