FBXXX Field Temperature Block
Field Temperature Block Performance Analysis
72
Accuracy Drift
The display temperature of the instrument will drift over time. This is due to a variety
of factors affecting the temperature control PRT. Any PRT is subject to changes de-
pending on how it is used and the environment it is used in. This is no different for any
PRT in a calibration application. In addition, manufacturing variables in the sensing el-
ement itself can result in greater or lesser impact from use and environment. Oxidation
and contamination from the sensor’s environment will create changes requiring new
calibration constants depending on the temperature range and normal operation of the
instrument. Oxidation and contamination are generally not factors when Field Tem-
perature Blocks are used exclusively below 200°C. Oxidation can form in the body of
the PRT platinum sensor wire in the range of 300 °C to 500 °C. Contamination is pri-
marily a problem following prolonged use above 500°C. Additionally, vibration from
handling or transportation will strain the delicate PRT element, changing its resistance.
Some of this strain may come out by annealing at a slightly higher temperature than
the instrument is typically used at. It is recommended to avoid unnecessary tempera-
ture cycling. Cycling the temperature up and down between minimum and maximum
temperatures excessively may also cause strain on the PRT element.
Effects from control sensor drift may be avoided by using an external temperature
reference. In the case that the calibration of the display value is required, a program of
monitoring and recalibration must be implemented, just as with any calibration stan-
dard. Regularly check the accuracy of the Field Temperature Block with an adequate
temperature reference and keep records as a part of your instrument maintenance rou-
tine. When the accuracy drifts to a point where it is no longer acceptable, then have the
instrument recalibrated. Your records will provide data for determining a calibration
interval appropriate for your history of use and accuracy requirements.
Stability
The stability specication of the Field Temperature Block was determined under labo-
ratory conditions of steady ambient temperature and air ow. While this instrument
has been designed to minimize ambient effects, they will still have some effect. For
the best results, avoid quickly-changing ambient temperatures and drafty conditions.
Axial Uniformity
Field Temperature Block axial uniformity should be checked periodically. Use the
process outlined in EURAMET/cg-13/v.01 or a similar process. If the axial uniformity
has changed outside the limits set by the user’s uncertainty budget, adjustment of the
axial gradient may be undertaken by trained personnel.
To Previous Page
Loading...
