PLCs that primarily perform automatic regulation or control of a process variable (temperature, pressure, flow) may fall under 9032, but many PLCs are classified elsewhere in Chapter 85 as automatic data-processing machines or programmable controllers depending on their principal function and design. A binding ruling from CBP is advisable for complex multi-function controllers.

A manostat is an instrument that automatically maintains a preset pressure level in a system — its sole function is pressure regulation. Subheading 903281 covers broader hydraulic or pneumatic automatic regulating or controlling instruments that may govern flow, position, or other variables using hydraulic or pneumatic actuation, not just pressure maintenance.