Professional Full Set Pressure Transmitter Selection Manual (Principle, Classification, Selection Parameters, Material, Explosion Proof, Working Condition Adaptation)
I. Core Working Principle (Professional Concise Version)
The pressure medium acts on the sensitive diaphragm, and through diffused silicon/single crystal silicon/ceramic capacitive sensing elements, converts the physical quantity of pressure into a weak electrical signal. The internal ASIC circuit performs temperature compensation, linear correction, and signal amplification, ultimately outputting industrial standard 4-20mA / voltage / digital signals, which are uploaded to DCS, PLC, or paperless recorders to achieve pressure monitoring, interlock, and automatic adjustment.
II. Professional Classification (By Measurement Type)
1. Gauge Pressure Transmitter: Uses atmospheric pressure as a reference, measures conventional pipeline and equipment pressure, suitable for general industrial applications.
2. Absolute Pressure Transmitter: Uses vacuum as a reference, suitable for vacuum tanks, negative pressure working conditions, and altitude pressure measurement.
3. Differential Pressure Transmitter: Measures pressure difference between two points, can replace liquid level measurement, closed tank liquid level, orifice flow, and filter differential pressure measurement.
4. Negative / Micro Pressure Transmitter: Suitable for furnace negative pressure, duct air pressure, and small low-pressure measurements.
III. Seven Core Selection Parameters (Must-Read)
1. Range: Select according to actual working pressure, typically with a 30% margin; do not operate at full scale for long periods, and avoid overly large ranges that reduce accuracy.
2. Accuracy Class: Ordinary conditions: 0.5 level; industrial control precision: 0.2 level, 0.075 level; for trade measurement, choose high-precision intelligent types.
3. Overload Pressure Resistance: Normally 1.5 times rated range; for water hammer and pulse impact conditions, select 2~3 times high-overload models.
4. Operating Temperature: Standard -20℃~80℃; for high-temperature steam or thermal oil, choose high-temperature heat-dissipation or remote diaphragm type; for low-temperature conditions, choose low-temperature compensated models.
5. Output Signal: 4-20mA: Industrial standard, anti-interference, long-distance transmission; 0-10V: Short-distance building or equipment matching; HART protocol: Intelligent calibration and remote parameter read/write; RS485-Modbus: Multi-instrument networking and IoT remote transmission.
6. Power Supply Voltage: Industrial standard DC24V; for mains electricity, AC220V supplied type is optional.
7. Response Time: Standard 100ms; for pulsating pressure and fast interlock conditions, choose high-speed response type.
IV.Selection of Wetted Materials
The selection of wetted materials is a core factor for pressure transmitters to match operating conditions and resist corrosion and damage. It must be precisely matched according to the characteristics of the measured medium on-site. 304 stainless steel is suitable for clean water, air, and non-corrosive common gas media; 316L stainless steel has greater versatility and can be adapted for tap water, ordinary sewage, weak acidic and alkaline fluids, as well as various oil media; Hastelloy C is specifically used for highly corrosive environments, capable of withstanding hydrochloric acid, dilute sulfuric acid, and other highly corrosive chemical media; titanium alloy excels in resistance to chloride ion corrosion, suitable for seawater, high-salinity, and salt spray corrosion scenarios; ceramic diaphragms offer high cost-performance, suitable for highly viscous, easily crystallizing media with slight particulate wear, while also providing excellent corrosion resistance.
V. Explosion-Proof & Protection Level Selection
Explosion-Proof Rating
Non-explosion-proof: Ordinary factories, HVAC systems, waterworks;
Ex d II CT6 Flameproof type: Chemical, petrochemical, oil and gas, sites with flammable and explosive gases;
Intrinsic safety type Ex ia: High-risk Zone 0 explosion-proof scenarios.
Protection Level
IP65: Standard indoor installation;
IP67: Outdoor open-air, rain-exposed environments;
IP68: Submerged underwater, long-term immersion in well pump stations.
VI. Professional Installation Method Selection
Threaded installation: M20×1.5, G1/2, most commonly used for small pipelines, air compressors, HVAC equipment;
Flange installation: DN50/DN80, tanks, large-diameter pipelines, sealed containers;
Sanitary clamp type: Food, pharmaceutical, and liquor industries; sterile quick installation, easy to clean;
Remote diaphragm type: High temperature, high viscosity, easy crystallization, particle-containing media, isolating the medium to protect the transmitter.
VII. Industry Standard Matching Schemes (Direct Application)
Chemical and petrochemical: 316L / Hastelloy, Ex d explosion-proof, 4-20mA HART, differential/ gauge pressure type;
Water treatment & environmental protection: 316L, IP67, ordinary non-explosion-proof, threaded/flange installation;
Boiler & thermal/steam: High-temperature heat dissipation type, 316L, furnace micro-pressure/steam pressure dedicated;
Food & pharmaceutical: Sanitary clamp, polished 316L, dead-angle-free clean type;
Metallurgy & oil & gas: High overload, explosion-proof type, vibration-resistant, remote diaphragm version.
VIII. Professional Key Points for Avoiding Pitfalls in Selection
Never use 304 for corrosive media; always choose 316L or higher special materials;
For negative pressure and liquid level measurements, prioritize differential pressure transmitters, which are more accurate than gauge pressure;
If the site has lightning strikes or frequency interference, always choose models with surge protection and anti-interference features;
High-temperature media must not directly contact the sensing core; use heat-dissipating tubes/remote diaphragms.
