UL 920401-2017 pdf download – Performance Requirements for Instruments Used to Detect Oxygen-Deficient/Oxygen-Enriched Atmospheres.
4 General requirements 4.1 Oxygen-monitoring instruments shall meet the applicable electrical and electronic measuring instrument safety requirement of ANSI/ISA-61 01 0-1 (82.02.01 ). (See Annex A.) 4.2 Any portion of a stationary oxygen-monitoring instrument and all portable instruments that are intended for installation or use in a hazardous (classified) location shall be suitable for use in the location. (See NFPA 70, Articles 500-504.) NOTE — Oxygen enrichment presents increased ignition risk, especially in a hazardous (classified) location. This Standard should not be interpreted as suggesting that these instruments may be used routinely in oxygen-enriched atmospheres. 4.3 All oxygen-monitoring instruments shall meet the minimum construction and test requirements contained in this Standard. If the manufacturer makes performance claims that exceed these requirements, all such claims shall be verified to the satisfaction of testing laboratory. 5 Construction 5.1 General 5.1 .1 Oxygen-monitoring instruments, their components, and remote detector heads specifically intended for use in the presence of corrosive vapors or gases shall be constructed of materials resistant to, or protected against, corrosion. 5.1 .2 Instruments of the sample-draw type shall include the sample-pumping mechanism. 5.2 Meters, indicators, and outputs 5.2.1 Instruments having an integral meter to indicate oxygen percentage or pressure shall employ a meter having sufficient resolution to permit measurement with the precision required for performing the tests referenced herein. 5.2.2 Nonlinear scales or indicators are permissible when prominently and clearly noted in the instruction manual. 5.2.3 Instruments that employ digital displays shall provide a means to indicate to the user that an oxygen percentage or pressure outside the range of the instrument has been detected. 5.2.4 When auxiliary outputs (e.g., 4-20 mA) from the gas detection instrument are provided, their malfunction shall not adversely affect instrument alarm functions.
5.2.6 Instruments of the sample-draw type shall incorporate a device to indicate either adequate or inadequate flow. In portable instruments, the flow device may be omitted provided that the instruction manual contains detailed instructions, as required by 6.2.1 . 5.3 Alarm/output function(s) (where provided) 5.3.1 All stand-alone gas detection instruments shall include alarm functions. Signal processing heads, approvable under this Standard, are designed as components of a data acquisition, central monitoring, or similar system in which the alarm and malfunction are inherently part of the system and, hence, alarm functions are not separately required as part of the sensing head. 5.3.2 The instrument shall employ an integral alarm device or provide outputs intended to indicate the specific minimum or maximum percentage or pressure of oxygen. Alarms shall be of the latching type, requiring a deliberate manual action to reset. If two or more setpoints or alarm positions are provided to show progressively greater degrees of oxygen depletion or enrichment, the higher of the two depletion alarms or the lower of the two enrichment alarms may be nonlatching. 5.3.3 The latching requirement may be omitted, or a defeating option permitted, if a clear and prominent statement in the instruction manual recommends that the instrument be connected to an auxiliary system that accomplishes the same purpose as latching. EXCEPTION: The latching requirement may be omitted on personal gas detection instruments designed to be carried at all times when in use.