Chemical Process Instrumentation: Fundamentals and Applications

A: Governing principle: span should cover normal operation with defined overpressure margin without sacrificing resolution. Applied here: a 0–10 barg gauge unit captures the operating range, tolerates spikes, and avoids unnecessary loss of accuracy. Absolute reference isn’t required for a vented liquid header. Distractor trap: oversizing the range feels safe, but the 0–25 barg choice quietly degrades signal quality at low pressure.

A: Governing principle: added mass in a mechanical sensing element increases inertia. Applied here: the heavier torque tube slows response, which the controller sees as dead time, driving sluggish control. Distractor trap: weight doesn’t change buoyancy physics, so span and zero aren’t the first-order effect.

A: Governing principle: thermal time constant scales with mass and heat transfer resistance. Applied here: a metal well adds mass and a conduction barrier, pushing response into the several‑second range, not minutes. Distractor trap: assuming velocity alone controls response ignores the metal wall between process and sensor.

A: Governing principle: DP measurement relies on equal, responsive impulse lines. Applied here: a cold LP line points to blockage or condensation, locking in pressure and driving the DP to zero. Distractor trap: a reversed orifice affects calibration sign, not impulse line temperature.