Diff Pressure
Measures the pressure difference between two ports — typically 0–25 hPa to 0–10 bar — and outputs a digital or 4–20 mA reading proportional to the differential, regardless of the absolute pressure level on either side.
A silicon or stainless diaphragm separates two pressure cavities. Piezoresistive elements on the diaphragm (or a Wheatstone bridge) convert flex into mV. Any common-mode pressure (line pressure) cancels because both sides see the same level; only the differential deflects the diaphragm. On-chip temperature compensation and digital ADCs in modern parts (e.g., Sensirion SDP800) deliver 0.1 hPa resolution across the working range.
In plain terms
Like a referee at a tug-of-war who reports only how hard team A is pulling vs. team B — the absolute strength of each team is irrelevant, only the differential matters.
Why designers use it
- Flow measurement via orifice plate or Venturi — the differential across a flow restriction is proportional to flow².
- Filter-blockage monitoring — as a HEPA or cartridge filter fouls, the upstream-vs-downstream pressure rises predictably.
- Medical ventilator airflow — measure inspiratory vs. expiratory limb pressure to control patient breathing precisely.
- HVAC duct static pressure — positive vs. ambient measurement controls fan speed in variable-air-volume systems.
Best for
- Flow
- Filter monitoring
- Ventilators
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Where line pressure exceeds the sensor's overpressure rating — high common-mode pressures rupture the diaphragm even when differential is small.
- Where one of the ports might dry out or get blocked — a clogged side gives a false high differential and the system misbehaves.
Common mistakes
- Routing the high-side and low-side tubes with different lengths or fluid columns — the static head difference creates a permanent zero offset.
- Skipping the bleed valves — air bubbles trapped on one side give a 'soft' reading that drifts as the bubble dissolves.
Where you will find it
- A Hamilton T1 ICU ventilator uses a Sensirion SDP31 differential pressure sensor across its proximal flow tube: the sensor's 0.06 hPa resolution at the −250 to +250 hPa range lets the ventilator deliver pressure-controlled breaths to neonates with tidal volumes as small as 5 mL.
- A Rosemount 3051CFP differential pressure transmitter on a Saudi Aramco natural-gas pipeline at a reducing station senses flow across an orifice plate: the transmitter's stable ±0.04 % differential reading sustains custody-transfer billing accuracy at 10 million scfm flow.
- A Camfil HEPA air-filter monitor in a TSMC fab cleanroom reads differential pressure across each filter bank with a Setra 264 transducer: when the differential rises 50 % above clean-filter baseline, maintenance schedules a swap before particle counts climb.
A short history
A differential pressure sensor measures the pressure difference between two points. For example, comparing the pressure before and after an air filter can help detect increasing restriction. The measurement reference is different from absolute or gauge pressure, but it does not by itself determine the sensor's electrical interface.