## Fill a TDR location record

Use `tdr-location-record.csv` to retain the measurement context, time reading, distance estimate and follow-up check in one row. Keep the 13 column names unchanged. The file contains a blank field-record row and a separate teaching example; it can be edited in ordinary spreadsheet software. It does not control an instrument, calculate results automatically or determine whether a component passes.

Use the record for a cable that has been isolated, confirmed de-energized and checked against the instrument's connection conditions. Follow the instrument and component documents for connection, calibration and permitted signal levels. The distance conversion needs a defined reference plane, a suitable velocity factor and an identifiable reflection along the path.

## Distinguish the two supplied rows

| `record_type` token | How to use the row |
| --- | --- |
| `BLANK_FIELD_RECORD` | Blank row for actual field or bench data. Apart from the row label, all supplied values are empty. Fill the fields from the actual setup and retain missing values as blanks. |
| `ILLUSTRATIVE_NOT_MEASURED` | Constructed teaching example. Its times, VF and distance describe the article's assumptions, not measured cable or instrument results. Keep this label with the example. |

A blank field is an unfilled or missing value. It is not a zero reading, a confirmed absence of delay or a passed check. Do not replace blank fields with the example values. To record an actual measurement, fill the blank row or copy it into another record row and retain enough specimen and setup information to identify that measurement.

## The 13 columns

| Column | Meaning and recording condition |
| --- | --- |
| `record_type` | Distinguishes the blank field-record template from the illustrative row. The supplied tokens are `BLANK_FIELD_RECORD` and `ILLUSTRATIVE_NOT_MEASURED`. |
| `specimen_and_revision` | Specimen identifier and the drawing, cable or assembly revision governing the recorded setup. The teaching row uses `teaching_example_A`. |
| `test_mode` | Instrument mode and the basis of the horizontal-axis reading. The teaching row uses `round_trip_time`. State whether the actual instrument reports round-trip time or has already converted it to one-way distance. |
| `reference_plane` | Electrical origin from which the reading is taken. The teaching row uses `instrument_port_with_known_adapter_delay`. Record the actual origin and any calibration or de-embedding already performed. |
| `termination` | Termination state and the reflection interpretation used for this record. The teaching row uses `assumed_single_identifiable_reflection`; this is an assumption, not a measured termination or confirmed fault. |
| `raw_round_trip_ns` | Raw round-trip time in ns from the recorded reference plane to the selected reflection and back. The example contains `40`. Keep the raw reading separate from the compensated time used for calculation. |
| `known_adapter_round_trip_ns` | Independently known round-trip delay in ns of the adapter segment to be removed from the raw reading. The example contains `10`. Record its basis and subtract it only if the same segment has not already been compensated for at the reference plane. |
| `velocity_factor` | Dimensionless VF used to convert the remaining time into distance along the target cable. The example contains `0.66`. Use the value applicable to the target cable, rather than assuming every adapter and cable segment has the same VF. |
| `velocity_factor_source` | Basis for VF, such as the relevant cable information or a check using a known length of the same cable type. The teaching row uses `assumed_for_example`. Preserve an assumption as an assumption. |
| `estimated_distance_m` | Manually recorded calculated distance in m from the defined cable start or reference plane along the relevant signal path. The example contains `2.96794533`. A numerical result does not validate the measurement assumptions or confirm a fault. |
| `candidate_location` | Physical cable section corresponding to the estimate, with its reference origin and route. The example contains `2.97 m along cable from cable start`. Map along the cable length rather than to a straight-line position in a cabinet. |
| `verification_result` | Outcome of the follow-up check used to assess the candidate location or cause. The teaching row contains `arithmetic_only`, meaning only the calculation is demonstrated. Record the actual visual, pinout/continuity, low-resistance or signal-integrity check as applicable. |
| `limitation` | Assumptions, unresolved conditions or limits needed to interpret the row. The example contains `No instrument control; no automatic acceptance; assumptions not measured`. |

The CSV has no dedicated fields for instrument identity, ports or waveform files. It also omits edge or frequency-span settings and cursor-selection rules. Record these details, the actual wiring and the compensation applied to each segment in companion notes at the time of measurement. Link the notes to the CSV by specimen/revision and the corresponding measurement record. Identify the instrument port, connection end and cable port in the notes. `reference_plane` records time zero and `termination` records the termination state; neither replaces port identity. Together, the CSV and these notes allow another engineer to restore the wiring and parameters.

## Read the 40 / 10 / 30 ns example

The illustrative row assumes a raw reflection time of 40 ns from the instrument port and a known adapter contribution of 10 ns. The round-trip time assigned to the target cable is therefore:

`Δt = 40 ns − 10 ns = 30 ns`

Using the article's vacuum light speed and assumed target-cable VF:

`L = 0.299792458 m/ns × 0.66 × 30 ns ÷ 2 = 2.9679453342 m`

The CSV retains this as `2.96794533` in `estimated_distance_m` and as `2.97 m along cable from cable start` in `candidate_location`. These decimal places represent arithmetic, not an instrument accuracy specification. Converting all 40 ns with the same assumed VF would instead give 3.9572604456 m, approximately 3.96 m. The approximately 0.99 m difference comes from reference-plane treatment.

Subtract the 10 ns only when it is the known contribution still present in the raw reading. If calibration has already placed time zero at the target cable start, subtracting it again would remove the same segment twice. If the instrument reports one-way distance, read that mode directly rather than dividing its distance by 2.

## Preserve the assumptions and the next check

The article's formula assumes that the selected time represents the round trip from the same reference plane through the target segment, with approximately uniform propagation velocity. For mixed media, check known segments in the time domain before converting the remaining target segment. Multiple branches, multiple reflections or strong attenuation may leave more than one candidate section.

Retain the VF basis and any uncertainty in the time or reference plane. Distance accuracy and the ability to separate two nearby reflections are different judgments. A reflection change does not by itself identify a defective crimp or confirm insulation performance; use the check that answers the specific cause question.

The article cites Keysight FieldFox's Time Domain documentation for implementation, reference-plane and response-resolution conditions, the historical Tektronix 1502C manual `070-7169-05` for the propagation-velocity/distance relationship, and Tektronix's TDR Test explanation for detection and two-point resolution. Use those sources within the scopes stated in the article. The CSV and this field guide do not supply current instrument-specific operating instructions or component acceptance limits.