Thermo Scientific APEX 100, Руководство пользователя, Страница: 153 / 442

Thermo Scientific APEX User’s Guide
Page 153
Enabling the Detector’s Phase-Tracking Function
The phase-tracking function allows the detector to account for the small changes
(“drift”) that occur in phase angle during a daily (or other long) production run.
Phase Tracking
Thermal Variations in the Product Can Affect Phase Angle
For example, when testing a hot, wet product, such as jars of spaghetti sauce moving
along a conveyor, the temperature of the product as it reaches the search head can
affect the phase angle. In many production environments, the ambient temperature of
the building changes throughout the day—for example, by becoming hotter in the
afternoon as the sun heats the sides and roof of the building. This, in turn, causes the
air temperature in the building to rise and the rate of cooling of the product to decrease
during the afternoon. Thus, product entering the search head will be cooler in the
morning and warmer in the afternoon, and this gradual change in temperature
throughout the day can cause the phase angle to gradually change, or drift, during the
daily production runs.
How Phase Tracking Works
By enabling phase tracking, the detector allows the phase-tracking setting to drift over
time, as long as the phase-angle setting stays within certain predetermined limits—and
these limits can be either the default limits or the user-defined limits you have keyed in.
The detector tracks the drift in phase angle over time by keeping a running average of
the phase angles recorded since the last reset, and comparing the most-recent phase-
angle value against this running average. If the new value falls within the prescribed
limits (the default or user-defined “acceptable change” limit), it accepts the value and
updates the running average. However, if the running average exceeds the phase-
tracking fault limits, the detector notifies you a fault has occurred.