CR200/CR200X Series Dataloggers - Campbell Scientific
CR200/CR200X Series Dataloggers - Campbell Scientific
CR200/CR200X Series Dataloggers - Campbell Scientific
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Section 7. Grounding<br />
Grounding the <strong>CR200</strong>(X) and its peripheral devices and sensors is critical in all<br />
applications. Proper grounding will ensure the maximum ESD (electrostatic<br />
discharge) protection and higher measurement accuracy.<br />
7.1 ESD Protection<br />
ESD (electrostatic discharge) can originate from several sources, the most<br />
common, and most destructive, being primary and secondary lightning strikes.<br />
Primary lightning strikes hit the datalogger or sensors directly. Secondary<br />
strikes induce a voltage in power lines or sensor wires.<br />
The primary devices for protection against ESD are gas-discharge tubes (GDT).<br />
All critical inputs and outputs on the <strong>CR200</strong>(X) are protected with GDTs or<br />
transient voltage suppression diodes. GDTs fire at 150 V to allow current to be<br />
diverted to the earth ground lug. To be effective, the earth ground lug must be<br />
properly connected to earth (chassis) ground. The power ground and signal<br />
grounds have independent paths to the ground lug.<br />
The 9-pin serial port is another path for transients. Communications paths such a<br />
telephone or short-haul modem lines should be provided spark gap protection at<br />
installation. Spark gap protection is often an option with these products, so it<br />
should always be requested when ordering. Spark gaps for these devices must be<br />
connected to either the earth ground lug, the enclosure ground, or to the earth<br />
(chassis) ground.<br />
A good earth (chassis) ground will minimize damage to the datalogger and<br />
sensors by providing a low resistance path around the system to a point of low<br />
potential. <strong>Campbell</strong> <strong>Scientific</strong> recommends that all dataloggers be earth<br />
(chassis) grounded. All components of the system (dataloggers, sensors,<br />
external power supplies, mounts, housings, etc.) should be referenced to one<br />
common earth (chassis) ground.<br />
In the field, at a minimum, a proper earth ground will consist of a 6 to 8 foot<br />
copper sheathed grounding rod driven into the earth and connected to the<br />
<strong>CR200</strong>(X) Ground Lug with a 12 AWG wire. In low conductive substrates, such<br />
as sand, very dry soil, ice, or rock, a single ground rod will probably not provide<br />
an adequate earth ground. For these situations, consult the literature on lightning<br />
protection or contact a qualified lightning protection consultant.<br />
In vehicle applications, the earth ground lug should be firmly attached to the<br />
vehicle chassis with 12 AWG wire or larger.<br />
In laboratory applications, locating a stable earth ground is challenging, but still<br />
necessary. In older buildings, new AC receptacles on older AC wiring may<br />
indicate that a safety ground exists when in fact the socket is not grounded. If a<br />
safety ground does exist, it is good practice to verify that it carries no current. If<br />
the integrity of the AC power ground is in doubt, also ground the system<br />
through the buildings, plumbing or another connection to earth ground.<br />
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