Arts: Instrumentation Diagrams, Symbols and Tag Language
GATE IN does not test fine arts. The representational content it does test is the graphical language of instrumentation: P&IDs, loop diagrams, ISA-style symbols and tag numbering. Reading a tag or a bubble correctly is a fast mark; misreading it is a common loss.
Core rules
- Tag format: letters are read left to right. The first letter is the measured or initiating variable: T temperature, P pressure, F flow, L level, A analysis. Succeeding letters are functions: I indicate, R record, C control, T transmit, E element, V valve.
- Examples: TT is a temperature transmitter; TIC is a temperature indicating controller; FE is a flow element such as an orifice plate; FIC is a flow indicating controller.
- Instrument bubble: no line means field-mounted; a solid horizontal line means panel-mounted; a shared display or DCS symbol is drawn differently. Check the legend, because project legends vary.
- P&ID line types distinguish process piping, electrical signal, pneumatic signal, capillary tubing and software links.
- A control valve symbol includes the actuator and the fail-safe action; the arrow or letters indicate fail-closed or fail-open.
- Loop diagrams show terminals, shield grounding, power supply and signal polarity, not just the process connection.
Worked example
A tag reads TIC-205. T = temperature, I = indicating, C = controlling, so it is a temperature indicating controller in loop 205. FT-101 is a flow transmitter in loop 101; FE-101 is the flow element in the same loop. If the bubble has no line, the instrument is field-mounted. The reasoning is purely positional: variable first, then function letters, then loop number.
Traps that cost marks
- Reading TIC as a temperature transmitter; that is TT.
- Assuming the first letter describes the function rather than the variable.
- Ignoring the legend and applying a generic symbol convention.
- Forgetting that a loop diagram must show shield grounding and polarity.