Metrohm 746 VA Trace Analyzer User Manual

Page 477

6 Data processing and evaluation

746 VA Trace Analyzer / 747 VA Stand

6-14

6.7.3

Baselines for peaks

With peak-shaped curves which have been recorded with the DPMODE,

SQWMODE, AC1MODE, DCTMODE (with SSWEEP) and CYMODE (with 1 ramp)

measurement mode, the following possibilities exist for calculation of the baseline:

•

Type = linear, Scope = whole

The baseline of type

linear

is determined using the tangent method. With

the peak base points

dU.front

and

dU.rear

determined beforehand as a

basis, an iterative search is made within a fixed range for identical slopes. The

range for the tangent search is ca. 20 mV outward and inward up to 1 point

before the peak maximum.
If two points with an identical slope are found, the two points of tangency are

connected to give the linear baseline. If no common slope is found, the linear

baseline is drawn directly through the two base points.
Instead of being deter-

mined automatically, the

two base points

dU.front

and

dU.rear

can also be

entered manually either by

numeric entry or by shift-

ing using the cursor keys

(see "CURVES", section

5.5.3). In contrast, the two

slopes

S.front

and

S.rear

are always calcu-

lated automatically, a nu-

meric entry here is ig-

nored.

linear, whole

dU.front dU.rear

•

Type = linear, Scope = f.half/r.half

The baseline of type

linear

f.half

is determined only by starting from the

peak front half, that of type

linear

r.half

only by starting from the peak

rear half. In the first case, the baseline is given by the tangent with the slope

S.front

at the base point

dU.front

, in the second case by the tangent with

the slope

S.rear

at the base point

dU.rear

The two base points

dU.front

and

dU.rear

as well as the two slopes

S.front

and

S.rear

can also be

entered manually instead of being

determined automatically.

linear, f.half

linear, r.half

•

Type = linear, Scope = f.double/r.double

This type of baseline is used for the evaluation of overlapping peaks; for the

peak the type

linear

f.double

must be used and for the 2

peak the

type

linear

r.double

. The baseline is calculated in exactly the same man-

ner as for

linear

whole

using the tangent method. With the previously de-

termined peak base points

dU.front

for the 1

peak and

dU.rear

for the 2

peak as a basis, an iterative search is made within a fixed range for identical

slopes. The range for the tangent search is ca. 20 mV outward and inward up

to 1 point before the corresponding peak maximum.

Point of tangency

(rear)

Subtracted

curve

Base point

(front)

Range for

tangent search

Range for

tangent search

Base point

(rear)

Point of tangency

(front)