Filled-system (pressure spring) thermometers: Vapour-actuated pressure spring thermometers do not require ambient temperature compensation. In gas or liquid-expansion pressure spring thermometers, ambient compensation is achieved primarily by which design choices?

Introduction / Context:
Filled-system thermometers translate temperature into pressure using a bulb, capillary, and receiving element (Bourdon/bellows). Gas and liquid expansion systems are sensitive to ambient temperature because the entire fill volume expands or contracts. Good instrument design mitigates ambient effects so the indicated temperature primarily reflects the bulb environment.

Given Data / Assumptions:

• Vapour-pressure systems are nearly self-compensated since pressure depends on saturation at the bulb.
• Gas/liquid systems require design-based compensation.
• We consider geometric volume choices for bulb, capillary, and receiver.

Concept / Approach:
The measured pressure change is proportional to the fraction of total fill volume within the bulb exposed to process temperature. By making the bulb volume large and minimizing volumes of capillary and receiving element, the percentage of fill impacted by ambient conditions is reduced, lowering ambient-induced errors. Thus, all three strategies contribute to compensation.

Step-by-Step Solution:

Verification / Alternative check:
Handbooks specify capillaries with small internal diameter and compact receiving elements; catalogues highlight “large bulb volume” designs for better accuracy.

Why Other Options Are Wrong:

• Any single option alone is helpful but insufficient; best practice applies all three simultaneously.
• Thicker dial glass does nothing to compensate thermodynamic volumes.

Common Pitfalls:
Overlooking capillary routing through hot zones; even with good volumes, poor routing can reintroduce ambient errors.

Final Answer:
All (a), (b) & (c)