Schonstedt Instrument MAC-51Bx User manual

Instruction Manual
Model MAC-51Bx
Magnetic and Dual-Frequency
Pipe and Cable Locator
Manufactured by
Schonstedt Instrument Company
4 Edmond Road
Kearneysville, WV 25430
Telephone: [phone]
Fax: [phone]
February 2000

TABLE OF CONTENTS
Page
Section I General
Introduction 1-1
Magnetic (MAG) Locating Mode 1-1
Cable/Line Tracing (HI/LO) Locating Modes With Fault Locating 1-1
Standard Accessories 1-2
Optional Inductive Signal Clamp 1-2
Specifications 1-3
Section II Magnetic Locator Operation
Theory of Operation 2-1
Mode Selection and Gain Setting 2-2
Low Gain Operation 2-2
High Gain Operation 2-3
Search Procedure 2-3
Section III Magnetic Locating Mode Application Notes
Basic Signal Patterns 3-1
Strongly Magnetized Markers 3-2
Locating Manholes, Septic Tanks and Water Wells 3-3
Locating Items Under Snow or Water and Tracing Barbed Wire 3-4
Searching Areas Along a Chain Link Fence 3-5
Locating Valve Boxes 3-6
Locating Cast-Iron Pipes 3-6
Locating Steel Drums 3-7
Additional Applications 3-7
Other Notes 3-7
Section IV Cable and Line Tracing
Theory of Operation 4-1
Transmitter, Turn-On and Battery Check 4-2
Inductive Signal Coupling (For HI and LO Modes) 4-3
Conductive Signal Coupling (For HI and LO Modes) 4-3
Inductive Signal Coupling With Signal Clamp (For HI Mode Only) 4-4
Mode Selection 4-4
Gain Settings for Tracing a Cable or Line 4-5
Cable Tracing (HI Mode) Using Inductive Coupling 4-5
Conductively Applied Tracing Signals (For HI and LO Modes) 4-6
Section V Cable and Line Tracing Application Notes
Inductive Signal coupling for Cable/Line Tracing in the High Mode 5-1
Conductive Coupling for Cable and Line Tracing in HI Mode 5-1
Conductive coupling for Cable and Line Tracing in the LO Mode 5-2
Dealing with Clutter Signals (HI Mode) 5-3
Single-Lobe Identification (HI Mode) 5-3
Bends and Junctions (HI and LO Mode) 5-4
Signal Spreading (HI Mode) 5-4
Magnetic (MAG) Mode Aids in Interpreting Ground Clutter 5-4
Isolators and Signal Path Continuity (HI Mode) 5-5
Isolators and Inductive Excitation (HI Mode) 5-5
Isolators and Conductive Excitation (HI and LO Modes) 5-6
Determining Target Depth by Triangulation 5-7
Section VI Maintenance
Replacement of Receiver Batteries 6-1
Replacement of Transmitter Batteries 6-1
Receiver Troubleshooting Guide 6-3
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Transmitter Troubleshooting Guide 6-3
Service Information 6-3
Warranty 6-6
LIST OF FIGURES
Figure Title Page
1-1 MAC-51Bx Magnetic and Dual Frequency Pipe and Cable Locator 1-1
2-1 Detecting Magnetic Field of an Iron Marker 2-1
2-2 Normal Range Gain Setting 2-2
2-3 Low Range Gain Setting 2-3
2-4 High Range Gain Setting 2-4
3-1 Signals from Vertical and Horizontal Targets 3-1
3-2 “X” Pattern Provides Precision Locating 3-1
3-3 Raising the Locator Eliminates Unwanted Signals 3-2
3-4 Signal Pattern From a Strongly Magnetized Marker 3-2
3-5 Locating Manhole Covers 3-3
3-6 Locating Well Casings 3-3
3-7 Signal Pattern Provided by Septic Tank Handles 3-3
3-8 Locating Objects under Snow or Water 3-4
3-9 Tracing Barbed Wire from Old Fence Lines 3-4
3-10 Searching in the Vicinity of a Chain Link Fence 3-5
3-11 Placement of Locator 3-5
3-12 Locating Valve Boxes 3-6
3-13 Signal Pattern Provided by Cast-Iron Pipes 3-6
3-14 Signal Pattern Provided by Steel Drums 3-7
4-1 Transmitter and Receiver Placement 4-1
4-2 Signal Pattern from HF/LF Tracing Signals 4-2
4-3 Transmitter Features 4-2
4-4 Transmitter Operating Positions 4-3
4-5 Transmitter Hookup For Conductive Coupling 4-3
4-6 Inductive Signal Clamp Hookup 4-4
4-7 Gain Setting for Normal Range 4-4
4-8 Null Shape Versus Gain Setting 4-5
4-9 Inductively Coupled Tracing Signals 4-6
4-10 Conductively Applied Tracing Signals 4-6
5-1 Inductive Coupling Setup 5-1
5-2 Conductive Coupling Setup 5-2
5-3 Conductive Coupling for Break Locating 5-2
5-4 Repositioning Transmitter to Reduce Interference 5-3
5-5 Single Lobe Identification Technique 5-3
5-6 Identification of Bends and Junctions 5-4
5-7 Shorting Wire in Place to Bypass an Isolator 5-5
5-8 Pedestal with Grounding Clip Installed 5-6
5-9 Pedestal with Ground Wire Removed 5-6
5-10 Determining Target Depth by Triangulation 5-7
6-1 Exploded view of Receiver Electronic Unit 6-1
6-2 Replacement of Transmitter Batteries 6-2
6-3 MAC-51Bx Receiver Repair Parts 6-4
6-4 MAC-51Bx Transmitter Repair Parts 6-5
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Important Notice
Schonstedt believes the statements contained herein to be accurate and reliable. But their accuracy, reliability,
or completeness is not guaranteed.
Schonstedt’s only obligation shall be to repair or replace any instrument proved to be defective within three years
of purchase. Schonstedt shall not be responsible for any injury to persons or property, direct or consequential,
arising from the use of any instrument.

Section I
General
Introduction
The all purpose MAC-51Bx Magnetic and Dual-Frequency Pipe and Cable Locator is the only underground locator that
combines magnetic locating (for iron and steel objects) with dual-frequency cable/line tracing into one compact system.
The system consists of two major units: a dual-frequency (LF and HF) transmitter and a three-mode receiver (MAG, LO
and HI). The transmitter operates up to 60 hours on eight alkaline C-cell batteries; the receiver up to 120 hours on two
9-volt lithium batteries.
Figure 1-1. MAC-51Bx Magnetic and Dual-Frequency Pipe and Cable Locator
Magnetic (MAG) Locating Mode
The receiver is the only unit for operation in the Magnetic mode. Set the Mode switch to MAG, adjust the Gain control,
and you have the best magnetic locator available. Operation in the Magnetic mode is explained in Sections II and III.
Switching between LO, HI and MAG modes while tracing a cable, is a unique method for unscrambling ground clutter.
Gas and water pipes in the immediate vicinity of the target with a HF trace signal being applied may emit parasitic
signals that can distort the cable locating null. In the magnetic mode, cast-iron water pipes and gas lines can be identi-
fied quickly and even classified as to their type by the conventional spacing of joints, which provide the strongest
signals.
Cable/Line Tracing (HI/LO) Locating Modes
The MAC-51Bx transmitter simultaneously transmits 571 Hz (LF) and 82.5 kHz (HF) signals. When applied to any
continuous metal conductor, the HF trace signal jumps gaskets between pipe sections and small breaks in the line. The
LF trace signal does not bleed onto adjacent or crossing lines, and will stop at a complete break in the conductor. With
the receiver you can select and compare received audio signals from both frequencies without having to return to the
transmitter.
Setting the receiver’s Mode switch to LO allows you to trace the cable, locate a complete break (where the signal disap-
pears), and then continue tracing beyond the fault by switching to the HI mode. The approximate depth of an
underground cable can be determined using the 45° null-point triangulation method. Operation of the MAC-51Bx in the
LO and HI modes is explained in Sections IV and V.
Standard Accessories
Basic accessories supplied with the MAC-51Bx include a headphone jack, spare batteries holders and a conductive
cable assembly with ground stake. An inductive signal clamp, mini transmitter and headphones are available as options.
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Optional Inductive Signal Clamp (HI Mode only)
This option increases the versatility of the MAC-51Bx by providing a convenient method of selectively applying the trace
signal to cable conductors covered with nonmetallic insulation in the HI Mode only.
It induces a strong signal to only the conductor that it is clamped around. This method allows you to put a stronger
signal on a specific cable to be traced in congested areas containing cables, water and gas lines, or other conductors
that may emit lower level parasitic trace signals.
Operation is simple and easy. Plug the clamp lead into the transmitter accessory jack and close the clamp around the
cable. No ground connection is required. Hook-up can be made to all continuous metal pipes and cables up to three
inches in diameter.
Optional Mini Transmitter
The Model MT-2 is a miniature transmitter (3 in. x 1 in.) used in combination with a MAC-51Bx receiver to trace
nonmetallic pipes, pinpoint obstructions, and locate concrete septic tanks. (The Receiver’s Mode switch must be set to
HI.)
As the MT-2 (Mole) is pushed through a buried nonmetallic pipe, it emits a signal that can be detected at depths up to
18 feet by using the MAC-51Bx receiver. The Mole has a concave surface so it can be secured with electrical tape to a
plumber or electrician’s snake, or it can be closed in a pipe “PIG”.
One AAA penlight alkaline battery provides up to 30 hours operation. Tightening the battery cap (CW) turns the unit on.
Loosening the battery cap (CCW) until the battery moves when the MT-2 is shaken turns the unit off.
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MAC-51Bx Specifications
TRANSMITTER
Operating Voltage 12V (8 alkaline C-Cell batteries)
Battery Life 60 hours (on & off usage @ 70F)
RF Output 82.5 kHz modulated at 382 Hz, Pulsed at 4.4 Hz
571 Hz pulsed at 4.4 Hz
Audio Indicator 2.58 kHz pulsed at 4.4 Hz
Weight Approx. 5.5 lb. (2.5kg)
Operating Temp. -13°F to 140°F (-24°C to 60°C)
Overall Size 43.5 in. x 7 in. x 5 in. (110.5cm. x 17.8 cm x 12.7 cm)
RECEIVER
Operating Voltage 9V (2 alkaline or 2 lithium batteries)
Battery Life 60 hrs, alkaline (on & off usage @ 70F)
120 hrs, lithium (on & off usage @ 70F)
Audio Output Approx. 40 Hz idling tone from speaker Frequency of pulsing tone
(increases or decreases) with signal intensity
Weight 2.64 lb. (1.20 kg.)
Operating Temp -13°F to 140°F (-25°C to 60°C)
Overall Length 42.3 in. (107.4cm.)
Waterproof Length 34.5 in. (87.6 cm.)
Nominal Sensor Spacing 20 in. (50.8 cm.)
(Specifications subject to change without notice)
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NOTE
The receiver’s manual gain feature gives you a significant advantage in being able to
adjust the sensitivity, based on your expertise, to optimize the locating and pinpointing
of a wide range of underground targets.
You will find that as your experience in evaluating the audio indications associated with
different types of targets and gain settings increases, manually adjusting the gain also
becomes second nature. This minimizes search time and helps you to determine the
type of target and its approximate depth. Your familiarity with various gain settings for,
and the audio indications from specific types of targets will become very cost effective
and personally satisfying.

Section II
Magnetic Locating Mode
Theory of Operation
In the Magnetic (MAG) mode, the MAC-51Bx receiver responds when the magnetic field strength at the two sensors,
which are 20 inches apart, is different. This response consists of a change in the idling frequency of the audio signal
emitted from the speaker.
Figure 2-1 illustrates an application of the locator in which it is used to detect an iron pipe marker of the type used for
property identification. The magnetic field of the marker is stronger at sensor Athan it is at sensor B. As a result, the
frequency of the signal from the speaker is higher than the 40 Hz idling frequency which exists when the field strength is
the same at both sensors.
Figure 2-1. Detecting Magnetic Field of an Iron Marker
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Mode Selection and Gain Setting
Set the Mode switch to MAG and adjust the Gain control for the normal range as shown in Figure 2-2.
In most areas the locator can be oriented in any direction without producing a significant change in the frequency of the
tone from its idling rate. However, in some areas where magnetic disturbances are encountered from nearby structures,
rocks, sand or ferrous trash, the control should be adjusted for a lower gain as illustrated in Figure 2-3.
Figure 2-2. Normal Range Gain Setting
Low Gain Operation
Unwanted background signals due to nearby magnetic objects may require that the effective range of the locator be
reduced. This is accomplished by turning the Gain control towards LO. Reduced range is also useful for pinpointing the
location of a strongly magnetized marker (see Figure 3-2).
Figure 2-3. Low Range Gain Setting
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High Gain Operation
The effective range of the locator is increased by turning the Gain control towards HI. A high gain setting is useful for
detecting smaller targets. Due to the increased sensitivity with high gain, the pitch of the output tone may vary due to
the instrument’s orientation relative to the Earth’s magnetic field.
Figure 2-4. High Range Gain Setting
Search Procedure
Set the Gain control for normal operation and hold the
locator just below the large end with the “box” resting
comfortably on the underside of your forearm, as illus-
trated in Figure 2-5. Because the upper sensor is
located near the area where the locator is usually
held, wrist watches may produce unwanted changes in
the signal frequency. Therefore, a watch worn on the
wrist of the hand holding the locator should be
removed. Avoid bringing the locator close to your
shoes, since the might contain magnetic material.
To obtain maximum area coverage, the locator should
be swept from side-to-side with the small end of the
instrument kept close to the ground. A higher
frequency tone from the speaker will be heard when
the locator is closest to an iron or steel object.
When using a high Gain setting, avoid turning the
locator about its long axis. This might produce
unwanted variations in the output signal. The pres-
ence of a ferromagnetic object will be indicated by a
change in the tone of the output frequency.
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Figure 2-5. Searching with the Locator

Section III
Magnetic Locating Mode Application Notes
Basic Signal Patterns
Figure 3-1. Signals from Vertical and Horizontal Targets
After you have detected the presence of a target, hold the locator vertically and move it back and forth in an “X” pattern.
The peak signal occurs directly over a vertical target, and over the ends of a horizontal target. Reduce the gain setting
as required to facilitate pinpointing a target.
The “X” pattern is ideal for pinpointing small objects. A standard 1-1/4 inch PK nail buried up to 12 inches can be
located so precisely with this technique that it can be uncovered using a 1/2-inch star drill.
Figure 3-2. “X” Pattern Provides Precision Locating
If you find more then one signal in the vicinity of a target, just raise the locator several inches higher (this has the same
effect as reducing the gain). Any signal that disappears when the locator is raised is probably not coming from the
actual target. The signal from a rusty bolt or other small item will decrease much faster with distance than the signal
from a larger target such as a corner marker. An 18-inch length of 3/4-inch pipe can be located at depths up to 9 feet.
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SIGNAL FOR A
VERTICALLY
ORIENTED
TARGET - GREATEST
OVER TOP
SIGNAL FOR A
HORIZONTALLY
ORIENTEDTARGET -
GREATEST OVER ENDS