Design Guide

ElectroStatic Discharge (ESD) Considerations
A DIVISION OF TRIMBLE
120 Appendix C: Environmental Considerations
Verify R-TNC knurled threaded nuts are tight and stay tight. Donʼt use a thread locking
compound that would compromise the grounding connection of the thread to thread
mate. If there is any indication that field vibration might cause the R-TNC to loosen,
apply RTV or other adhesive externally.
Use antenna cables with double-shield outer conductors, or even full metallic shield
semi-rigid cables. ThingMagic specified cables are double shielded and adequate for
most applications. ESD discharge currents flowing on the outer surface of a single
shield coaxial cable have been seen to couple to the inside of coaxial cables, causing
ESD failure. Avoid RG-58. Prefer RG-223.
Minimize ground loops in coaxial cable runs to antennas. Having the ThingMagic
Nano and antenna both tied to ground (per item 1) leads to the possibility of ground
currents flowing along antenna cables. The tendency of these currents to flow is
related to the area of the conceptual surface marked out by the antenna cable and
the nearest continuous ground surface. When this conceptual surface has minimum
area, these ground loop current are minimized. Routing antenna cables against
grounded metallic chassis parts helps minimize ground loop currents.
Keep the antenna radome in place. It provides significant ESD protection for the
metallic parts of the antenna, and protects the antenna from performance changes
due to environmental accumulation.
Keep careful track of serial numbers, operating life times, numbers of units operating.
You need this information to know that your mean operating life time is. Only with this
number will you be able to know if you have a failure problem in the first place, ESD
or otherwise. And then after any given change, whether things have improvement or
not. Or if the failures are confined to one instantiation, or distributed across your
population.
Raising the ESD Threshold
For applications where full ThingMagic Nano power is needed for maximum tag read
range and ESD is suspected the following components are recommended additions to the
installation to raise the level of ESD the reader can tolerate:
Select or change to an antenna with all radiating elements grounded for DC. The MTI
MT-262031-T(L,R)H-A is such an antenna. The Laird IF900-SF00 and CAF95956
are not such antennas. The grounding of the antenna elements dissipates static
charge leakage, and provides a high pass characteristic that attenuates discharge
events. (This also makes the antenna compatible with the ThingMagic Nano antenna
detect methods.)
Install a Minicircuits SHP600+ high pass filter in the cable run at the ThingMagic Nano
(or Vega or other finished reader) end. This additional component will reduce
transmit power by 0.4 dB which may affect read range in some critical applications.
However the filter will significantly attenuate discharges and improve the ThingMagic
Nano ESD survival level.