NARDA NBM-550, Operating Manual

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5 Measuring with the NBM-550 and HF probes
44
NBM-550 Narda
5.1 Avoiding measurement errors
The measurement result can be falsified by external
influences when measuring electromagnetic fields.
Considerable measurement deviations can occur under
certain circumstances, particularly when measuring low
field strengths. The following tips may be of assistance in
recognizing sources of interference so as to avoid
measurement errors. The following factors can affect the
measurement result:
• Electrostatic charges
• Changes in temperature
• Strong low frequency fields (e.g. due to high tension
lines)
Electrostatic charges
The following effect will be noted with all field strength
meters: If you move the probe quickly, excessive field
strength values will be displayed which do not reflect the
actual field conditions. This effect is caused by electrostatic
charges.
The NBM has been designed in a way that minimizes this
effect. However, if you move the probe very quickly, field
strengths on the order of a few V/m can be displayed.
Recommendation:
Hold the device steady during the measurement. Delete the
stored maximum values and average values by pressing
Clear
before using the
Max
,
Average
or
Max Average
result types. Do not touch the probe at any time during the
measurement.
Changes in temperature
Ambient temperature changes as well as warming by direct
sunlight will create offset voltages that may impact the
measurement result. Zeroing eliminates offset voltages
within the instrument only. Offset voltages caused by the
probe or the probe connector can not be eliminated.
Particularly probes with thermocouple sensors are affected
by offset voltages until stable temperature conditions are
achieved.