Grounds

Proper grounding lends stability and protection to a data acquisition system. Grounding the data logger with its peripheral devices and sensors is critical in all applications. Proper grounding will ensure maximum ClosedESD Electrostatic discharge. protection and measurement accuracy. It is the easiest and least expensive insurance against data loss, and often the most neglected. The following terminals are provided for connection of sensor and data logger grounds:

  • Signal Ground () - reference for single-ended analog inputs, excitation returns, and a ground for sensor shield wires.

    • 6 common terminals

  • Power Ground (G) - return for 3.3 V, 5 V, 12 V, U or C terminals configured for control, and digital sensors. Use of G grounds for these outputs minimizes potentially large current flow through the analog-voltage-measurement section of the wiring panel, which can cause single-ended voltage measurement errors.

    • 6 common terminals

  • Resistive Ground (RG) - used for non-isolated 0-20 mA and 4-20 mA current loop measurements (see Current-loop measurements for more information). Also used for decoupling ground on RS-485 signals. Includes 100 Ω resistance to ground. Maximum voltage for RG terminal is ±16 V.

    • 1 terminal

  • Earth Ground Lug () - connection point for heavy-gage earth-ground wire. A good earth connection is necessary to secure the ground potential of the data logger and shunt transients away from electronics. Campbell Scientific recommends 14 AWG wire, minimum.

NOTE:

Several ground wires can be connected to the same ground terminal.

A good earth (chassis) ground will minimize damage to the data logger and sensors by providing a low-resistance path around the system to a point of low potential. Campbell Scientific recommends that all data loggers be earth grounded. All components of the system (data loggers, sensors, external power supplies, mounts, housings) should be referenced to one common earth ground.

In the field, at a minimum, a proper earth ground will consist of a 5-foot copper-sheathed grounding rod driven into the earth and connected to the large brass ground lug on the wiring panel with a 14 AWG wire. In low-conductive substrates, such as sand, very dry soil, ice, or rock, a single ground rod will probably not provide an adequate earth ground. For these situations, search for published literature on lightning protection or contact a qualified lightning-protection consultant.

In laboratory applications, locating a stable earth ground is challenging, but still necessary. In older buildings, new ClosedVAC Volts alternating current. receptacles on older VAC wiring may indicate that a safety ground exists when, in fact, the socket is not grounded. If a safety ground does exist, good practice dictates to verify that it carries no current. If the integrity of the VAC power ground is in doubt, also ground the system through the building plumbing, or use another verified connection to earth ground.

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