RF energy burns

[chris kennedy]

Yesterday I went to an awning manufacture to prep for an automated fabric cutter. I was told that this machine is very RF sensitive.
They have 2 heat sealing machines that generate DC RF oscillating currant at 27.12MHz.They asked me if there is any way to reduce or shield the RF output.
Thats question 1.
Now it gets interesting. They tell me that these machines burn them. They can touch flat surfaces no problem, but the metal table edges will burn them on contact.
The guy that services these said that RF energy will build up on points and edges???
One of these also has a warning that it emits X-rays.
Anyone have an opinion?
View attachment 640

 

[ghostbuster]

Yesterday I went to an awning manufacture to prep for an automated fabric cutter. I was told that this machine is very RF sensitive.
They have 2 heat sealing machines that generate DC RF oscillating currant at 27.12MHz.They asked me if there is any way to reduce or shield the RF output.
]

Yes, at considerable cost these machines can be shielded.

At one site, these machines were radiating so much RF energy (1/4 mile radius), the electrical utility bucket truck crews communication systems were knocked out as well as their remote control systems.

 

[chris kennedy]

Yes, at considerable cost these machines can be shielded.

How would one go about this?

 

[ghostbuster]

How would one go about this?

Normally,a computer generated rf shield design is created ( $$) ,specifying xxdb. of attenuation is required.:smile:

 

[don_resqcapt19]

Ghost,

At one site, these machines were radiating so much RF energy (1/4 mile radius), the electrical utility bucket truck crews communication systems were knocked out as well as their remote control systems.

How did these machines get FCC approval?
Don

 

[chris kennedy]

Ghost,

How did these machines get FCC approval?
Don

Thats a great question. In my case the newest machine was built in 73. I found no date on the older machine. Again they generate 27.12MHz. Who knows what the FCC regs were 35 years ago?

I still want to know if anybody has heard of RF energy build up on points.

 

[Pierre C Belarge]

Ghost,

How did these machines get FCC approval?
Don

That is the same question I have...I am surprised the Utility company did not pursue this incident.
I wonder how good/bad this is for the people working there?

 

[dlhoule]

I don't know about heat build up on various points. I did once witness a 15 amp 250 Volt fuse have the paper catch on fire without blowing the fuse. We found a shorted componet and wound up with a very high frequency on the circuit.

It took us a while to figure out how we could have fuse catch on fire without enough current to blow the link inside of the fuse.

Edited for punctuation.

 

[mxslick]

Ummmmm..what about

Ummmmm..what about

..putting the access covers to all that electronics back on? (Unless the covers were removed just for the taking of the picture.)

Bet that's where a LOT of the RF leakage is coming from.

And a huge violation of various safety regs too.

 

[zbang]

Lessee...
Wrap the machine with copper windows screen, connect to a 4g or larger cable to the best ground there is around there, use type W cable so the skin effect is minimised..

or...

Contact the transmitter or chief engineer at the largest local TV station and hire them as a consultant.

 

[barbeer]

Ghost,

How did these machines get FCC approval?
Don

May not have to go thru the ringer since it is not communication equipment? I know a company in Melbourne FL specializing in RF testing and such-maybe they could help you. If you would like the info, PM me.

 

[don_resqcapt19]

barbeer,
I believe that FCC part 15 rules apply to any device that radiates energy that may interfere with communication systems.
Don

 

[pfalcon]

I still want to know if anybody has heard of RF energy build up on points.

The first time I saw this type of thing was with a vibration table and holographic pictures. You could actually see the vibration waves collect around defects in a plate of metal.

The second time I saw this type of thing was high frequency induction heating. After case-hardening a gear we would cut them apart to examine the heating pattern. The induced currents collect around points, edges, and defects.

I don't know this but then again I do ...

The RF energy is moving throughout the metal just as electricity would move through a fuse. Some heat is generated in the flats but the energy density is low enough that the heat can be shed by the surface. Near points and edges you get to see the knothole effect where the energy must concentrate to move around the defect. The point or edge will continue to heat until it radiates enough to equal the incoming energy. This would be like the necking down area of the fuse material.