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| Technical Note No. 103 |
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| TRAVELOG - Measurement Accuracy and Calibration | |||||
| These notes are intended to advise TRAVELOG users and prospective users of some of the design aspects of the TRAVELOG in respect of measurement accuracy and calibration. | |||||
| 1 | The TRAVELOG was designed primarily as a low cost, in-transit monitor for checking of the storage conditions of temperature sensitive material during transport. As such, the temperature measurement techniques used, and the method of logged data storage, are inherently less accurate than those used, for example, in the ALARMLOG. | ||||
| 2 |
Because of the temperature measurement technique used, the measurement resolution
of the TRAVELOG, at least for Models TR1 and TR2, varies from 0.2 șC at 0
șC to 0.6 șC at +/- 40 șC. The Model TR3 TRAVELOG,
which has a larger range of logged measurement values, at the expense of log length,
has a resolution of 0.1 șC over almost the whole of its operating range.
In this context, the resolution is defined as the minimum step value by which the logged measurement changes as the temperature value is slowly increased or decreased about a particular temperature, and represents the minimum uncertainty in the value of any temperature measurement, even assuming absolute temperature measurement accuracy. |
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| 3 |
The accuracy of the TRAVELOG can not be considered totally separately from the
problem of resolution. As manufactured, the TR1 and TR2 TRAVELOGs have a
measurement accuracy, with the calibration constants set to factory default values, of
approximately +/-0.5 șC at 0 șC, rising to approximately +/- 1.0
șC at the measurement range limits.
These values are governed entirely by tolerances on the values of components used in the construction of the TRAVELOG, and the limits of measurement resolution referred to above. This accuracy is considered to be acceptable for the purposes for which the TRAVELOG is primarily intended and TRAVELOGs are normally shipped from the factory with their calibration constants set to factory default values. |
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| 4 | For users who require greater precision of measurement under particular conditions, provision is incorporated within the TRAVELOG for Windows 32 program to change these calibration constants to adjust out errors. By using this technique, temperature measurement errors can be removed, at any particular temperature, to within the limits of resolution of the TRAVELOG. At 0 șC, this means that the temperature can be adjusted, for a model TR1 or TR2 TRAVELOG, to an accuracy of 0.2 șC. | ||||
| 5 |
It must be noted, however, that this order of accuracy can only be achieved by using
the SINGLE POINT calibration technique, calibrating at a true temperature around 0
șC. If the TWO POINT calibration technique is used, with temperatures measured at
opposite ends of the operating range, the uncertainty of temperature measurement at
these points, because of the TRAVELOG resolution, will be in the order of 0.6
șC. This willl reflect in the calculation of the calibration constants
and is likely to cause similar errors in mid-band measurements, around 0
șC.
It is therefore essential, if you wish to achieve the highest accuracy of measurement at a particular temperature to follow the following procedure:
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| 6 | Irrespective of any comments made above on the absolute accuracy of TRAVELOG measurements, the long term stability of TRAVELOG calibration is excellent. For any state of calibration, the measured value may be expected to stay constant within the limits of TRAVELOG resolution over a period of many months. | ||||
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Derived from Document 0351/UA/07 Issue B Last modified: 23 October 1999 |
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