AMPP CP1 Tester cheat sheet

Rectifier cabinets carry line-voltage AC at the input terminals; de-energize and lock/tag the AC disconnect before opening a cabinet, and treat the DC output as a separate shock source.

Measure AC voltage between the structure and remote earth before touching test leads; induced AC from parallel power lines creates touch and step potential hazards.

Test stations inside pits, vaults, or manholes can hold oxygen-deficient air, hydrogen sulfide, or flammable gas; classify the space and test the atmosphere before entry.

Saturated copper sulfate electrolyte is a skin and eye irritant and is toxic to aquatic life; wear gloves and eye protection and contain spills.

Verify the polarity of temporary CP bonds and test leads with a meter before energizing; reversed DC connections cause arcing, unexpected potentials, and shock.

Lead-acid batteries and TEG units can vent hydrogen; keep spark and flame sources away and ventilate before working on the enclosure.

Locate buried structures before excavating or driving rods; hand-expose the pipe before installing a permanent test point.

Disconnect survey equipment and leave the right-of-way when lightning is present; long test leads and interrupters increase exposure.

Compare each portable Cu/CuSO4 half-cell against a second reference in the same electrolyte; a difference greater than about 5 mV indicates contamination or a blocked junction.

Keep excess copper sulfate crystals in the half-cell; a clear, crystal-free solution means the electrolyte is no longer saturated and the potential will shift.

Pipe-to-soil voltmeters require an input impedance of at least 10 megohms; a lower-impedance meter draws current through the soil path and biases the reading.

Verify current-interrupter timing with a timing device or oscilloscope, and confirm that GPS-synchronized units start and stop together.

Wenner four-pin soil resistivity: rho = 2 x pi x a x R, where a is pin spacing and R is measured resistance; keep units consistent (cm and ohm give ohm-cm).

Confirm meter and logger calibration status and record instrument serial numbers before the survey; a known-voltage check on each channel catches gain errors.

Before energizing a rectifier, confirm the tap or mode setting, the AC input voltage, and the fuse rating against the nameplate.

Verify the rated resistance of current shunts and the millivolt-to-amp conversion before using them for anode or bond current.

The -850 mV CSE protection criterion applies to the polarized (instant-off) potential; applying it to an IR-included reading can leave the structure underprotected.

100 mV polarization criterion: at least 100 mV of cathodic shift from the native potential, evaluated using the instant-off reading.

Galvanic anodes, solar panels, TEGs, and foreign rectifiers that cannot be interrupted contaminate instant-off data; identify every current source before an interruption survey.

Take the instant-off reading within roughly 0.1 to 0.5 s of interruption; a longer off period allows depolarization and biases the value positive.

Rectifier with no DC output: check the AC supply, fuse, tap setting, and diode or stack condition, then confirm with a clamp-on DC ammeter on the output.

Current follows the path of least resistance; bare pipe near a foreign grounded structure may pick up stray DC and require a bond or drainage system.

Monitor rectifier output during the survey; a tap change or AC brownout mid-survey invalidates readings taken under the previous setting.

Where multiple rectifiers protect one structure, all must be interrupted simultaneously or the off reading includes current from the units still running.

Close interval survey spacing is typically 1 to 3 m, tighter in congested or urban areas and near coating defect indications; record both on and instant-off values at each point.

DCVG percent IR = defect voltage gradient divided by total pipe-to-soil voltage shift, times 100; a higher percent IR indicates a more severe coating defect.

Native potential requires all CP current off until the structure depolarizes, often hours to days, and is the baseline for the 100 mV polarization criterion.

Current requirement test: apply current from a temporary source, record potential shift versus current, and extrapolate the current needed to meet the criterion.

Place the half-cell in undisturbed, moist soil directly over the structure; pavement, dry backfill, and gravel raise contact resistance and bias readings.

Repeat any reading that is out of trend with adjacent data, and check lead continuity, electrode contact, and AC noise before recording it as valid.

Verify reference electrode polarity and sign convention on the first reading of a survey; a reversed lead inverts the sign of the entire data set.

Record location, structure, test point ID, time, electrode type, and whether the source was on, off, or instant-off for every data point.

Each data record must include date, time, technician, structure, test point identification or location, reference electrode type, instrument serial number, calibration date, and current state.

Reports must name the protection criterion applied, such as -850 mV instant-off or 100 mV polarization, and state whether IR drop was removed.

Convert readings to a common reference electrode and document the conversion; a Cu/CuSO4 reading converts to SCE by adding about 76 mV.

Rectifier log entries include date, time, AC input voltage, tap or mode setting, DC output volts, DC output amps, and any adjustment made.

Record as-found and as-left conditions for every adjustment, and identify who authorized the change.

Data must be traceable; back up raw logger files before leaving site, because unsaved, unsigned, or uncorrected data is not defensible survey evidence.

Document anomalies, nonconformances, and areas not surveyed with the reason, such as access limits, traffic, or frozen ground.

Pipe-to-soil potential measurement: structure to the positive voltmeter terminal, reference electrode to the negative or common terminal; a negative value indicates cathodic polarity.

IR drop error: current flowing through the soil resistance between structure and reference makes readings more negative; interruption and instant-off measurement remove it.

Convert a shunt millivolt drop to current: I = (mV / 1000) / R_shunt; confirm the shunt rating and kelvin lead placement first.

Soil resistivity from a Wenner array: rho = 2 x pi x a x R; report the pin spacing used, because resistivity varies with depth and moisture.

Measure AC structure-to-remote-earth voltage to assess induced AC exposure; values near or above 15 V are commonly treated as requiring mitigation review.

Telluric currents cause slow potential swings; take repeat readings minutes apart and during quiet geomagnetic periods to separate them from CP effects.

Check half-cell contact by measuring between two reference electrodes a short distance apart; a large difference indicates poor contact or a contaminated electrode.

Only readings with negligible current in the measuring circuit reflect structure potential; a voltage measured across a resistive soil path is a voltage drop, not a potential.