Metrohm 746 VA Trace Analyzer - Manual (Page 469)

6 Data processing and evaluation
746 VA Trace Analyzer / 747 VA Stand
6-6
6.3 Data acquisition
After the start of a determination the first step involves the acquisition and storage
of the experimental data. The 746 VA Trace Analyzer operates according the poten-
tiostatic, 3-electrode principle in which the voltage of the working electrode is con-
trolled with the aid of a virtually currentless reference electrode to the preset desired
value and the current flows across a separate auxiliary electrode. The voltage drop
in the analysis solution is automatically compensated. Measurement of the current
with digitalization involves automatic matching of the amplifier sensitivity to the lat-
est measured value so that measurements are always performed with optimum ac-
curacy.
The type of measured value recording, the measurement range and the measure-
ment frequency are defined by the selection of electrode, measurement mode and
sweep. The following combinations are possible here:
Electrode Measurement mode Sweep Measured variables
DME SMDE HMDE RDE DCT DP SQW AC1 AC2 PSA CYC y axis x axis
l l l l l l l l l SWEEP current voltage
l l l l ¡ l l ¡ ¡ FSWEEP current voltage
l l l l l SSWEEP current voltage
l l l l l l l TSWEEP current time
l l n PSWEEP voltage time
l l n CYCSWEEP current voltage
l adjustable n no other choice possible ¡ adjustable, but without function
You will find details regarding the different measurement modes and sweeps in the
description of the corresponding program instructions in section 5.7.3.
The measured value pairs (current/voltage, current/time or voltage/time) recorded
per single measurement with the SWEEP instruction are stored in data blocks which
are unambiguously characterized by the segment name and the VR number
(variation and replication). This identification can be used to select the single
sweeps for the display and the output of results, reports and curves.
In connection with the measured value recording, the following rules apply to seg-
ments and sweeps:
– Per method maximum 8 segments are allowed.
– Per segment only 1 sweep instruction is allowed.
– Per single sweep maximum 1000 measured values are allowed
(with PSWEEP 704 measured values, with RAMP 6000 measured values).
– The maximum number of variations (V) and replications (R)
is limited to 8 each (that is a total of 9 single sweeps).
– Per determination maximum 60 single sweeps are allowed.
The measured values recorded in the data acquisition are stored in the determina-
tion as original measured values ( original ) and can not be changed later. All other
steps in the data processing are based on these original data and are recalculated
each time the determination is loaded.