P&C LOCATOR – BASICS

  1. TRANSMITTER & RECEIVER
  2. FIELD ANALYSIS INSTRUMENT
  3. IT DETECTS EMF NOT UTILITIES
  4. FOUR METHODS OF USE
  5. MOST SECURE AND ACCURATE METHOD
  6. FREQUENCY SELECTION
  7. A QUALITY SIGNAL
  8. KEEP THE RECEIVER STRAIGHT UP AND DOWN
  9. SWEEP FOR THE TARGET LINE
  10. SIGNAL STRENGTH

11. THE MANUFACTURERS

Pipe & Cable Locators are the backbone of tracing out buried utilities.

Locating buried utilities is a process of tracing out the invisible (buried utilities), and coming to conclusions on the position of those utilities without ever having seen them.  This requires a combination of science, intertwined with logic and the knowledge of the utilities.   The most common geophysical instrument for locating buried utilities is the Pipe & Cable Locator.

A Pipe & Cable Locator is not at all the most advanced geophysical instrument for tracing out buried utilities.  Yet, it is the backbone of utility detection and mapping.  The reason for this is in the way that they function which makes them the only geophysical instrument that can trace out a single pipe or cable with confidence.  They can also do this using 4 separate methods: direct connection, induction, coupler induction, and passive.

This section covers the most important elements about the instrument and how it functions.  It is not meant to replace an actual training course, but only to ensure that the fundamental functions of the instrument have been covered for those who have never received any solid training on the instrument.

1 – TRANSMITTER & RECEIVER

A Pipe & Cable Locator is a 2-piece instrument, the transmitter and the receiver. The transmitter applies a very small amount of current (in milliamps) to a conductive portion of the utility.  The receiver contains coil antennas which detect the “signal” that results from that current.

There are numerous manufacturers of these instruments but they all function under the same principles: the transmitter applies current – the current produces signal – and the receiver detects the signal.  The big differences in the manufacturers are the weight of the instrument, the output power potential of the transmitter, the response time of the receiver, the variety of frequencies available to be used, and many other optional features.

The most secure method of locating is using the lead wires - attaching the red lead to the utility and the black lead to a ground connection.

2 – FIELD ANALYSIS INSTRUMENT

One of the most important elements of a P&C Locator to realize is the fact that it is a field analysis instrument.  In other words, ground penetrating radar can be moved across the ground and the data stored internally.  This allows the data to be analyzed by several people later on in the comfort of an office, with the screen/data easier to view, and the final conclusions to be discussed.  This is also true with several other more involved instruments such as gradiometers, the EM-61, the Spar 300, etc.

What’s more, much of the importance of a P&C Locator comes from its operational capabilities in the field.  The operator of the instrument has a great deal of control in how it is being used in order to give it wide capabilities in being able to trace out tracer wire, electric cables, steel gas pipes, old iron water pipes, etc.  If the utility line contains conductive material (as the majority do), then it can be located out using a P&C Locator.

Other benefits include being able to follow a utility line across swamps, up steep hills, through thick vegetation, and so on.

Another very important point is that although other instruments can capture the data to be viewed later, they do not capture the surrounding environment of the utility which can be crucial in determining if the data is correct.  A telephone service does not necessarily lead to a telephone.  A municipality may have an old telephone service running to a water tank which they use to monitor the operation of the tank.  Only in the field will you be able to see that SNI connection next to a control box at the water tank indicating that you do have the telephone service traced out properly.  There are literally thousands of other examples of this kind of situation.

3 – IT DETECTS EMF NOT UTILITIES

Although the instrument is called a Pipe & Cable Locator, technically it does not detect pipes or cables.  In fact, it is impossible to do so.  What a P&C Locator actually detects is an electromagnetic field, or EMF.  This is true with any P&C Locator no matter which make or model, or which method of locating is being used.

Current on the utility produces an invisible field, EMF, a fluctuating field that radiates outward from the utility.  It is this EMF that is always being detected by the instrument.  This is why the signal on a buried utility will always be greatly wider than the utility line itself.

Pipe & Cable Locators do not actually detect utilities. They detect the EMF that the transmitter applies to the utility and radiates outward from the utility line.

The distance that the EMF can reach is not specific.  It depends on the power output of the transmitter and other factors.  However, it helps to know that a typical EMF field produced by a 10 watt transmitter is only detectable at roughly 15 feet (4.5 meters) from the source of the current.

That will never be an exact measurement.  One utility may only be detectable at 12 feet, while another under certain circumstances may be detectable at closer to 18 feet (5.5 meters).  But 15 feet is a good rule of thumb for knowing how far the receiver can be from the utility line, and still be able to detect that utility.

4 – FOUR METHODS OF USE

A P&C Locator can be used in 4 completely different methods: direct connection, standard induction, clamp/coupler induction, and passive.

Direct Connection requires using the red and black lead wires; the red wire is attached to the utility, and the black wire is attached to a ground connection.  This applies current directly to the utility line or to the tracer wire that is placed next to the utility line.

With Standard Induction the transmitter can be placed on the ground where the utility line is suspected to be.  Simply make sure that neither the lead wires or the clamp/coupler are plugged in, and the transmitter will automatically switch to an internal induction coil which will produce a dual field, both up and down.

The upward portion of the field is only a side affect of induction, and does not typically help in locating.  It is the downward field that of course applies EMF down on to the utility line below.  Induction can be very ineffective if the utility line is deep, because it can be much deeper than the EMF can reach.

Commonly called a clamp, this device is actually used for coupling around the utility, and inducing a signal on to the utility.
Drop Box induction sends energy both upward and downward from the transmitter.

Most P&C Locators come with an attachment commonly called a Clamp.  This actually functions as a coupler because it is used to couple the utility line, but “clamp” is the more common word.  Plug the cable of the clamp into the transmitter and then place the clamp around the utility.

This is a form of induction because it induces current onto the utility from the clamp.  Induction current behaves differently than direct current, though you have to get into more involved details of what is happening to illustrate that point.

Clamps are most commonly used on cables along pole lines, and cables in manholes and handholes.  Clamps are only rarely used on pipes, not because they would not work, but because access to short sections of a pipe are far less common than access to short sections of a cable.  However, a clamp can certainly be used on a pipe exposed in a vacuum test hole or anywhere else.

The fourth method of using a P&C Locator is in Passive Mode.  In this case only the receiver is used.  In Passive Mode you can take advantage of the currents which are already present on buried utilities.

Those currents can be originating in two ways: those which are being applied to the utility by the utility owner, such as electric power on power cables; or they can be stray currents coming from a wide variety of sources.  We live in a world of electricity, radio broadcasts, TV broadcasts, wi-fi, Bluetooth, CB radios, NOAA weather broadcasts, and hundreds more.  Either way, there is not a single buried utility in the world which is not carrying at least some amount of stray current.

The two most commonly used Passive frequencies are Power Passive (50Hz to 60Hz), and Radio Passive (16 kHz to 19.5 kHz).

Power Passive is usually set to the 50Hz to 60Hz band in order to detect any electric power being generated in any country.  The United States, Canada, and South American countries generate electricity at 60Hz, while the rest of the world generates electricity at 50Hz.  Setting the instrument at 50-60 Hz covers the electric power transmissions no matter which country you are in.

The most critical issues here are that: some electric power, especially 3-phase electric power can eliminate its own field.  In other words, you can be standing directly above high voltage 3-phase transmission power lines – and yet not detect anything.

Another important point here is that all coaxial cable carries electric power as well as its communication signals.  This is injected into the Cable TV system at the Power Supplys and is mandatory for the operation of Cable TV.  So, coaxial cable in the United States contains 60Hz power which can be detected just as easily as any true power line.

Then there is the issue that any other buried conductor can attract stray power current.  This will be most common with any ferrous metal (iron or steel) pipe, and with any cable which has a steel sheath and is well insulated to retain that current (telephone cables).

So, Power Passive can detect buried power lines – but it will also be detecting buried coaxial cable, telephone cables, probably some large steel gas pipes, and other possibilities.  And if that is not enough, Power Passive often does not detect the most high profile power lines – 3-phase high voltage.

Radio Passive detects dying radio waves on buried utilities.  However, those radio waves are not simply from “radio broadcasts”, but from any type of broadcast in the radio wave format.  This includes radio broadcasts, TV broadcasts, Bluetooth, wi-fi, cellular telephone, and right down to the truck driver using a CB radio.

These radio waves are easily attracted to very long conductors without connections.  In other words, if you have two utility lines, both of them running for two blocks.  One is a large steel gas pipe and the other is only a tracer wire placed along side a fiber optic cable.  The gas pipe has regular connections (service attachments), but the fiber cable is only bypassing the neighborhood.  Which one will be most likely to attract radio waves?  The long tracer wire, not the large steel gas pipe.

The third most common Passive frequency is CPS, but that is covered in the Cathodic Protection text under MISC INFO.

Passive should never be used as a main method of tracing out utilities.  They can be very useful in double-checking a utility line by knowing which type of utility is most likely to be carrying that frequency range.  And they are very useful in sweeping across an area for any unknown utilities.

5 – MOST SECURE AND ACCURATE METHOD

Although there are 4 different methods of using a P&C Locator, one stands far above the rest and that is direct connection.  With direct connection you have several advantages in determining the correct position of the utility.

First of all, with direct connection you know exactly which utility is receiving the current because you applied it yourself.  Is the signal you are detecting coming from the tracer wire of the plastic gas pipe?   If you connected the transmitter to the tracer wire, then it most likely does.

Second of all, only with direct connection do you have the option of using the lower frequencies.  Neither clamp/coupler induction or standard induction can function with the lower frequencies, so they are not even available.  With any type of induction, the lower frequencies by default become unavailable to you.

This is crucial because the lower the frequency the more likely the current will remain on the utility you applied it to.  Just because you connected to the tracer wire does not mean the current will remain there.  If your frequency is too high, then that signal can easily jump to another utility line, especially any utility that has more metallic content than a tracer wire – which is every utility line out there!

With direct connection you are also applying more current on to the utility, and therefore less chance of your signal being distorted by other ferrous metal objects in the area.  This includes street lights, metal dumpsters, manhole lids, and especially automobiles.

So, while direct connection is far superior, much of that superiority is in the fact that direct connection allows the use of low frequency, because it is the low frequency that will remain on the utility you applied it to.

512 Hz is often the lowest frequency available, and the lower the frequency, the less chance of bleeding over to another utility.

6 – FREQUENCY SELECTION

Some P&C Locators have only one frequency, usually a very high frequency, but most of the instruments today come with a wide variety of frequencies.

All of these frequencies are within the range of about 250 Hz to 480 kHz.  This is a frequency range which is not typically used for any other purpose.  The reason for that is because this is a frequency range which is above electric current – but below radio broadcasts.  In other words, the advantage of this frequency range is that the current being applied has elements of both current and radio waves.  Any of these frequencies can apply current to a buried conductor, yet, the higher you go in frequency – the more the current can move from one conductor to another.  This is the good and bad side of high frequency.  We can get the current where we need it, but that high frequency current is also just below AM radio waves and can behave as much like a broadcast wave as it does an applied current.

While direct connection on low frequency will provide the most accurate and secure locate, it is not always possible.  In fact, the medium frequencies and even high frequencies can be very useful in many circumstances, and sometimes they make the difference in whether it is possible to locate out the line or not.

Low frequency can be considered to be anything up to 1 kHz.  The reason is that induction of any kind begins at roughly 1 kHz.  This is why the low frequencies are not available when using either standard induction or clamp induction.  The low frequencies do not work when trying to induce.  However, this also means that with direct connection they remain on the conductor where you applied it.  If you have direct access to the conductive portion of the utility, and you want the current to remain on that same utility – then use low frequency.  It could be 512 Hz, or 760 Hz, or 940 Hz – anything below 1 kHz.

Medium Frequency is a limited area starting at 1 kHz and going up to about 15 kHz.  This is the most common frequency range for induction of any kind while still keeping the frequency at a reasonable level.  For the longest time 8 kHz was the only frequency available in this range, and even today 9.8 kHz is usually the only other mid frequency available.  However, these are excellent frequencies for using the clamp/coupler, and even for most standard “drop box” induction.  This is a high enough frequency range to produce induction, but not so high that the current will indiscriminately jump to another utility.

Manufacturers do not produce P&C Locators which offer a frequency anywhere in the range of 15 kHz to about 21 kHz.  This is the area of dying radio waves, the bandwidth used in Radio Passive.  To be purposely producing a signal on buried utilities in this range would only create a lot of unnecessary confusion.

High Frequency is anything from about 25 kHz and above.  It could also be said that anything above 100 kHz or so is very high frequency.

Though high frequencies should never be a first choice with most utility lines, they do provide a great benefit.  Many utilities may need to be induced and yet mid-range is not high enough to produce the needed results.

High frequency, and for that matter, very high frequency, is very useful in sweeping an area to see if there are any unmarked utilities.  In this case use the highest frequency you have available.

To help visualize frequency better, think of the frequency as the speed of a car.  The faster you go the more likely you are to go flying off the road.  However, it is not the speed of the current that is different.  All current travels at the same speed – 186,282 miles per second – the same as the speed of light.

The speed that is changing with frequency is the speed of that fluctuating EMF.  At 512 Hz, the EMF is fluctuating back and forth at 512 times per second.  At 98 kHz, the EMF is fluctuating back and forth at 98,000 times per second.  That is what is making such a big difference between low frequency and high frequency.  High frequency is much like a speeding car.  There is a great deal more motion taking place, but that motion is more difficult to control.

The electromagnetic field (EMF) is in constant fluctuation, expanding and collapsing. How fast that fluctuation occurs depends entirely on the frequency being used.

7 – A QUALITY SIGNAL

Utility locators often use wording such a “good signal” or “great signal”, but it is rarely defined.

Since what is being detected is an invisible field of electromagnetic energy, the utility line will be directly below the high point of that energy – the apex of the EMF.  Yet that field will be detectable even several feet away from that apex, and it will be detectable on both sides of the apex, and in equal lengths.

In other words, a quality signal will have a definite high point, an apex, and an even drop off on both sides of the apex.  You are detecting a circle of energy, and the utility line is below the highest point of the circle.

Also, since the transmitter is sending a constant stream of current, the signal on the utility should also be a constant.

Therefore, we have the definition of a quality signal – a constant signal in a circular form – a high point in the center with an even drop off on both sides.  When you have that – then you are detecting a utility line with a “great signal”.

8 – KEEP THE RECEIVER STRAIGHT UP AND DOWN

Always keep in mind that what you are detecting is a round ball of energy.  If you were standing five feet off to the side of the utility you can still detect it just fine.  All you have to do is to point the receiver towards the utility – and the EMF will register on the internal coils.

In other words, since the EMF can be detected far to the side of the utility, the only way to determine the actual horizontal position of the utility is to keep the receiver pointed downwards at all times.  Knowing the utility is directly below you is only possible if you are pointing the receiver downward, and moving it back and forth.  It is that highest point of the ball of energy that will be directly above the utility line.  That is the apex of the EMF.

Many locators, including those with years of experience, have never been able to understand that swinging the receiver back and forth like a pendulum will result in marks that are several feet off from the true location.

Moving an object perfectly back and forth in front of you while keeping the object at the same distance from the ground is not a comfortable thing to do.  It is not a natural movement for the human arm.  But what you can do is to curve the receiver slightly as you move it, sort of like clearing a path in front of you.

Never swing the receiver in a pendulum fashion. You will only be constantly marking the utility in the wrong place.

9 – SWEEP FOR THE TARGET LINE

Each time you connect to a utility you are searching for a new utility line.  You probably have a good idea of which direction that utility is going from your connection point – but that is not at all good enough.

The purpose of locating/designating is not to put paint down where the utility is supposed to be – but to put paint down where the utility line actually is.  It is up to the operator of the instrument to determine the location of the utility, not to just follow the utility prints, to follow past marks on the ground, or to assume that what ever signal is first detected is the target utility line.

Anytime you apply current into the ground you will be applying current to every single conductor in the ground to some degree.  The target line, the utility you applied current to, should have good current, but every other buried utility will have at least some current as well.

Never assume that just because you have a signal, that it is the target signal.  You must sweep the area around your connection in order to determine which is the strongest signal.  It is never just signal that you should be looking for but the strongest signal.  That will almost always be the target utility line.

Keep the receiver straight up and down – stand a good 15 feet away from the entire connection area – and make a large circular walk around the connection area.  You will usually come across several signals (current on other utilities).  But which ever is the strongest signal will almost always be the target utility.

For each and every locate you must do a full sweep around the connection area to find the strongest signal.

10 – SIGNAL STRENGTH

Typically, the most noticeable display on a receiver is the signal strength.  This is not a single display, but a combination of three displays: Most noticeable is a graph display which usually moves side to side; there is also a numerical readout with a percentage symbol (%); and third is the audio tone of the receiver.

These three readouts are often thought of as being separate indicators – three indicators of three separate pieces of information.  But that is not the case.  Few technicians seem to pay attention to the fact that these three indicators all move in unison.  If one goes up – they all go up.  If one goes down – they all go down.  These are the indicators of signal strength.

The percentage readout on the receiver does NOT tell you which type of utility is below ground.
11 – THE MANUFACTURERS

3M DYNATEL

6801 River Place Road

Austin, Texas 78726-9000

Phone: 903-994-4192

www.3M.com/dynatel

 

AMPROBE

P.O. Box 9090

Everett, Washington 98206

Phone: 877-267-7623

www.amprobe.com

 

AQUA-TRONICS

1795 N. Yellowstone Highway

Idaho Falls, Idaho 83401

Phone: 208-528-8875

www.aquatronics.com

 

DITCH WITCH

1959 W. Fir Street

Perry, Oklahoma 73077

Phone: 800-654-6481

www.ditchwitch.com

 

FISHER LABS

1465 – H. Henry Brennan

El Paso, Texas 79936

Phone: 915-225-0333

www.fisherlab.com/industrial

 

GOLDAK

15835 Monte St. Unit 104

Sylmar, California 91342

Phone: 818-367-0149

www.goldak.com

 

HEATH CONSULTANTS INC.

9030 Monroe Road

Houston, Texas 77061

Phone: 713-844-1300

www.heathus.com

 

MCLAUGHLIN

2006 Perimeter Road

Greenville, South Carolina 29605

Phone: 864-277-5870

www.mclaughlinunderground.com

 

PIPEHORN

Utility Tool Company Inc.

2900 Commerce Blvd

P.O. Box 100519

Birmingham, Alabama 35210

Phone: 205-956-3710

Phone: 800-952-3710

www.pipehorn.com

 

RIDGID

Ridgid Tool Company

400 Clark Street

Elyria, Ohio 44035

Phone: 800-474-3443

Phone: 800-4-RIDGID

www.ridgid.com

 

RYCOM INSTRUMENTS, INC

9351 E 59th Street

Raytown, Missouri 64133

Phone: 816-353-2100

www.rycominstruments.com

 

SCHONSTEDT

Schonstedt Instrument Company

100 Edmond Road

Kearneysville, West Virginia 25430

Phone: 800-999-8280

Phone: 888-367-7014

www.schonstedt.com

 

SPX RADIODETECTION

(United States)

28 Tower Road

Raymond, Maine 04071

Phone: 207-655-8525

Phone: 877-247-3797

www.radiodetection.com

 

SPX RADIODETECTION

(Canada)

Unit 34, 34-344 Edgeley Road

Concord, Ontario L4K 4B7

Canada

Phone: 905-660-9995

Phone: 800-665-7953

www.radiodetection.com

 

SUBSITE

The Charles Machine Works

P.O. Box 66

Perry, Oklahoma 73077

Phone: 800-846-2713

www.subsite.com

 

SUBSURFACE INSTRUMENTS INC.

1841-C Plane Park Drive

De Pere, Wisconsin 54115

Phone: 855-442-6346

www.ssilocators.com

 

VIVAX-METROTECH

3251 Olcott Street

Santa Clara, California 95054

Phone: 408-734-1400

www.vivax-metrotech.com