Microwave oven leakage detector.  - Page 1
Forum section: electronics / rf-microwave

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 09, 2020, 12:47:11 am
content: An acquaintance of mine was heating food on its microwave oven, when a stray aluminum foil sitting next to its door showed occasional sparks.The sparks were tiny, according to her description as I’ve not seen them, but piqued her curiosity enough to give me a call.I told her to turn off the oven to see if the sparking disappeared. It did, thus I told her that it must be leakage.The oven is relatively new and she is now in a state of panic.I would like to assist her to make a claim, but the sparky foil is a very subjective test.I know there are leakage detectors out there, and the price range is all over the place.What would be your recommendation?

author: james_s
author_rank: Super Contributor
timestamp: January 09, 2020, 12:57:08 am
content: I would check the door and latch mechanism for mechanical damage, it's possible the door is not closing fully. I also would not panic, a microwave oven is nothing more than a radio transmitter in a box. I wouldn't stick my hand inside one but leakage is not a dire issue, it's not ionizing radiation and the inverse square law mandates that the field strength drops off with the square of the distance. You would not have to get far from an oven operating with the door fully open to feel nothing.

author: wraper
author_rank: Unknown
timestamp: January 09, 2020, 01:05:10 am
content: See if 2.4 GHz wifi stops working in close proximity when oven is on. Placing device directly on oven often will kill wifi even with good oven.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 09, 2020, 01:06:39 am
content: That is scary. The fact that reports like this are casually dismissed even in RF enthusiasts community. Scary. As bad as the claims that X-Rays emitted from TV vacuum tubes are harmless. And look at everyone now 50 years later. Aren't we finally noticing the loss of hair, teeth and clarity of thought.

author: wraper
author_rank: Unknown
timestamp: January 09, 2020, 01:16:03 am
content: Quote from: unitedatoms on January 09, 2020, 01:06:39 amLOL. Drink less Kool-Aid. FYI simply living in certain areas of earth will expose you to such natural radiation dose in a year or even less that you will never experience in your whole life. And people are still fine and alive. Also never fly on airplane, you'll be exposed to high radiation levels when high in the sky.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 09, 2020, 01:26:00 am
content: Quote from: schmitt trigger on January 09, 2020, 12:47:11 amSparks on Al foiloutsidethe oven? I would panic, too.No matter what a leakage detector will show, return that oven and buy another model, or just throw it away if it can not be returned.Would be interesting to make a movie of the sparks before returning it, thought.

author: james_s
author_rank: Super Contributor
timestamp: January 09, 2020, 01:26:16 am
content: Quote from: unitedatoms on January 09, 2020, 01:06:39 amYou clearly have no idea what you're talking about. Please look up the difference between RF radiation and ionizing radiation.CRTs do not emit xrays to any meaningful degree. There were some TVs in the early days that could experience certain failure modes that caused the EHT to go WAY up, thus the mandating of protection circuitry and leaded glass. In even older sets it was the HV rectifier tube that could emit xrays.So yes, we dismiss things like this because we know what we're talking about, while you clearly don't. Unless you're just trolling in that yeah 50 years later a lot of people are losing hair, teeth and cognitive function because duh, people get old and nothing lasts forever. Lifespans in the developed world are longer now than at any point in recorded history. You shouldn't make jokes because someone might think you're serious.

author: StillTrying
author_rank: Super Contributor
timestamp: January 09, 2020, 01:44:19 am
content: Quote from: schmitt trigger on January 09, 2020, 12:47:11 amI'll believe it when I see it.

author: wraper
author_rank: Unknown
timestamp: January 09, 2020, 02:01:14 am
content: Quote from: schmitt trigger on January 09, 2020, 12:47:11 amIf you record it on video, it's a pretty serious claim. To the point of making product recall. Although I have some doubts about what she had actually seen.

author: David Hess
author_rank: Super Contributor
timestamp: January 09, 2020, 03:16:41 am
content: Quote from: wraper on January 09, 2020, 01:05:10 amThat will happen whether the door is leaking significantly or not.

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2020, 03:17:45 am
content: The sparks may also be caused by an open ground to the oven. Mains leakage currents can find a path to the nearby sink, countertop or fridge etc.I doubt it is due to microwaves because the door mesh and housing are well designed and need a large gap for anything to get out - at which point the door switches should trip.Unless your acquaintance wants you to come by and check her oven

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 09, 2020, 03:20:27 am
content: I understand the skepticism, and to a certain degree I am skeptical too. The amount of leakage would have to be very significant.Unfortunately, I did not witness the event personally. We are about 350 kilometers away.But she is what I consider an educated and pretty level headed person, and cannot simply dismiss her claim as an ignorant or hysterical rant.Let’s say I am giving her the benefit of the doubt and would like to investigate further.That is the reason for my original question: does anyone know of a microwave leakage detector which is trustworthy?There are many Amazon offerings, of all price levels, but have not the experience to decide what would be a decent one.

author: David Hess
author_rank: Super Contributor
timestamp: January 09, 2020, 04:10:40 am
content: Quote from: schmitt trigger on January 09, 2020, 03:20:27 amI would probably hack something together using a neon bulb and wire loop. But with any microwave oven leak detector, I would make a comparison measurement with another presumed good microwave oven to get an idea of what a good leakage measurement result should be.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 09, 2020, 05:06:30 am
content: A piece of Aluminum foil won't spark, even inside a microwave oven, unless it comes too close to the wall. And if it did spark, the sparks wouldn't be tiny. But a piece of foil next to the door might flutter in the air stream from the fan in the oven and reflect light that might look like tiny sparks.However, when you consider that a microwave oven can generate up to 1000 watts of microwave energy, the possibility of even a small leak has to be taken seriously. Microwave radiation is known to cause cataracts at surprisingly low levels. The damage is cumulative, so even low levels over a long period of time can cause problems. The problem is that the eye's lens is sensitive and, when injured, doesn't heal very well. I believe this problem was identified decades ago in telecom workers who worked on the microwave radio systems. These systems had output power levels in the 1 - 5 watt range.Ed

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2020, 06:38:57 am
content: Perhaps make one, they are simple. Examplepatent US 4338595Microwave leakage detector. A dipole antenna, hot carrier (Schottky) diode and panel meter or LED. Copper FR4 box.But a big issue is calibration, where is the line saying the energy is significant and can cause damage?You may be able to borrow/rent a leakage tester from a repair shop if you're on good terms with them.

author: ogden
author_rank: Super Contributor
timestamp: January 09, 2020, 07:39:56 am
content: Quote from: floobydust on January 09, 2020, 06:38:57 amExactly. Such "DIY detector" is no better than just foil mentioned. My suggestion here would be to make sure that sparking foil is repeatable, then contact/consult local authorities that are responsible for consumer product quality claims. Simple warranty claim may help for particular single customer, but it definitely will not result in product recall because manufacturers are not keen to admit their faults.

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2020, 08:08:19 am
content: "A Federal standard (21 CFR 1030.10) limits the amount of microwaves that can leak from an oven throughout its lifetime to 5 milliwatts (mW) of microwave radiation per square centimeter at approximately 2 inches from the oven surface. This limit is far below the level known to harm people. Microwave energy also decreases dramatically as you move away from the source of radiation. A measurement made 20 inches from an oven would be approximately 1/100th of the value measured at 2 inches from the oven."In that patent:"...If the LED is still activated at this [4" from door] distance, an excessive leakage condition is occuring whereby the amount of radiation emanating from the oven is greater than that permitted by FDA standards.""The antenna length and the particular LED employed are dependent on the sensitivity desired and the intensity of the leak-source."I figure the dipole antenna is two 1/4 wave 30.6mm elements (2450MHz). Anyone have suggestions for a suitable diode?

author: ogden
author_rank: Super Contributor
timestamp: January 09, 2020, 10:25:07 am
content: Quote from: floobydust on January 09, 2020, 08:08:19 amJust use two anti-parallel *red* 5mm through-hole LEDs. Mount resulting "indicator" on non-conductive stick.

author: wraper
author_rank: Unknown
timestamp: January 09, 2020, 10:40:01 am
content: Quote from: David Hess on January 09, 2020, 03:16:41 amThat will not happen if you don't place your wifi device directly on normally working oven but keep some small distance away.

author: Gyro
author_rank: Super Contributor
timestamp: January 09, 2020, 11:42:52 am
content: A bare neon lamp run around the door seals will give a quick and dirty leakage indication.P.S. There's a 1/4 wave trap built into the metalwork of the edge of the door, combined with lossy ferrite. Food contamination can affect their efficiency (as can wrong door gap).

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2020, 01:32:46 pm
content: the field strength would need to be really strong to spark

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 09, 2020, 01:56:29 pm
content: Guys, guys, guys!You are missing my point.As a test equipment-nut, which most if not all of the EEVB members are, I am lookingat an excuseto purchase an additional meter!I know that I've got a TE disease, but if I'm going to spend some money, I would like to purchase something that is at least mildly useful.Plus, as other poster commented, I would also like to have an excuse to make the trip to visit a nice lady.

author: MagicSmoker
author_rank: Super Contributor
timestamp: January 09, 2020, 01:59:59 pm
content: Quote from: wraper on January 09, 2020, 01:16:03 amQuote from: james_s on January 09, 2020, 01:26:16 amMaybe unitedatoms needs to adjust his tin foil helmet, or maybe he was trolling:Quote from: unitedatoms on January 09, 2020, 01:06:39 amAfter all, lots of people will have lost "hair, teeth and clarity of thought," after aging another 50 years...

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 09, 2020, 03:51:29 pm
content: Apologies if someone thought I am trolling. I am half joking, but not disrespecting people's critical thinking and sense of humor.BTW the X-Ray from TV CRT at 25kV on anode is so named Hard X-Ray at 50 picometers, not even Soft X-Ray.Some calculation result I found:https://www.numerade.com/questions/3835-x-rays-from-television-screens-accelerating-voltages-in-cathode-ray-tube-crt-tvs-are-about-250-/Some wavelength table:https://commons.wikimedia.org/wiki/File:Light_spectrum.svgAlso the tinfoil hats should be renamed to aluminum foil hats. It causes unnecessary confusion for people, who consider using EMI protection.

author: james_s
author_rank: Super Contributor
timestamp: January 09, 2020, 05:42:37 pm
content: There have been several studies on CRT xray emissions, every one that I've come across has found negligible emission. All CRT displays made since sometime in the mid 70s have incorporated xray protection circuitry that shuts down the display if the EHT rises beyond a safe level.https://oer.unimed.edu.ng/OTHER%20OER%20VARIETIES/5/1/Ife-Adediran-O-O-Arogunjo-A-M--EXPOSURE-RATE-ASSESSMENT-FROM-SELECTED-CATHODE-RAY-TUBE-DEVICES.pdf25kVp xrays do not penetrate well and are easily blocked by the leaded glass the tube is made from. Low kVp xray tubes used for specialized purposes like mammography use thin beryllium windows because even a few mm of ordinary glass heavily attenuates the radiation.

author: chris_leyson
author_rank: Super Contributor
timestamp: January 09, 2020, 09:26:24 pm
content: @schmitt trigger, get your arse over there and film it, seriously, or get your friend to film it.If it's leakage then..QuoteProbably the best comment so far.If you can make little sparks from oven leakage then you are already several orders of magnitude over the perscibed safety limits. You are in W/cm2territory, look pretty sparks followed by boiled eggs for eye balls, and if you can get a neon bulb to light when placed next to a door seal you are also in very dangerous territory, well over prescibed safety limits.Gyro is right about the 1/4 traps and the ferrite is optional, it's cost up. For 1/4 wave traps to work the trap to oven distance tolerances are very tight. Misaligned hinges don't help and neither do misaligned door switches.Measuring power density mW/cm2in three axes doesn't come cheap and costs an order of magnitude more than the oven so I wouldn't waste time looking for a cheap uncalibrated leakage detectors.P.S. I work for a large microwave oven manufaturer where customer safety is paramount.

author: grizewald
author_rank: Frequent Contributor
timestamp: January 09, 2020, 09:39:00 pm
content: Quote from: unitedatoms on January 09, 2020, 03:51:29 pmI thought your humour and irony shone through your post like a laser!Maybe people looked at the flag under your name and thought "Americans can't do irony, so unitedatoms must be serious!"I stuck with how it read the first time.

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 10, 2020, 12:16:41 am
content: Thanks Chris for the advice, I won’t waste my time and money on unreliable meters.And since I don’t do this for a living, I am not keen on spending a fortune on a good one.As someone else explained, it could -most likely- be an improper grounding issue. I can troubleshoot that easily.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 10, 2020, 02:54:02 am
content: There is article "Microwave Leakage Detector" in Everyday Practical Electronics, April 2017.Basically dipole antenna at RF diode MMBD301, some stripline voodo, 220pF cap, 220 Ohm load. Rest is comparator's string from 52mV up to 417mV with LEDs.Picture shows a human hand (presumably of living person) holding detector near running microwave oven. The level is full scale 417mV. Scary.

author: 0culus
author_rank: Super Contributor
timestamp: January 10, 2020, 02:59:25 am
content: Quote from: schmitt trigger on January 09, 2020, 01:56:29 pmIf you have access to a spectrum analyzer you could at least gain a qualitative idea of how much leakage there is.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 10, 2020, 04:17:22 am
content: You can also test how much 2.4GHz leaks into the (unpowered) oven.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 10, 2020, 02:32:40 pm
content: Quote from: NiHaoMike on January 10, 2020, 04:17:22 amTo my knowledge, one of the main mechanisms for sealing in the 2.4 GHz is not a faraday cage - it is using a 1/4 lambda trap. This way they can get away with far less perfect mating of surfaces on the door. It also means that the box won't be that well sealed at other frequencies. since 2g/3g/4g use different bands you can't really make any usefull claims about the seal not working if you can call the phone (or vice versa, really)

author: james_s
author_rank: Super Contributor
timestamp: January 11, 2020, 01:26:57 am
content: Quote from: grizewald on January 09, 2020, 09:39:00 pmI was on the bus on my phone so I didn't see the flag, and I've encountered a number of people who make it difficult to tell if others are just joking or not.Anyway as far as leakage detectors I don't think it should matter too much. If the leakage is sufficient to make something spark then I would think that the most deaf detector you can find will peg off the scale. I too am somewhat skeptical after thinking about it though, I wonder if it could be capacitive coupling of much lower frequencies? Maybe it's an inverter oven and not properly grounded? Still seems unlikely, but while playing with HV I have seen metal objects several feet away sparking between each other as corona was spraying all over out of a big old DC flyback transformer.