© 2019 Department of Petroleum Resources. All rights reserved Department of Petroleum Resources (DPR) PROCEDURE GUIDE

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2.1 Calibration of Mercury in Glass Thermometers
2.1.1 Accreditation
Only corporate bodies with current permits to render such specialized services to the oil
industry by the Department of Petroleum Resources shall be eligible to carry out calibration
of thermometers used in taking measurements at custody transfer points with participation
of representative(s) of The Department of Petroleum Resources.
2.1.2 Principle
Thermometers used generally for measurement of liquid temperatures are always under
partial immersion conditions, hence calibration shall be as specified for instruments of this
type. Temperatures shall be referred to ice points and other fixed points on a secondary
standard thermometer.
2.1.3 Frequency of Calibration
2.1.3.1 All new thermometers shall be deemed calibrated and an attestation to this fact by
the manufacturer shall be sufficient.
2.1.3.2 All thermometers in service shall be calibrated annually. All calibration operations for
facility instruments shall be witnessed and certified by representative(s) of the Department
of Petroleum Resources.
2.1.4 Applicable Standard
This shall be the latest ASTM Standard under title “Standard Method for Verification of
liquid- In –Glass Thermometers’’.
2.1.5 Calibration Equipment
2.1.5.1 Comparators as specified in the reference standard shall be used.
2.1.5.2 Secondary Thermometers which shall be calibrated annually against a primary
standard thermometer of the platinum resistance type which has been certified by
recognized bureau of standards.
2.1.5.3 Other ancillary equipment as outlined in the reference standard.
2.1.6 Verification and Calibration
2.1.6.1 The thermometer shall be inspected for entrapped gas, bubbles found shall be
eliminated by the process outlined in the reference standard.
2.1.6.2 Similarly, inspection shall be carried out for the presence of liquid globules, any
foreign matter, entrapped air and glass faults. Any of these defects that could not
be rectified shall constitute enough reason to reject such defective thermometers.
2.1.6.3 Linear dimensions of the stem with regards to diameter, length and uniformity of
graduation spacing, shall be checked in accordance with the procedure outlined in
the Standard. Also, it shall be tested for bulb stability and for this purpose, the 24-
hour heating period in the test bath shall be sufficient.
2.1.6.4 Thereafter, the thermometer shall be calibrated at ice point and at a minimum of two
(2) other fixed points in accordance with the prescribed method for total immersion
thermometers in an appropriate comparator device equipped with a certified
secondary standard thermometer.