Rockwell-automation System Design for the Control of Electrical Noise Manual do Utilizador descarregar pdf (Página 95)

Publication GMC-RM001A-EN-P — July 2001

Measuring Noise Reduction Effectiveness 11-5

Measuring AC Circuits

Line voltage AC circuits are more difficult to measure since 50/60Hz

AC waveforms will swamp the noise signals if a standard 10x or 100x

scope probe is used.

Professional noise probes include a 150kHz high-pass filter to

attenuate power frequency signals, but such a filter is easily built

(refer to Figure 11.3).

Figure 11.3

High-pass filter circuit, 150kHz, 1 pole

With this filter installed between a 1x scope lead and the scope input,

AC lines may be examined for noise. The 50/60 Hz waveform will be

reduced to around 200 mV peak.

Note: Note that a 10x probe will attenuate far more than 10x in this

situation and should not be used.

1000 pF

2 kV

Shielded enclosure

BNC plug to scope

BNC socket

from probe

1000 Ω

0.25 W

ATTENTION

To avoid personal injury or damage to equipment,

the capacitor must be rated at 2 kV or higher.

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Rockwell-automation System Design for the Control of Electrical Noise Manual do Utilizador Página 95