Pressure Measurement · Glossary

What is Zero Elevation and Suppression?

range offset from liquid legsPressure Measurement

Zero elevation and suppression shift a transmitter range to cancel the head of liquid in impulse lines or seal capillaries.

Zero Elevation and Suppression Explained

If a transmitter is mounted below its tap with a filled line, it sees extra pressure at zero level, so the range starts above zero: a suppressed zero range such as 20 to 120 kPa.

If a wet leg or seal capillary on the low side adds pressure there, the range starts below zero: an elevated zero range such as −80 to 20 kPa. These terms follow ISA 51.1.

Zero Elevation and Suppression Formula

Offset = ρ_leg × g × h_leg

ρ_leg	density of liquid in the leg or capillary
h_leg	vertical height of the leg

Example: A transmitter 2 m below its tap on a water filled line sees 1000 × 9.80665 × 2 ≈ 19.6 kPa at zero level.

Calculators for Zero Elevation and Suppression

CalculatorPressure Transmitter Elevation CorrectionFree online calculator with formula and worked example.CalculatorRemote Seal CalculatorFree online calculator with formula and worked example.CalculatorDP Level Transmitter CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Zero Elevation and Suppression?

Zero elevation and suppression shift a transmitter range to cancel the head of liquid in impulse lines or seal capillaries.

How do I remember which is which?

Suppressed zero: zero of the measured variable is below the LRV (LRV positive). Elevated zero: zero is above the LRV (LRV negative).

Can I just zero the transmitter instead?

You can set the LRV with the legs filled at zero level, but you must still keep the span the same.

Learn more on the blog

Differential pressure transmitter working principle

A practical guide on instrumentationblog.in with more detail on zero elevation and suppression and how it is applied on real plants.

Read Full Article

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