Atec Narda-EMR-20-30 User Manual

Page 3

Spatial averaging

The spatial distribution of a field is seldom homogeneous, even

within the confines of a low-reflection absorber chamber.

Measurements at several points within the area are thus needed.

By measuring at different positions, it is also possible to estimate

complete body exposure levels. The root mean square of these

values is required. The EMR-30 makes light work of this. When

set to Spatial Averaging mode, a new measurement is made

simply by pressing a key. The squares of these values are summed

automatically, providing a display of the average field strength

for the area. If the ``Spatialº key is held down, the EMR-30 will

calculate the average for the time that the key was pressed.

All instruments in the EMR range are also equipped with an

averaging function for the 6-minute average specified by the

relevant standards.

Non-directional measurement

Free-space electromagnetic fields are seldom due to a single

source, but are generally the result of several transmitters from

different directions. To be able to correctly determine the radiation

exposure, any measurement must be non-directional, i.e. iso-

tropic. The value measured by an isotropic instrument is also not

affected by the position in which the instrument is used. For these

reasons, the probe of the EMR-20/EMR-30 is fitted with three

sensors which measure the field strength of the X, Y and Z direc-

tions separately. The field strength is calculated by the instru-

ment's processor by summing the squares of the three measured

values. This method has the advantage over conventional analog

summing within the probe that all three sensors can be indepen-

dently calibrated to achieve very high linearity. It also eliminates

dependence on the square-law sensor characteristic which leads

to large measurement errors as it no longer holds true at high field

strengths. Use of this novel, innovative method means that the

EMR-20 and EMR-30 can measure the entire field strength range

from 1 V/m to 800 V/m for the first time using just a single probe.

This simplifies measurement and makes the purchase of

additional probes unnecessary.

PC Transfer Set

If high field strengths are to be measured or long-term monitoring

is required, the measured values can be transferred to a PC or

printer using an optical interface and the ETS-1 Transfer Set.

All products in the EMR range can also be fully remote-controlled

via this interface. The software supplied with the Transfer Set

makes it easy to record the results and then process them using

programs such as Excel. The EMR-30 can, in fact, store up

to 1500 measured values, complete with timestamp and all

parameters, so it is capable of monitoring for a whole day without

needing to be connected to a PC or printer. The results can be

displayed later or read out together with all major parameters by

using the ETS-1 Transfer Set.

The Transfer Set allows independent output of the measured

values, i.e. spatial field strength and the three measurement axes

X, Y and Z.

Zeroing

Normally, an instrument for measuring electromagnetic radiation

requires zeroing every time it is switched on or the temperature

changes, if accurate measurements are to be obtained. Up till

now, the instrument had to be placed in a room where no field

was present in order to zero it. More often than not, such a room

is not available, and the whole procedure is inconvenient. A new

zeroing method is used in the EMR range of products that is fully

automatic and which is also valid even in the presence of high

field strengths. The measurement errors due to inaccurate zeroing

can be excluded as far as the EMR range of instruments is

concerned.

Rugged casing

The casing is specially constructed to withstand shocks and

impacts, to allow use under difficult conditions, e.g. outdoors or

at industrial sites. The basic unit includes anti-slip, impact-

resistant shock protection. All mechanical connections such as

the test probe are designed to withstand rough handling. Practical

details like the tripod bush and built-in stand make the instrument

equally suitable for laboratory applications.