Keithley 2520, Руководство пользователя, Страница: 307 / 329

Model 2520 User’s Manual Measurement Considerations F-23
Electromagnetic Interference (EMI)
The electromagnetic interference characteristics of the Model 2520 comply with the elec-
tromagnetic compatibility (EMC) requirements of the European Union as denoted by the
CE mark. However, it is still possible for sensitive measurements to be affected by exter-
nal sources. In these instances, special precautions may be required in the measurement
setup.
Sources of EMI include:
• Radio and TV broadcast transmitters.
• Communications transmitters, including cellular phones and handheld radios.
• Devices incorporating microprocessors and high-speed digital circuits.
• Impulse sources as in the case of arcing in high-voltage environments.
The effect on instrument performance can be considerable if enough of the unwanted sig-
nal is present. The effects of EMI can be seen as an unusually large offset, or, in the case of
impulse sources, erratic variations in the displayed reading.
The instrument and experiment should be kept as far away as possible from any EMI
sources. Additional shielding of the instrument, experiment and test leads will often
reduce EMI to an acceptable level. In extreme cases, a specially constructed screen room
may be required to sufficiently attenuate the troublesome signal.
External filtering of the input signal path may be required. In some cases, a simple one-
pole filter may be sufficient. In more difficult situations, multiple notch or band-stop fil-
ters, tuned to the offending frequency range, may be required. Connecting multiple capac-
itors of widely different values in parallel will maintain a low impedance across a wide
frequency range. Keep in mind, however, that such filtering may have detrimental effects
(such as increased response time) on the measurement.