handheld comms radio "interference"

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zooby

Senior Member
Location
Indiana
Occupation
maint. electrician
I was shown a video yesterday of an employee keying a handheld radio (to talk) and when he did the pump for the dry fire system started running. I am going up there soon to check this out but........thoughts anyone? All I can add right now is that we do have repeaters on our radio system and from a print it appears there is possibly a radio charging station on "a" circuit involved with the fire stuff --which if true seems like a big NO. Appreciate you guys.
 
ptonsparky said:
I've heard of handheld radios tripping GFCIs so this does not surprise me.
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this building has been open about a year now but i suppose it could have gone unnoticed until now. tried going down this rabbit hole last evening and it does seem reasonable that certain frequencies could work their magic on low voltage relays and such....I think.
 
VCS.jpg So it no doubt is turning on when radio is keyed. I have a short video of my own but dont think i can put that on here. 4SQ is toggle switch for it. Panel schedule says ....compressor & general plugs. thats it for now.
 
zooby said:
I was shown a video yesterday of an employee keying a handheld radio (to talk) and when he did the pump for the dry fire system started running. I am going up there soon to check this out but........thoughts anyone? All I can add right now is that we do have repeaters on our radio system and from a print it appears there is possibly a radio charging station on "a" circuit involved with the fire stuff --which if true seems like a big NO. Appreciate you guys.
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I saw something similar last century. On a research ship there was a trawl winch below decks. If you keyed a radio, it would start doing the hurdy-gurdy.
 
TwoBlocked said:
I saw something similar last century. On a research ship there was a trawl winch below decks. If you keyed a radio, it would start doing the hurdy-gurdy.
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I reached out to "Gast" and they actually responded saying " they have seen this a few times and we may try changing frequencies and/or channels
( neither of those is going to happen) and that they are working with their pressure switch supplier. well thats a starting point for sure.
 
zooby said:
I reached out to "Gast" and they actually responded saying " they have seen this a few times and we may try changing frequencies and/or channels
( neither of those is going to happen) and that they are working with their pressure switch supplier. well thats a starting point for sure.
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Just so we're clear, based on the information you provided later, this is the compressor that starts running, not the "pump". And it's technically known as an "air maintenance device", but even sprinkler guys still call it a compressor. So, with that said, there is no restriction on having other loads served by the same circuit that serves the air maintenance device, either by code or by the manufacturer. On the other hand, we always recommend a dedicated circuit.
 
gadfly56 said:
Just so we're clear, based on the information you provided later, this is the compressor that starts running, not the "pump". And it's technically known as an "air maintenance device", but even sprinkler guys still call it a compressor. So, with that said, there is no restriction on having other loads served by the same circuit that serves the air maintenance device, either by code or by the manufacturer. On the other hand, we always recommend a dedicated circuit.
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Thanks for clarifying. I do appreciate it. I will be getting the "AMD" onto its own circuit now that we realize it wasn't. It just seems like it should be.
So looking at your occupation line.....have you seen this before?
 
zooby said:
Thanks for clarifying. I do appreciate it. I will be getting the "AMD" onto its own circuit now that we realize it wasn't. It just seems like it should be.
So looking at your occupation line.....have you seen this before?
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This particular issue, no. On the other hand, now that I know about it, I'll keep it in the back of my mind in case some sprinkler tech runs into a similar situation. The fire protection industry is pretty conservative, so moving to things like digital pressure switches takes a while. And this is an excellent illustration of why that is so.
 
winnie said:
RFI mucking with low voltage control circuits is a known issue. There are filter and shield techniques, but without circuit details I can't suggest specific fixes.
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I will try to get more info. Thank you--
 
So as it happens often here, this is now been passed up the line and I may not know what gets done. To satisfy everyone (here) I did put this on its own circuit. If and when there is more to add I will do that in case it helps someone latter on.
 
This a solid state pressure transducer sending a signal to some solid state controller and not a dry contact pressure switch directly controlling a magnetic contactor, I am presuming?
 
zooby said:
So as it happens often here, this is now been passed up the line and I may not know what gets done. To satisfy everyone (here) I did put this on its own circuit. If and when there is more to add I will do that in case it helps someone latter on.
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Thanks for the update.

Hopefully they implement a good solution. But the solution may be a simple as having a defined area where radio transmissions are prohibited.

-Jonathan
 
kwired said:
This a solid state pressure transducer sending a signal to some solid state controller and not a dry contact pressure switch directly controlling a magnetic contactor, I am presuming?
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kwired - I am not one to bs about what I know and what I don't. Sorry to say the image I posted is all I know. Thank you though!
 
zooby said:
kwired - I am not one to bs about what I know and what I don't. Sorry to say the image I posted is all I know. Thank you though!
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I guess my point was it seems unlikely to have such effect from interference on a dry contact driving a magnetic contactor.

Solid state devices, particularly if operating on low signal levels would be more sensitive to RF interference that could possibly cause undesired responses.

Can't tell what you have there is why I was asking. Guess if you don't know maybe this is one of the things you maybe need to be checking out.

From the image it does look like some electronic control is involved which does tend to lean itself to solid state pressure detection being a possibility as well as solid state output to control the driven load.
 
RFI can be a fun with to mitigate. Get some Ferrite beads (the kind that snap around the wires / cables etc) and put then on the control wires. As many as you can get on there. In a desperate pinch I have stolen the ferrite bead from and old keyboard or mouse cable and used them. The snap on kind are much easier to install, just snap them onto the wiring.
Your radios are likely UHF radios. So the wavelength is fairly short. The wires become quarter wavelength multiples everywhere. And are perfect antennas
 
I used to work at a venue where if the stage manager keyed up her radio near the light board, it would reboot mid-show. That was fun.

I had another instance on a cruise ship where our DMX-controlled LED venue lighting was interfering with emergency satellite coms for the ship.

We solved the coms interference with lots of snap-on RF chokes after doing an RF survey onboard with a spectrum analyzer. We never really solved the light board problem, except to tell the SM to move her radio away from the light board before keying it.


SceneryDriver
 
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