Pressure Transmitter Selection: Five Steps from Duty to Model

Pressure transmitters are among the most widely used process instruments, yet selection errors are common. These five steps cover most situations.

Step 1: Establish the measurement type

Gauge, absolute or differential? This is the most frequently overlooked and most critical step. For a closed vessel, if the vapour space is pressurised and the instrument references atmosphere, you must use a differential or submersible (barometrically compensated) transmitter — a gauge transmitter alone will drift with barometric pressure.

Step 2: Determine the range

The usual practice is to place normal working pressure between 60% and 80% of span. Too narrow risks overload; too wide sacrifices resolution and accuracy. Confirm overload capability — water hammer and pump start-up surges are often several times working pressure.

Step 3: Assess media compatibility

316L stainless covers most neutral media; strong acids need Hastelloy or tantalum diaphragms; chloride-bearing media raise stress-corrosion concerns; hydrogen service requires attention to embrittlement and permeation. Above 85 ℃, consider a condensate syphon or a high-temperature model.

Step 4: Choose the accuracy class

Higher accuracy is not automatically better. ±0.5% FS satisfies most process monitoring; only material-balance or custody-transfer duties justify ±0.1% to ±0.25% FS. Note that catalogue accuracy is typically measured at a specific temperature — total error under real conditions adds temperature effects.

Step 5: Confirm electrical and installation conditions

Verify supply voltage, output type, load capability and ingress protection. Where VFDs and other strong interference sources exist, choose EMC-protected products and use shielded cable grounded at one end. Outdoor installation requires surge and sun protection.