Endress+Hauser iTHERM TrustSens TM371, Руководство по эксплуатации

Страница: 52 / 106

Technical Data iTHERM TrustSens TM371, TM372
52 Hauser
For accredited calibrations according to IEC/ISO 17025, the measurement uncertainty
must not be twice as high as the accredited measurement uncertainty of the laboratory. If
the limit value is exceeded, only a factory calibration can be carried out.
For manual calibration in calibration baths the maximum immersion length of the
device ranges from the sensor tip to the lower part of the electronic housing. Do not
immerse the housing into the calibration bath!
A0032391
Self-calibration
The self-calibration procedure uses the Curie temperature (Tc) of a reference material as a
built-in temperature reference. A self-calibration is performed automatically, when the
process temperature (Tp) falls below the nominal Curie Temperature (Tc) of the device. At
the Curie temperature, a phase change of the reference material takes place, which is
associated with a change in its electrical properties. The electronics automatically detects
this change and simultaneously calculates the deviation of the measured Pt100-
temperature to the known, physically fixed Curie temperature. The TrustSens
thermometer is calibrated. A green flashing LED light indicates the ongoing self-
calibration process. Subsequently the thermometer electronics stores the results of this
calibration. The calibration data can be read via an asset management software like
FieldCare or DeviceCare. A self-calibration certificate can be created automatically. This
inline self calibration allows a continuous and repeated monitoring of changes to the
Pt100 sensor and to the electronics’ characteristics. As the inline calibration is being
performed under real ambient or process conditions (e.g. heating of electronics), the result
is closer to reality than a sensor calibration under laboratory conditions.
Process criteria for self-calibration
To ensure a valid self-calibration within the given measurement accuracy, the process
temperature characteristics needs to fulfil the criteria, which are checked by the device
automatically. Based on this, the device is ready to perform a self-calibration under the
following conditions:
– Process temperature > calibration tempe3 °C (5.4 °F) for 25 s before cooling
down; t1 - t2.
– Cooling rate: 0.5 to 16.5 K/min (0.9 to 29.7 °F/min), while the process temperature
crosses the Curie temperature; t2 - t3 + 10 s.
The process temperature ideally declines continuously below 116 °C (240.8 °F). A valid
self-calibration process is done when the green LED flashes with a frequency 5 Hz for 5 s.