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<title>PC1000 Antenna Design Overview</title>
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<td align="right" valign="bottom" bgcolor="#fffff2" colspan="2"><font size="6" color="#000000">PC1000</font><br>
<font size="5"> Antenna Design</font></td>
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<strong> Safety Note</strong></font></p></td>
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<p align="center"><font size="1"> </font></p>
<p align="center"><strong>This overview is meant to illustrate
some basic principles of antenna design - it is not intended to act as a
substitute for the detailed instructions contained in the PC1000
User's Manual.</strong></p>
<p align="center"></p>
<p align="center"><font size="4"><strong>Please read the manual carefully before attempting
an actual installation.</strong></font></p>
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<p> </p>
<p><strong>Antenna Definition</strong> - A rigid conductor, mounted on insulators
and placed around or adjacent to an area to be protected. See the PC1000
<a href="pc1000app.htm">automatic assembly application</a>, for an example of a
typical antenna.</p>
<p> </p>
<p><strong>Mounting Distance </strong>- OSHA Regulation 1910.217(c)(3)(iii)(e)
defines the <strong>Minimum Safety Distance</strong> for mounting an antenna by
the formula below.</p>
<p><font size="1"> </font></p>
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<strong>Formula for Calculating Minimum Safety Distance</strong></font></p></td>
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<td bgcolor="#FFFFc2" align="center"><font color="#FF0000" size="5"><strong>Ds = K(Ts + Tp)</strong></font></td>
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<p><strong><font color="#FF0000">Ds</font> = Minimum
safety distance between antenna and point of operation</strong></p>
<p><strong><font color="#FF0000">K</font> = 63<sup>"</sup>/second (1.6 m/s)</strong></p>
<p><strong><font color="#FF0000">Ts</font> = Total stopping time
of the electromechanical system</strong></p>
<p><strong><font color="#FF0000">Tp</font> = Total response time
of the Proxagard<font size="1">�</font> (0.025 seconds)</strong></p>
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<font color="#000000" size="3"><strong>Example:</strong>
If the mechanical stop time of a machine is 0.3 seconds, then the minimum safety
distance for mounting the PC1000 Proxagard</font><font color="#000000" size="2">�</font>
<font color="#000000" size="3">antenna is 20.475" [20.4785" =
(63"/s)(0.3s + 0.025s)]</font></p></td>
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<p> </p>
<p><strong>Materials</strong> - Antennas may be constructed of metal rod, flat stock,
1/2" or 3/4" copper pipe or 3/4" electrical
conduit; materials must be rugged enough for the environment and
hollow, in order to maximize field.</p>
<p> </p>
<p><strong><a NAME="insulators">Insulators</a></strong> - Any rigid, nonporous insulating material is suitable to
isolate the antenna from ground. The antenna must not touch
ground, and should be kept 4" or more from grounded metal,
if possible. Insulators should be wiped clean regularly, to
insure proper operation. The <a href="Pipe%20Clamps.htm">insulators page</a>
gives prices and specifications on some insulators that are commonly used.
These items may be purchased directly from Gordon, purchased from a plumbing supply
or made by you.</p>
<p> </p>
<p><strong>Sensing Field</strong> - The coupler generates an electromagnetic field
around the antenna elements. This field is sensitive to
personnel, machinery and metal parts. Changes in the field are
detected by the Proxagard<font size="1">�</font> and acted upon
when the preset alarm levels are exceeded.</p>
<p> </p>
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<strong>Field Shape Around a Tubular Antenna Element</strong></font></p></td>
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<td bgcolor="#FFFFc2" align="center" width="300"><strong>This cross-sectional
view of a sensing field around an antenna element depicts the effective
field at the maximum and minimum alarm point settings.
<p>In all illustrations in this section, green is used to depict
the sensing field.</p></strong></td>
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<td align="center" bgcolor="#FFFFF2" height="250"><img src="images/ant1.gif" width="285" height="223"></td>
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<p> </p>
<p>If a single antenna element is not sufficient to guard the
area, two antenna elements may be placed parallel to one another
12" to 24" apart, which creates a strengthened field
between them. When the optimum design and alarm point settings
are achieved, the field between the elements is oblong, with no
"holes" and very little peripheral sensitivity.</p>
<p>At the maximum setting the field may become bulbous and extend
more than a desirable distance from the antenna. At the minumum
alarm setting "holes" can develop in the protective
field. If the unit's alarm setting is at maximum and a
"hole" still exists in the protective field, the
antennal elements must be moved closer together or an additional
element must be added.</p>
<p> </p>
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<strong>Optimum Field Adjustment Between Parallel Antenna Elements</strong>
</font></p></td>
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<td bgcolor="#FFFFc2" align="center" width="350"><strong>There are no "holes" in the
field and there is very little peripheral field sensitivity.</strong></td>
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<p> </p>
<p><strong>Grounded Shields </strong>- Another way to shape the sensing field is to
construct grounded shields adjacent to the sections of the
antenna where an attenuation of sensitivity is required. </p>
<p>Shields can be made of any rigid, conductive material that is
electrically isolated from the antenna and is grounded to the
control unit's electrical ground. </p>
<p>Grounded shields can be employed to shape the sensing field
away from an operator's workstation or the travel path of a
machine component. The field will not extend past the shield, and
will be diminished on the antenna side relative to the size and
proximity of the shield. The closer the shield is to the antenna
element the greater the amount of attenuation. </p>
<p> </p>
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<strong>Effects of Ground Proximity on the Sensing Field</strong>
</font></p></td>
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<td bgcolor="#FFFFF2" align="center" valign="top"><img src="images/ant3.gif" width="269" height="325"></td>
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<td bgcolor="#FFFFF2" align="center" rowspan="2"><img src="images/ant4.gif" width="278" height="417"></td>
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<td width="325" height="25" bgcolor="#FFFF00" align="center" valign="center"><strong>
<font size="2">Safety Note: </font></strong><font size="2">It is extremely important
that the shield and antenna be rigidly mounted and unable to move in relation to
each other or the machine. Failure to observe these design rules can cause a
hazardous condition,nuisance alarms, or both.</font></td>
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<p> </p>
<p>This principle of proximity to ground and attenuation of field
sensitivity is also applicable to any metal machine parts which
encroach on the antenna. It is possible for the attenuation to be
severe enough to open "holes" in the protective field.
One way to counteract this effect is to place an additional
antenna element to reinforce the field in this location. Whenever
possible, the preferred solution is to shape the antenna away
from ground by at least 4", as ground proximity decreases
overall system sensitivity. </p>
<p> </p>
<p><a href="planar.htm" name="planar"><strong>Planar Field Antenna</a> </strong>-
The Planar Field Antenna is a design which employs the principles of
reinforcing fields and shielding to provide a flat sensing
field with no lateral sensitivity and immunity to crosstalk from other
Proxagard<font size="1">�</font> antennas in the vicinity.</p>
<p>This configuration is ideally suited to single point of entry
applications where the operator's controls are in close proximity
to the antenna. A concentrated zone of protection is provided and
unintended alarms by operators or machine movement are avoided by
virtue of the shielding.</p>
<p align="center"><img src="images/ant5.gif" width="585" height="418"></p>
<hr>
<p><font size="5">Summary:</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">The antenna and any shields must be rigidly mounted
to prevent movement relative to each other, the machine and
ground.</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">The antenna must be isolated from ground.</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">The antenna should be mounted no closer than the
derived Minimum Safety Distance, and at least 3 inches up from the
base of the machine.</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">Moving parts should not have excessive influence on the antenna, if
they do shielding may be required.</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">The space between parallel antenna elements must be
filled with field, to insure protection.</font></p>
<p><font size="4"><img src="images/BlueBall.gif" width="25" height="13">Install and test according to the PC1000 manual.</font></p>
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