# How to calculate the current from electrometer when connected with oscilloscope screen?

I am using a 6517b electrometer to measure of current with a 3-series oscilloscope for output value on its screen.

I have connected the oscilloscope with an electrometer, but since the oscilloscope cannot show the current value the measurement from the electrometer is converted into a voltage on its screen.

The maximum output value from the electrometer is 2V so we cut the voltage value to more than 2V.

To calculate the current (x), we multiply the range of the electrometer with the oscilloscope voltage value and divide by 2V.

I am not sure if this method to calculate the current is alright. Is there any other way to calculate the current?

According to the reference manual for the Tek/Keithley 8517B electrometer, the method you are using is (almost) correct.

From section 5-7:

The 2 V ANALOG OUTPUT provides a scaled 0 to 2 V output that is non-inverting in the volts mode. Connections for using this output are shown in the following figure. For a full-range input, the output is 2 V; typical examples are listed in the table below.

Divide the voltage reading from the scope by -2V (you said you were using 2V,) then multiply by the full scale value for whatever range you are using.

Table of examples from the manual:

Take note of the text under the table:

*Output values within ± 15 % of nominal value.

There is also this bit of info:

The 2V ANALOG OUTPUT signal is not corrected during calibration. Gain errors of up to 15 % may appear at this output, depending on function and range selection.

• The 2V output can be up to 15% off the true, measured value as shown on the meter itself.
• The 2V output is not calibrated.

If you need precise values, you would do better to read them out using the IEEE-488 (GPIB) or RS232 interface.