>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-16 20:32:23 Id:14
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.
I recently had this question from a customer who is configuring a ClearSCADA system to poll for diagnostic information from Trio radios. This could just as easily apply to alarm limits set in the TView+ Diagnostics package. The discussion below might help you understand how to set your own alarm limits._**
**_Question: I need some help with reasonable ranges and alarm setting for a number of items:_**
**DC Volts (E, M & K)**
For the E and M I'd likely go with 11 volts for low and 15 volts for high. For the K's I'd go with 11 and 28 volts. No real hard science to these numbers, but they give some warning before reaching the hard limits. For a solar system you might want to evaluate the low voltage numbers more carefully to avoid damaging batteries.
**Forward Tx in dBm**
Depends on what the radio has been configured for. I'd set the high alarm perhaps 2 dB above the configured value, and the low alarm 2 dB below the configured value.
**Reverse Tx in dBm**
This also depends on what the radio's configured Tx power has been set to. I would like to know if the reflected power rises to more than 1/10th of the forward power. So I'd set a Reverse (reflected) power alarm at 1/10th of the forward value. Eg If the radio has been configured for 30 dBm Tx I'd set the alarm at 3 dB. If there's both a Hi alarm and a HiHi, I'd set Hi at 1/10th and HiHi at 1/4 of the Tx setting. No need for a low alarm. Zero is perfect.
**Max Tx Power**
I don't know exactly what this parameter does. My guess is it's just a way for you to query the radio as to how high Tx power can be set. So with an E Series it ought to respond with a 37 dBm value. I wouldn't bother with this one. Quite a few of the available parameters in the ClearSCADA radio diagnostics driver are for information only.
Another one that's variable depending on radio type, and on how good each path is. My preference would be for each path to have at least a 20 dB fade margin. So I'd put a low alarm at (radio's Rx sensitivity + 20 dB) and maybe a LoLo alarm at (...+15 dB or so). As for a high alarm, might set that at about -40 dBm. Much above that and most radios start getting distortion.
**Rx Freq error**
Variable depending on radio type. E Series is accurate +- 1 ppm. So at 450 MHz that means the frequency should be within 450 Hz plus or minus. Might go with a 500 Hz Hi alarm for the E Series, and a 1000 Hz HiHi alarm if you want to do both. If you just want one alarm I'd likely use 1000 Hz.
The M, K and J Series do not report frequency error. The M is a less expensive radio and so this feature was not included. And spread spectrum radios are far more forgiving of frequency inaccuracy due to their far greater receiver bandwidth.
The E and M Series are rated for -22 to +140 F (-20 to +60 C). K is rated -40 to +70C, which is -40 to +158. J is rated -40 to +65 C, which is -40 to +149 F. The radios will not fail immediately if the temperature limits are exceeded, but the frequency error will get worse and eventually the radio may stop communicating due to this. So I'd put the Hi and Lo temperature alarm limits at or perhaps slightly inside the high and low spec values.
**I can't remember what the ratio of Forward Tx power to Reverse Tx Power is called and what a reasonable ratio range would be...**
There is a parameter called VSWR which is likely what you're referring to. (voltage standing wave ratio) It is usually calculated in a different way, but can be done with forward & reflected power. I just can't find that equation right now, darn it! There are plenty of calculators that will do the job for you however. Eg Times Microwave has one you can download. (In Tech Resources, then Cable Performance Calculators)
That calculator tells me that if reflected power is 1/9 of forward power, you have a 2:1 VSWR. I use a 2:1 VSWR as my guide for when to start looking for problems in an antenna system. I tend to round the 1/9th to 1/10th for ease of use. If reflected power is 1/4 of forward power you have a 3:1 VSWR and at that point you really need to be getting out and fixing it ASAP. Most manufacturers aim to keep their antenna's VSWR below 1.5:1, which is a reflected power 1/25th of forward power.