Prove the meter before you use it, then test a cable, a fuse and a switch

short · 50 min · Objective 5.2

Task

Establish that the instrument works before believing any result from it, then take three continuity measurements and record each as evidence rather than as a tone you heard.

Steps

  1. PROVE THE INSTRUMENT FIRST: touch the probes together on the continuity setting and record the reading and whether the tone sounded in lab/meter/proof.txt. A meter with a broken lead reports everything as open.
  2. Record the meter's own details in lab/meter/meter.csv with header field,value -- make, model, and the functions it offers.
  3. Test a cable end to end, conductor by conductor where it has several, and also BETWEEN conductors, recording results in lab/meter/cable.csv with header from,to,continuity,expected.
  4. Test a fuse and a switch in both positions, recording in lab/meter/parts.csv with header part,state,continuity,expected,verdict.
  5. Write lab/meter/functions.csv with header function,question_it_answers,parallel_or_series,powered for voltage, current, resistance and continuity.

Verify

grep -c . lab/meter/proof.txt
awk -F, 'NR>1 && NF>=2 {n++} END {print n" meter detail(s)"}' lab/meter/meter.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" cable measurement(s)"}' lab/meter/cable.csv
awk -F, 'NR>1 && tolower($3)!=tolower($4) {n++} END {print n+0" unexpected cable result(s)"}' lab/meter/cable.csv
awk -F, 'NR>1 && NF>=5 {n++} END {print n" part measurement(s)"}' lab/meter/parts.csv
awk -F, 'NR>1 && NF>=4 {n++} END {print n" function(s) described"}' lab/meter/functions.csv
grep -Eic 'series' lab/meter/functions.csv

The instrument proof recorded first, four or more cable measurements including at least one between-conductor test, a switch tested in both states, and four functions described with current marked as series. A functions table that marks current as parallel is the error that blows a meter's fuse.

Notes

The between-conductor test is the one people skip. Testing each conductor end to end finds opens and never finds a short, and a short is exactly as fatal to a cable.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.