Measuring very high AC voltage using PIC16F876A

[wiqi136]

hi friends, i want to measure a high voltage ( 0 - 30kv ) using a PIC16F876A micro controller. Actually i need to use output voltage of an auto-transformer as a feedback to my control circuit...
Please help me out.
Thanks

 

[goldsmith]

Dear wiqi
Hi
Is isolation important for you ? is your voltage DC ? or perhaps AC ? if it is AC , is that sine wave ? if yes , how much is it's frequency ? there are many simple ways available but you should mention the parameters that i told .
Best Wishes
Goldsmith

 

[wiqi136]

Actually I am working on a project, Automatic control for an auto-transformer.
user will sett the angle of rotation or the required output voltage. motor with some gear mechanism will rotate the tap of the auto-transformer.
for that the control circuit must develop a positive and negative voltage for forward and reverse. To set the required output voltage i can design a fairly sophisticated control circuit that used a PID loop and when user enter a setpoint it compares the output voltage with that setpoint. The output of the loop would be amplified and sent to the motor.
Yes Isolation is important as its a very high voltage. Actually this project is a part of a big project, that is to measure the breakdown voltage of polymeric materials. for that we need to supply voltage from 0V to 30KV to a thin film of polymeric layer using an auto-transformer.
i need to step down this 0-30kv to 0-5v so that it can be used as an input to ADC.

 

[goldsmith]

30kv ? it is pretty familiar for me ! i think it is for another thing ! anywhere . why that way to achieve 0-30kv ? why not an SMPS ? it will be pretty simpler . and a notation , be careful , when you want work with this voltage . and remember , at least one millimeter instead of each kv ! at low frequencies and DC ! anywhere , if you need bilateral circuit to measure , you won't need to measure both cycles . because both are the same ! hence , you can use two dividers and then rectify it , and then a linear opto coupler such as IL300 . . don't forget that resistors should be for this voltage and with high value such as 100Mohms , or 1Gohms .
Best Wishes
Goldsmith

 

[BradtheRad]

If you wind a few turns of loose wire around the autoformer, you may find you have sufficient AC volts that you can measure. It may require some experimentation.

In fact you might try simply positioning a small coil next to the autoformer. It may generate some amount of ACV across the leads.

I suppose you are running a lower V than 30 kV in the autoformer, because that high a potential is likely to arc over between the windings.