R E - A U T O - Z E R O

12 . 1 % S T D

27 . 5 M A X C F 1 . 0 0

A L T M A X R M E N U F R E Q

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•Whenever the meter continues to show low-level values and never seems to get back to a zero-field condition, positive zero drift is a possibility. This can be confirmed by shielding the probe to see if the meter goes back to a zero reading. See Shielding the Probe on the following page for suggested methods.

Temperature Concerns

It is important to allow the meter and probe to become conditioned to the ambient temperature before attempting to zero the system. This is especially important when the meter and probe have been transported or stored at a different temperature such as in a vehicle, for example. Diode sensor-based probes require only a few minutes to stabilize. The thermo-couple sensors used in microwave band and ultra broadband probes may require 15-20 minutes to stabilize.

Establishing a Zero Field

It is important to “zero” the probe while the probe is not exposed to a significant RF field level. For accuracy, the field level should be lower than the lowest value that the probe is capable of reading. If previous measurements have indicated that the ambient field level is very low, the probe can be zeroed without shielding. This is often the case in a typical office environment. It is recommended that the ambient field level be at least 30 dB below the full scale measurement range of the probe. When it is necessary to zero a probe in higher field areas, the probe must be shielded.

Chapter 14 Probe Zero

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