Analytical · Glossary
What is Sample Lag Time?
transport delayAnalytical
Sample lag time is the delay for a sample to travel from the process tap to the analyser.
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Sample Lag Time Explained
Long lines, large tubing and low flow add delay that hurts control and alarms. Fast loops and short lines reduce it.
For gases, compressibility means the delay depends on pressure along the line.
Sample Lag Time Formula
t = V ÷ Q = π d² L ÷ (4 Q)
| d | tube inside diameter |
| L | length |
| Q | flow |
Example: 4 mm ID, 30 m at 1 L/min: V ≈ 0.38 L, t ≈ 23 s.
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Calculators for Sample Lag Time
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Frequently Asked Questions
What is Sample Lag Time?
Sample lag time is the delay for a sample to travel from the process tap to the analyser.
What lag is acceptable?
Often under about 60 s for control analysers; set by process needs.
Do filters add lag?
Yes, their internal volume adds delay and mixing.
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