Measurement Computing ZonicBook 618E rev.3.4 - Manual (Page 82)

10-4 CE-Compliance & Noise Considerations 878196 ZonicBook/618E User’s Manual
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. Required for CE Compliance. Ensure that the
chassis of the primary data acquisition device, e.g., ZonicBook/618E is connected to earth
ground. This practice: (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.
Details regarding how to connect the ground-line are provided in the document entitled
Ethernet CE Kit Installation Instructions (p/n 1077-0901). A copy of the document follows.
• Use short Ethernet cables. The use of short Ethernet cables will reduce noise. The shorter
the cable the better.
• Use shielded cables. Loose wires are effective antennae for radio frequency pickup and can
form loops for inductive pickup. The use of properly connected shields will greatly reduce
such noise.
• 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. Power supply switch transients can vary in strength and frequency.
Ethernet cables can radiate digital switching noise. For these reasons route the power supply
and Ethernet cables such that they are as far as possible from analog lines. By analog lines
we mean both the analog channel input lines on the front panel and the analog expansion
(optional WBK18 expansion) on the rear panel.
• Use ferrite inductive collars. Required for CE Compliance. A clamp-on ferrite collar is to
be secured on both ends of the Ethernet cable and on the DIN5 end of the power supply cable
[and/or near the DC power source]. The collars on the Ethernet cable will reduce digital
switching noise. The ferrite inductive collars will not reduce the integrity of the Ethernet
channel if the system is making use of shielded Ethernet cables, IOtech part number CA-242.
A properly placed ferrite collar(s) on the power cable will reduce power supply switch
transients.
Note that the Ethernet CE Kit, discussed in the following section, includes three ferrite
collars.