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
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