How to Select the Range and Accuracy of Standard Pressure Gauges
The selection unit of the pressure gauge and the scale (scale) of the pressure instrument shall all use the legal measurement unit. That is, Pa, kPa and MPa. For foreign-related design projects, international general standards or corresponding national standards can be adopted. The implementation of these Provisions shall also comply with the provisions of the current national standards. Select according to the use environment and the nature of the measuring medium 1. In the severe environment such as strong atmospheric corrosivity, more dust and easy to spray liquid, the appropriate enclosure material and protection grade shall be selected according to the environmental conditions. 2. Measurement of general medium (1) When the pressure is between - 40kPa - 0 - 140kPa, capsule pressure gauge should be selected. (2) When the pressure is above plus 40kPa, the spring tube pressure gauge or bellows pressure gauge is generally used. (3) When the pressure is - 100kPa {{10}} plus 2400kPa, the pressure vacuum gauge shall be selected. (4) When the pressure is between - 100kPa and 10kPa, the spring tube vacuum gauge should be selected. 3 Acid resistant pressure gauge or stainless steel diaphragm pressure gauge shall be selected for dilute nitric acid, acetic acid and other general corrosive media. 4 Thin hydrochloric acid, hydrochloric acid gas, heavy oil and similar medium with strong corrosivity, solid particles, viscous liquid, etc. shall be selected as diaphragm pressure gauge or diaphragm pressure gauge. The diaphragm and its material must be selected according to the characteristics of the measuring medium. 5 Flange diaphragm pressure gauge shall be selected for medium such as crystallization, scabbing and high viscosity. 6 In case of strong mechanical vibration, shock proof pressure gauge or marine pressure gauge shall be selected. 7 In flammable and explosive places, if electric contact signal is required, explosion-proof pressure controller or explosion-proof electric contact pressure gauge shall be selected. 8 For the pressure gauge measuring high and medium pressure or medium with strong corrosivity, the pressure gauge with overpressure relief facilities on the shell should be selected. Special pressure gauges shall be used for the following measuring media: (1) gaseous ammonia, liquid ammonia: ammonia pressure gauge, vacuum gauge, pressure vacuum gauge; (2) Oxygen: oxygen pressure gauge; (3) Hydrogen: hydrogen pressure gauge; (4) Chlorine: chlorine resistant pressure gauge, pressure vacuum gauge; (5) Acetylene: Acetylene pressure gauge; (6) Hydrogen sulfide: sulfur resistant pressure gauge; (7) Alkali liquor: alkali resistant pressure gauge, pressure vacuum gauge. 10 When measuring the differential pressure, the differential pressure gauge shall be selected. Selection of accuracy class 1. For general measuring pressure gauge, capsule pressure gauge and diaphragm pressure gauge, class 1.5 or class 2.5 shall be selected. 2. The pressure gauge for precision measurement shall be Class 0.4, 0.25 or 0.16. Selection of overall dimensions 1. Pressure gauges installed on pipes and equipment, with a dial diameter of 100 mm or 150 mm 2. Pressure gauges installed on instrument pneumatic pipelines and auxiliary equipment, with a dial diameter of 60 mm o 3. Pressure gauges installed in places with low illumination, high position or difficult to observe indications, with a dial diameter of 150 mm or 200 mm o When measuring stable pressure, The normal operating pressure value shall be 1/3 - 2/3 of the upper limit value of the instrument measuring range. 2 When measuring the pulsating pressure (such as the pressure at the outlet of pumps, compressors and fans), the normal operating pressure value shall be 1/3 - 1/2 of the upper limit value of the instrument measuring range. When measuring the high and medium pressure (greater than 4MPa) on the 1/3 side, the normal operating pressure value shall not exceed 1/2 of the upper limit value of the instrument measuring range. 2. For flammable and explosive occasions, pneumatic transmitter or explosion-proof electric transmitter shall be selected. 3 Flange transmitter shall be selected for crystallization, scabbing, blocking, viscous and corrosive media. The material in direct contact with the medium must be selected according to the characteristics of the medium. 4 If the measurement accuracy is required to be high, but it is difficult for ordinary analog instruments to achieve it, intelligent transmitters should be selected, and the accuracy is better than 0.2. When the location of the measuring point is not close to or the environmental conditions are bad, the intelligent transmitter should also be selected. 5 For occasions with good operating environment and low requirements for measurement accuracy and reliability, resistance type, inductance type remote pressure gauge or Hall pressure transmitter can be selected. 6 When measuring micro pressure (less than 500Pa), micro differential pressure transmitter can be selected. 7 When measuring the differential pressure of equipment or pipeline, the differential pressure transmitter shall be selected. 8 Direct mount transmitter can be selected in the situation of good use environment and easy access. Selection of installation accessories 1 When measuring water vapor and medium with temperature greater than 60 degree , condensate pipe or siphon shall be selected. 2 When measuring liquefied gas, if the pressure tapping point is higher than the instrument, the separator shall be selected. 3 When measuring the gas containing dust, the dust remover shall be selected. 4 When measuring pulsating pressure, damper or buffer shall be selected. 5 When the ambient temperature is close to or lower than the freezing point or freezing point of the measuring medium, thermal insulation or heat tracing measures shall be taken.
