esca User’s Manual v1.2
The
Range
buttons enable to choose between two ranges:
from -200 pA to +200 pA
or
from -20 nA to + 20 nA
The
Bandwidth
buttons select the input signal bandwidth:
10 kHz button: 10 kHz bandwidth, 20 kHz sampling rate
5 kHz button: 5 kHz bandwidth, 10 kHz sampling rate
1.25 kHz button: 1.25 kHz bandwidth, 2.5 kHz sampling rate
625 Hz button: 625 Hz bandwidth, 1.25 kHz sampling rate
The value of the constant control voltage (
Vc
) applied at the ESCA input pin is
controlled with the “
Vc Value
” box in the following range:
from -355 mV to +355 mV with 1mV steps
In order to be sure of the applied control voltage, a digital offset compensation
procedure must be followed. In the next section the digital compensation is described.
The “
Triangular Wave
” check box is used to force a 48 Hz triangular wave control
voltage of peak to peak amplitude of 118 mVpp. This voltage signal is used to estimate
the input capacitances as described in the “Statistic Data” section.
The “
Reset
” check box keep the ESCA device in reset mode. This function can be
useful to reset the digital offset compensation value to the initial value (see the “Digital
Offset Compensation” section for details).
D
IGITAL
O
FFSET
C
OMPENSATION
To compensate the voltage offset due to internal opamp offsets or unwanted electrode
potentials, ESCA has an internal calibration procedure that can be activated with the
“
Digital Compensation
” check box.
The compensation circuit, when activated, sets the Vc to 0 V and adds to it a variable
voltage in the range from -118 mV to +118 mV until the current is 0 A.
