Temperature concerns, Establishing a zero field – NARDA 8718B User Manual

Page 84

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Chapter 14 Probe Zero

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.

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

1 2 . 1

%

S T D

2 7 . 5

M A X

C F

1 . 0 0

A L T

M A X R

M E N U

F R E Q

F1

F2

F3

F4

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