Trying to design an Isolated, High Voltage Probe.

[HIPPMS]

Let me try to make this simple....

I design and build Pulsed Power supplies for Magnetron Sputtering.

The output voltage is anywhere from 600 to 1700 VDC, and the current can reach as much as 1,000 Amps. (If you deal with Magnetrons....you will know what I mean.)

Measuring current is no problem..I use LEM current sensors and custom current sensors. These signals are all isolated galvincaly, so I have no problems.

But I am having a problem measuring the voltage, and having the signal isolated.

Any of you guy's have anyideas?

 

[VEBill]

Is this a Test Equipment application, or something to be built-into the system in production quantities?

What sampling rate is required?

Is there a low voltage PS available on 'this' side of the isolation?

In advance of these details, I'm already thinking of those opto-couplers that are several inches in length. They could be used to transmit digital data while providing isolation even for thousands of volts. This concept requires a data capturing and transmitting circuit on 'this' side of the barrier. The initial input would of course be a suitable (high voltage) voltage divider.

 

[VEBill]

For test equipment purposes, one might use two high voltage probes (output and return) and differential mode.

 

[zzzjim]

A question
Are supply and magnetron separated by a reasonable distance , or will there be some RFI as well as high voltages & Magnetic fields in the area ?

 

[HIPPMS]

To VE1Bll....

This is for our production units. Testing is no problem, as I have Textronix HV Differential Probes.

Sampling rate is not the issue. (Output frequency is 20-50Khz)

I currently have a voltage divider, and it is referenced to the Positive output. (Again, Magnetrons...)

The noise induced into my control circuits is causing havoc. So I want to isolate the input from my control circuit grounds.

I am trying to find a simple circuit without having to use a $50 isolation amplifier.

I guess what I am looking for is an analog optoisolator circuit.

(providing isolated supplies for this circuitry is not a problem.)

Hope this answers your questions....

 

[HIPPMS]

to zzzjim.....

You asked..." Are supply and magnetron separated by a reasonable distance , or will there be some RFI as well as high voltages & Magnetic fields in the area ?"

All of the above.....

 

[VEBill]

...an analog optoisolator circuit...

Incorporating the optoisolator directly into an all-analog solution is unlikely to be stable and accurate over temperature. Ultimately possible, but probably a time-sink.

The concept that I was suggesting is a digital optoisolator. Assuming you can provide a local low voltage power supply, you build a checp and cheerful uC ciruit to measure the voltage, the results are then transmitted out digitally.

Another approach is V-to-F, it should be practical.

 

[sreid]

LEM also makes voltage isolators.

 

[HIPPMS]

I appreciate the reply's.....

I have been experimenting with the Avago HCNR200 analog isolator, but it just isn't fast enough.

I know that LEM makes voltage sensors....but they very expensive, and not much faster than their current sensors.

I need a fast response to both Voltage and Current to detect an Arc.

Arc conditions in Plasma don't matter much if you are coating drill bits with TiN.....but if you are coating Silicon Wafers, it is a big deal.

I can't really put an isolated microprocessor anywhere near the outputs of this machine......the noise when switching 1000 Amps is horrendous.

I will keep searching...appreciate all the comments and suggestions.

 

[Comcokid]

I was going to suggest Avago, but I see you've tried them.

I seem to also recall that Linear Tech made a isolation barrier device of some type. If they don't still have it, you might check their list of app notes and circuits because this sounds like something they might have published.

 

[sreid]

If you only need an AC voltage measurement, a Ferrite core transformer would give you the isolation along with steping down the voltage for use with subsequent electronics.

 

[VEBill]

I need a fast response to both Voltage and Current to detect an Arc.

Arc detecting circuit breakers are apparently now mandated for bedrooms in residential construction (at least around here, so I've been told). Would it be useful if you bought one of those commercial items (maybe $80?) and reverse-engineered it?

1700 Vdc is "only" ;-) 10x household power peak voltage.

 

[DHambley]

When I've had to step down from a noisy high voltage to a control circuit, I amplify the signal first, referenced to its return (your HV positive reference) then send the signal to the step-down circuit. By doing this the s/n ratio is divided by the gain of the first amplification. Or, put more circuitry "upstairs".
I looked at that Avego part. If accuracty is the problem, then maybe your arc detection analog circuitry can be up at the high voltage, then only a 1/0 needs to be isolated and sent down.

 

[HIPPMS]

to hgldr.....your answer is the only one that seems to make sense.

I just don't understand it yet.....but I think you may have the key to my problem.....

 

[VEBill]

Resistive voltage dividers are relatively quiet compared to the voltages being discussed here.