Flush Diaphragm Pressure Sensors

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Reach for a flush connection in two situations. The first is cleanliness: pharmaceutical, food and beverage points where a recessed bore cannot be rinsed residue-free; the clamp-fitted version of this idea is our SI-350 sanitary pressure transmitter. The second is media that defeats a normal port: high-viscosity liquids, pastes, crystallizing products and slurries that clog the channel, or media that hardens as the process cools. If the medium would also damage or contaminate the instrument itself, step up to a diaphragm seal pressure transmitter with a remote capillary instead.

Models at a glance

Model	Range	Accuracy	Output	Media temp	Connection	Notes
SI-703	0–0.6 to 0–200 MPa	0.1 / 0.2 / 0.5% FS	4–20 mA; 0–5 / 1–5 / 0–10 V	−20 to 75 °C	M20 × 1.5, G1/2-14	Base model; metal sealed terminal or 4-core aviation connector
SI-703F	0–1 to 0–200 MPa	0.2 / 0.5 / 1.0% FS	4–20 mA; 0–5 / 1–5 / 0–10 V	−20 to 75 °C	M20 × 1.5, G1/2-14	Waterproof cable outlet
SI-703K	Spans to 0–100 MPa	0.1 / 0.2 / 0.5% FS	1–1.5 mV/V, 10 VDC	−20 to 85 °C	Φ19 standard core	Bare OEM core, direct leads, for transmitter builders
SI-703W	0–1.5 kPa to 0–500 kPa; 1–60 MPa	0.25 / 0.5% FS	4–20 mA; voltage options	−20 to 65 °C	M24 / M25 × 1.5, M27 × 2	Micro-pressure spans; Hirschmann connector
SI-703C	0–10 to 0–500 kPa; 1–7 MPa	0.1 / 0.2 / 0.5% FS	4–20 mA; voltage options	−20 to 65 °C	M20 × 1.5, G1/2-14	Micro-pressure, compact
SI-703G	0–5 to 0–500 kPa; 1–7 MPa	0.1 / 0.2 / 0.5% FS	4–20 mA; voltage options	−20 to 65 °C	M20 × 1.5, G1/2-14	Built as an alternative to common imported flush sensors
SI-703GB	0–5 kPa to 1 MPa; 2 / 3 / 10 MPa	0.1 / 0.2 / 0.5% FS	4–20 mA; voltage options	−20 to 65 °C	G1	Large G1 face for the lowest spans; imported-pattern port

Technical specifications

Parameter	Specification
Power supply	24 VDC (10–30 VDC); SI-703K core runs on 10 VDC
Load resistance	Current output: 800 Ω max; voltage output: greater than 50 kΩ; 703K: 1500 Ω
Insulation resistance	Greater than 2000 MΩ at 100 VDC
Long-term stability	0.1% FS per year
Vibration effect	Less than 0.1% FS over 20–1000 Hz
Overload structure	Elastomer and fitting in fully sealed or one-piece construction; impact pressure capability to 100 MPa, model dependent
Sensing element	Diffused-silicon strain gage bridge behind a flush stainless steel membrane
Electrical interface	Metal sealed terminal, 4-core aviation connector, Hirschmann connector or waterproof outlet, by model
Protection	IP65
Custom threads	Other process threads designed to order

Specifications apply at room temperature and rated supply unless stated. Per-variant figures are in the table above; confirm the exact figure for your model and range on the order sheet.

Working principle

Resistors are diffused or ion-implanted into a silicon die and wired as a Wheatstone bridge under a micro-machined pressure diaphragm. Pressure deflects the diaphragm, the bridge resistance shifts, and the output is a linear signal proportional to pressure; the conversion electronics turn it into two-wire 4–20 mA or a voltage. The flush face in front of that bridge solves clogging. It does not solve chemistry.

From the case file: a battery-materials plant in the US needed pressure on a caustic slurry at pH 14, 0–30 psi at 20 to 90 °C. Clogging was only half the problem there; pH 14 attacks stainless steel, so that job went to a ceramic diaphragm with a PTFE fitting at 0.25% FS. The selection lesson carries over to every flush-diaphragm inquiry: check the diaphragm material against the medium before you check the span.

OEM cores

The SI-703K is the series stripped to its core: a Φ19 flush-diaphragm cell with direct leads and a 1–1.5 mV/V raw output, made for manufacturers who package their own electronics. It is priced and toleranced for volume production. Custom builds are routine here; a test-equipment maker in the UK ordered sensors carrying their own logo and custom threads, and that order shipped as a standard job, not an exception.

Ordering information

No SI-703 is a stock item. Variant first, span second; the variant table above settles most inquiries in one pass.

Ordering example: SI-703C, 0–300 kPa gauge, G1/2-14 thread, 4–20 mA, Hirschmann connector, for a coatings line running at 30 psi (207 kPa). The working point sits at 69% of full scale.

Applications

Related products

FAQ

What is the flushing ring on a pressure transmitter?

A flushing ring is a separate accessory: a metal ring fitted between the process flange and a diaphragm-seal transmitter, with side ports you can open to rinse or vent the diaphragm face without removing the instrument. It is not the same as a flush diaphragm. A flush (flat) diaphragm transmitter has its sensing diaphragm level with the process connection so nothing collects in front of it, which is what the SI-703 uses for viscous and crystallising media; a flushing ring is an add-on for cleaning a recessed seal in place.

What is the diaphragm in a pressure transmitter?

The diaphragm is the thin metal or ceramic membrane that the process pressure pushes against; its deflection is what the sensing element turns into a signal. In a flush-diaphragm transmitter the membrane sits flat at the process connection, welded to the cell or backed by a stable fill fluid, so it transmits pressure cleanly while keeping the medium out of any pocket where it could clog or harden.

How does a diaphragm level transmitter work?

Mounted low on a tank, a flush-diaphragm transmitter reads the hydrostatic head, the pressure from the column of liquid above it, which is proportional to level. Because the diaphragm is flush, thick or sticky products do not build up in a cavity and skew the reading. You convert the measured pressure to height using the liquid density (P = density x g x height), which is why a clean, drift-free diaphragm matters for level service.

Request a quote

Tell us the medium, the working pressure, the thread and the output signal. We respond with a configured variant, lead time and price, usually within one working day.