BS IEC 62990-1:2019 pdf free download – Workplace atmospheres
4.2.1 General
For Type HM equipment the upper limit of measurement shall be equal to or greater than 2 times the reference value. (See Table A.1.) The requirement for the lower limit of measurement is in 6. 4.2. The equipment shall be constructed in such a manner that regular functional checks can be easily undertaken by the user and that it can be equipped with suitable devices for application of test gas (field calibration kit). Toxic gas detection equipment or parts thereof (e.g. remote sensors) shall be constructed of materials known to be resistant to degradation by the environment in which they are intended to be used. Equipment specifically intended for use in the presence of corrosive vapours or gases，or which can produce corrosive by-products as a result of the detection process (e.g. catalytic oxidation or other chemical process) shall be constructed of materials known to be resistant to corrosion by such substances. Materials and components used in the construction of the equipment which are relevant to performance of the equipment shall be used within the material and component manufacturer’s ratings or limitations unless otherwise specified by appropriate safety standards. If such material and component ratings are not available， demonstrated functionality of the equipment may be used. AlI materials along the gas path shall not cause an inaccurate reading due to adsorption and absorption effects of materials in contact with the toxic gas. For aspirated equipment, inlet and outlet ports shall be unambiguously marked to ensure the correct connection of any sample and exhaust lines.
4.2.8. Separate gas detection control units for use with gas detection transmitter(s)
A specification shall be supplied with the equipment that describes the relationship the input signal has with the calculated gas concentration (transfer function). Such specification shall be detailed to the extent that the accuracy of this transfer function can be verified. As a minimum, the manufacturer shall provide data showing the relationship between the input signal and the gas concentrations corresponding to 0 %，10 %，30 %, 50 %, 70 %, 90 % and 100 % of upper limit of indication. Required inputs for upper limit of indication and status signals (e.g. fault, calibration mode) shall also be specified by the manufacturer. The manufacturer shall provide the details of the input signals, which will enable the accuracy of the transfer function to be verified.
4.2.9.1 General
In the design of software-controlled equipment, the risks arising from faults in the program shall be taken into account by applying 4.2.9.2 to 4.2.9.7. In addition, where accessories are software-controlled, the risks arising from faults in the programme shall be taken into account where related to safety.
4.2.9.2 Conversion errors
The relationship between corresponding analogue and digital values shall be unambiguous. The output range shall be capable of coping with the full range of input values within the equipment specification. A clear indication shall result if the conversion range has been exceeded. The design shall take into account the maximum possible analogue-to-digital, computational and digital-to-analogue converter errors. The combined effect of digitization errors shall not be greater than the smallest deviation of indication required by this document.