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4 Measurement Tutorials
Grounding techniques
The purpose of grounding is to avoid ground loops and minimize noise. Most systems should have at least three
separate ground returns.
1. One ground for signals. You may also want to provide separate signal grounds between high-level signals, low-
level signals, and digital signals.
2. A second ground is used for noisy hardware such as relays, motors, and high-power equipment.
3. A third ground is used for chassis, racks, and cabinets. The AC power ground should generally be connected to
this third ground.
In general, for frequencies below 1 MHz or for low-level signals, use single-point grounding (see image below).
Parallel grounding is superior but it is also more expensive and more difficult to wire. If single point grounding is
adequate, the most critical points (those with the lowest levels and/ or the most precise measurement requirements)
should be positioned near the primary ground point. For frequencies above 10 MHz, use the separate grounding
system. For signals between 1 MHz and 10 MHz, you can use a single-point system if the longest ground return path
is kept to less than 1/20 of a wavelength. In all cases, return-path resistance and inductance should be minimized.
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Keysight DAQ970A/DAQ973A User's Guide
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