Overview

Direct Current Voltage Gradient (DCVG) is a survey technique used to assess the effectiveness of corrosion protection on buried steel structures, such as pipelines. It measures voltage gradients set up in the soil by defects in coatings, which cause electrical currents to flow in the soils surrounding the structure. DCVG surveys require two data probes (one red-handled, the other green-handled), since these surveys involve measuring the potential difference between two locations on the surface of the soil above the pipe.

Close-Interval Survey (CIS) is a voltage potential survey technique performed at regular intervals, which are sufficiently small to permit a detailed assessment of corrosion protection flaws. CIS surveys can be performed using one or two data probes. A current-interrupted CIS survey is slower when only one data probe is used, as the operator must have the probe in contact with the soil for a complete interruption cycle after triggering a voltage recording. The CIS process is more efficient when two data probes are used, as at least one data-probe is in contact with the soil at all times as the operator walks down the length of the pipeline, and there is no delay in recording On/Off voltages. Also, by using two data-probes, voltage recordings can be triggered via the push-button switch on one of the probes while the location of survey flags (typically at 100-foot intervals) can be registered via the push-button switch on the second data-probe.

Combined DCVG/CIS Surveys can be performed using M.C. Miller equipment using two data probes and the M.C. Miller Switch Box Controller (Cat. #12555, illustrated). The Switch Box allows DCVG and CIS data to be collected on a single pass down the length of the pipeline. It includes a cable to connect the Switch Box to an M.C. Miller data-logger.

Data Probes

Type I: Data-Probes with Fixed Reference Electrodes

These data-probes come with non-detachable RE-5C type reference electrodes.

Red-Handled Data-Probe (Cat. #SIN015)

Green-Handled Data-Probe (Cat. #SIN0155)

Type II: Data-Probes with Detachable Reference Electrodes

These data-probes have a sealed, threaded socket that can accommodate various M. C. Miller reference electrodes, including the traditional RE-5C (Cat #15210), the slim, 1 inch diameter RE-7 (Cat #15301) and, the IonX RE-5C calibrated electrode (Cat #14555). Electrodes sold separately.

Red-Handled Data-Probe (Cat. #SIN0156)

Green-Handled Data-Probe (Cat. #SIN0157)

 
Close-up of Data probe end with replaceable O-ring (Cat. #ELE016)

Data Probe Cables

Data-probe cables are used to connect M.C. Miller reference electrode data probes to the voltmeter in M.C. Miller data loggers. When connected via a data probe cable, the color of the band on a data-probe cable indicates to which side of the voltmeter the reference electrode will be connected.

If a black-band data-probe cable is used (Cat. #12660), the reference electrode data-probe will be connected to the negative side of the voltmeter. Such a data-probe cable will result in negative pipe-to-soil readings when the positive side of the voltmeter is connected to the pipe.

If a red-band data-probe cable is used Cat. #12665), the reference electrode data probe will be connected to the positive side of the voltmeter. Such a data probe cable will result in positive pipe-to-soil readings when the negative side of the voltmeter is connected to the pipe.

CIS & DCVG Survey Accessories

Belt Pack

The M.C. Miller Belt Pack (Cat. #12710) is used to carry the G1 data-logger at waist level in a hands-free fashion. It has an integrated dual-probe adapter for use on both CIS and DCVG surveys. The dual-probe adapter is used to connect the data-probes to an M.C. Miller data logger. The Hip Pack trail wire dispenser is used in conjunction with the Belt Pack for CIS. A Belt Pack is recommended if a Backpack is purchased to carry trail wire. (The counter/display illustrated above is not included.)

Trail Wire Dispensers

A trail wire dispenser is required for CIS and Combined DCVG/CIS surveys. It is not required for DCVG surveys. When a wire chainer and a counter unit are used in conjunction with a trail wire dispenser system, an audible signal is generated every 2.5 feet (or every meter, in the case of the metric system), and the operator triggers readings in response to the audible signal. Alternatively, readings can be triggered automatically via a trigger cable. Automatic triggering is not possible for Combined DCVG/CIS surveys, as in this case the DCVG voltage is recorded first (at each measurement location), and the CIS voltage recordings are triggered internally by the data-logger itself.

M.C. Miller Hip Packs dispenser accommodates either 1 mile of # 30 gauge or 3 miles of # 34 gauge trail wire spools.

M.C. Miller Backpacks accommodate 5 miles of # 30 gauge trail wire spools.
 

Option 1: Hip Pack (Cat. #HIP010)	Option 2: Hip Pack with Chainer & Counter Unit      U.S. Version (Cat. #HIP040),      Metric Version (Cat. #HIP045)
Option 3: Backpack with Chainer & Counter Unit      U.S. Version (Cat. #12715)      Metric Version (Cat. #12720)

Wire Measure Continuity Tester

For testing and troubleshooting trail wire kits. If the counter display does not register an increase in footage as trail wire is pulled through the chainer unit, there are three possible causes: First, the sensor in the chainer unit is not properly positioned or is broken; second, there is a problem with the harness and; third, there is a problem with the black coiled cable. The Wire Measure Continuity Tester (Cat. #HIP048) allows you to systematically determine which of the above possibilities is the actual cause of the problem.

Trail Wire Spools

M.C. Miller supplies spools of trail wire for use in Hip Pack and Backpack trail wire dispensers. The trail wire comes in two thickness options (# 30 gauge and # 34 gauge) for the Hip Pack and one thickness option for the Backpack (# 30 gauge).

Option 1 (Cat. #TRI021): Spool of # 30 gauge wire for Hip Pack (approx. 1 mile).
Option 2 (Cat. #TRI022): Spool of # 34 gauge wire for Hip Pack (approx. 3 miles).
Option 3 (Cat. #TRI020): Spool of # 30 gauge wire for Backpack (approx. 5 miles).