SI-503K Gas Pressure Sensor

A compact, all-stainless gas pressure transducer for natural gas, flue and exhaust gas, compressed air, and other dry or weakly corrosive gases. The Phi 8 pagoda nozzle pushes straight onto soft tubing, so it drops into OEM gas skids without an adapter.

Range: -100 kPa to 0, up to 0–10 MPa (gauge and compound)
Accuracy: 0.25% FS or 0.5% FS
Output: 4–20 mA (2-wire); 0–5 / 1–5 / 0–10 V (3-wire)
Wetted parts: 304 stainless steel, laser-welded
Connection: Phi 8 pagoda quick-connect nozzle
Protection: IP65

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Bolt a general process transmitter onto a gas line and two things go wrong: the threaded port needs an adapter for the soft tube, and the price is built for liquids you never run. The SI-503K is sized for the gas job instead. It reads gauge or compound pressure from a few kPa up to 10 MPa, ships in 304 stainless, and ends in a Phi 8 pagoda barb that a silicone or PU tube slides straight onto.

Overview

The SI-503K is a strain-gauge gas pressure transducer built for natural gas, biogas, exhaust and flue gas, compressed air, and weakly corrosive gases or liquids that 304 stainless can hold. The whole wetted path is laser-welded stainless, so there is no soft seal to swell or leak on a gas line. It carries a high-precision bonded foil strain gauge, gives a 4–20 mA or voltage output, and runs off a standard 24 VDC supply.

Typical duty cycle is continuous monitoring or closed-loop control on a gas skid: burner trains, gas distribution headers, HVAC and air-conditioning lines, water-works air charging, and vehicle brake-air test rigs. Where the medium is genuinely corrosive (wet chlorine, strong acids), step up to a flush-diaphragm pressure sensor with a ceramic or coated cell instead.

Working principle

Gas enters through the pagoda nozzle and presses on a thin 304 stainless diaphragm. A bonded foil strain gauge on the back of that diaphragm changes resistance as the metal flexes, and a Wheatstone bridge turns the tiny resistance change into a millivolt signal. On-board electronics amplify and linearize it to 4–20 mA or a voltage. Because the diaphragm and body are one welded stainless piece, the gas never touches a fill fluid or an O-ring.

Technical specifications

Representative specifications, at room temperature and rated supply unless stated. Values typical; confirm the exact build per datasheet.

Parameter	Specification
Measuring range	-100 kPa to 0 (compound) through 0–1 MPa up to 0–10 MPa gauge (10 MPa is about 1450 psi / 100 bar)
Comprehensive accuracy	0.25% FS or 0.5% FS
Output signal	4–20 mA (2-wire); 0–5 V, 1–5 V, or 0–10 V (3-wire)
Supply voltage	24 VDC nominal (9–36 VDC)
Medium temperature	-20 to +105 °C
Ambient temperature	-20 to +85 °C
Load resistance	Current output ≤ 800 ohm; voltage output ≥ 50 kohm
Insulation resistance	≥ 2000 Mohm at 100 VDC
Response time	< 1 ms
Long-term stability	0.1% FS per year
Vibration	20–1000 Hz, output change < 0.1% FS
Protection	IP65
Wetted material	304 stainless steel, laser-welded
Electrical connection	Hirschmann (DIN 43650) connector, optional
Process connection	Phi 8 pagoda quick-connect nozzle; threaded options on request

Output and wiring

Pick the output by the distance and the input card on your controller. The 4–20 mA loop is the safe default for any run longer than a few meters: it is a 2-wire current loop, so cable resistance and electrical noise do not shift the reading, as long as the loop load stays at or below 800 ohm. The voltage versions (0–5, 1–5, 0–10 V) are 3-wire and suit short runs into a PLC analog input with a high-impedance load above 50 kohm. A 1–5 V or 4–20 mA span also gives you a live-zero, so a broken wire reads as a fault instead of a true zero.

Selecting the range

Size the range to the working pressure, not to the worst case the line could ever see. For a sensor read in percent of full scale, a span you mostly use at 30–80% gives you the best resolution and the smallest error in real numbers.

Two range families cover most gas work. A compound range (-100 kPa to 0, or -100 kPa to a positive value) is the one to pick when the line can pull a vacuum, for example a gas blower suction or a pump-down step. A plain gauge range (0–1 MPa, 0–2.5 MPa, up to 0–10 MPa) covers positive pressures: 0–1 MPa is about 0–145 psi, and 10 MPa is about 1450 psi or 100 bar. For very low air or draft pressures in the kPa or inches-water range, a dedicated low pressure transducer resolves the small span far better than a 10 MPa unit turned down.

Applications

The SI-503K shows up wherever a gas or clean-air line needs a rugged, low-cost pressure reading:

Natural gas and biogas distribution headers and burner trains
Exhaust and flue-gas back-pressure monitoring
Compressed air and HVAC / air-conditioning charge pressure
Water-works and water-conservancy air-charging and pump skids
Chemical and medical gas lines running dry, weakly corrosive media
Vehicle brake-air and pneumatic test benches

Application example

Industrial gas supplier, compressed-air skid. A specialty-gas supplier was building an air skid around a mass flow controller and needed a compact pressure element on the supply side, in stainless, that would push onto the existing tubing without a new fitting. We quoted the SI-503K with the Phi 8 nozzle and a 4–20 mA loop into the skid controller, in 304 stainless for the clean dry-air service. It went forward as the pressure element on the skid.

FAQ

What does a gas pressure sensor do?

It measures the pressure of a gas and converts it to a 4–20 mA (or voltage) signal. The SI-503K measures industrial gas pressure, such as compressed air or process gas, on its sensing diaphragm and reports it for monitoring or control.

What happens if a pressure sensor is bad?

It drifts, sticks at a value, or loses output. On a gas line that can hide a leak or let an overpressure go unseen, so a robust sealed sensor and a clear fault behaviour matter; compare the reading against a known reference if you suspect it.

What are the types of pressure sensors?

By sensing technology: piezoresistive (diffused silicon), ceramic, capacitive, strain gauge, and resonant; by reference, gauge, absolute, and differential. A gas pressure sensor is usually a gauge sensor sized to the gas line.

Where is a gas pressure sensor located?

At the gas tapping point: it mounts on the pipe, manifold, or vessel through its process connection so the diaphragm sees the gas directly, away from liquid traps where possible.