Unknown Instrumentation: Antenna voltage monitor?

[Booshh]

I have this piece of instrumentation that I am trying to model that I am not entirely sure how it functions. I am certain that it is a voltage monitor. It's basically a voltage divider (v_out = .017*v_in) enclosed in a grounded box with two holes on either side for the connections to the voltage divider. One end of the voltage divider has a connector for a coax cable that would lead to an oscilloscope. The other end has a guide that allows the wire connecting to the voltage divider to stick out of the grounded box by about 3mm.

This instrumentation was placed in a pulsed power system that would be producing a great deal of TEM waves that would travel off of various parts of the system.

If it were acting like an antenna I am aware that the TEM waves would induce a current on the 3mm bit of wire. I am unsure the strength or the orientation of the TEM waves that are produced in the system. Does anyone have any insight on how I could initially approach trying to come up with a model? Or suggest an experiment/test that I could set up to see if the instrumentation actually works? (I can't use the pulsed power system in any testing.)

 

[berkeman]

pulsed power system

What kind of pulsed power system? Pulsed RF? If so, what frequencies are involved? If not, how is the pulsed power generating TEM radiation? Is there arcing or something?

Do you know the values of the resistor divider? Is it a 50 Ohm system?

 

[Booshh]

What kind of pulsed power system? Pulsed RF? If so, what frequencies are involved? If not, how is the pulsed power generating TEM radiation? Is there arcing or something?

Do you know the values of the resistor divider? Is it a 50 Ohm system?

We are working with a system that is producing hundreds of kV. The system is new to us so we haven't run it. We are trying to determine how all of the pieces function first to ensure safe testing. Based on the manuals that were provided to us we know that the voltage monitor was located under a Marx generator with opposite polarity capacitors that would produce 600kV. When the Marx generator was in configuration to run it would be located in capacitor oil to avoid any breakdown. I'm assuming that the TEM waves were produced when the capacitors discharged.

The wire that is sticking out of the box is attached to 9 330 Ohm resistors connected in series. This is connected to the coax output which would be measuring the voltage across two 106 Ohm resistors connected in parallel. The other end of the two parallel resistors are connecting to the grounded box.

 

[davenn]

We are working with a system that is producing hundreds of kV. The system is new to us so we haven't run it. We are trying to determine how all of the pieces function first to ensure safe testing. Based on the manuals that were provided to us we know that the voltage monitor was located under a Marx generator with opposite polarity capacitors that would produce 600kV. When the Marx generator was in configuration to run it would be located in capacitor oil to avoid any breakdown. I'm assuming that the TEM waves were produced when the capacitors discharged.

you didn't state any of this in the first post which would have been helpful

so there is a manual ? is this for the overall generator and the voltage monitor or just the monitor ?
does it not give specific info ?
photos of the said voltage monitor ... inside and out would be awesome for people here to try and understand what you are talking about


the more info you provide, the better the help you will get


Dave

 

[jim hardy]

Or suggest an experiment/test that I could set up to see if the instrumentation actually works? (I can't use the pulsed power system in any testing.)

Well a resistive voltage divider should be indifferent to frequency. You could check that with DC.

3mm sounds like maybe a 24 ghz radar antenna ? I'd see what i could learn from makers of test equipment for that stuff.
https://www.infineon.com/cms/en/product/sensor/radar-sensor-ics/24ghz-radar/

 

[Booshh]

you didn't state any of this in the first post which would have been helpful

so there is a manual ? is this for the overall generator and the voltage monitor or just the monitor ?
does it not give specific info ?
photos of the said voltage monitor ... inside and out would be awesome for people here to try and understand what you are talking about


the more info you provide, the better the help you will get


Dave

The manuals are for the entire system. There is only a single paragraph mentioning this instrumentation stating that it is a voltage monitor and it's location on the Marx. There isn't anymore relevant information given in the manuals, otherwise I would have stated it.

The only bit that is important here is that this is monitoring TEM waves produced off of a Marx Generator. Info about the Marx Generator is irrelevant because any kind of testing I do to see if this instrumentation device is even working will not be done with the Marx.

I cannot supply photos but it is a simple voltage divider (which i provided the equation of how it steps the voltage down) and a piece of wire is sticking out of a grounded box which we believe to be an antenna.

Basically we were given this thing and told to figure it out. I have little to no information on what it is besides everything I just told you.

I do not see how my second comment provides anymore insight to the problem than my original statement.

 

[berkeman]

The wire that is sticking out of the box is attached to 9 330 Ohm resistors connected in series. This is connected to the coax output which would be measuring the voltage across two 106 Ohm resistors connected in parallel. The other end of the two parallel resistors are connecting to the grounded box.

If it were acting like an antenna I am aware that the TEM waves would induce a current on the 3mm bit of wire. I am unsure the strength or the orientation of the TEM waves that are produced in the system.

Given your description of this sensor, it is not an antenna, and will not be picking up any high frequency TEM waves. It is most likely an E-field sensor with a bandwidth of a few MHz. It has a 50 Ohm output impedance (so set your 'scope input at 50 Ohms, not 1MOhm). There is no way a high-frequency antenna would have a string of resistors in series with the antenna element.

and a piece of wire is sticking out of a grounded box which we believe to be an antenna.

It's not.

I do not see how my second comment provides anymore insight to the problem than my original statement.

Well, any details help. I think the only way you can test it is with the high voltage generator nearby. That's what the low-capacitance, high-impedance voltage divider is designed to detect. I think I'd add some protection to the 'scope input just in case. I'll see if I can find a standard in-line protection circuit to post for you...

 

[Booshh]

Well, any details help. I think the only way you can test it is with the high voltage generator nearby. That's what the low-capacitance, high-impedance voltage divider is designed to detect. I think I'd add some protection to the 'scope input just in case. I'll see if I can find a standard in-line protection circuit to post for you...

Whenever we decide to run some tests we plan on using a string of attenuators to protect the scope based on the max voltage that we will be introducing to the setup just to be safe.

 

[anorlunda]

It is not really RF, but rather very short pulses that a Marx Generator makes. The purpose of the box might be to prevent EM radiation from getting out (see the red text below)

Does anyone have any insight on how I could initially approach trying to come up with a model?

It sounds like a case where only Maxwell's Equations in 3D will help analyze.

The Marx generator is also used to generate short high-power pulses for Pockels cells, driving a TEA laser, ignition of the conventional explosive of a nuclear weapon, and radar pulses.

Shortness is relative, as the switching time of even high-speed versions is not less than 1 ns, and thus many low-power electronic devices are faster. In the design of high-speed circuits, electrodynamics is important, and the Marx generator supports this insofar as it uses short thick leads between its components, but the design is nevertheless essentially an electrostatic one. (In electrodynamic terms, when the first stage breaks down it creates a spherical electromagnetic wave whose electric field vector is opposed to the static high voltage. This moving electromagnetic field has the wrong orientation to trigger the next stage, and may even reach the load; such noise in front of the edge is undesirable in many switching applications. If the generator is inside a tube of (say) 1 m diameter, it requires around 10 wave reflections for the field to settle to static conditions, which restricts pulse leading edge width to 30 ns or more. Smaller devices are of course faster.) When the first gap breaks down, pure electrostatic theory predicts that the voltage across all stages rises. However, stages are coupled capacitively to ground and serially to each other, and thus each stage encounters a voltage rise that is increasingly weaker the further the stage is from the switching one; the adjacent stage to the switching one therefore encounters the largest voltage rise, and thus switches in turn. As more stages switch, the voltage rise to the remainder increases, which speeds up their operation. Thus a voltage rise fed into the first stage becomes amplified and steepened at the same time.

 

[berkeman]

I think I'd add some protection to the 'scope input just in case. I'll see if I can find a standard in-line protection circuit to post for you...

It looks like most of these in-line protection devices are for Cable TV and similar applications (makes sense, I guess)... Here are a few examples. You'd need to get BNC adapters for each end to make it compatible with your 'scope and coax.

https://www.amazon.com/s/?ie=UTF8&keywords=coax+cable+surge+protector&tag=pfamazon01-20

 

[davenn]

The manuals are for the entire system. There is only a single paragraph mentioning this instrumentation stating that it is a voltage monitor and it's location on the Marx. There isn't anymore relevant information given in the manuals, otherwise I would have stated it.

not everyone thinks of that

and you still haven't provided any photos of this voltage monitor inside and out so that we know what the heck you are talking about

 

[berkeman]

and you still haven't provided any photos of this voltage monitor inside and out so that we know what the heck you are talking about

Yeah, whatever his is working on must be pretty proprietary, with folks who may or may not know what they are doing. GHz TEM detector with series-soldered axial resistors...

https://thumbs-prod.si-cdn.com/9D-x...1e6b3-855d-44c7-9ebf-d92cc6c68c82/human_2.jpg

 

[Booshh]

not everyone thinks of that

and you still haven't provided any photos of this voltage monitor inside and out so that we know what the heck you are talking about

I have already stated that I cannot provide photographs of the box. Figured the description would be enough for your imagination to run off of

 

[berkeman]

I have already stated that I cannot provide photographs of the box. Figured the description would be enough for your imagination to run off of

Well, it would be good to confirm that the resistors are just through-hole components, and not SMT. That would help to confirm the low-frequency nature of the operation of the sensor. Most likely they are big-body through-hole resistors, since they appear to be trying to have a large standoff voltage (so they don't arc-over).

 

[Booshh]

Well, it would be good to confirm that the resistors are just through-hole components, and not SMT. That would help to confirm the low-frequency nature of the operation of the sensor. Most likely they are big-body through-hole resistors, since they appear to be trying to have a large standoff voltage (so they don't arc-over).

They are indeed through-hole components.

 

[Baluncore]

I have already stated that I cannot provide photographs of the box. Figured the description would be enough for your imagination to run off of

Your experience has not given you the ability to identify the item, so why do you think you have the experience to judge what information is relevant or needed for us to identify the device?

So there are terminations and connectors, what type of connectors? How thick is the insulation, or how wide are the air gaps? I suspect it is not a voltage monitor, but is a current monitor on the low voltage side of the HV generator. The attenuator is needed because of the peak discharge current spike. Why are you so sure it is a voltage monitor.

What is the title on the manual? Who wrote the manual? What language is the manual written in? What year? How about a sketch circuit diagram? How are the connector / ports labled? Any text would be helpful, even if it is in Cyrillic.

Science prefers an abstract that informs, not one that mystifies. You are an entertaining story teller. I expect the dribble of information will go on and on, there may never be an end. Will we find the last page has been torn out of the novel, and that your question can never be answered through lack of information?

Maybe you are trying to reverse-engineer some other manufacturers product and that is why you are being so secretive. We do not know what country are you in, nor what organisation are you working for.

 

[berkeman]

I have already stated that I cannot provide photographs of the box. Figured the description would be enough for your imagination to run off of

Okay, this nonsense has gone on long enough. Thread is closed for now. @Booshh -- If you have lots more details that you want to post in order to get our help, please send me a PM (personal message -- click on my avatar). Barring that, we are done wasting our time guessing.