Pressure Transmitters — Capacitive, Piezoelectric, Strain Gauge, DP Cell

Electronic pressure transmitters measure process pressure and output a proportional electrical signal (4–20 mA, HART, Profibus, FOUNDATION Fieldbus, or IO-Link) for DCS/PLC integration, remote monitoring, and control loops. Capacitive transmitters use the deflection of a metallic diaphragm that changes the capacitance between the diaphragm and a fixed electrode — the most common industrial transmitter type, characterised by wide range, high accuracy, and long-term stability. Strain gauge types bond silicon or metallic strain resistors to the diaphragm — resistance changes under strain (Wheatstone bridge circuit). Differential pressure (DP) transmitters have two process ports (high and low side) and measure the difference between them.

What It Is

How It Works

What It Is

How It Works

Challenges

Solutions

Pressure Limiter Valve (1.2× Maximum Range) on Each Transmitter Inlet: Chemical seal or pressure limiter prevents overrange — diaphragm never sees more than 120% of rated range.
Hastelloy C-276 or Tantalum Diaphragm for Aggressive Chemical Service: Exotic alloy diaphragm resists corrosion from HCl, HF, and strong oxidising acids — no fill fluid contamination.
Shielded Twisted-Pair Cable (STP, 24 AWG) + Earth at One End Only: Shielded cable blocks EMI; single-end earthing prevents ground loop currents — clean 4–20 mA signal.
IP 67 / IP 68 Housing + Self-Draining Cable Entry (Gore-Tex Breather): IP 67-rated housing; breather vent allows pressure equalisation without moisture ingress — prevents condensation.
Auto-Zero Function in Smart Transmitter (Periodic Zero Confirmation via HART): Smart transmitter periodic zero check (valve closed, no flow) confirms zero drift — alerts if drift exceeds 0.05% FS.

Applications

Process Control: Pressure control loops, flow measurement (with orifice plate), level measurement — 4–20 mA + HART standard.
Pharmaceutical: Cleanroom pressure monitoring, autoclave pressure, fermentation vessel pressure — SIL 2 rated for safety loops.
Oil & Gas: Wellhead, pipeline, and separator pressure measurement — intrinsically safe Zone 0/1, SIL 2 certified.
Utilities: Steam, water, compressed air header pressure monitoring — installed density of 1 per 30–50 m of main pipeline.
HVAC: Differential pressure transmitters for filter condition monitoring, fan pressure, and clean room cascade monitoring.

Models & Capacities

Pressure Transmitters — Models & Range Reference
Type	Pressure Range	Accuracy [% FS]	Long-Term Stability	Turn-Down Ratio	Output Signal	Process Connection	Wetted Material	Max Process Temp [°C]	IP Rating	SIL Rating
Capacitive DP (standard)	0–1 mbar to 0–700 bar; ΔP 0–100 mbar to 0–100 bar	±0.04–0.1	±0.1%/year	100:1	4–20 mA + HART/FF/PA	1/2″ NPT; G 1/2 flange	SS 316L; Hastelloy; Tantalum	121 (direct)	IP 67	SIL 2 (optional)
Capacitive gauge/absolute	0–10 mbar to 0–700 bar	±0.04–0.075	±0.1%/year	100:1	4–20 mA + HART/FF/PA	G 1/2; DIN / ANSI flange	SS 316L; Hastelloy	121	IP 67	SIL 2
Strain gauge (silicon)	0–100 mbar to 0–600 bar	±0.1–0.25	±0.2%/year	10:1	4–20 mA + HART	G 1/4 to G 1/2	SS 316L	150	IP 67	SIL 1
Piezoelectric (dynamic)	0.001 mbar peak to 10,000 bar peak	±1–3% FS	Charge drift	—	Charge amplifier; voltage	Flush diaphragm	SS 316L; Inconel	400	IP 68	Not rated (dynamic only)
Multivariable DP + SP + T	ΔP 0–100 mbar to 0–100 bar; static to 300 bar	±0.04% DP; ±0.1% SP	±0.1%/year	100:1 (DP)	4–20 mA + HART / FF (multivariable output)	G 1/2; flange	SS 316L; Hastelloy	121	IP 67	SIL 2
Flush diaphragm (sanitary)	0–100 mbar to 0–40 bar	±0.1–0.25	±0.25%/year	10:1	4–20 mA + HART + IO-Link	Tri-Clamp; DIN 11851	SS 316L Ra <0.8 µm; PTFE	150	IP 69K	SIL 2
Intrinsically safe (IS, Zone 0)	0–1 mbar to 0–700 bar	±0.04–0.1	±0.1%/year	100:1	4–20 mA + HART IS	G 1/2; flange	SS 316L; Hastelloy	150	IP 67	SIL 2 (IEC 61508)
Wireless (WirelessHART)	0–100 mbar to 0–700 bar	±0.1	±0.2%/year	10:1	WirelessHART (ISA 100.11a)	G 1/2; flange	SS 316L	121	IP 67	—