Integrated Equipment Improves Efficiency of Locating Buried Plant
By Michel Belanger
Cable locating has become a complex task requiring a multi-frequency unit. "3M's new 5 watt Dynatel Model 2250-U5T3/A Cable/Pipe locator is the best locator available on the market today", says Colin Barron, president of Cable Masters Inc., a fault locating company. He offers other tips and helpful hints on what makes a great locator, as well as how to perform a good locate below.
What Makes A Great Locator:
TRANSMITTER:
- At least 4 transmitter frequencies covering a wide band from low to high (500 Hz to 200 kHz)
- Should have 3 transmit modes: Direct Connection, Coupling and Induction
- Variable output.
- Indication of battery level each time the unit is used
- Voltage protection up to 240 VAC
- Automatic voltage reading and audible warning
- Frequency and current flow should be simultaneously shown on the display
Ohmmeter to read resistance
- Ability to test leads, coupler and A-frame
- Transmitter should be able to run off internal batteries or optional external source with long cord
- Any connection jacks should be on the top for easy access, but protected by the lid from rain
and snow
- All internal batteries should be held firmly in place so they can't move and cause intermittent problems
- The carry straps should be long enough to allow congested areas (usually industrial locations) to be swept with the transmitter while the locate person is standing up (i.e. the transmitter is set to Induction mode and moved over the area in question)
- User friendly
RECEIVER:
- Light weight and well balanced
- User friendly
- In addition to the 4 transmitter frequencies, the receiver must detect 2-60 Hz Harmonics, 31.5 kHz (TV), 120 Hz Harmonic (Cathodic Protection) and frequencies from rack mounted transmitters
- Peak, Null and Differential Modes (Peak with arrows and auto gain)
- Special Peak Mode for cable/pipe detection at increased depths
- 3 signal responses: sound, number and bar graph
- Depth and current readings
- Duct probe (Sonde) depth reading
- One piece construction to avoid any moisture problems
- A coupler/probe jack for cable or conductor identification
- An ear phone jack for noisy locations
- Indication of battery level each time the unit is used
THE LOCATE PERSON:
- Should be well-trained in the use of maps, drawings, and micro-fiche
- Should have a good knowledge of the underground facilities they will be locating
- Be fully trained on the use of the locator he/she is using and know its limitations
- Knowledge of the locator frequencies and when to use them
In addition to the standard equipment, every good locator should have the following accessories:
- A three foot stainless steel ground probe with tee handle at the top to ensure a good ground
- Insulated ground wire extension lead of at least 100 feet.
- Vise grips for difficult direct connections
- A horseshoe magnet for direct connection to large metallic objects such as water pipes
- Wire strippers and other hand tools as required
- A large 6 inch inductive coupler for large cables
- A small 1 inch coupler for small cables in confined locations
TIPS FOR BETTER APPLICATION OF SIGNAL TO CABLES/PIPES ETC.
Using the Transmitter in INDUCTIVE Mode:
- Place the transmitter as close as possible to the cable or pipe to be traced. At a riser pole, place the transmitter on end so that the maximum signal will be induced onto the cable above ground as it goes up the pole. Make sure the dead zone is facing any other cables on the pole.
- When looking for the end of a buried cable, search for it by moving the transmitter, while a second person with the receiver is at least 30 feet away in the common trench or known area of target cable. The signal on the receiver will rise and fall as the transmitter crosses back and forth over the cable path. Now follow the path with the transmitter until the signal drops off quickly. This will be the end of the buried cable.
- When clearing an area for a bore hole or post hole, have one person stand at that location with the receiver. Have a second person walk with the transmitter in a circle around the first person and at least 30 feet away. The end of the transmitter must always face the receiver. The first person must turn so that the front of the receiver is always facing the transmitter.
Using The Transmitter in DIRECT CONNECT Mode:
- Make sure that you have the correct lead (usually the red clip) connected to the conductor/pipe to be traced
- Make sure the connection is clean at both ends and tight. Vise grips can be used to make a good connection to water hydrants or gas valves.
- Where possible, disconnect grounding strap at the terminal box and connect it directly to the red lead of the transmitter. The grounds must be left connected at the far end.
- Always check for a good far end ground using the built-in ohmmeter.
- Use the lowest frequency available
- Place the ground probe at 90 degrees to the target line (cable/pipe) and as far away as possible. Avoid putting the ground probe on the same side of the target line as other utilities (if known or previously marked). Other items, such as steel access holes, catch basin covers, steel traffic signs, posts or isolated down guy-wires can also be used as ground connections as long as they are isolated from common utility grounds. Use your horseshoe magnet where necessary to connect to the steel access holes and catch basin covers.
- Avoid using other utilities as your return ground.
- To locate short runs of continuously-grounded services, use your 100 foot insulated ground wire extension as a return path. For example, if you have trouble locating a water pipe from a stop cock valve to the main pipe, connect the red clip from the transmitter to the stop cock. Connect one end of your long insulated ground extension lead to the transmitter's black clip, and connect the other end to the next water stop cock valve. You now have a direct connect loop. The signal must travel from the first stop cock out the pipe to be located, along the main pipe, back on the second water pipe to the second stop cock and back to the transmitter on the ground extension lead. You have three to four times the current flow because of this closed loop, and the pipe can now be traced very easily.
Receiver:
- Check battery level every time you turn on the receiver.
- When passive locating only (without transmitter) make sure your receiver is set to the correct frequency. Example: For 60 Hz Power: for power cable locating, use H60 (9th harmonic); for locating on 3 Phase Delta Power systems, use L60 (5th harmonic).Why use L60 on 3 Phase Delta systems? Often, you can get phase cancellation at the 9th harmonic of 60 Hz, so there is no signal to detect. At the 5th harmonic there is usually an unbalance, and therefore a detectable signal.
- Use 120 Hz or CPS to trace cathodic protection signals on pipes.
- Use 31.5 kHz to trace some Cable TV cables.
- Use 512 Hz and 560 Hz to trace signals from some rack mounted transmitters and sondes or duct probes.
- Confirm target line in Peak and Null (or Differential) Modes.
- Confirm target line with Current and Depth Measurement.
- If the received signal is weak or the target line is very deep, activate Special Peak Mode. This makes the receiver much more sensitive by activating only the lower peak coil.
- You locate position is standing up straight, keeping your eyes and ears open.
- In differential mode, there are two distinctively different sounds when the receiver is on each side of the target line. When crossing a road or other hazardous areas, the operator can listen for the sound to change rather than watching for the arrows on the receiver display to change direction.
Items to Remember:
- Keep a spare set of batteries in your truck.
- In Passive or Active locating modes, no magnetic field can exist without current flow (No Current Flow = No Signal).
- Low Frequency (500 Hz to 900 Hz): travels the furthest; does not couple; use direct connect only.
- Medium Frequency (8 kHz to 33 kHz): travels good distance; couples to cables/pipes that are grounded at both ends; use direct connect, coupler or induction.
- High Frequency (>33 kHz to 200 kHz): signal only travels a short distance; couples very easily, but will spread to other cables; great to trace open ended cables/pipes; great for locating tee connections or laterals; use direct connect, coupler or induction.
- Grounding is very important for signal return. Frozen ground acts like an insulator. The ground probe should always be below the frost line.
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