PC-01Process measurement · PT
Pressure Transmitters, Switches & Gauges
Gauge, absolute and compound pressure for liquids, gases and steam — from local indication to transmitters for control, alarms and interlocks. Selection starts with the range, the medium and the process connection.
01Scope
What's included
Gauge and absolute pressure transmitters, switches and gauges.
- Pressure transmittersGauge, absolute or compound ranges with 4–20 mA / HART or fieldbus output for control and monitoring.
- Pressure switchesSet-point switching for alarms, interlocks, pump and compressor protection.
- Pressure gaugesLocal indication with Bourdon-tube, diaphragm or capsule elements; liquid-filled for pulsation and vibration.
- Diaphragm sealsIsolate the sensor from hot, viscous, corrosive, crystallizing or hygienic media — direct or capillary mounted.
- Installation accessoriesBlock-and-bleed valves and manifolds, siphons for steam, snubbers for pulsation, mounting brackets.
02Compare
Sensing principles
The sensing element decides the usable range, the overload tolerance and how the sensor meets the medium.
| Principle | How it works | Suited for | Considerations |
|---|---|---|---|
| Piezoresistive (silicon)Media: LiquidGasSteam | How it worksPressure deflects a silicon diaphragm carrying diffused resistors in a bridge; the change in resistance follows the pressure. | Suited forGeneral process and utility pressure; compact transmitters and switches across a wide span of ranges. | ConsiderationsUsually isolated from the process by a metal diaphragm and fill fluid — the fill must suit process temperature and vacuum. |
| Capacitive (metal or ceramic)Media: LiquidGasSteam | How it worksA measuring diaphragm moves relative to a fixed electrode, changing the capacitance between them. | Suited forLow ranges, differential pressure and high-accuracy process transmitters; ceramic cells for abrasive or corrosive media. | ConsiderationsCeramic cells are dry (no fill fluid) and tolerate high overload, but rely on an elastomer seal whose material must suit the medium. |
| Thin-film / strain gaugeMedia: LiquidGas | How it worksStrain gauges deposited on a stainless-steel diaphragm change resistance as the diaphragm deflects. | Suited forHigher pressure ranges, hydraulics, pulsating service and equipment-mounted applications. | ConsiderationsRobust, fully welded and free of fill fluid; less suited to very low ranges. |
| Mechanical elementsMedia: LiquidGasSteam | How it worksA Bourdon tube, diaphragm or capsule deforms elastically and drives a pointer through a movement. | Suited forLocal indication without power — Bourdon tubes for medium to high pressure, diaphragms for low pressure and difficult media, capsules for low gas pressure. | ConsiderationsNo remote signal unless fitted with contacts or a transmitter; pulsation and vibration call for liquid filling or snubbers. |
General engineering guidance. Limits and performance depend on the specific instrument and variant — confirm them against the manufacturer's datasheet for the selected model.
03Specify
What to specify
The parameters that decide the selection. State each with its unit; where a value is not known yet, say so — it becomes part of the engineering review.
Pressure reference
Gauge pressure references atmosphere, absolute references vacuum; vacuum and compound service need the right reference and sensor.
Range and unit
The normal operating point should sit well inside the span; smart transmitters can be ranged down from their upper range limit.
Overpressure and spikes
Water hammer, pump starts and pulsation can exceed the rated overload — state the maximum and consider a snubber.
Medium
Corrosive, viscous, crystallizing or hygienic media change the wetted materials and often call for a diaphragm seal.
Process temperature
Above the sensor's limit, use a siphon (steam), a cooling element or a diaphragm seal with capillary.
Process connection
Thread (e.g. ½ in NPT, G ½), flange or hygienic clamp — it must match the tapping and its pressure rating.
Wetted materials
316L stainless steel is common; higher alloys, tantalum or lined seals are used for aggressive media.
Accuracy
Compare total performance over the ambient temperature range, not only reference accuracy — and state whether it is % of span or of range limit.
Output and communication
4–20 mA / HART for most control systems, fieldbus where the architecture uses it, switch contacts for alarms and trips.
Area classification
Hazardous areas need a device certified for the zone and gas group — intrinsically safe or flameproof.
Enclosure and ingress protection
Outdoor, washdown or flooded locations need a suitable IP rating, housing material and cable entry.
04Integrate
Outputs & communication
Interfaces typically offered in this category, and what each means for the control system. Availability depends on the specific model.
- 4–20 mAAnalog
- Current loop with a live zero: 4 mA is the bottom of the range, so a broken wire (0 mA) is distinguishable from a zero reading. Two-wire (loop-powered) on most transmitters; four-wire with an active output on line-powered instruments such as analyzers — the I/O channel must match. Accepted by practically every PLC and DCS analog input.
- HARTDigital over analog
- A digital signal (Bell 202 FSK, 1200/2200 Hz) superimposed on the 4–20 mA loop — configuration, diagnostics and secondary variables over the existing two wires.
- Modbus RTUSerial
- Serial client/server (formerly master/slave) protocol, typically over RS-485: several devices share one multi-drop cable and the client polls each for its values — common on analyzers, multivariable meters and packaged equipment.
- PROFIBUS PAFieldbus
- Two-wire, bus-powered process fieldbus at 31.25 kbit/s, coupled to PROFIBUS DP — several instruments share one cable, with intrinsically safe variants for hazardous areas.
- FOUNDATION Fieldbus H1Fieldbus
- Two-wire, bus-powered digital fieldbus at 31.25 kbit/s with function blocks in the field devices — used mainly where the DCS architecture is built around it.
- Relay / discreteDiscrete
- Switched contact or transistor output for alarms, interlocks and pump or valve control — it carries a state, not a value.
05Install
Installation practice
- Liquid service: tap at the side of the pipe and mount the transmitter below the tapping so gas bubbles vent back to the process.
- Gas service: tap at the top of the pipe and mount the transmitter above it so condensate drains back.
- Steam service: use a condensate-filled siphon or impulse line so live steam never reaches the sensor.
- Fit an isolation valve or manifold so the instrument can be vented, zero-checked and removed without shutting the process down.
06Products
Pressure products
Status · no models listed
Specific models are not listed on the site.
Our engineers can recommend instruments against your process data. The selection checklist on this page is the information that decides it — send what you have.
How a review runs
PT01Share the process data
Medium, range, conditions, connection and the system it reports to.
02Engineering review
The measuring principle and the installation are checked against the application.
03Instrument options
Suitable devices are proposed with the data needed to confirm the selection.
Next steps
Where to go next
- 01SolutionInstrumentationProcess measurement and final control elements — selected for the process conditions, installed, calibrated and loop-checked.
- 02ResourcePressure vs Differential Pressure MeasurementGauge, absolute and differential pressure — what each measures and where each is used.
- 03Related categoryDifferential PressureDP transmitters for flow, level, filter and pressure-drop measurement.
Engineering enquiry
Specifying a pressure measurement?
Share the medium, the range, the process conditions and the system it has to connect to. Our engineers can help match the principle and the instrument to the application.