Omega OMB-DAQSCAN-2000 Series Manuale Utente

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., DaqLab/2001 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.  Use a shielded Ethernet cable, e.g., CA-242, to connect the DaqLab or DaqScan 

chassis to the host computer’s chassis. 

 

• 

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 all analog lines.  The 

analog lines include those that connect to P1 on the front panel, as well as those that 

connect to the rear panel via an expansion port, or through the P4 connector.  

• 

Use ferrite inductive collars.  A clamp-on ferrite collar can be secured at each end of 

the Ethernet cable and at both ends of the power supply cable.  The collars on the 

Ethernet cable will reduce digital switching noise.  Note that the collars will not reduce the 

integrity of the Ethernet channel if the system is making use of shielded Ethernet cables, 

part number CA-242.  Ferrite collars on the power cable will reduce the effects of power 

transients. 

 

 

This partial view of the host PC shows the 

Ethernet cable with a ferrite collar.  The 

PC’s connection to the ground-line is also 

visible.

 

This partial view of the data acquisition device 

shows its connection to the ground-line. It also 

shows two ferrite collars, the foremost of which is 

clamped to the power cable.  The background 

collar is clamped onto the Ethernet cable. 

 

7-4     CE-Compliance & Noise Considerations 

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DaqLab/2000 Series and DaqScan/2000 Series