API MPMS 7:2001(2012) pdf download

API MPMS 7:2001(2012) pdf download.Manual of Petroleum Measurement Standards Chapter 7- -1 Temperature Determination.
5.4 ELECTRONIC TEMPERATURE DEVICES
Electronic temperature devices for measurement generally use one of the following telliperature sensors:
a, Thermistor, h Thermocouple.
c. Resistance temperature detector IRTD).
These devices are usually housed in metal probes that mount into thermowclls. The probes are generally tip-%cnsitis . Thus. the probes must he securely seated in the bottom nt the thermussell for optimum heat transfer. Spring-boded or adjustable-length probes are recommended. An appropriate heat-conducting material should be used between the temperature sensor and the thennowell wail. – wiring to the probe is mntical because of the low signal levels of the devices. These devices should be installed as recommended by the manufacturer for best accuracy. These transducers require lineanration that is typically accomplished within the assacialcd transmitter. Each type of probe requires its ossii type of circuil
Safely must also he included in the equipment specihcatians. The equipment and transducers should be installed in acconLmnce with API RI’ 500 and RI’ 551 and with NFPA 70. National Electrical Code (NEC) haiardous area specifications.
All electronic temperature devices should he provided with displays that pros ide a resolution ol 0.1 °C or 0.1°F or better.
5.4.1 Thermistors
Thermistors are very small ceramic resistors with high coefficients of resistance. While much more sensitive to small changes in temperature compared with platinum resistance temperature devices, thermistors are not recommended ftw custody transfer applications without very frequent calibration and veriticazion testing.
They are subject to long-term drill due to aging. their accuracy and ambient temperature compensation are usually less than cons’entamal temperature sensors. They are also less stable and are nonlinear. They are normally used for less precise temperature control and switching in the teniperattire range from about —100°C to 500CC (—200°F to XX)°Ft.
5.4.2 Thermocouples
Themsocouples are temperature-sensitive devices coisting of a pair of dissimilar metals so arranged that the electmmotive force (F.MFI produced by the couple depends on the difference in temperature between the hot and reference junetions of the metals. Thermocouple temperature devices. depending on type. measure temperature over a wide range from about – I5OC (—3OOF) to about l300C (23(8lFL Electronically compensated single-junction thermocouples shall not be used for custody transfer measurement due to the following: they suft’r from drift and corrosion as they age. the millivolt signal is quite loss and subject to noise pickup. the length. composition and condition of the thermocouple lead wires affects accuracy. Other thermocouple systems that meet the requirements of Section 8 may be used for custody tiansfer measurements.
5.4.3 ResIstance Temperature Detectors
A resistance temperature detector RID) is a sensing dcment with an electrical resistance that is a function of temperature. The resistance temperature detector is usually a small coil of platinum wire and when used with appropnate circuits will provide temperature signals to readouts and other equipment RiDs are more accurate than thermocouples and almost all other temperature sensors, and they maintain their accuracy (or long periods. [he current how of an Ru) is much higher than that of a therotocouple so they are less subject to noise pickup or cmws from lead-in wires RTL>s are recommended (or highly accurate temperature measurement such as custody transfer servicc for narrow span temperature measurement (under 40°C (lOO°FhJ: fur temperature difference measurement: and for control and other critical applications.
Note: ibrec or tour ss ire RTl)s arc recommended to oimjnate fiw lead length rcsisuince.
5.4.4 Temperature TransmItters
A tcinpcraturc transmitter is des ice that CoOsCfls a signal from a temperature sensor into a form suitahte for propagating the teniperature data from the site of the measurement to the location wheir the data will be used. The temperature signal is typically converted into a current or serial digital loon. A temperature sensor may or may not be part of the transmitter. Sensor lineantatiun can be typically provided by the transmitter, and the proper lincan,.ation option must he selected.
Electronic, digital (“smart”) transmitters may have the following benefits over the conventional analog transmitters:
• Wider rangeahiliy
• Calibration procedures
• Improved pertonnance
• Lower drift rate.