CHAPTER 4 Data acquisition
31
When data are obtained from the integrator output, it is obvious that the pA
range allows the highest sensitivity. Each range has a different maximum
zero compensation (Table II). For example, in the nA range a current of 100
nA full scale can be managed. Together with a zero compensation of 160 nA,
the maximum current that can be handled is 260 nA.
Due to the nature of data generation the integrator output is unusable in the
pulse and scan mode.
Recorder output
Several steps occur before sending the signal to the recorder output. After
analog-to-digital conversion (ADC), a number of recorder range settings can
be selected in the central processing unit (CPU). This selection occurs in the
‘DC SET’ or ‘DC STAT’ screen.
Fig. 6. Selection of the recorder output range in the ‘DC SET’ or ‘DC STAT’
screen.
After digital to analog conversion (DAC) the signal is sent to the REC output.
The recorder range selection has several consequences for the data
acquisition (Table III).
Table III. Parameters affected by the recorder range setting.
parameter output
comment
signal output
REC
gain increases with more sensitive
range
offset REC/INT
see
Table
V
marker
REC
10% of full scale REC output
In the DC mode the signal can be smoothened by a rise time filter. In addition,
more complex signal manipulation, needed for pulse and scan is possible.
Although the name of this output suggests otherwise, it is often used in
connection with an integrator.
The recorder output ranges b1 and -1 V with 12 bits resolution,
which means that the output resolution is 0.5 mV (2 V/2
12
). The best way to
exploit this output resolution is to set the range as sensitive as possible.
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