Rev 6 – Feb 2022
Page 35 of 44
Survey Techniques
The Hexcorder Pro is designed and built to perform above ground assessment of cathodic protection
and coating integrity for buried metallic structures. Used correctly it can provide an indication of
areas that are more likely to corrode or do not meet industry accepted criteria for protection. A
background in corrosion or a training course from Cath-Tech is highly recommended prior to
surveying for the first time.
The Hexcorder Pro is supplied with all the parts and accessories necessary to start surveying CIPS
and DCVG. ACVG surveys require a separate transmitter operating at both 320Hz and 640Hz
(320+640Hz). If an interrupted CIPS or a DCVG/ACVG survey is to be done, the current
interrupters need to be installed in the rectifiers prior to starting. Any stationary data loggers also
need to be placed.
CIPS
Turn on the Hexcorder Pro and program it for the survey as
described earlier in the manual. Clean off the end of the light
survey wire with some emery paper and connect it to the pipe
at a convenient test station. Fill the half cells with distilled
water then insert the half cells into the poles. Remove the
plastic caps from the half cells so the ceramic tip makes
contact with the soil. Hook the Hexcorder Pro onto the 4
point harness and connect the survey poles and wire dispenser.
The surveyor should use both survey poles and keep one half-
cell in contact with the soil at all times to minimize delay
while the half cell stabilizes. In areas where the soil is dry, it
may be necessary to wet the soil to reduce half-cell to soil
contact resistance. Higher input impedance or double-impedance surveys can also assist in dry areas.
A close interval survey is best accomplished at a comfortable walking speed. Most surveyors prefer
a 1 second cycle where the rectifier is turned OFF for 200 to 300 milliseconds every second. The
one-second cycle will yield a stored reading approximately every two meters at a comfortable
walking speed.
To take and store a reading, observe the potential on the Hexcorder Pro display - then when you have
a valid pipe-to-soil potential, press one of the buttons on the survey pole. The value you see on the
screen at the time of the button press is stored. The values on screen will update once per cycle.
These values along with the chainage and GPS coordinates are written to the display every second
and stored to memory.
DCVG and ACVG
DCVG and ACVG both work by measuring the voltage change between two half cells placed on the
ground. To undertake a DCVG survey, typically a minimum potential swing of 300-500 mV
between the rectifier ON and OFF is sought and the current source output of the rectifiers is adjusted
accordingly. The interrupted rectifier enables coating defects to be distinguished based on the
potential differences between the half-cells. An ACVG survey requires the use of a transmitter that
