Measurement Computing 6222 - Manual (Page 21)

User’s Manual CE-Compliance & Noise Considerations 5-3
Noise Considerations
Controlling electrical noise is imperative because it can present problems even with the best measurement
equipment. Most laboratory and industrial environments suffer from multiple sources of electrical noise.
For example, AC power lines, heavy equipment (particularly if turned on and off frequently), local radio
stations, and electronic equipment can create noise in a multitude of frequency ranges.
Local radio stations are a source of high frequency noise, while computers and other electronic equipment
can create noise in all frequency ranges. Creating a completely noise-free environment for test and
measurement is seldom practical. Fortunately, simple techniques such as using shielded/twisted pair wires,
filtering, and differential voltage measurement are available for controlling the noise in our measurements.
Some techniques prevent noise from entering the system; other techniques remove noise from the signal.
While many techniques for controlling noise in signals provide a means of removing the noise that is
already present, the preferred solution is to prevent the occurrence of noise in the signal in the first place.
The following practices, some of which are required for CE compliance, should be employed to minimize
noise.
Make a solid earth ground connection. Using insulated, low resistance wire, connect the
chassis to solid earth ground. This practice accomplishes the following:
(a) keeps radiated emissions low by keeping the chassis electrically quiet,
(b) keeps potential common-mode voltages low,
(c) improves user safety, and
(d) provides a safe path for Electrostatic Discharge energy back to earth ground.
Minimize ambient EMI. The lower the ambient EMI, the better. Sources of electromagnetic
interference include solenoids, motors, computer equipment, high power distribution wiring,
etc.
Distance cables. Route signal cables away from Ethernet lines, Mains and other high voltage
cables and equipment to minimize signal interference from radiated noise.