Frequently asked instrumentation questions
Short answers to common measurement-system questions.
Why is 4 mA used for zero instead of 0 mA?
A 4 mA live zero leaves a current region below the normal measurement range that can help distinguish some fault conditions from a legitimate zero process value.
What is the difference between calibration and adjustment?
Calibration establishes the relationship between indication and reference values. Adjustment changes the instrument to alter its indication.
Does more display resolution mean better accuracy?
No. Additional digits can improve display resolution without reducing sensor error, drift, noise or measurement uncertainty.
What is the difference between gauge and absolute pressure?
Gauge pressure is referenced to local atmospheric pressure; absolute pressure is referenced to vacuum.
Which flowmeter is most accurate?
There is no universal answer. Performance depends on fluid, range, installation, process conditions and the exact specification being compared.
Is HART the same as 4–20 mA?
No. HART is a digital communication protocol. It is often used on instrumentation that also provides a conventional 4–20 mA process signal.
Can I use the calculators for calibration certificates?
They can check simple arithmetic, but formal calibration work requires the approved method, reference standards, uncertainty evaluation and applicable quality system.
Does this site provide safety instrumented system settings?
No. Safety instrumented systems require engineered functional-safety lifecycle work; this site stays at a high-level educational overview.
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