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These are original study notes from the app visual library. They are not copies of standards or vendor manuals. No artwork is published on this page.
Strain gauge bridge on a silicon diaphragm
A silicon diaphragm deflects under process pressure, stretching diffused resistors. The resistance change unbalances a Wheatstone bridge, producing a millivolt signal proportional to pressure. Used in most modern smart transmitters.
Image file is not published on the website.
Capacitor plates separated by a pressure-sensitive diaphragm
Process pressure deflects a sensing diaphragm between two fixed capacitor plates. Deflection changes the capacitance gap, which is measured by onboard electronics. Highly accurate, low hysteresis — common in Rosemount and EJX families.
No image file in the app. Placeholder note only.
Wire frequency shifts with tension caused by pressure
A taut wire is excited into vibration. Applied pressure changes wire tension, shifting the resonant frequency. The frequency is measured electronically and converted to pressure. Very stable for static measurements.
No image file in the app. Placeholder note only.
Diaphragm displacement changes magnetic reluctance
Two coils face a metallic diaphragm. Pressure deflects the diaphragm, changing the magnetic flux in each coil differently. The differential inductance signal is processed to give pressure output. Robust for harsh environments.
No image file in the app. Placeholder note only.
C-shaped or helical tube that straightens under pressure
A flattened metal tube (C-shaped, helical, or spiral) is sealed at one end and connected to process pressure at the other. Pressure causes the tube to straighten, moving a pointer via a linkage and gear mechanism. The most common local indicator.
No image file in the app. Placeholder note only.
Flexible disk deflects under low differential pressure
A corrugated metal or elastomeric diaphragm clamped between two flanges deflects under process pressure. Deflection is transmitted to a pointer. Suited for low pressures, viscous fluids, and processes that would clog a Bourdon tube.
No image file in the app. Placeholder note only.
Accordion-shaped element for low-pressure measurement
A series of circular convolutions forms a bellows that expands and contracts with pressure changes. The linear displacement drives a pointer. Used for very low pressures (vacuum to a few bar) where Bourdon tubes lack sensitivity.
No image file in the app. Placeholder note only.
Two diaphragms welded face-to-face for draft/low pressure
Two corrugated diaphragms welded at their periphery form a capsule. Very small pressure differences expand the capsule, which moves a pointer through a lever system. Common in HVAC and very low-pressure gas measurement.
No image file in the app. Placeholder note only.
One process connection — measures pressure above atmosphere
The high-side (H) port connects to process. The low-side vent is open to atmosphere. Output represents gauge pressure: process pressure minus atmospheric. Used for tank pressure, pump discharge, filter ΔP relative to atmosphere.
No image file in the app. Placeholder note only.
Measures pressure relative to perfect vacuum (zero reference)
The low-side is sealed and evacuated to near-perfect vacuum internally. Output represents absolute pressure. Used for barometric reference, vacuum measurement, and processes where atmospheric variation must be excluded.
No image file in the app. Placeholder note only.
Gas-filled impulse lines, high side connected to process
Both H and L impulse lines contain gas (no liquid fill). The high-pressure tap connects below the minimum level, low-pressure tap above. Suited for clean, dry gas service or liquid service where lines are sloped to drain back to process.
No image file in the app. Placeholder note only.
Low-side impulse line filled with reference liquid
The low-pressure impulse line is intentionally filled with a reference liquid (often condensate or a fill fluid). A condensate pot maintains a constant head. Used for steam service and condensing vapours to prevent variable liquid columns.
No image file in the app. Placeholder note only.
Capillary-connected diaphragm seal isolates corrosive process
A flush diaphragm seal at the process connection is filled with a compatible fill fluid (silicone, glycerin, etc.) connected via a capillary to the transmitter. Isolates the sensing cell from corrosive, viscous, or crystallising fluids.
No image file in the app. Placeholder note only.
Isolate and equalise — for gauge pressure transmitters
Two valves: one block valve to isolate the transmitter from process, one vent to atmosphere. Used with single-sided (gauge or absolute) transmitters. Procedure: close block → open vent → remove transmitter safely.
No image file in the app. Placeholder note only.
Two block valves and one equalising valve for DP service
High-side block, low-side block, and one equalising valve. To isolate a DP transmitter: close both block valves, then open equalise. This prevents overpressure on one side of the cell. Critical for safe DP transmitter removal.
No image file in the app. Placeholder note only.
Two blocks, two vents, one equalise — full isolation capability
Extends the 3-valve manifold with separate vent/drain valves on each side. Allows individual side venting for calibration, testing, and purging without breaking process connections. Common in critical measurement loops.
No image file in the app. Placeholder note only.
Slope, fill, and drain orientation by service type
Liquid service: slope impulse lines upward from process to transmitter to allow gas to escape back. Gas service: slope downward so condensate drains back. Steam: use condensate pots. Correct slope prevents measurement error from trapped gas or variable liquid heads.
No image file in the app. Placeholder note only.
Transmitter below tap, lines sloped upward
For liquid process connections, mount the transmitter at or below the process tap. Slope impulse lines upward toward the process to allow any trapped gas to vent. Fill lines with process liquid before commissioning to prevent measurement offset.
No image file in the app. Placeholder note only.
Transmitter above tap, lines sloped downward to drain
For gas or vapour service, mount the transmitter above the process tap. Slope impulse lines downward so any condensate drains back to the process pipe. Prevents liquid accumulation that would create a false positive head pressure.
No image file in the app. Placeholder note only.
Condensate pots equalize liquid columns on both sides
For steam, install condensate pots above both high and low taps. Allow steam to condense and fill the pots to a constant level before commissioning. Ensures both impulse lines have equal liquid heads so ΔP reflects only the process differential, not a variable condensate leg.
No image file in the app. Placeholder note only.
Flush mount for viscous, crystallising, or corrosive fluids
Where the process fluid would block or corrode standard impulse lines, a flush diaphragm seal is welded or bolted directly to the nozzle. The fill fluid transmits pressure via capillary to the transmitter body. Seal must be rated for process temperature and compatible with fill fluid.
No image file in the app. Placeholder note only.
Primary standard — known mass on a calibrated piston area
A precision piston-cylinder assembly with known masses generates a reference pressure: P = F/A. The device under test (DUT) is connected and compared. Accuracy can reach ±0.005% of reading. Used as the primary traceable standard for pressure calibrator verification.
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0 / 25 / 50 / 75 / 100% — ascending and descending
Connect a reference calibrator to the transmitter under test. Apply pressure at 0%, 25%, 50%, 75%, and 100% of range in ascending order, then descend. Record the transmitter mA output at each point. Pass criteria: error within ±0.1% of span (or per site spec). Document as-found and as-left values.
No image file in the app. Placeholder note only.
End-to-end verification: transmitter to DCS input card
Apply a known pressure to the transmitter and verify the mA signal at the DCS or PLC input card matches the expected value. Checks the complete signal chain: sensing cell → electronics → transmitter output → field cable → barrier/isolator → I/O card. Documents loop accuracy, not just transmitter.
No image file in the app. Placeholder note only.