Interpreting a Drawing Change During Assembly
A student is assembling a small control enclosure from a drawing revision marked 'Rev C'. The drawing shows a 24 V DC power supply feeding a relay coil, with a flyback diode across the coil. A handwritten note on the bench copy, initialled but undated, says 'diode reversed on Rev C'. The student's supervisor is unavailable. The student has already soldered the diode according to the printed drawing. On power-up, the relay energises but the power supply's overcurrent indicator flickers when the relay de-energises. The student must decide whether to trust the printed drawing, the handwritten note, or the observed symptom.
1. Analyse the three sources of information and decide what the student should do next.
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The three sources conflict, so the student should reason from the circuit's function.
- The printed Rev C drawing shows the diode orientation. Printed drawings are controlled documents, but revisions can contain errors, which is exactly what a handwritten correction may be flagging.
- The handwritten note is initialled but undated and uncontrolled. It is a lead, not authority.
- The observed symptom is strong evidence. A flyback diode placed in reverse across a coil will not clip the inductive spike; instead it can conduct during normal energisation or fail to protect at de-energisation. Flickering overcurrent at de-energisation is consistent with an unprotected inductive kick.
The student should not simply choose a source. They should power down, isolate, and check the diode orientation against the circuit's intended function, then seek the controlled drawing's revision history or a supervisor's confirmation. The symptom suggests the note may be correct, but the student needs controlled confirmation before changing a soldered joint.
2. Describe the documentation the student should produce and how the assessor would judge the drawing-interpretation competency.
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The student should record:
- The drawing revision used and the handwritten note, with its location.
- The observed symptom and the conditions under which it appeared.
- The test performed to check diode orientation, with results.
- The action taken and the authority for it, such as a supervisor's confirmation or a revised drawing.
- The final re-test result.
The assessor judges drawing interpretation by whether the student can read the drawing, recognise the conflict, use the circuit's function to reason, and escalate appropriately. A student who blindly followed the printed drawing and ignored the symptom would not meet the criteria. A student who changed the joint on an undated note alone would also fall short, because they did not seek controlled confirmation. The satisfactory path combines drawing literacy, fault reasoning, and proper escalation.