TW-7700
Digita l Lin e Tr a cer
Op e ra ting Ma nua l
F I S H E R R E S E A R C H L A B O R A T O R Y
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DESCRIPTION
The TW-7700 Dig ita l Line Tra c e r c o nsists o f a tra nsm itte r, re c e ive r,
g ro und -p la te / g ro und -ro d a sse m b ly, c a rrying c a se (ha rd o r so ft),
a nd a n op e ra tors ma nua l. The TW-7700 is a sing le fre q ue nc y line tra c e r.
The TW-7700 is an active locating line tracer. There
are three methods of active locating that an operator
can use to trace a utility. The con d u ctive method is
the most preferred method, since a strong transmitter
signal is transmitted through the intended target. The
in d u ctive method is the easiest method to use, but
may not yield the best results. When a direct connec-
tion is not available, but the operator has good knowl-
edge of where one point of the utility may be, the op-
erator can place the Transmitter over the utility mak-
ing sure that the arrow on top of the transmitter is
parallel to the path of the utility. The third method of
active locating involves using the cou p lin g cla m p ac-
cessory. The coupling clamp is used when the utility is
exposed, but a direct connection is not available. The
clamp jaws are opened and placed around the utility.
The clamp never makes a direct connection with the
utility, that is, the utility can move freely with the
clamp around it.
The features of the TW-7700 make it a very easy and
practical instrument in today’s world of underground
locating.
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TW-7700 TRANSMITTER
Tra nsm itte r
Located on the transmitter are the power mode and
the accessory output. The power mode enables the
operator to turn the transmitter on or off, and to
check the condition of the batteries. When checking
the batteries, a reading if 50 or greater on the display
meter indicates that batteries are usable.
The accessory output is for the ground plate/ground
rod assembly, and for the coupling clamp. There is a
Red LED light that blinks when the transmitter is
on. The batteries are located underneath a lid on top
of the transmitter housing.
WARNING: Do no t ha nd le o utp ut le a d s unle ss p o we r is o ff.
ELECTRIC SHOCK HAZARD: Se rvic ing to b e p e rfo rm e d b y
q ua lifie d p e rso nne l o nly.
The TW-7700 Tra nsm itte r.
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TW-7700 RECEIVER
Re c e ive r
The TW-7700 Re c e ive r.
Controls
Mod e
This button does not have a function on the TW-7700.
(It allows users of the TW-8800 Multi-Frequency Line
Tracer to change frequencies.)
Powe r On/ Off
Turns the receiver on or off.
Light
Lights up the display for usage in dark areas. When the
display is backlit, LIGHT is shown on the bottom left hand
side of the display screen.
Ba t
Press and hold this pad to check the battery level of the
receiver. A bar graph on the right side of the display will
give status of the batteries. When the graph shows 1 bar,
it is time to replace the batteries. Additionally, as the
operator uses the Receiver, if the batteries get low, RE-
PLACE BATTERIES will appear in the lower area of the
Display screen.
Vol(up )/ Vol(d own)
Increases or decreases the volume of the speaker.
De p th
After determining the centerline of the utility, set the
blade of the receiver on the ground, press and hold this
pad to get the depth to the center of the target.
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TW-7700 RECEIVER
Displa y
Fre q ue nc y Mod e s
The frequency at which the receiver is operating.
<< Le ft/ Ove r Ta rg e t>/ Rig ht>>
Indicates where the receiver is in relation to utility.
Num e ric Disp la y
Serves a dual function:
• Relative signal strength of the transmitted signal (%
shown). Responds in conjunction with the bar graph.
• Depth to the center of the target (when DEPTH pad is
pressed - IN or CM shown)
Light
Indicates the display is lit (activated by pressing LIGHT pad).
Ba r Gra p h
Serves three purposes:
• Responds in conjunction with signal strength.
• Visual indicator for battery test (when BAT pad is pressed).
• Volume loudness indicator (when VOL(up)/VOL(down)
is pressed.
Re p la c e Ba tte rie s
When the receiver batteries fall below a nominal level,
REPLACE BATTERIES will be displayed.
No Sig na l
When no signal is received by the receiver, NO SIGNAL
will display. This response may be due to the transmitter
not being turned on, or the transmitter and receiver not
be set at the same frequency.
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ACCESSORIES
Coup ling Cla m p
The coupling clamp is useful when the utility is exposed,
and a direct connection is not possible. It is plugged into
the same plug-in socket as the ground-plate/ground-rod
assembly. The coupling clamp only operates at the 82
kHz frequency. The coupling clamp will fit around utili-
ties that are 3-¼ inches in diameter or smaller. The length
of the cable is approximately 10 feet.
Coup ling Cla m p Ap p lic a tions Dia g ra m
D. Tra c e sig n a l w ill re tu rn to
A. The c o up ling c la m p is fo r a ll
tra c ing a p p lic a tio ns with c o n-
d uc to rs e xp o se d ; e xc e p tio n, a n
op e n c irc uit a t line ’s te rmina tion.
B. A g ro und m ust b e p ro vid e d fo r
the p ro p e r c urre nt flo w whe n the
c o up ling c la m p is use d a t a te r-
m ina tio n.
C . The c o up ling c la m p m ust b e
u se d b e tw e e n th e g ro u n d in g
a nd whe re the line g o e s und e r-
g ro und .
g ro u n d
w h e n
in c o rre c tly
c o up le d .
E. Sig na l will b e tra nsm itte d in
b o th d ire c tio ns whe n c o nne c t-
ing is mid wa y in a long c ond uc tor.
F. Dro p line s o r la te ra ls d ivid e the
sig na l stre ng th in ha lf a t e a c h
junc tio n.
This re p re se nts a jum p e r
He a d se ts
Fisher Research Laboratory has a variety of headsets avail-
able.
• Ultra-quiet deluxe Fisher Phones. High quality sound
while reducing the outside noise.
• Standard Stereo Headphones
• Single Earpiece Headset. Enables the operator to effec-
tively listen to the TW-7700 and remain aware of noise in
close proximity.
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OPERATING INSTRUCTIONS
The fo llo wing instruc tio ns a re d e sig ne d fo r a sa fe a nd e ffe c tive
m e tho d o f line tra c ing a nd utility a vo id a nc e . So m e o f the ste p s
m a y no t b e a p p lic a b le in a ll situa tio ns. The und e rlying g uid e line is
tha t o p e ra to r sa fe ty m ust b e m a inta ine d a t a ll tim e s. Use o f
sa fe ty e q uip m e nt, e xtra p e rso nne l, a nd up to d a te a s-b uilt p la ns
sho uld b e c o nsid e re d whe n ne c e ssa ry.
INITIAL SCAN
Set-up Transmitter either Inductively or Conductively
Ind uc tive
Be aware of air coupling, the transmitted signal travelling
to the Receiver via the air, not the utility.
Cond uc tive
Connect the ground plate/ground rod assembly to the trans-
mitter. Connect the red lead to the non energized utility. Con-
nect the black lead to the ground plate/ground rod. Place the
plate/rod at a 90 degree angle in reference to the utility. Be
sure not to place the wires over any other utility.
After transmitter set-up, move away from the point of con-
nection (or Induction) about 25 feet (8 meters). Sweep a
circle around the point of connection. Initially, disregard
the LEFT/RIGHT indicator and rely on the signal strength
readout. Make note of the high readings. These are areas
that need to be traced/examined in more detail.
Tra c ing
After locating the point(s) where the signal strength was
the highest, return to that/those points and start tracing
your utility. This is where the LEFT/RIGHT indicator is
very helpful. Swing the receiver from left to right and lis-
ten for the change of tone. When the target is to the RIGHT
of the receiver, the tone is pulsed tone. As the receiver
gets closer to the target, the pitch gets higher. When the
target is to the LEFT of the receiver, the tone is a continu-
ous tone. As the receiver gets close to the target, the pitch
also becomes higher. When the receiver is over the target,
OVER TARGET is displayed on the display screen, and the
tone is at its highest peak sound.
De p th Me a suring
When an OVER TARGET response is displayed, position
the blade of the receiver directly over the utility and
place the tip on the ground. Hold the receiver steady,
press and hold the DEPTH pad. Depth will be measured
to the center of the utility.
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DEPTH ACCURACY
De p th m e a sure m e nt is a fe a ture o f the TW-7700. Ac c ura c y is
d e fine d o n a n id e a l ta rg e t, tha t is, o ne tha t is c o ntinuo us, a
g o o d c o nd uc to r, a nd no t surro und ing b y o the r utilitie s. The re a re
fa c to rs tha t c a n c a use the o p e ra to r to q ue stio n the a c c ura c y
o f the utility b e ing tra c e d .
Ind uc tive Tra nsm itte r Se tup
Inductively, only a small portion of the signal attaches
itself to the utility. With a weakened signal, trace should
be accurate, but depth may not. The conductive method
will yield better results.
Low Re c e ive r Sig na l Stre ng th
When the signal strength falls below 20 – 25%, depth
readout may not be accurate. It would be beneficial to
move the transmitter to a closer point of contact.
Ne a rb y Utilitie s
Close, nearby utilities may have some influence on the
accuracy of the Depth readout. This is more prone to
happen in the higher frequencies where signals can jump
to nearby utilities. Switching to a lower frequency can
give better results.
Moisture
Ground that is too dry or overly saturated may skew the
depth readout.
“T’s”, e lb ows, or sp lits in the utility c a n d istort the
tra nsm itte d sig na l in tha t g e ne ra l a re a .
WARNING: Do no t c o nne c t o utp ut le a d s to a live
(e ne rg ize d ) utility. Ple a se p re ve nt sho c k ha za rd a nd
e q uip m e nt d a m a g e .
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SPECIFICATIONS
Sub je c t to im p ro ve m e nt o r m o d ific a tio n witho ut no tic e .
RECEIVER
Depth Accuracy ...................... +1 inch per foot in nominal condi-
tions
Readout Units ........................ Inches or cm (factory preset)
Left/Right Guidance ............... Audio: continuous tone=Left,
pulsed tone=Right. VCO (varying pitch) output for easy over
........................................... target location. Visual: Left/Right/
........................................... Over Target messages
Signal Strength ...................... Digital Numeric Readout (0-99%)
& Bar Graph
Sensitivity Adjust ................... Automatic
LCD Backlight ........................ Included
Battery Test ........................... Automatic Low Battery alert
Push button readout
Battery Type ........................... Six “C” cells
Battery Life ............................ 80 Hours
Weight ..................................... 5.4 lbs.
Operating Temp ..................... -4 0 to +1400F (-200 to +600C)
TRANSMITTER
Output Frequency .................. 82kHz,
Output Power (nominal) ........ .5Watts,
Battery Test ........................... Yes
Battery Type ........................... Two 6 Volt lantern batteries
Battery Life ............................ 80 Hours
Weight ..................................... 5.0 lbs.
F ish er Resea r ch La bor a tor y d oes n ot w a r r a n t su ita bility to sp ecific u se. F ish er
Resea r ch La bor a tor y sh a ll in n o even t be lia ble for a n y d ir ect, in cid en ta l, con se-
qu en tia l or in d ir ect d a m a ges.
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NOTES
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QUALITY
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Ea c h d e te c to r is ha nd c ra fte d in the USA with p rid e
PERFORMANCE
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se a rc h d e e p e r.
REPUTATION
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o ve r 70 ye a rs, the Fishe r lo g o ha s b e e n a m a rk o f e xc e lle nc e .
2 YEAR WARRANTY
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with a 2 ye a r lim ite d wa rra nty. Wa rra nty m a y va ry o utsid e the
Unite d Sta te s. Se e yo ur d e a le r fo r d e ta ils
SERVICE
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yo u ha ve a ny q ue stio ns o r p ro b le m s, c o nta c t:
FISHER RESEARC H LABO RATO RY
200 W. Willm o tt Rd .,
Lo s Ba no s, CA 93635
Te l 209.826.3292 Fa x 209.826.0416
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EXPORT DEPARTMENT
P.O. Bo x 1896
Ne w Ha ve n, CT 06508 USA
Te l 203.288.1638 Fa x 203.287.8099
e m a il:m b @e xp ortd e p t.c om
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FRL 8708002-A
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