Goldak 720 Manuale utente

CONTENTS PAGE NO.

A. General Description . . . . . . . . . . . . . . . . . . . . . . . .1

B. Operating Procedures . . . . . . . . . . . . . . . . . . . . . . .3

1) Mechanical Adjustment . . . . . . . . . . . . . . . . . .3

2) Electronic Adjustment . . . . . . . . . . . . . . . . . . .3

C. Notes and Suggestions . . . . . . . . . . . . . . . . . . . . .6

D. Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

E. Servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

A) General Description:

The Model 720 Valve Locator is a portable, solid-state, electronic

detection instrument. It is used by municipalities, water and gas

utilities, contractors, maintenance people, and others to locate valve

caps, boxes, valve risers, manhole covers, etc. The major parts of

the Model 720 are: (see Figure 1)

1. The Detection Head

2. The Head Swivel

3. The Telescoping Handle

4. The Control Box with:

a. Built-In Speaker

b. Indicating Meter, Signal Strength and Battery Condition

c. Sensitivity Control/On-Off Switch

d. Battery Test Push-Button

e. Headphone Jack

5. Pistol Grip

6. Battery Supply

Model 720/820-S Valve Locators

The Model 820-S Valve Locator is a simplified version of the 720

with the same general detection capabilities. It uses a fixed-

length (non-telescoping) handle and on the control box uses only

a speaker and a sensitivity control. The 720/820-S DETECTION

HEAD is a sealed metallic foils to either the top or bottom surface

of the detection head. The star decal on the detection head is the

center of sensitivity when sweeping an area to detect valve caps,

etc.

The detection head SWIVEL and the TELESCOPING HANDLE

(720 only) are mechanical fittings to enable the operator to place

the instrument in a comfortable position for searching.

On the control box, the SENSITIVITY, “ON-OFF” KNOB is the

key to the successful operation of the instrument. It is used to

turn the instrument on, to control the sensitivity, and to compen-

sate for uneven terrain, mineralized ground, etc.

The SPEAKER (720 only) produces a tone that enables the

operator to pinpoint buried manhole covers, valve caps, etc.

(The optional headphones on the 720 do the same thing.)

The METER on the 720 has several functions. It is an indicator to

assist the operator in properly adjusting the instrument. It quickly

“tells” the operator if a buried valve cap or other metallic object

has been detected, and in conjunction with the BATTERY TEST

BUTTON it shows the condition of the batteries.

The HEADPHONE JACK on the control panel of the 720 is used

if headphone operation is preferred. When the pone plug is

pushed into the jack, the speaker circuit is opened automatically

which gives the operator a privacy feature. The instrument sensi-

tivity and operating characteristic are the same in either case. The

PISTOL GRIP is used, of course, to carry the locator. The BAT-

TERY SUPPLY consists of two 9-volt batteries mounted inside

the pistol grip. They can be replaced by simply removing the sin-

gle screw and the plate at the bottom of the pistol grip. Views of

the control panels for the 720 and 820-S instrument are shown in

Figure (1).

B) Operating Procedures:

1. Mechanical Adjustment

a) Loosen the knurled nut (720 only) on the telescoping

handle and extend the detection head to a comfortable

carrying position with the arm extended as shown in

Figure 2A.

b) Keep the extension arm vertical and set the detection

head flat and as low to the ground or pavement as is

practical for sweeping the area.

2. Electronic Adjustment

a) First test the condition of the battery supply. Turn the

unit “ON” by turning the SENSITIVITY/ON-OFF

control know clockwise unit until it clicks on. Now

push the BATTERY TEST PUSH-BUTTON and

observe the METER. A reading anywhere in the green

shows that the battery supply is OK.

b) With the unit “ON” and with the DETECTION HEAD

away from any mental objects slowly turn the control

clockwise. For the first one-quarter of a turn there will

be no tone from the speaker and the meter will stay at

zero. As the control is advanced a full tone or signal

will be heard from the speaker. The meter needle will

move quickly to the full-scale position as the speaker

and meter always track together.

Model 720/820-S Valve Locators

c) To “tune” the instrument for maximum sensitivity, set

the detection head flat and as low to the ground as is

practical (see section B1-b on page 2).

d) The correct operating point is with no tone (meter set

at zero) but it must be at the edge of the signal. In

other words, no sound, but any clockwise turn of the

control will immediately bring in the signal.

It should be mentioned that if an attempt is made to

locate a valve cap or some other buried metal object

with the sensitivity Control too low or too far into the

“dead” area, then the instrument will be very weak and

insensitive. Of course, if the control is advanced too far

during the initial tuning and a signal is constantly pres-

ent, then there will be no charge when the detection

head is carried over a manhole cover, buffalo box or

valve cap.

e) IMPORTANT: Remember; tune (or adjust) the instru-

ment with the detection head at the distance above

the ground that it is to be carried. Do not hold it a foot

or two above the ground while turning and then lower

it to the operating position. This will reduce the sensi-

tivity or cause false signals.

f) Now sweep the area keeping the detection head flat

and at a constant distance above the ground. (See

Figure 2A)

g) Follow the same rules when attempting to spot an

electrical outlet box or other metal objects behind

walls: (See Figure 2B)

1) Set the detection head close to the wall and parallel

to it.

2) Find the “dead” area and very slowly turn the knob

clockwise until the signal is just ready to appear.

3) Now “sweep” the wall keeping the distance from

it the same.

Model 720/820-S Valve Locators

h) To localize or pinpoint a valve cap or other object that

has been detected and is producing a full signal, slowly

decrease the sensitivity (turn control counter-clockwise)

without moving or removing the detecting head. At

some point the tone will disappear. Now turn it back

up only enough to bring the signal back in. Slowly

move the detection head away. The signal is weak now

(because the sensitivity control is turned down) so very

quickly as the head is moved away the signal will

disappear. Eventually as the head is moved back and

forth, while reducing the sensitivity control, a point will

be reached where the signal “peaks” or is very narrow.

This is the pinpointing operation and the metal object

being detected will be directly under the star decal on

the detection head.

C) Notes and Suggestions:

1. Remember when initially tuning the instrument to try to

find a spot that is relatively free of metal. If it is difficult to

adjust and signals seem to be very strong, move away a

few feet and try it again.

2. If the terrain is uneven and the detection

head must be raised and lowered during the sweep

operation be aware of the fact that false signals may

occur. Particularly if the instrument is very sharply tuned.

To solve this problem it is suggested that the detection

head be raised to clear the terrain as the area is covered.

This will result in a slight loss of sensitivity.

3. During the tuning procedure the operator is actually

compensating for mineralization or conductivity of the

earth at that particular point. Different areas have different

amounts of mineralization and must be “tuned out” at

each locating site. If this were not so, then the instru-

ments could be tuned and locked at the factory. On some

rare cases the conductive mineral content of the earth is

so high that the sensitivity control must almost be turned

off to find the dead spot for proper tuning. This, of course,

will reduce sensitivity.

4. Check the battery supply frequently. The test can be done

quickly and easily while the instrument is being used.

Even though tuning is usually possible, low battery volt-

ages will result in low sensitivity.

D) Maintenance:

1. Both the 720 and 820-S employ solid-state circuitry and

they use no adjustable tuning coils so routine mainte-

nance is limited to occasional battery replacement. Two

transistor-type 9-Volt batteries are used and Figure 3

shows where they are located and how they are mounted.

Since the cost is very low it is our suggestion that both

batteries be replaced at the same time. Remove the small

screw holding the plate in place at the bottom of the

pistol grip. Disconnect the snaps, discard the old batter-

ies, install the new ones and reassemble.

Model 720/820-S Valve Locators

E) Servicing:

Should the Model 720 or the Model 820-S Valve Locator

require repair or servicing aside from normal product mainte-

nance, we suggest that you contact the factory at the

following address:

Goldak, Inc.

15835 Monte Street, Unit 104

Sylmar, CA 91342

Phone: 818-367-0149

Fax: 818-833-7694

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