🔍 Key Concepts

• Standard pneumatic instrument signal range used in process control • Difference between full-scale signal span and the zero point of the signal • Why pneumatic systems avoid 0 psig as the lower signal limit

💭 Think About

• Think about what pressure range many control valves and older controllers are calibrated for in classic pneumatic systems. • Ask yourself which range provides a clear, small span that can be linearly interpreted from 0% to 100% of signal without ever being truly zero pressure. • Consider which option represents a traditional industry standard that electronic signals (like 4–20 mA) were later designed to imitate in concept.

✅ Before You Answer

• Confirm which option has a narrow span that is practical for sensitive instruments rather than a very wide range. • Check which range has a non-zero lower limit to help detect line breaks or loss of air supply. • Verify which range can easily represent 0–100% of control signal in many legacy pneumatic control systems.