6
NL
Safety Precautions
Refer to
Safety Precautions for All Limit Switches
.
Make sure that the antenna does not come into contact
with the human body, otherwise an electric shock may
be received.
Antenna Grounded through Sensing Object
<Size of Sensing Object>
•
Grounded Object
If the sensing object is the following grounded conductor, its size
will not affect the operation of the NL. Check for the presence of
insulators sticking to the sensing object or the corrosion of the
sensing object, however, so that the ground resistance will not
exceed 3 k
Ω
.
Contact with Grounded Conductor
The sensing object is equivalently grounded through ground resistor R.
R: 3 k
Ω
max.
The sensing object must not come into contact with the human body.
•
Non-grounded Object
If the sensing object is the following non-grounded conductor, the
NL will operate if the capacitance between the sensing object and
the ground is 100 pF or more. The larger the surface area of the
sensing object is, the higher its capacitance will be. The shorter the
distance between the sensing object and the ground is, the higher
the capacitance will be. Furthermore, the capacitance greatly
varies with the ground condition (e.g., dry sand, concrete, or wet
soil).
Contact with Non-grounded Conductor
The sensing object is equivalently grounded through capacitor C.
C: 100 pF min.
<Conditions of Sensing Object>
•
The detection of conductors (e.g., iron, stainless steel, aluminum,
and brass objects) poses no particular problem. A conductor
coated with paint cannot be detected, however, because there is no
electrical continuity between the antenna and the conductor.
•
Non-conductive objects (e.g., plastic, ceramic, glass, and cloth
objects) can be detected by grounding them indirectly.
Antenna
<Shape and Extension>
If a metal plate is used as an antenna by connecting it to the built-in
or separated antenna of the NL, the surface area of the metal plate
must be 200 cm
2
maximum. The antenna can be extended, provided
that the total length of the antenna is 1 m maximum and that the
bottom of the antenna is at least 10 cm away from the ground. Refer
to the illustrations below.
Antenna Connection
To connect a suitable antenna to the high-frequency coaxial cable of
the NL
@
-S, perform the following steps.
Braided Shield
•
The shield is connected to the casing of the NL. Pay the utmost
attention so that the conductor connected to the antenna will not
come into contact with the shield. Secure the shield with insulation
tape.
•
If the antenna cable needs to be extended, use the separated
antenna model. Do not use a standard cable in place of the high-
frequency coaxial cable.
CAUTION
Precautions for Correct Use
3 k
Ω
max.
R
Grounded
conductor
100 pF min.
Generally, the conductor will
be detectable if the ambient
humidity is 60% to 70%RH and
the surface area of the conductor
is approximately 300
×
500 mm.
C
Non-grounded
conductor
NL
Fig. 1
Metal plate
200cm
2
max.
NL
NL
10 cm min.
1 m max.
Ground
Fig. 2
Fig. 3
+ ---
≤
1 m
5
6
6
4
3
2
1
1
Antenna
High-frequency
coaxial cable
Screwing (I)
Screwing (II)
Antenna
High-frequency
coaxial cable
High-frequency
coaxial cable
Soldering
Antenna
Insulation tape
Braided shield
Conductor
Incorrect
Correct
NL
Standard cable
High-frequency coaxial cable
NL (separated
antenna model)
Antenna
Installation
Installation
