But this one is .. http://www.vk2zay.net/article.php/9
and if you don't have 10µA FSD meter you can try to use 0-200mV device suggested in my previous post ..
I really need an electrometer which is capable of measuring electrical field. I need it to measure voltage of human body for ESD testing. The input impedance Rin=infinite.
The precision requred is 5%.
However, as it is related to human safety, you should buy one, it is not expensive, rather than build by yourself. It is very dangerous for you, both by the circuit itself and the safety law.
You can use INA116 for very high input impedance amp (10E15Ω) and bootstrap it to desired voltage. Although, getting accurate measurements might be very difficult even for very experienced engineer and every aspect of design would be critical. If you don't have really a lot of time to burn, buy Kethley or some other electrometer as suggested.\][/u]