Idiomas disponibles
Idiomas disponibles
4 Measurement Tutorials
Shielding techniques
Shielding against noise must address both capacitive (electrical) and inductive (magnetic) coupling. The addition of
a grounded shield around the conductor is highly effective against capacitive coupling. In switching networks, this
shielding often takes the form of coaxial cables and connectors. For frequencies above 100 MHz, double-shielded
coaxial cable is recommended to maximum shielding effectiveness.
Reducing loop area is the most effective method to shield against magnetic coupling. Below a few hundred kilohertz,
twisted pairs may be used against magnetic coupling. Use shielded twisted pair for immunity from magnetic and
capacitive pickup. For maximum protection below 1 MHz, make sure that the shield is not one of the signal
conductors.
Separation of high-level and low-level signals
Signals whose levels exceed a 20-to-1 ratio should be physically separated as much as possible. The entire signal
path should be examined including cabling and adjacent connections. All unused lines should be grounded (or tied
to LO) and places between sensitive signal paths. When making your wiring connections to the screw terminals on
the module, be sure to wire like functions on adjacent channels.
Source of system cabling errors
Radio frequency interference
Most voltage-measuring instruments can generate false readings in the presence of large, high-frequency signals.
Possible sources of high-frequency signals include nearby radio and television transmitters, computer monitors, and
cellular telephones. High-frequency energy can also be coupled to the internal DMM on the system cabling. To
reduce the interference, try to minimize the exposure of the system cabling to high-frequency RF sources.
If your application is extremely sensitive to RF1 radiated from the instrument, use a common mode choke in the
system cabling as shown below to attenuate instrument emissions.
Keysight DAQ970A/DAQ973A User's Guide
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