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Measuring high voltages

Started by TTman March 30, 2015
I have a  circuit that generates a floating ( both sides) ~  +/- 1500V. 
The final output is generated by a standard diode cap multiplier block, 
giving 1mA current. The +ve output is monitored via a 1G resistor into 
an opamp then an ADC. The negative output is allowed to follow the 
positive which is in a closed loop controlto set the output voltage.
What is the best way to monitor the -ve output ? 100:1 probe ? a fet 
probe? 1000:1 probe ? Output is pulsed in the small uS range...
TIA

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On Mon, 30 Mar 2015 21:46:19 +0100, TTman wrote:

> I have a circuit that generates a floating ( both sides) ~ +/- 1500V. > The final output is generated by a standard diode cap multiplier block, > giving 1mA current. The +ve output is monitored via a 1G resistor into > an opamp then an ADC. The negative output is allowed to follow the > positive which is in a closed loop controlto set the output voltage. > What is the best way to monitor the -ve output ? 100:1 probe ? a fet > probe? 1000:1 probe ? Output is pulsed in the small uS range... > TIA > > --- > This email is free from viruses and malware because avast! Antivirus protection is active. > http://www.avast.com
What do you mean by 'floating'? Does the measuring device also float, or is it referred to some other potential/ground? How accurate do you need this to be? Also - are you expecting to follow the dynamics of this pulsed voltage? To what bandwidth?
How is it pulsed if it is derived from a CW multiplier?

Tim

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"TTman" <pcw1.cad@ntlworld.com> wrote in message 
news:mfccl6$jan$1@dont-email.me...
>I have a circuit that generates a floating ( both sides) ~ +/- 1500V. >The final output is generated by a standard diode cap multiplier block, >giving 1mA current. The +ve output is monitored via a 1G resistor into an >opamp then an ADC. The negative output is allowed to follow the positive >which is in a closed loop controlto set the output voltage. > What is the best way to monitor the -ve output ? 100:1 probe ? a fet > probe? 1000:1 probe ? Output is pulsed in the small uS range... > TIA > > --- > This email is free from viruses and malware because avast! Antivirus > protection is active. > http://www.avast.com >
On 3/30/2015 3:46 PM, TTman wrote:
> I have a circuit that generates a floating ( both sides) ~ +/- 1500V. > The final output is generated by a standard diode cap multiplier block, > giving 1mA current. The +ve output is monitored via a 1G resistor into > an opamp then an ADC. The negative output is allowed to follow the > positive which is in a closed loop controlto set the output voltage. > What is the best way to monitor the -ve output ? 100:1 probe ? a fet > probe? 1000:1 probe ? Output is pulsed in the small uS range... > TIA > > --- > This email is free from viruses and malware because avast! Antivirus > protection is active. > http://www.avast.com >
Here's a reasonable priced 20ua meter, series seven 10meg and one 5 meg resistors in series with the meter. and it will read full scale at 1500V. Maybe I'd use ten 10meg in series and the you could see an over voltage condition. Caution High Voltage, us proper techniques and insulation. Also remember it's a negative voltage when hooking it up. 20ua will have negligible affect on your voltage. Mikek --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com
On 3/30/2015 5:08 PM, amdx wrote:
> On 3/30/2015 3:46 PM, TTman wrote: >> I have a circuit that generates a floating ( both sides) ~ +/- 1500V. >> The final output is generated by a standard diode cap multiplier block, >> giving 1mA current. The +ve output is monitored via a 1G resistor into >> an opamp then an ADC. The negative output is allowed to follow the >> positive which is in a closed loop controlto set the output voltage. >> What is the best way to monitor the -ve output ? 100:1 probe ? a fet >> probe? 1000:1 probe ? Output is pulsed in the small uS range... >> TIA >> >> --- >> This email is free from viruses and malware because avast! Antivirus >> protection is active. >> http://www.avast.com >> > > Here's a reasonable priced 20ua meter, series seven 10meg and one 5 meg > resistors in series with the meter. and it will read full scale at 1500V. > Maybe I'd use ten 10meg in series and the you could see an over voltage > condition. > Caution High Voltage, us proper techniques and insulation. > Also remember it's a negative voltage when hooking it up. > 20ua will have negligible affect on your voltage. > Mikek
Forgot the meter, http://www.ebay.com/itm/20-UA-DC-Meter-/391098122469?pt=LH_DefaultDomain_0&hash=item5b0f43c0e5 --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com
On 30/03/2015 22:04, Frank Miles wrote:
> On Mon, 30 Mar 2015 21:46:19 +0100, TTman wrote: > >> I have a circuit that generates a floating ( both sides) ~ +/- 1500V. >> The final output is generated by a standard diode cap multiplier block, >> giving 1mA current. The +ve output is monitored via a 1G resistor into >> an opamp then an ADC. The negative output is allowed to follow the >> positive which is in a closed loop controlto set the output voltage. >> What is the best way to monitor the -ve output ? 100:1 probe ? a fet >> probe? 1000:1 probe ? Output is pulsed in the small uS range... >> TIA >> >> --- >> This email is free from viruses and malware because avast! Antivirus protection is active. >> http://www.avast.com > > What do you mean by 'floating'? Does the measuring device also float, or > is it referred to some other potential/ground? How accurate do you > need this to be?
The -ve of the + supply is connected to the pos of the -ve supply, which is ground referenced. 2-3% would be good...
> > Also - are you expecting to follow the dynamics of this pulsed voltage? > To what bandwidth? >
No just the peak DC voltage which is about 50uS --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
On 30/03/2015 22:14, Tim Williams wrote:
> How is it pulsed if it is derived from a CW multiplier? > > Tim >
there's a front end pulsed oscillator feding the D/C multiplier. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
On Mon, 30 Mar 2015 21:46:19 +0100, TTman <pcw1.cad@ntlworld.com>
wrote:

>I have a circuit that generates a floating ( both sides) ~ +/- 1500V. >The final output is generated by a standard diode cap multiplier block, >giving 1mA current. The +ve output is monitored via a 1G resistor into >an opamp then an ADC. The negative output is allowed to follow the >positive which is in a closed loop controlto set the output voltage. >What is the best way to monitor the -ve output ? 100:1 probe ? a fet >probe? 1000:1 probe ? Output is pulsed in the small uS range... >TIA > >--- >This email is free from viruses and malware because avast! Antivirus protection is active. >http://www.avast.com
I'd try one of those TV flyback HV probes. They are about 10G ohms and will lightly load the supplies. But they are not frequency compensated, you might have to build one yourself if frequency response is important. Cheers
On a sunny day (Mon, 30 Mar 2015 23:17:37 +0100) it happened TTman
<pcw1.cad@ntlworld.com> wrote in <mfci0c$b4t$1@dont-email.me>:

>On 30/03/2015 22:04, Frank Miles wrote: >> On Mon, 30 Mar 2015 21:46:19 +0100, TTman wrote: >> >>> I have a circuit that generates a floating ( both sides) ~ +/- 1500V. >>> The final output is generated by a standard diode cap multiplier block, >>> giving 1mA current. The +ve output is monitored via a 1G resistor into >>> an opamp then an ADC. The negative output is allowed to follow the >>> positive which is in a closed loop controlto set the output voltage. >>> What is the best way to monitor the -ve output ? 100:1 probe ? a fet >>> probe? 1000:1 probe ? Output is pulsed in the small uS range... >>> TIA >>> >>> --- >>> This email is free from viruses and malware because avast! Antivirus protection is active. >>> http://www.avast.com >> >> What do you mean by 'floating'? Does the measuring device also float, or >> is it referred to some other potential/ground? How accurate do you >> need this to be? > >The -ve of the + supply is connected to the pos of the -ve supply, which >is ground referenced. 2-3% would be good... >> >> Also - are you expecting to follow the dynamics of this pulsed voltage? >> To what bandwidth? >> >No just the peak DC voltage which is about 50uS
If it is truely a 50 us pulse from 0 to whatever, then you could use a capacitive divider, and measure AC. Else as you use a resistor divider for +, why not do the same for -. BTW if you connect both together the output should be zero for DC. If you have problems with negative voltages, then hang a resistor from the end of the - divider to some stabilized +, so reference + of the ADC range
>"I'd try one of those TV flyback HV probes. They are about 10G ohms "
Nope, like 1.1 G.