As much as Pipe & Cable Locators are the backbone of the utility marking and mapping industry, they are far from being the only instrument available, especially now days. Some of these “instruments” are better described as tools which can be used in conjunction with a P&C Locator. While others are entirely different technological instruments, and many of them far more technologically advanced, yet, just like a P&C Locator, they all have their limitations.
None of this material here is meant to replace a true training course, especially with the very involved instruments such as the EM-61, or a Gradiometer. The information here is only meant to introduce the reader to the various instruments and hopefully give a better understanding of why each one of them has its uses.
ACOUSTIC LOCATOR – AML – EM-61 – GRADIOMETER –
MAGNETOMETER – METAL DETECTOR – PIPE INSPECTION CAMERA –
RFID (MARKER BALL) – RODDER – SONDE
ACOUSTIC LOCATOR
There are a number of different manufacturers of acoustic locators. These instruments send sound waves on water pipes so that even plastic pipes without a tracer can be followed out.
The procedure is to connect a device to the fire hydrant, and have the water turned on at the hydrant so the barrel is full, even on a dry barrel hydrant. The device includes what is similar to a tiny metal hammer that produces a pounding action. This device is based on the fact that sound travels over long distances through water.
The receiver is an extremely sensitive listening device with headphones and an extended rod with a microphone at the bottom. You hold the receiver rod down toward the ground and listen for the tapping sound.
Today some of these acoustic locators can be extremely sensitive, to the point of requiring the operator to use extreme caution because a car passing by can cause a deafening noise level. Typically the instrument will default to a much lower volume when an excessive noise occurs, but there can still be a bit of a delay in the volume drop.
AML – ALL MATERIALS LOCATOR
This is a patented instrument, manufactured only by Subsurface Instruments Inc. The AML uses ultra-high radio frequencies to detect the smooth surface on the side of pipes. They can function in clay soil which gives them an advantage in detecting utilities such as plastic pipe without a tracer wire.
This is a very sensitive instrument to operate and many people struggle to use it unless they have been properly introduced to how it functions. Like a GPR unit, you do not follow out the utility line. Instead, you cross the pipe and detect the buried pipe at specific points.
When you turn the instrument on you will notice that there are two small red lights facing towards you, and they are flashing incessantly. Walk towards the pipe slowly pointing the instrument towards the ground. Those red lights will be flashing, but the flashing means it is not aimed at a buried pipe, not that it is.
When you get to a point where either one of the red lights stops flashing and remains on constantly, then you may be over the pipe. Turn the instrument slightly sideways, left and right, to see if you can get both lights to stay on. When both red lights remain on, then it is because you have it pointed at a smooth surface object in the ground – probably the side of a utility pipe.
If the pipe is a 10-inch, then you will also probably notice that if you move about 10 inches forward, then it will be detecting the other side of the pipe, and both lights will remain on again.
The advantage here is that unlike GPR, the AML still functions on clay soil. The disadvantage is that the instrument is very sensitive and must be moved slowly. If you were walking at a regular pace you might well walk right over the pipe and never notice the change on the lights. Overall, this instrument does have the capability to detect pipes that can not be found any other way. Check with Subsurface Instruments for further information.
CLAMPMITTER
A Clampmitter is an instrument for producing clamp induction by use of a combination of transmitter and clamp combined. These are manufactured by Rycom who also produce PCLs (Pipe & Cable Locators).
These allow you to clamp to various utility lines without hauling a regular PCL transmitter up and down the street. They operate on rechargeable batteries and have 3 available frequencies on each unit: 33 kHz, 65 kHz, and the third frequency can be ordered as 82 kHz, 83 kHz, or 131 kHz.
These can be very handy in various situations as well as removing the hauling of a transmitter throughout the day. They can also be used in manholes. The Clampmitter can be ordered in 2 different sizes: the standard 4.2-inch clamp and a larger 6.5-inch clamp.
EM-61
The EM 61 is technically a Time Gate Metal Detector. These are an extremely expensive unit to purchase and are therefore mainly rented by various users.
Unlike most metal detectors an EM 61 can detect metal at much greater depths. They are mainly used to detect deep metal objects of various types such as buried military ordinance and USTs. They have been used on occasion in conjunction with utility surveys.
GRADIOMETER
A Gradiometer, like the EM 61, is a very expensive unit and usually rented, not purchased. They are also often used for locating buried military ordinance. The basic layout of a gradiometer is using multiple specialized magnetometers, either side by side or in a vertical layout (one above the other). They can also be used with 4 individual magnetometers spaced apart from each other.
The layout of a Gradiometer is related to its specific purpose, and there are several. Some are meant for geological purposes only; however, just like the EM61, they have also been used in conjunction with utility surveys on occasion. In this case, it is usually the vertical Gradiometer that is used to determine the depth of ferrous metal objects such as subsurface gas tanks or other USTs.
MAGNETOMETER
Schonstedt Instruments invented the magnetometer in the 1950’s. They have become so popular that many people say “Schonstedt” when they actually mean magnetometer. After all, Schonstedt manufactures more than just magnetometers. They also manufacture P&C Locators, and other electronic instruments.
A magnetometer is NOT a metal detector. They detect the magnetic flux which occurs between ferrous metal and the surrounding soil. They detect iron and steel, not aluminum beer cans. There will be a minor amount of magnetic flux occurring with non-ferrous metals such as aluminum, but usually too minor to be detected. Also, metal detectors can only detect buried metal at a very shallow depth, usually a maximum of one foot, and commonly only a few inches. A magnetometer can hypothetically detect buried ferrous metal at a depth of possibly 20 feet.
Ferrous metal is the most reactive metal with soil. So, any iron or steel object placed underground will have an automatic reaction with the soil producing a weak magnetic field. Though the overall reaction will be weak, it will be its strongest at any pointed or sharp edge of the metal. The best example of this is probably with a manhole lid. The lid is large and round and does not have any area that would be typically called “sharp” and yet, the edge of the lid is somewhat pointed. Therefore, if you swipe a magnetometer across a buried manhole lid, you can detect the magnetic flux at the edge of the lid on both sides. That is where the largest amount of flux is occurring. So, when searching for a buried manhole lid you should be expecting a large round signal, not a pinpoint in the middle of the lid. Buried water valve lids will give the same results, only of course with a much smaller circle of signal.
They can also be used to detect the end point of culvert pipes, and for that matter, they can detect the end point of a metal pipe which has been stubbed out. Don’t expect to follow out an iron pipe with a Mag. The pipe itself lacks edge, so although there is some magnetic flux occurring, it is usually far too weak to detect. The iron or steel pipe will only be detectable at end points, or flange joints, or any portion of the metal that is pointed or edged in some way.
The most common use of magnetometers is in survey where they are used to detect buried survey nails (PK nails), which are often magnetized meaning they are steel with an iron core and pre-magnetized before being sold at survey shops. They can also easily detect standard nails because of the sharp point.
Magnetometers can also be used to detect underground storage tanks, and again they will show the strongest response at the edge of the tank.
METAL DETECTOR
Metal detectors have long been used for finding buried water valve lids, manhole lids, and other buried utility features. They certainly do work for this task but with limitations.
Metal detectors are a transponder which both sends and receives electromagnetic energy into the ground. They transmit current into the ground, which can then react with any type of metal, and the reaction is detected in the hoop portion of the instrument. Most people use them to look for metal objects made of silver or gold. However, they will react with any type of metal, and this includes not only iron items, but silver, gold, and even aluminum. This is one of their biggest weaknesses. They detect flattened beer and pop cans more than any other type of metal because there is a great deal of trash underground.
Another weakness is that they have a very limited depth penetration, less than one foot. Most water valves that have become buried are usually less than one foot down, but some may be more than that.
Another weakness is that they have a very limited depth penetration, less than one foot. Most water valves that have become buried are usually less than one foot down, but some may be more than that.
Another weakness is that, being a transponder-type device, they do not detect an outer reaction of iron as magnetometers do, but instead react with the center of the metal. A manhole lid may have a slightly larger reaction than a water valve lid, but this will still be a centered reaction and therefore give only a vague indication of the size of the buried target.
All in all, a metal detector can be very useful in locating buried iron utility targets, but a magnetometer is superior in this task if you have one.
PIPE INSPECTION CAMERA
These instruments are also well named, as well as being very easy to understand. A small video camera is contained in the head of the cable with a fiber optic strand running back to the main unit which houses the electronics, and the screen to see what the camera is seeing. Most of these have built-in lights at the head to illuminate the inside of the pipe. Many of these units have a built-in sonde so they can be traced out with a P&C Locator to determine the position of the head/camera.
These are becoming very common, both for utility mapping as well as for plumbers to determine the problems inside of clogged sanitary pipes. The less expensive ones will have only the cable/camera to be pushed down the pipe. There are however more expensive units which come with a roller frame to make it easier to push them farther, and some expensive units which have robotic frames at the head which can be controlled from the main unit. So, instead of pushing the cable, the robotic end is pulling the cable down the pipe. More expensive units even have robotic cameras so you can turn the camera to the side to get a better view of damaged pipe, or giving you the capability to drive the robotic head all the way to an underground pipe connection, and allowing you to look down into the connecting pipe. This is very useful for sanitary sewer pipes where almost all service pipe connections are “ghost connections”, not at manholes.
Although the use of pipe inspection cameras for the utility industry in general is obviously limited, their practicality with storm and sanitary pipes is also very obvious.
RFID (Radio Frequency Identification Device)
This instrument requires some explanation, not just in what it is doing, but in the name listed here. First of all, the term RFID is only used intermittently for these instruments. Many technicians simply refer to the device placed underground – marker balls. Some people refer to them as EMS markers or Omni markers.
Let’s start at the beginning. These devices originated with the 3M Company which named them EMS for Electronic Marking System. Another company called their marker ball system OMNI. Another firm uses the name Uni-Marker. There are two components to this device: the marker placed underground; and the instrument which can detect the device aboveground.
Although many of the devices placed underground are small plastic balls, those are for standard depth utilities such as handholes. Deeper utilities can be marked by placing a more sizable marker often called a “toilet seat” because that is what they resemble. These were needed for very deep utility marking, such as pressurized sanitary lines.
The Bell Telephone System wanted something more specific for their cables, so a large round marker was produced with spokes. These are often called “steering wheel markers” because of their resemblance to a steering wheel. These steering wheel markers were used almost exclusively by the Bell Telephone System for strapping down on to the top of buried cable splices.
So, there are three common marker devices: marker balls, toilet seats and steering wheels. No matter the shape, they all function the same way. They consist of a circular wire with a small capacitor inline with the wire. That wire must be facing upward in order for the device to be detected. That is obvious enough with the two larger markers, but the ball markers are only dropped down into a handhole. This would seem to defeat their purpose. If you did not drop it just right, then the wire inside would not be facing upward. Yet if you hold one in your hand you will notice that there is obviously a fair amount of fluid in the marker ball. Glycerin is used inside the marker balls to prevent them from freezing up in northern regions. The circular wire rests on top of this fluid. All you have to do is to drop the marker ball into the handhole, and the glycerin will level out and keep the inner wire facing upward. So, despite the variety of shapes and sizes, all of these markers function the same way, with an inner circular wire attached to a capacitor.
What is different between the markers is the frequency. The steering wheel markers are for telephone and the toilet seat markers are for sanitary, but the ball markers can be used for different utilities. The color of the marker ball denotes which utility it should be placed with. Although all of the marker balls are constructed the same, the capacitor can vary. This is where the locator instrument comes in.
The locator both sends and receives. It produces a pulsation of energy downward that interacts with the coil of wire, and just as importantly with the capacitor. It is the inner capacitor which identifies the type of utility, and of course in conjunction with the color of the marker ball. That pulsation of energy produces a small amount of current onto the wire, and that in turn produces a specific frequency signal based on the type of capacitor. This is how the locate instrument knows which marker ball is blue and on top of a water line, and which ball is red and on top of an electric cable. It detects a specific frequency from the marker ball.
These RFID locators are very simple to use. Turn it on, and push the button for the type of utility you are looking for: red for electric, blue for water, etc. Turn the gain well up so you do not have to be standing directly over the marker in order to detect it. Now sweep the ground in front of you as you are walking. When the signal lights up, then you can turn it down to a more reasonable level and pinpoint the marker.
Realize that unlike a metal detector, the RFID locators DO NOT need to be kept in motion in order to function. You can hold the locator directly over the marker and get a quality signal.
RFID locators have also become very common as an added feature with some of the P&C Locators. Lower the loop portion at the base of the locator, set the instrument for which type of utility (capacitor) you are looking for, and sweep back and forth.
Again, there are many names used for these types of instruments. It may be called a ball marker locator, an EMS Locator, an OMNI locator, an RFID locator, or by some other name. They all function the same way.
All RFID markers are limited in the depth at which they can be detected, and that limitation is determined by their size/shape. The larger the diameter of the coil, the deeper the signal can penetrate. Below are the official names of each type of marker – plus the common nickname (based on its appearance) – and the depth range.
NEAR SURFACE MARKER – (“Flashlight”) – 2 feet
BALL MARKER – (“Ball” – the most common marker) – 5 feet
DISC MARKER – (“Disc”) – 5 feet
MINI-MARKER – (“Steering Wheel” – used almost exclusively for telephone cable splices) – 6 feet
FULL RANGE MARKER – (shaped like a “Toilet Seat”) – 8 feet
RODDER
A Rodder is a simple device which can be pushed down pipes or empty conduits so they can be located out using a P&C Locator
Fishtape is manufactured for use in pulling cable through conduit. Reel out the thin metal fishtape, push it down the conduit, connect the cable to the end, and now pull it back toward yourself.
Many locate technicians realized that this could be used for locating since it is metal tape. Push the fishtape through, connect the transmitter to the end, and light up the conduit. This can often require higher frequencies because the far end of the fishtape may not be coming into contact with earth or anything conductive.
Eventually, a manufacturer realized that they could easily produce a better product. Fishtape easily curls up, especially in large conduit. But if you manufacture a product that has some width to it, basically a thick insulated fishtape, then it will fit farther down the conduits, even larger conduits or pipes.
Since this is a conductive product, you should never use it on electric conduits. It does not matter that the conduit is empty right now. If the far end of the conduit extends into a transformer or J-Box then you are running a great risk of electrocution.
SONDE
Sondes come in a variety of sizes but always in a shape rather resembling a pickle. They are a watertight electronic device requiring a battery, usually a 9 volt, and usually unscrew in the middle.
They always have a solid hook connection where a rope can be tied. Place the battery inside, screw the device back together, then lower it down a storm or sanitary pipe, and obviously it has to be lowered into the pipe upstream from where you want to locate. The water/sewage flow carries the device downstream as slow as you want to let out the rope.
The sonde will emit a signal at a specific frequency, usually 8 kHz, but they may have a lower frequency such as 512 Hz. This signal can then be detected using a P&C Locator.
Since the signal exists only at one point, directly at the sonde, you must follow out the sonde as it is being let out or it can be difficult to find where it is at. This means it requires at least two people to operate a sonde.
One very important thing to realize about sondes is that the signal will interact with any Pipe & Cable Locator set to the same frequency, but the electromagnetic field will be in a position perpendicular to what it would be on a utility line. In other words, you must hold the receiver sideways to detect the field. This can take some getting used to, so try it out first when the sonde is barely down the pipe. Don’t wait until the sonde is well down the pipe. Or you can try it above ground to see what to expect.
One other point on this same subject. Some of the nicer P&C Locators today offer a sonde mode at various frequencies. This is usually shown on the screen as a sonde image instead of the usual line locating image (concentric circles with a line through them). When you set the receiver to sonde mode, then you do not have to hold the receiver sideways. You can hold it in the same position as you would when following out a pipe or cable, which is far more natural and easy.