API MPMS 7.2-2018 pdf free download
API MPMS 7.2-2018 pdf free download.Manual of Petroleum Measurement Standards Chapter 7—Temperature Determination Section 2—Portable Electronic Thermometers.
5 Units of Measure For custody transfer, the means of temperature determination should be agreed to among the parties involved. Temperatures referenced in this document are those defined by the International Temperature Scale of 1990 (ITS-90). Temperatures may be measured and expressed in degrees Celsius or in degrees Fahrenheit. This standard presents both SI and USC units, and either may be implemented. The presentations of both units are for the convenience of the user, and are not necessarily exact conversions. The units of implementation are typically determined by contract, regulatory requirement, the manufacturer, or the user calibration program. Once a system of units is chosen for a given application, they should not be arbitrarily changed. (See API MPMS Ch. 15.) 6 Equipment and Design Requirements A wide range of portable electronic thermometers are available that are designed to take spot temperatures at any location within a tank that is accessible from the available gauging access point(s). The PET may be used as a precise measuring device for measuring the temperature of petroleum or petroleum product. It may also be used as reference thermometer for verifying the calibration of other (permanently installed) temperature-measuring devices. 6.1 Environment A PET unit used for tank measurement with the display and any ancillary devices shall: — be certified by a nationally or internationally recognized testing agency as safe for use in flammable atmospheres and with liquids that can accumulate static charges; — have a method of bonding to the vessel or structure; — have a protective case or enclosure with appropriate ingress protection, and be self-contained; — be robust and shockproof, but should be sufficiently light to be carried by an operator without undue fatigue; — be resistant to immersion in petroleum products; and — at a minimum, be suitable for use for ambient temperatures of 0 °C to 35 °C (32 °F to 95 °F).
6.3 Stabilization The temperature reading of a PET has come to equilibrium in liquid when the reading varies no more than ± 0.1 ºC (0.2 ºF). The PET may also have a visual or audible method of indicating that the temperature reading has stabilized. Table 4 shows typical stabilization times in liquid, but this may vary due to the mass of the probe sensor assembly. 6.4 Cable and Probe The cable connecting the temperature sensor to the measuring instrument shall be long enough to cover the full depth of the tanks for which the PET is likely to be used. It may be marked at meter or foot intervals in order to assist in lowering to the required level. In applications where the PET will be used with a thermowell, the probe dimensions shall permit full insertion into the thermowell. NOTE Cables wrapped on a spool device may be damaged prematurely if used with heavy products, such as asphalt or heated, viscous products. A PET constructed with a hand-wrapped cable may be more appropriate for heavy or heated products. 6.5 Voltage Indicator Include with each unit a test system or switches to indicate low battery voltage. If the equipment has a rechargeable battery, provide a suitable-voltage battery charger and only charge in an intrinsically safe area. 6.6 Additional Functionality Additionally functionality, such as listed below, is not required, but may be useful in some applications: — averaging of temperature readings; — minimum/maximum storage of temperature readings; — backlighted or illuminated display characters; or — visual or audio indication of temperature stabilization. 6.7 Thermowells The use of thermowells is required to isolate the liquid material from the temperature sensor. There are two general classification types of thermowells: test wells and sensor wells. Both these classifications of thermowells should be filled with conductive fluid, grease, or paste to ensure proper temperature readings.
