【2026 Pressure Gauges】The “mathematical code” behind the accuracy classes of pressure gauges: 1.0, 1.6, 2.5”
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1 Mathematical Code: Uncovering the “hidden facts” behind the R5 number system. Why are the accuracy grades of pressure gauges 1.0, 1.6, and 2.5? These numbers were not arbitrarily set by the manufacturer; rather, they strictly follow the priority number system (R5 number system). It is a geometric sequence with a common ratio of approximately 1.5849 (the fifth root of 10).
Scientific basis: The R5 number system enables seamless coverage of different precision requirements with the fewest values. For example, the allowable error range of a 1.6-grade gauge matches the measurement range of a 2.5-grade gauge perfectly, with no overlap that would lead to waste, nor any gaps. This is also why the 1.5 level in the old standards was eventually replaced by the more scientific 1.6 level.
National standard red lines: Remember two key standards: for ordinary pressure gauges (GB/T 1226-2017), pay attention to 1.0, 1.6, 2.5, and 4.0； For precision pressure gauges (GB/T 1227-2017), the accuracy grades of 0.1, 0.16, 0.25, and 0.4 should be considered.
3 Key factors for selection: range, medium, and environment. “2/3 principle” for range: When measuring a stable pressure, the maximum value should not exceed 3/4 of the range； When measuring fluctuating pressure, it should not exceed 2/3 of the range. At the same time, to ensure accuracy, the minimum measurement value should not be lower than 1/3 of the range.
Medium compatibility: For measuring viscous, crystalline, or corrosive media (such as acids and bases), a diaphragm pressure gauge must be used. For measuring oxygen, a gauge that is oil-free should be used; for measuring ammonia, a gauge designed for ammonia use with copper-free components should be chosen.
👉 In harsh on-site environments with heavy vibration, remember to choose an oil-filled gauge (glycerin or silicone oil), which can effectively protect the movement. If the ambient temperature is too high or too low, remember to install buffer tubes (condensation coils) or provide heat tracing for insulation.
4 Mnemonics for selecting pressure gauges: First, consider the accuracy level – 1.6 is suitable for general use, while 0.25 is appropriate for precision applications; there’s no need to pursue excessive accuracy, as standard grades provide the most reliable performance. Range selection: About twice the working pressure is the most suitable, avoiding the dead zones at the upper and lower limits. Three checks for the medium: acids and bases require diaphragms; oxygen demands oil-free conditions; vibration necessitates oil filling for longevity.
For reference only: 1. TSG 21-2016 \"Regulations on Safety Technical Inspection of Fixed Pressure Vessels\", 9.2.1.3 (3) For pressure gauges used with steam, a trap should be installed between the pressure gauge and the pressure vessel. (4) For pressure gauges used with corrosive or highly viscous media, a buffer device that can isolate such media should be installed between the pressure gauge and the pressure vessel.