Pressure Measurement

Quick pick (TL;DR)

Reference: gauge for most process; absolute for vacuum / vapour pressure; differential for flow, level & filters.
Size the range so the normal operating pressure is ~50–75% of span (never >90%), respecting the transmitter turndown.
Add a remote/diaphragm seal for viscous, clogging, corrosive or high-temperature fluids.
Default output 4–20 mA + HART; SS316L wetted parts unless the fluid demands better.

Step 1 — Choose the reference

Type	Measures vs	Use for
Gauge	Atmosphere	Most process
Absolute	Vacuum	Vacuum systems
Differential	Two points	Flow / level / filters

Step 2 — Range & turndown

Range for a 6 barg process

Given normal pressure = 6 barg occasional max = 8 barg Rule — normal at 50–75% span ≥ normal / 0.75 = 6 / 0.75 = 8 span ≥ max / 0.9 = 8 / 0.9 = 8.9 choose range = 0–10 barg Check operating point 6 / 10 = 60% span → in sweet spot 8 / 10 = 80% span → below 90% limit Turndown check URL 16 bar, set 10 → turndown 1.6:1 ≤ 10:1 capability → OK

Normal at ~60% of span gives surge headroom; over-ranging wastes resolution where you operate.

Step 3 — Seals & protection

Seal for clogging/corrosive fluids.
Snubber on pulsating lines.
Over-range & manifold for isolation.

Range & turndown calculator

Calibrated range & operating point

Range so normal ~50–75% of span, max < 90%.

Normal (barg)

Max (barg)

Sensor URL (barg)

Max turndown

Keeps the operating point in the sweet spot & leaves surge headroom.

Common mistakes

Operating near full span.
No seal on clogging fluid.
Gauge where absolute is required.

Requisition & datasheet

Reference, fluid, pressure, service.
Range, turndown, accuracy, seal, Ex.

Frequently asked questions

What should I know about Pressure Measurement?

Reference: gauge for most process; absolute for vacuum / vapour pressure; differential for flow, level & filters. Size the range so the normal operating pressure is ~50–75% of span (never >90%), respecting the transmitter turndown. Add a remote/diaphragm seal for viscous, clogging, corrosive or high-temperature fluids. Default output 4–20 mA + HART; SS316L wetted parts unless the fluid demands better.

Which standards or codes apply?

IEC 61298 (instrument performance), EN 837 (pressure gauges), ASME B40.100, ISA-RP for installation.

Standards — IEC 61298; EN 837; ASME B40.100; ISA-RP.