>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-16 21:34:02 Id:30
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.
This topic comes up regularly, and so is well worth discussing._**
While Schneider does offer a path study service using the PathLoss software package, it is often desirable to actually go to the field and do real world link tests. While at site the technician can often see issues that may cause a system not to work. Eg trees very near the site, or a nearby tall building in the path. These things may not be visible to the person doing the software path analysis.
**Hardware Setup and Antenna Aiming:**
• The antenna types should match those which will be used in the final system if possible. (eg 5 dBd omni at the master and 10 dBd yagi at the remotes) If the antennas are not a perfect match, understand the differences. Eg if you're using a 6.5 dBd yagi for the test but the installed system will use 10 dBd antennas, add 3.5 dB to every RSSI measurement taken.
• The antennas should be mounted as high as possible even for initial testing, particularly at the master site. Make sure your master antenna is up above all buildings and near the tree tops if not above. (this is more critical in 900 MHz systems) For testing at remote sites, a painter's pole or similar which can extend up 15 feet is very useful.
• Be careful when aiming the yagi. It can be very easy to let the antenna wave around and thus get inaccurate or varying readings. Know in advance where to aim your antenna. (a terrain map is vital) Have a compass with you, and make sure its declination adjustment is properly set.
• When taking RSSI (received signal strength indication) values, ensure you wait several seconds after moving the antenna before taking the next reading. Move the antenna only a few degrees at a time, while looking for the strongest level.
• RSSI values are like temperatures at the South Pole. They're always going to be negative numbers, but closer to zero is better. (eg -60 dBm is better than -90 dBm, just as -60 degrees is not as cold as -90)
• Configure the radios in a manner similar to that which will be used by the desired final system. Eg if you need 64 kbps in a K Series system, make sure your radios are configured to match.
• Make sure your radios are communicating with each other, and that you know how to use the TView+ Diagnostics software, BEFORE you leave the shop. This will greatly increase the likelihood of your field test going well.
• You can use a volt meter connected to the RSSI pin on the radio's DE9 connector. (typically pin 9) This will give a relative indication of RSSI only. It can be useful for finding the best direction to aim the antenna, but will not give you an actual RSSI level. (see the user manual for more details)
**Measuring RSSI with TView+ Diagnostics**
• Open TView+ then click the Diagnostics button. Create a database to hold the radios to be used in this test.
• Enter the radios to be used in the test. You'll need the serial numbers!! Make sure you name them appropriately, choose the right radio model and type. (eg K Series - Remote) Note that for the E Series they are always called "Remote" unless you're working with the 19" rack mountable EB450.
• For the serial radios leave the Communications Port at Serial. For Ethernet radios select eDiags. Enter the IP address of the laptop which will be running the Diagnostics software, and IP port 1040.
• To configure the comms channel for serial radios, go to the Settings menu, then Controller Settings for serial radios. Set Controller Address to 100, select the correct com port, and always set speed to 19200 bps. Click Apply Changes.
• To configure the comms channel for Ethernet radios, go to the Settings menu, then eDiags Port Settings. Enter the laptop's IP address and port 1040.
• Connect the laptop to the System port of the Remote radio. Click on the Individual Poll button and select the Master radio (the far end of the link) then click Toggle to start polling.
• Watch the RSSI level while SLOWLY moving the yagi antenna. (eg wait at least 5 seconds before moving again) Look for the strongest signal. (smallest negative number is best)
Testing the Link
• While still in TView+ Diagnostics (with the database open) go to the Tools menu and select Statistical Performance.
• Choose the distant radio you want to test to. (typically the Master when you're at a remote)
• Specify a Time Between polls. Typically longer if there is user data traffic on the system and you don't want to slow it down too much.
• Click Start. The software will send a random data packet to the distant radio. That radio will recognize the packet as a test packet and send it back. There is NO need for a loopback plug on the radio's serial port!
• When the software gets the packet back (IF it gets it back) it will compare the returned packet to the sent one.
• The software will track the number of good vs bad packets. Let it run long enough to thoroughly test the link. Eg minimum 10 minutes.
>>Responses imported from previous forum
Reply From User: joelw, posted: 2018-10-16 21:34:35
While at the remote site, look for obstacles near the antenna. Keep the antenna away from buildings (it needs to be above the roofline if shooting across a building) and away from trees. If the trees are tall and most of the path to the master site is blocked by trees, the signal will (particularly on 900 MHz) be heavily attenuated. If doing the testing in winter when there are no leaves on the trees, you must realize that in the spring the leaves will reduce the signal level significantly. (how much depends on how much of the path is through trees)
It is best to design a path for at least a 20 dB fade margin, in order to have a radio link that is reliable in all weather and even when interference occurs. To know the fade margin, you must know the radio's receiver sensitivity (varies with RF data rate) and the measured (or calculated) RSSI value. A path with a fade margin of less than 20 dB may still work under average conditions, but will be more susceptible to problems of various sorts.
If you cannot get a reasonable signal from the master site, look for another site in the same system between the two which might be useable as a repeater. Or look for a decent hilltop site nearby which might be useable for this purpose. When contacting Control Microsystems to have a software analysis done, this information will be very useful.
**Radio Type RF Data Rate Sensitivity (at 1x10-6 BER)**
32 kbps -108 dBm
64 kbps -106 dBm
128 kbps -104 dBm
256 kbps -102 dBm
256 kbps -102 dBm
512 kbps -92 dBm
9600 bps -108 dBm
19200 bps -106 dBm
9600 bps -106 dBm
Joel A. Weder
SCADA & Telemetry Solutions Specialist