Active Search (Blind Search)
A technique used to investigate an area with unknown buried utilities and no opportunity to apply a signal using direct connection of a clamp. Typically two operators are used, one holds the transmitter (in induction mode) and the other holds the receiver. Both transmitter and receiver should be set at the same (medium to high) frequency (between 65 kHz & 200 kHz). The two operators walk in a coordinated grid pattern across the blind search area such that all buried conductors can be first located and then traced one by one.
Active Locating
A transmitter is used to apply one or more signals to a buried pipe or cable, the position of which is then located by a receiver tuned to the same frequency.
Active Signal
The signal applied by the locator transmitter to a buried line. Typically this is a very precise frequency.
The receiver for a Cable or Sheath Fault Locator. See Cable Fault Locating for more detail.
Air Coupling
Coupling of the signal from the transmitter to the receiver through the air - rather than through the target line to be located. Air coupling will interfere with the signal from the line and cause a false indication of the location. Air coupling can be determined in two ways. Firstly, the receiver may be pointed towards the transmitter. Move the receiver left and right in the general direction of the transmitter. If an indication ("Peak" or "Null" - dependant on mode setting) is achieved, then air coupling is probably present and will result in a false target indication. An alternate method is to hold the receiver in a vertical position and directly over the line, if lifting the receiver straight up causes the signal strength to decrease smoothly, air coupling is probably not an issue.
In the locating context it is the reduction (loss) of the electromagnetic locating signal from a pipe or cable as the distance from the transmitter increases.
Automatic Gain Control (AGC)™
A feature of a receiver, where the gain or sensitivity of the receiver is changed automatically, responding to the wide range of field strength encountered in practice, to achieve optimum ease of use and fast locating.
A feature associated with a dot matrix and liquid crystal displays, lighting the display so that it may be used in low light conditions.
Ball Marker
A marker in the form of a ball that is used to mark "features" (splice boxes, Tee's etc) Three types are used, they are generally locatable to 5 feet (1.8m):

· a ball in which the resonant circuit is floated in a liquid such that the resonant circuit is always horizontal to the ground.
· a ball containing three orthogonal resonant circuits producing a uniform field regardless of orientation.
· a "peg" which contains the resonant circuit - these can only be located if they are in a vertical or nearly vertical orientation.
Bleed-off or Bleed-over
This occurs when the signal from a target line jumps to adjacent lines without a direct electrical connection. This coupling, which occurs more readily for signals at high frequencies, may result in two difficulties. First, the signal dissipates providing a weaker signal for locating. Second, the signals induced in nearby pipes and cables may produce false targets. As this effect is more pronounced for higher frequencies, the problem is minimized by selection of lower frequency.
Cable Fault Locating or Sheath Fault Locating (SFL or FFL)
A popular accessory for a locator is a sheath fault locator (or A-frame as it is known). The process of locating a fault in the sheath of an electrical power cable is to measure the electrical voltage in the ground above the fault (caused by the current leaking into the ground around the fault). This process is similar to finding a leak in a water pipe by tracing the water on the ground back to its source at the leak. SLF systems generally use a higher signal output voltage than FFL systems.
CE Mark
A marking on an instrument that indicates the instrument has been tested in accordance with the requirement for the European Union with regard to electromagnetic compatibility and electrical safety. This mark is required on products that are used in the member states of the European Community.
Clamp (or Coupler)
An accessory for a locator transmitter that applies the transmitter signal to an insulated line, removing the need to connect the transmitter signal directly to a conductor or cable sheath.
The imaginary line that extends along the ground directly over the line to be traced. Also, the center of the display that indicates the locator is to the left or right of the line.
Common-Bonded Conductors
Lines or ground conductors, such as telephone lines, power cables or pipes, that are electrically connected together at some point. Conductors common bonded to the target conductor, carry the signal, making it difficult to locate the target beyond the common bond.
Line direction indicator (although visually like a compass, this is the only relation to a compass) is used to assist in orientating the locator to the direction of the line.
Conductive Attachments (Direct Connection Leads)
Accessories used with the transmitter for direct connection. The most commonly used are red and black cables with alligator clips on the ends.
Continuous, Real-Time Gain™
See Automatic Gain Control™.
This is where the signals attach to lines to which they were not originally applied. Coupling can be "direct" where the target line has an electrical connection to another line (commonly bonded), or "induced" where the signal radiates from the target line to another line or lines (bleed over).
Current Measurement
A feature (receiver) where an indication is given of the current in the target line. The indication of current does not change as the depth of the line changes. Although the indicated current will decrease slowly as the distance of the receiver from the transmitter increases, an abrupt change in the indicated current may be caused by a lateral, tee or damage to the line. Current measurement may also be used in a crowded environment to confirm the signal is on the target line rather than coupled to an adjacent utility.
Direct Connection
The connection of the transmitter to the target line. The preferred method for placing a signal on the target conductor is by connecting the red wire to the line and the black wire to the ground stake. This is advisable for a normal transmitter and essential if using features such as Signal Select (SiS) or Signal Direction (SD).
Is where the information acquired by the locator is visually displayed (generally a dot matrix or LCD display).
Distance Sensitive Left/Right Guidance™
A unique feature of some Metrotech receivers, where the display of the receiver indicates the distance and direction to the centerline. Using additional locating coils, it provides an indication of whether the target line is to the left or the right as well as how far it is to the left or to the right. This intuitive feedback provides for a higher productivity.
Left/Right Indication
Similar to the "Distance Sensitive Left/Right Guidance" but the information is generated using only the locator's standard antennas.
Many metals (such as iron or steel) are magnetized, and because of this, it can be located. Although the science is quite complicated, it is best described as the alignment of the all the "north" poles of the magnetism in the metal. When these are not aligned, the material has little or no magnetic field. However, when an external magnetic field is applied, all these small magnets within the material become aligned and interact, and distort, the earth's magnetic field. It is this distortion that is detected by ferromagnetic locators (or magnetometers as they are known). They determine the location of the ferromagnetic object.
The electromagnetic field produced by the transmitter reverses its direction many times each second. The frequency of the signal is the number of these cycles completed in one second. Proper frequency selection is important for successful locating. The unit of measurement for this is Hertz (Hz). Most locators operate in the range of 50Hz to 500 kHz.

The permissible use of the electromagnetic frequency spectrum mandated by the Federal Communications Commission (FCC) as given in the Code of Federal Regulations, 47 (Telecommunications), Part 15 section 15.213. The FCC regulates the frequencies and power levels that may be used in the equipment for locating underground lines. Below 9 kHz any power level may be used. From 9 kHz to 45 kHz a maximum of ten watts of power may be generated by the transmitter. From 45 kHz to 490 kHz a maximum of one watt of power may be generated by the transmitter.
The signal at the antenna of a locator receiver is increased before it is processed and displayed. The signal generated by the current in the target line is very small, and it must be increased in size many times before it can generate a perceptible indication on the display or sound in the receiver. This amplification is known as the "gain" and is measured in decibels (dB).
Ghost Conductor
A false indication by the receiver that a line is present. A "ghost" may appear when the antenna of the receiver receives an equal amount of signal from two adjacent conductors. One clue that this is occurring - is when the signal strength drops as the receiver is moved toward the "ghost." Other indications include the distance sensitive left/right guidance™ bar moving in the same direction as the movement of the receiver (normally it moves in the opposite direction) and also pushbutton depth provides an illogical depth, or no depth at all. SiS and SD are two systems that can in many cases resolve the confusion caused by ghost signals.
A return path for electrical current through the soil. For example, when using the direct connection mode - the grounding is accomplished by pushing a grounding rod into the ground. One of the transmitter leads (red) is connected to the target line and the other (black) to the grounding rod. Grounding provides a continuous and complete path for the transmitter signal current to travel along the target line, then through the ground and back to the transmitter via the ground rod. Without such a path the current will not flow and the receiver will receive no signal.
High Frequency (Locator)
Examples of high frequencies used in locating equipment are 82 kHz to 500 kHz. The high frequencies provide the best performance on target lines with poor continuity due to corrosion or the use of insulating gaskets. High frequency is also useful when the buried line is not grounded at all. However, the signals at high frequencies will go a shorter distance down the line than lower frequencies and may be more susceptible to bleed-over to other lines.
The generation of current in a conductor caused by running current through an adjacent conductor - with no electrical contact or connection between the two. Signals can be induced on the line by a transmitter (set to induction mode), a signal clamp, by overhead power lines, or by other lines carrying current that are in close proximity to the target line.
Inductive Clamp
A device used to induce a signal onto a line without using a direct electrical connection. The jaws of the device are spring-loaded so they can be snapped around the line.
Induction Mode
A method of applying the transmitter signal to the target line without a direct connection. The signal from the transmitter is applied to the target line by means of an internal antenna in the transmitter. The transmitter is placed over the line, causing a signal to be induced in the line. This is the least effective way to apply a signal and it may result in bleed-over of the signal to other conductors nearby.
ISO 9000
A standard of "The International Standards Organization (ISO)" and adopted by the "American National Standards Institute (ANSI)", to help companies develop and maintain quality assurance. ISO 9001 is the model that applies to design, development, production, installation and servicing. ISO 9002 is the model that applies to production, installation and servicing. ISO 9003 is the model that applies to quality assurance and final inspection. Companies may either self-certify or be certified by an external body. If the company is certified by an external body, the logo of the certifying body will be associated with the ISO 9000 certification. Metrotech is certified to ISO 9001.
Leak Detector
A device used for detecting and locating water leaking from pressurized fluid pipe, such as water distribution pipes. The device is comprised of a microphone, amplifier and signal processes of electronics and headphones. A leak is located by listening to the loudest, most consistent sound generated by escaping water.
A generic term for any buried pipe or cable.
Low Frequency (Locator)
Low Frequency is generally defined as any frequency between 220Hz and 8 kHz. The signal at the low frequency is the least susceptible to bleed-over and may travel further along a buried line than signals at higher frequencies. However, the signal at low frequency will be less able to jump discontinuities in the line, such as insulating gaskets.
Magnetic Field
The force field around a permanent magnet or a conductor in which is flowing electrical current. It is the magnetic field that is detected by electromagnetic locators.
Manual Gain Control
A feature of the receiver, whereby the gain of the receiver can be adjusted manually to optimize the sensitivity of the receiver. This feature allows fine-tuning of the receiver to increase the success in locating lines in congested areas or under difficult conditions.
A passive device that may be located by means of a marker locator. This device is a resonant circuit that is excited by the energy from the transmitter of the locator and emits a signal that is detected by the receiver of the locator (see also ball markers).
Medium Frequency (Locator)
Examples of medium frequencies are 8 kHz to 40 kHz. The signals at the medium frequencies are less able to jump discontinuities in the line than at high frequencies, but they may travel farther down the line and be less likely to bleed-over.
Null Response
Is when the response to buried line reduces as the locator gets closer to the line.
Operating Temperature
The range in temperatures over which an instrument can be used. Locator performance will degrade as the temperature changes from ambient to the extremes. This degradation in performance is sometimes called ambient derating. The specifications for an instrument usually refer to operation at ambient temperature (25oC or 70oF).
Overhead Interference
The interference caused by energized, overhead power lines. The signal from the overhead lines is picked up by the receiver and may interfere with the signal from the line, causing a false locate.
Passive Mode
The receiver mode used to search for a wide range of signals that radiate from buried pipes or cables. These signals come from a variety of sources in the environment and couple to the buried (& overhead) lines. Typical examples 50/60Hz and LF/VLF radio.
The indicate response to buried line which increases as the locator gets closer to the line.
The act of using a (locator) receiver to identify the exact position of a buried line.
Push-Button Depth
A feature of a locator receiver, which allows the operator to press a single button to view an estimate of the depth of the target line (for alternative way of establishing depth - see Triangulation Depth).
Real-Time Continuous Gain Control™
See "Automatic Gain Control".
A device to detect, process and display signals that are generated by the current on an underground line. The receiver comprises one or more antennas, batteries and signal processing electronics. It is tuned to the specific frequency of the signal to be received, and provides visual and/or audible indication in the presence of the target line. Additional features/accessories are available on many receivers to estimate depth, confirm identification, detect sheath faults and to provide different responses to the signal being located.
The reaction produced in the receiver to the signal received from the buried line is known as the response. It can be communicated to the user in different forms - visual, audio or both. Most locators provide a visual response (moving coil meter, LCD or dot matrix displays) and an audible response from a loudspeaker (real sound) or a beeper.
Search (Sweep)
This describes the act of looking for a buried line within a given area.
Sensitivity (Locator)
A measure of the electromagnetic signal that can be reliably identified by the receiver. This value is typically established in controlled conditions in the laboratory.
Sheath Fault Locating (SFL)
See Cable Fault Locating.
Signal Direction (SD)
A (patented) system used to identify the target line. This is presented to the User in the form of an arrow - which indicates the direction that the signal is flowing. If the arrow does not appear, or flashes, or points in the opposite direction the line being located is not the target line. The receiver allows the user to reset the direction manually as the phase of the signal deteriorates with distance.
Signal Select (SiS)
A (patented) system used to identify the target line. This is presented to the User in the form of an arrow - which indicates the direction that the signal is flowing. If the arrow does not appear, or flashes, or points in the opposite direction the line being located is not the target line. The receiver automatically adjusts the SiS system to account for phase shift.
Signal Strength
A feature of the receiver, whereby the relative strength of the signal being received is indicated either visually or audibly. Visual indications are by means of a digital bar graph or analog meter. Audible indication is by the pitch or loudness of a tone. The signal strength depends on the current in the target line and its depth among other factors.
A small transmitting coil which may be built into a product such as a sewer camera or packaged as a small self contained battery powered transmitter. A receiver tuned to the same frequency can locate the position and depth of the Sonde and hence whatever it is attached to or in. Frequently used for locating sewer cameras, and the non metallic pipes.
Storage Temperature
A range of temperatures, both maximum and minimum, within which the equipment may be stored for long periods of time, without damage to the operating characteristics.
Target Line
The underground pipe or cable that is the target of the location activity. It may be a power line, gas line, water pipe, telephone line or other conducting medium buried in the ground.
Thermal Shock Testing
An environmental test used to prove out a design - it involves taking an instrument from an environment at one temperature and putting it into an environment with a very different temperature.
A device that is used to generate a current in an underground line. The transmitter is used with a receiver that is tuned to the same (very precise) frequency.
Triangulation Depth
An estimate of a target cables depth can be obtained by the triangulation method. The target line position is first established as accurately as possible. The receiver is then tilted by 45 degrees and the "centerline", corresponding to maximum signal strength is then established on each side of the target line. The depth is approximately equal to one-half the distance between the two "centerlines". In some receivers a bubble gauge is provided to help the operator tilt the receiver by 45 degrees. There are other ways of establishing triangulation depth, but they are specific to individual makes and models of locator and are described in the appropriate operating manual.

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