Metrohm 763 PVC Thermomat Manual - Manual (Page 66)

4.5 Methods
763 PVC Thermomat
59
Induction time
The induction time is the time up to the inflection point of the conduc-
tivity vs. time curve recorded by the PVC Thermomat. The induction
time is a characteristic value for the thermal stability of the sample un-
der investigation.
For automatic evaluation of the induction time the second derivative of
the measured curve is used. This derivative has a maximum at the in-
flection point and can be displayed in the Live graph window. In order to
recognize an inflection point certain criteria concerning the height and
width of the peak in the second derivative must be fulfilled. The inflec-
tion point can also be evaluated manually as point of intersection of the
two tangents of the extended straight arms of the curve.
Induction time
Evaluation
suppression
Start End
Evaluation
delay
Inflection
point
Time
Conductivity
With certain samples it is possible for the conductivity to increase in
small steps a long time before the induction time itself. In order that this
increase is not evaluated as the endpoint the operator can delay the
evaluation or suppress it in a particular range.
Stability time
The stability time is the time required to achieve a given conductivity
alteration of
Delta Kappa
.
Stability time
Delta
Kappa
Time
Conductivity
The input of an evaluation delay or evaluation suppression has no influ-
ence on this evaluation mode; the calculation is always carried out from
the time that the measurement was started.