Print Reading and Schematics Flashcards

A drawing uses chain dimensioning to locate three drilled holes in a row. The first hole is dimensioned 1.000" ± 0.005" from the left edge. The second hole is 2.000" ± 0.005" from the first, and the third is 2.000" ± 0.005" from the second. What is the maximum possible positional error of the third hole relative to the left edge?

Answer: ± 0.015"

Chain (datum-to-datum) dimensioning causes tolerances to accumulate. Each link in the chain adds its own tolerance: ± 0.005" + ± 0.005" + ± 0.005" = ± 0.015" worst-case error at the third hole. This is why baseline (datum) dimensioning is preferred when tight positional accuracy is required across multiple features.

A ladder logic rung reads (left to right): [L1] — [/CR1] — [CR2] — (M) — [L2], where [/CR1] is a normally-closed contact for relay CR1 and [CR2] is a normally-open contact for relay CR2. Output coil M will energize under which condition?

Answer: CR1 de-energized AND CR2 energized

A normally-closed contact passes current when its coil is de-energized and opens (breaks) when its coil is energized. A normally-open contact passes current only when its coil is energized. For current to flow through both contacts in series: CR1 must be de-energized (so the NC contact remains closed) AND CR2 must be energized (so the NO contact closes). Any other combination breaks the rung.

On a technical drawing, a line type consisting of a long dash followed by two short dashes (— · · — · ·) is classified as a phantom line. This line type is correctly used to represent which of the following?

Answer: An alternate position of a moving component or the outline of an adjacent part not part of the assembly

Phantom lines (long-short-short pattern) show alternate positions of moving parts — such as the full travel range of a lever — or adjacent parts included for reference only. Hidden lines use a medium-weight dashed line. Cutting planes use a chain line with arrowheads. Center lines use a thin alternating long-short pattern (one short dash, not two).

In a hydraulic circuit schematic, a flow control valve is placed in the hydraulic line between the directional control valve outlet port and the actuator's rod-end port. How is this circuit configuration classified, and what does it control?

Answer: Meter-out circuit — it regulates the flow of fluid leaving the rod end of the cylinder during extension

A meter-out circuit positions the flow control valve on the exhaust side (outlet) of the actuator. When the cylinder extends, oil leaving the rod end must pass through the flow control valve, which restricts and controls exit flow — thereby governing actuator speed. Meter-out is preferred for overrunning or gravity loads because back-pressure prevents uncontrolled movement. Meter-in controls inlet flow; bleed-off diverts flow to tank before the actuator.

A welding symbol on a fabrication drawing shows the reference line with weld specifications, and a small circle drawn at the junction where the arrow meets the reference line (the elbow). What does this circle specifically indicate?

Answer: The weld is to be applied completely around the entire joint perimeter

A circle at the elbow (junction of arrow and reference line) is the 'weld all-around' symbol, indicating the weld continues around the complete perimeter of the joint. A flag (pennant shape) at the elbow indicates a field weld. The 'both sides' condition is shown by placing weld symbols both above and below the reference line, not by a circle.

On a Process and Instrumentation Diagram (P&ID), an instrument bubble is tagged 'FIC-101.' Using ISA 5.1 instrument identification conventions, what does this instrument tag describe?

Answer: A flow-indicating controller — a device that both displays flow rate and sends a corrective output signal to regulate it

Per ISA 5.1 instrumentation symbology: the first letter (F) identifies the measured variable — Flow. Subsequent letters identify the functions: I = Indicator (displays the value), C = Controller (computes and outputs a correction signal). Therefore FIC = Flow Indicating Controller, an instrument that both shows the operator the current flow rate and automatically controls it. The loop number (101) is simply an identifier, not a value or ratio.