- Certification Review
Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.
When working with an instrument air system, the _________ of the air is a critical measurement and is dealt with in the ANSI/ISA 7.0 standard.
B. dew point temperature
C. source humidity
D. molecular weight
The correct answer is B, "dew point temperature".
Dew point temperature is a measure of how much water vapor there is in a gas. The more water vapor in the instrument air, the higher the dew point. In instrument air piping, lowering the temperature of the flowing gas to a temperature below the dew point due to ambient temperatures or expansive cooling will cause condensation. Condensation in instruments or actuators that use instrument air can cause those instruments to malfunction or become damaged.
Instrument air systems are usually designed so that the dew point of the air steam is less than -40C or lower. Instrument air systems are typically outfitted with knock-out drums and dryers to remove as much moisture (water vapor) as possible prior to entering the instrument air header.
Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, 2nd Edition (2005), ISA Press
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