RF detector circuit design

Hello, I want to measure RF power ranging from 20Mhz to 1000Mhz during the field operation. Any DC voltage above 200mv is dangerous to ignite the detonator during perforation operation in the field. The circuit should be IC based and with small antenna at the input. Pl. help.
yadav

First of all could you please explain your question in a bit details. I coudnt get why the detonator came in between the RF power measurements, and where comes the DC volatge above 200Mv, and why?

pranam77 said:

First of all could you please explain your question in a bit details. I coudnt get why the detonator came in between the RF power measurements, and where comes the DC volatge above 200Mv, and why?

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During perforation operation of oil well, we use 50-105 ohm detonator which has 200ma no firing current. If the voltage cross a thresold limit, it can fire the detonator and the gun can blast on the surface and there may be fatal accidents. To avoid the incident we need a device which measure a RF Power in the vicinity of 300 mtrs to be safe, if the RF power is avalable, it is not desirable to do the job. In that case another RED type detonators are used which are safe to RF power. I hope the point is clear now. Thanks for your reply. Yadav

Sounds like they want a wide-band field strength meter rather than an RF detector.
Brian.

yadav_mrs said:

During perforation operation of oil well, we use 50-105 ohm detonator which has 200ma no firing current. If the voltage cross a thresold limit, it can fire the detonator and the gun can blast on the surface and there may be fatal accidents.

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I am also confused about the voltage, 50R*200mA=10V, but in your 1st post, you said it's 200mV. Could you give more explanation?

Suddenly I understand why oil rigs blow up.

jack

tony_lth said:

I am also confused about the voltage, 50R*200mA=10V, but in your 1st post, you said it's 200mV. Could you give more explanation?

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There is always a Fuse (Detonator of 50 ohm) at the input of loaded gun, which blast at subsurface when nearly 100 volts dc is applied through a conductor. I mean to say that the detonator blast between 200ma to 800ma firing current is given. The main purpose is when any RF power available within the 300 mtrs circle and the voltage available around it, the fuse/detonator can blast. The thresold volt is set at 250mv DC , if the voltage is more than the thresold it can fire the fuse. Now it will be clear.

Ok..the post is still confusing with two different topics or fields. There may be a 50 ohm fuse on one side and it may blast with 220Ma current at 100volts odd. Thaz ok.. But in that situation the two wires of the fuse will be connected with a detonator device which generates the required charge. But nothing will go wrong even if the two fuse wires are layed near a 10 Kw radio station coz the RF radition can never generate 100volts @220ma. But i am still not getting where you set 250mv of threshlod and why?

123jack said:

Suddenly I understand why oil rigs blow up.

jack

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Yes, this is scary....
I'm not sure which is the most scary... The fact that local RF signals over a huge spectrum can (alledgedly) predetonate oil rig gear or the fact that they are relying on a field strength meter as an early warning device or the fact that the solution to this (potentially serious) issue is being 'developed' on an internet forum...

Supposed there's an empirical evidence or at least a suspicion of RF fields being able to trigger a detonator, how do you relate RF field strength to known DC trigger currents? Obviously the relation will be frequency dependant and the susceptibility to RF fields strongly depend on the wiring geometry.

It may be the case, that a safety limit for RF field strength has been arbitrarily fixed, although it can't be validated by empirical observations. If so, you should tell the specification or refer to the respective regulation. The dubious "200 mV" is possibly a voltage observed with a particular field strength sensor. But it's a meaningless number without telling the whole story.

pranam77 said:

Ok..the post is still confusing with two different topics or fields. There may be a 50 ohm fuse on one side and it may blast with 220Ma current at 100volts odd. Thaz ok.. But in that situation the two wires of the fuse will be connected with a detonator device which generates the required charge. But nothing will go wrong even if the two fuse wires are layed near a 10 Kw radio station coz the RF radition can never generate 100volts @220ma. But i am still not getting where you set 250mv of threshlod and why?

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Dear Sir, The detonator (Fuse) of 50 ohm is current sensitive and should not fire upto 200ma current, it has the range from 200ma to 800ma firing current. it is not voltage sensitive. Any power generated by generator, mobile phones, tv broadcasting etc. etc. can create a firing current upto 200ma, which is not desirable. During perforation operation, all the power gerating sources are closed, mobile phones are switched off, transmission lines are shut,and the private as well as all BSNL/ other players mobile phones towers are requested to switched off so that the area will be RF power free zone. If some towers are still operating, or transmission lines are nearby, we use RED i.e RIG ENVIRONMENT DETONATOR an ultra safe detonator having a SCB, semi conductor bridge which is a device designed to ignite energetic material when subjected to a fast discharge current, that is more expensive This device when subjected to intense RF energy, will continuously dissipate upto 5 watts of power without inadvertent ignition.This device has an incredibly high immunity to RF energy, stray voltage and static charge buildup.It has been developed by JRC. It is more clear now. One more point in the matter, the fuse is 50 ohm added by another resistance of cable upto 60 or 70 ohms.

So, you shut down everything. Mobile phones, broadcast stations, power lines, CATV, (you forgot the satellites), instead making a simple and immune RF circuit.

vfone said:

So, you shut down everything. Mobile phones, broadcast stations, power lines, CATV, (you forgot the satellites), instead making a simple and immune RF circuit.

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Thanks for your kind reply pl. Kindly let me know the details of ERA-2.

Products - Hittite Microwave Corporation

Notice HMC611LP4, from 1M~10GHz, RMS detector.

---------- Post added at 09:24 ---------- Previous post was at 09:24 ----------

ERA-2 is amplifier from Mini-Circuits.

---------- Post added at 09:25 ---------- Previous post was at 09:24 ----------

At hittite website, there are application note for you ref.

G0HZU said:

Yes, this is scary....
I'm not sure which is the most scary... The fact that local RF signals over a huge spectrum can (alledgedly) predetonate oil rig gear or the fact that they are relying on a field strength meter as an early warning device or the fact that the solution to this (potentially serious) issue is being 'developed' on an internet forum...

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hmmm... indeed.

My concern was with your second concept. (I was just a bit shy about saying it)
My RF experience suggests the first issue is unlikely and static would be a much
larger concern but I'm out of date on that and wouldn't consider trying to
give a definitive comment.

But developing explosive systems and factory and other supposedly "failsafe"
equipment on internet forums seems to be more popular these days. It troubles
me more than a little.

There's nothing wrong with asking for support but some of the questions I see
suggest the people doing the asking shouldn't be allowed anywhere near the projects they describe.

I can only hope there's a new breed of techno trolls out there.

jack

Any power generated by generator, mobile phones, tv broadcasting etc. etc. can create a firing current upto 200ma, which is not desirable.

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I've been thinking about the statement and found, that it's not actually plausible. The detonator trigger level isn't just 200 mA, but 200 mA @ 50 ohms, or in other words, 2 W. A GSM mobile phone has a peak RF power of 2 W, but an average (thermal) power considerably below 1 W. So even if the total RF power would be transferred to the detonator, which is effectively impossible, it can't ignite.

FvM said:

I've been thinking about the statement and found, that it's not actually plausible. The detonator trigger level isn't just 200 mA, but 200 mA @ 50 ohms, or in other words, 2 W. A GSM mobile phone has a peak RF power of 2 W, but an average (thermal) power considerably below 1 W. So even if the total RF power would be transferred to the detonator, which is effectively impossible, it can't ignite.

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I guess it depends what the detonator looks like at 900MHz etc. Maybe it doesn't look like 50 ohms resistive any more. Also, the OP implies the device is triggered by voltage (then he said it was current) so if the detonator looks a diifferent impedance (at RF) compared to a 50 ohm load then I can easily see how it could get a high voltage difference across it (or even a high RF current) in the presence of RF fields.

I guess it depends what the detonator looks like at 900MHz etc.

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Why? The ignition threshold will be determined by thermal parameters. The calculation is already assuming perfect impedance matching. Then the delivered power can't be increased by changing the impedance to any value.

However, I mainly wanted to show that the arguments are rather meagre. The original poster don't give a rational explanation for his assumptions nor refers to a safety regulation, so everything is more or less speculation.

I agree it is all speculation but I think the action of a detonator can't be simply modelled as requiring 2W. But then I know next to nothing about detonators

I assume the detonator fires instantly when given the correct control signal (this signal will be brief?)
But I have no idea what happens if the detonator is bathed in a high RF field over the course of a longer time eg several minutes.

However, from a power transfer point of view even a high power mobile phone mast operating at 900MHz and over 1kW ERP can't transfer much power to a pickup antenna placed 50 metres away so I can see where your argument comes from.
But I wouldn't want to sit on the detonator to prove this was OK...

G0HZU said:

However, from a power transfer point of view even a high power mobile phone mast operating at 900MHz and over 1kW ERP can't transfer much power to a pickup antenna placed 50 metres away so I can see where your argument comes from.
But I wouldn't want to sit on the detonator to prove this was OK...

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And thats my thoughts as well, you would have to have a strong transmitter sitting beside the detonator (or any wire/device) to be able to induce 200mA (a coupleof volts) or more into it.
by the time you move a few metres away that wonderful inverse square law play the game and induced voltages and currents and going to fall into the uV (uA) region.

my 2cents worth for some fun discussion

Dave