Radiodetection ABC to XYZ of locating buried pipes and cables - For the beginner to the specialist Radiodetection Corp. 154 Portland Rd Bridgton ME, 04009 877 247 3797
Why does it matter? Because fields do things that pipes and cables don’t do
Buried conductors don’t move, but the fields we’re tracing are subject to…
...Distortion Affected by: 1. Method of signal application 2. Grounding 3. Peak or Null 4. Congestion 5. Frequency applied
What is a Magnetic Field ? A magnetic field is radiated by a current carrying conductor
Volts Aerial …Which can be detected by a receiving coil which is excited by the expansion and contraction of the field.
S N 0 volts + What is Electromagnetic Induction? If a bar magnet is inserted into a coil of wire, a voltmeter will show a deflection but only while the magnet is moving. When the magnet stops, the meter reads Zero. When the movement of the magnet is reversed, the meter deflection is reversed.
one a.c. cycle What is an Alternating Magnetic Field? Alternating current creates a moving and reversing magnetic field
What is Electromagnetic Induction ? Bulb will not light Direct current does not produce an electro - magnetic field detectable with a locator. DC Current builds to its voltage and produces a constant level of magnetism. There is no change in this voltage to excite an adjacent receiving coil.
Ö Passive Active There are two methods of signal detection
Passive Passive signals are a by-product of the 20th century. The proliferation of power and radio technology in this century has caused almost every underground metallic pipe or cable to emit detectable magnetic fields.
Passive Detectable Radio signals come from high power, low frequency international communication and navigation systems. Such signals are present nearly everywhere on earth.
Fast Easy Does not identify Passive
Passive However tracking lines to their source can also aid identification
Passive Ensure a full grid search is done to detect conductors laid in different directions.
Passive Ö Active There are two methods of signal detection
Active Increases Locator Versatility Depth Measurement Positive Identification
…Distortion Affected by: 1. Method of signal application
Applyinga signal Connection "Clip" Signal Clamp "Clamp" Induction "Spill" There are three main methods of Active Signal Application
mA mA Connection A successful connection to the metallic pipe or cable will be indicated by a change in the transmitter audio or visual indicator. Always make the best possible connection for reliable signal.
DirectConnection Locating Requires three components: 1. A transmitter or signal source 2. A metallic conductor 3. A return path. Ideally, the earth.
…Distortion Affected by: 1. Method of signal application 2. Grounding
Connection The ground return point is the "back door" that the outgoing signal returns to. What you ground to and where you place the ground can significantly affect your results. Remember: Every milliamp of signal that is going out the metal to metal connection on the red lead has to come back in through a metal to dirt connection on the ground lead.
Connection Ground stake too close to target conductor: Less range, some signal transfer.
Connection Badly positioned remote ground causes more signal transfer Where possible, place ground rod away from known adjacent utilities which may act as return paths.
Connection Remote ground = better range, less signal transfer. As a general rule, try to position the ground point at right angles to and 5-10' from the connection point and direction of conductor.
Connection Grounding to a structure which is also grounded can produce multiple signals. The signal returns on every conductor that shares the same ground
Connection Positioning the ground stake in the direction you wish to locate will often encourage the signal to flow in that direction
Connection When locating Tees, position ground stake in the direction you wish to locate.
Connection For greater signal travel, an extension cable can be used to place the ground stake further away.
Connection A double-ended connection does not use ground as part of the circuit and is more dependable. This is particularly true when trying to locate metallic pipes buried close together.
Connection Metal fences may seem a convenient ground point, but might produce interfering signals. Always use an independent ground such as a ground stake, large screwdriver or other isolated metallic object buried in the ground.
Connection After making a connection, sweep a complete circle around a signal source; measure and mark all occurrences of signal. Repeat to assure accuracy.
Connection At older buildings where the services are all metallic and may share a common ground, connecting close to multiple service bondings may produce multiple signals.
Connection Energizing in the street and tracing toward the bonding point can be more reliable
Clamp The Signal clamp is a current transformer which induces or spills a locate signal onto a target line
TransmitterClamps A clamp safely applies a signal to a live cable without interrupting the supply
Clamp The Signal Clamp is a means of applying a transmitter signal to an insulated pipe or cable, without physical connection. It's most useful for live electric cables. Signal Clamp must be completely around line with jaws closed.
Clamp When using a clamp, the applied signal moves away from the nearest ground to a distant ground. For this reason, it's a useful way to put a locate signal on a specific line.
Clamp At higher frequencies - or with longer lines - capacitive leakage completes the circuit.
Connection 6 12 14 6 Direct connection does not give reliable identification on multiple bonded lines As an exception, connection to the bonding ribbon in a manhole will send tone in one direction, allowing the conduit run to be located.
Clamp 6 22 10 6 Generally, clamping produces more reliable signal identification. Excellent on headers. Especially with using current measurement and direction.
Clamp Place the clamp below the earth bond when locating cables. Do not place above the earth bond. If there is no bonding strap, the clamp may not transmit a signal.
Clamp If using the clamp around a metallic pipe, any insulating flange must be bridged.
Induction Induction allows the user to quickly and easily apply a locate signal, by placing the transmitter in the vicinity of a known conductor or conductors