Thermometers used to measure the temperature of hydrocarbon liquids in tanks shall conform to the requirements of API
Manual of Petroleum Measurement Standards (MPMS), Chapter 7, “Temperature Determinations” and American
Society of Testing & Materials Standard E1, “Standard Specification for ASTM Liquid-in-Glass Thermometers”:
The accuracy of each mercury-in-glass (cup-case) thermometer shall be verified by a Saudi Aramco laboratory or a
recognized independent inspection company before initial use and at least once per year thereafter in accordance with
API Manual of Petroleum Measurement Standards (MPMS), Chapter 7:
The verification shall be conducted by comparing readings at three or more temperatures over the range of the
working thermometer to readings from a reference thermometer.
The uncertainty of the reference thermometer shall have been established using a thermometer certified against
national weights and measures standard.
The cup-case assembly shall conform to the requirements set forth in API Manual of Petroleum Measurement
Standards (MPMS). It shall be constructed from wood or other non-sparking, corrosion resistant material. The cup shall
have a capacity of at least 100 milliliters. It shall be constructed to ensure the thermometer bulb is at least 3/8 inch (9.5
millimeters) from the side and 1±3/16 inch (25.4±5 millimeters) above the bottom of the cup.
PORTABLE ELECTRONIC THERMOMETERS (PET’s)
Portable electronic thermometers used to measure the temperature of hydrocarbon liquids in tanks shall conform to the
requirements of API Manual of Petroleum Measurement Standards, Chapter 7, “Temperature Determination”:
The portable electronic thermometer shall be suitable for use in a Zone 1 hazardous area. The thermometer display
shall have a minimum resolution of 0.1 ºF (0.1 °C), shall be capable of being read in direct sunlight and shall be equipped
with a backlight to enable it to be read at night. The thermometer shall have a probe cable with a length suitable for the
tallest tank at the location. The cable shall be marked at intervals not to exceed 5 feet (1.5 meters).
The thermometer shall be calibrated and its accuracy checked in accordance with the requirements of API Manual of
Petroleum Measurement Standards, Chapter 7. The accuracy of each portable electronic thermometer (PET) shall be
calibrated by a recognized independent inspection company before initial use and at least once per year thereafter in
accordance with the manufacturer’s instructions:
The calibration shall be conducted by comparing readings at three or more temperatures over the entire range of
the portable electronic thermometer (PET) to readings from a reference thermometer.
The uncertainty of the reference thermometer shall be traceable to a national weights and measures standard.
If required, the thermometer calibration shall be adjusted to ensure that its readings differ from the reference
thermometer by no more than the required accuracy specification.
The calibration of each portable electronic thermometer (PET) shall be verified at least once per month at site:
The calibration shall be verified by comparing the readings at two or more temperatures covering the full range of
the portable electronic thermometer (PET) to the readings of a reference thermometer. Each comparison shall
be conducted by immersing both thermometers in a constant temperature bath for at least 10 minutes before
taking the respective readings.
The uncertainty of the reference thermometer shall be traceable to a national weights and measures standard.
If either comparison indicates a difference more than the required accuracy specification, the portable electronic
thermometer (PET) shall be re-calibrated by a recognized independent inspection agency before it is used.
The accuracy of each portable electronic thermometer shall be checked before initial use each day:
The check shall be conducted by comparing the ambient reading of the portable electronic thermometer (PET) to
the ambient reading of a reference thermometer.
The reference thermometer used for this check shall be an ASTM certified mercury-in-glass thermometer.
If the readings differ by more than 0.5 ºF (0.25 oC), the portable electronic thermometer (PET) shall be re-
calibrated by a recognized independent inspection agency before it is used.