ISO 13689 pdf download.Refrigerated light hydrocarbon fluids — Measurement of liquid levels in tanks containing liquefied gases — Microwave-type level gauge
1 Scope
This International Standard specifies the essential requirements and verification procedures for microwave-type level gauges to be used for ship and shore tanks containing refrigerated light hydrocarbon fluids.
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. IEC 60079-1 0:1 995, Electrical apparatus for explosive gas atmospheres — Part10: Classification of hazardous areas. 1 )
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. 3.1 antenna generic term for equipment that radiates into, and receives from, the tank vapour space, electromagnetic energy in the microwave frequency band 3.2 datum level reference level, equal to the zero level in the tank calibration table, from which liquid level L is calculated 3.3 dead zone zone above the minimum measurable ullage 3.4 deflection plate metal plate set obliquely near the tank bottom to avoid influence of microwave reflection from the bottom or any obstacles NOTE A deflection plate may also be used to reduce unwanted reflections from the tank structure or fittings 3.5 hazardous area space where gas or vapour may form a flammable mixture, as described in IEC 60079-1 0 NOTE This is similar to gas-dangerous space on board the ships as described in the IMO IGC Code (1 993). 3.6 upper reference point basic point for measurement of ullage, set on the level-gauge centre-line near the gauge flange NOTE The height of the upper reference point is the distance between the datum level and the upper reference point (H in Figure 1 ). 3.7 L liquid level distance between the liquid surface in a tank and the datum level NOTE See Figure 1 . 3.8 microwave generic form for electromagnetic radiation, with wave length lying in the range 3 mm to 300 mm (equivalent to a frequency of 1 00 GHz to 1 GHz) 3.9 microwave beam main directional beam formed by the electromagnetic signals radiated from the antenna into free space 3.10 still pipe perforated metal pipe, extending throughout the height of the tank, used to reduce surface turbulence in the liquid that may cause fluctuations in the reflected signal NOTE It may also be used to guide the microwave signal in difficult installation conditions 3.11 ullage distance between the liquid surface in a tank and the upper reference point, measured along the vertical measurement axis
4 Function and construction of microwave-type level gauges
4.1 A microwave-type level gauge functions by using electromagnetic radiation determining the distance from its antenna to the liquid surface. The distance is then subtracted from the height of the upper reference point and the level of liquid in the tank thereby computed and transmitted electronically to a point outside the tank. 4.2 A microwave-type level gauge consists of functional components comprising an antenna, microwave transceiver and other optional items. Figures 1 and 2 show examples of arrangements. 4.3 The materials and construction of a microwave-type level gauge shall be such that it can operate safely and effectively under applicable environmental conditions for which it is intended.4.4 A microwave-type level gauge shall be of gastight construction in order to prevent the escape of vapour from the tank. 4.5 All microwave-type level gauges shall be manufactured and installed in accordance with appropriate National and International electrical safety codes and standards (IMO, IEC, ISO, etc.). All level gauges shall be certified for use in the hazardous-area classification appropriate to their installation. NOTE The design and installation of the microwave-type level gauges may be subject to the approval of the national measurement organizations and classification societies, who may have issued a general type approval for the design of the microwave-type level gauge for the particular service for which it is to be employed. The type approval is normally issued after the microwave-type level gauge has been subject to a specific series of tests and is subject to the microwave-type level gauge being installed in an approved manner. Type-approval tests may include the following: visual inspection, resistance, vibration, performance, humidity, dry heat, inclination, electromagnetic compatibility, and fluctuation in power supplies.