>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-16 21:23:07 Id:26
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.
I have five 2.4 GHz J Series radios set up in my shop's warehouse as a test before it goes out into the field. I have noticed that the two closer Trio radios showed one or two comm losses (5 minute delays, always clears under 10 min) while the further two worked all weekend. I kept all settings at default beside changing Radio ID and enabling AES encryption. This is a PTMP scenario, one master, 4 slaves. Just looking for any recommendations or ideals to find out what is causing the comm losses and what to do to fix them.**_
I'm not quite clear about what you mean by 5 minute delays. Perhaps you mean that these two radios will lose comms for about 5 - 10 minutes then come back? If this is the case, please look at the Sync/NoRx LED on these radios while they are not communicating. Check to see if they're still sync'd or not. (if sync'd the LED is flashing green)
If the radios are not sync'd to the Access Point this is more likely to be a radio-related problem. If they are sync'd while the comm fail problem is ongoing, then something else may be at fault.
As for recommendations to follow for a more robust network, here are a few:
- Ensure the Antenna 1 Tx Power is suitable for the path (typically 30 dBm at 900 MHz or 27 dBm at 2.4 GHz but can be reduced on very short paths) Watch the RSSI to make sure you have a good receive level. (see note below) A too-strong signal level can also be a problem. eg During a test you may have the radios very close together. With the power turned all the way up the radios will be "shouting at each other." Distortion in received signals may result. So on very short paths it's a good idea to reduce the Tx power to eg below 20 dBm. (10 dBm is minimum allowable)
- A faster hopping interval tends to reduce the effects of interference relative to a slower hopping interval. So 50 ms may be better if you feel you are suffering from interference-related com fails. Slower hopping (eg 250 ms) is a bit more efficient if you're trying to maximize bandwidth.
- Data Retransmissions can be set higher to increase the likelihood of the Remotes hearing a message from the Access Point. A value of 2 is usually plenty but you could try 3 or 4. This will reduce available bandwith a bit.
- Force Retransmissions Across Separate Hops - Enabling this will make the Access Point send each copy of its retransmissions on a separate channel. If there is noise or interference blocking any channel, turning this on can significantly improve the AP - Remote comms. It does however have significant latency (delay) implications as any AP - Remote message is not considered delivered until all retransmissions have been sent, one on each of several hops.
- No Acnowledge Retry Limit - The default of 10 is plenty. This tells a Remote that it can retry up to 10 times if it does not get an ACK from the Access Point to any message it sends up to the AP.
- Digital Collision Avoidance - It is recommended that this be enabled in most systems. Remote radios carrying traffic such as TCP may generate messages even when there is no active data traffic, and these messages may collide with new traffic. It also helps when you may have more than one polling source eg two protocols in use or one protocol and the Trio diagnostics software.
- It is possible for multi-path issues to cause problems in some circumstances eg in a metal sided building or if the signal is passing over a lake. This is where the direct path ends up fighting against parts of the signal bouncing off reflective surfaces. Sometimes changing the position of one or both antennas can help. Using high gain yagi (directional) antennas at the remotes can help keep signals from spreading too much also. (eg 14 dBi yagi CMI part #297852)
A couple of general comments:
- In urban areas, or even just in an office space anywhere, 2.4 GHz radio systems often share the available bandwidth with many consumer grade devices. This typically means you need good strong receive signal levels to compete. Eg if the radio's receiver sensitivity is -102 dBm then the very minimum you should aim for is -82 dBm, and in cases where you need high reliability you should aim for even higher levels. This accounts for changes in signal level due to moving obstacles, weather, maintenance issues, as well as high RF noise levels due to all those consumer grade products. The RSSI (receive signal strength indication) can be seen on the Diagnostics page when you're connected to a radio.
- AES encryption has significant bandwidth overhead implications. If you don't absolutely need it I typically suggest that you do not use it. If maximizing your available bandwidth is not a concern then this does not need to be worried about.
As always, in a time sensitive support situation please contact Tech Support directly at 1-888-226-6876 or at SupportTRSS[at]schneider-electric.com
I have a 300 sec comm fail timer in my program. If i dont get a valid receive back from the remote in 300 secs then i trigger a comm alarm. Looking at the alarm history, the comm alarms usually clears within a minute or two._**