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Active Locating
Locating an underground line by means of signals generated by the transmitter.

A-Frame
The receiver for the 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 may 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 directly at the transmitter. If the receiver indicates a maximum signal, then air coupling is probably present and may result in a false target indication. On the other hand, with 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.

Automatic Gain Control (AGC)™
A feature of a receiver, whereby 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, accurate locating.

Backlighting
A feature associated with a liquid crystal display whereby the display may be used in darkness.

Ball Marker
A marker in the form of a ball that is used for depths up to five feet. Two types are used. One is a ball in which the resonant circuit is floated in a liquid such that the resonant circuit is always horizontal to the ground. The other has three orthogonal resonant circuits producing a uniform field regardless of orientation.

Bleed-off or Bleed-over
The affect wherein 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 the proper lower frequency.

Blind Search
A technique used to investigate an area with unknown buried utilities and with no direct connection to the utilities available. Typically two operators are used. One holds the transmitter and other holds the receiver. Since direct connections or inductive clamps are not feasible, indirect inductive coupling at 82 kHz is chosen. 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.

Cable Fault Locating or Sheath Fault Locating (SFL)
The process of locating a fault in the sheath of an electrical power cable by measuring the electrical voltage on the ground above the fault that is caused by the current leaking into the ground around the fault in the cable. 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. An "A-Frame" and receiver are used to measure the voltage along the ground, directing you towards the fault in the cable.

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 imported into any of the member states of the European Community.

Centerline
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.

Conductive Attachments
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™

Current measurement
A feature on the receiver, whereby 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, whereby the transmitter is connected by a (red) wire to the line and another (black) wire to the ground stake. This is the preferred method for placing a signal on the target conductor.

Distance Sensitive Left/Right Guidance™
A unique feature of Metrotech receivers, whereby the display of the receiver indicates the distance and direction to the centerline. 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.

Ferro-magnetism
The property of some metals such as iron to become magnetized or to influence an external magnetic field. Although the effect is quite complicated, it may be explained as the alignment of many small magnets within the ferro-magnetic material. When these small magnets are not aligned, the material has no magnetic field. However, when an external magnetic field is applied, the small magnets within the material become aligned and interact with the applied field. The earth's magnetic field interacts with ferromagnetic objects, distorting the earth's magnetic field. It is this distortion of the earth's magnetic field, which is detected by ferromagnetic locators, such as the 880B, that determine the location of the ferromagnetic object.

Frequency
The electromagnetic field produced by the transmitter reverses its direction itself 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.

Frequency
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.

Gain
The amount the signal at the antenna of the 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.

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 indication that this is occurring is that 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 push button depth provides an illogical depth, or no depth at all.

Grounding
A return path for electrical current through the soil. For example in the direct connect mode grounding is accomplished by pushing a grounding rod into the ground. In other cases a line or pipe that is sticking out of the ground may be used. Grounding provides a continuous and complete path for the signal current to travel over the line and back to the transmitter. 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 Metrotech equipment are 82 kHz or 83 kHz. The high frequencies provide the best performance on target lines with poor continuity due to corrosion or the use of insulating gaskets. However, the signals at high frequencies may go a shorter distance down the line and may be more susceptible to bleed-over than the signals at lower frequencies depending on the particular situation.

Induction
The generation of current in one conductor due to current running in an adjacent conductor even though the conductors are not common bonded (electrically connected). Signals can be induced on the line by air coupling, from adjacent conductors or from energized overhead power lines.

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.

Inductive coupling
A method of applying the signal from the transmitter onto the target line without a direct connection. The two types of inductive coupling are direct and indirect. ~ Direct inductive coupling - A form of coupling, wherein the signal from the transmitter is applied to the target line by means of an inductive clamp. The jaws of the inductive clamp are spring-loaded such that they may be snapped around the line. This mode is used when direct connection is not possible. ~ Indirect inductive coupling - A method of coupling, wherein the signal from the transmitter is applied to the target line by means of an internal antenna in the transmitter. The transmitter is placed near the line, and the signal is 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.

Liquid Crystal Display or LCD
A type of display wherein a voltage potential is applied to electrodes that surround a special type of liquid the optical transmission of which changes from transparent to opaque depending on the voltage applied to the electrodes. The advantage of this type of display over others is that it requires very little electrical power to operate such that it results in very little drain on the battery of portable equipment.

Low Frequency (locator)
An example of low frequency is 982 Hz. The signal at the low frequency is the least susceptible to bleed-over and may travel further than the 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 most 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.

Marker
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

Marker
A locator that is used to locate markers.

Medium Frequency (locator)
Examples of medium frequencies are 35 kHz or 9.82 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.

One Call Center
An organization that has developed standards for locating and marking underground facilities to prevent damage during excavation. One-call services have been established wherein a contractor may call within a certain time period before excavating a site and a locator will be sent to locate and mark all of the underground facilities at the site. Established throughout the US and other parts of the world.

One-Button Depth
The feature of a receiver, whereby the operator can push one button to get a estimate of the depth of the target line. See Triangulation Depth.

Operating Temperature
The range in temperatures over which an instrument can be. It is often the case that the performance of the instrument 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 (25 C or 70 F).

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 Locating
A method of locating, wherein no transmitter is required. The current in the line is generated by electromagnetic fields in the environment such as those generated by power lines (50 or 60 Hz) and those generated by radio stations (RF). This technique is quick, but it is more error prone than active locating.

Real-Time Continuous Gain Control™
See Automatic Gain Control.

Receiver
A device that can detect, process and display signals that are generated by current in an underground line. The receiver comprises at least one antenna, battery power supply and signal processing electronics. It is tuned to the specific frequency of the signal to be received. It may give a visual or audible indication of the presence of a target line, the location of the line and the depth of the line.

Sensitivity (locator)
A measure of the minimum 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 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 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.

Sonde
A small transmitter that emits electromagnetic energy at a specific frequency. This device is pushed into a pipe or duct by means of a rod, and its location is found by means of a receiver. These devices are often used to find faults in sewer pipes. Sondes that emit signals at the lower frequencies may used to locate faults in pipes of cast iron. The term is an abbreviation of Radio Sonde.

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 facility 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
An environmental exposure used to prove out a design involving taking an instrument from an environment at one temperature and putting it into an environment with a very different temperature.

Transmitter
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 frequency.

Triangulation Depth
The estimate of depth obtained by the triangulation method. In 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" found in this manner. In some receivers a bubble gauge is provided to help the operator tilt the receiver by 45 degrees.