Extech Instruments 480846 Manuel utilisateur

User's Guide

RF EMF Strength Meter

Model 480846

480846 V2.3 7/09

Safety Information

CAUTION

•Before making a measurement, check if the low battery symbol ( +) is

shown on the display when the meter is switched on. Replace the

battery if the symbol is displayed.

•In the case of prolonged storage, it is preferable to remove the battery from

the meter.

•Avoid shaking the meter, particularly in the measurement mode.

•The accuracy and function of the meter may be adversely affected by

exceeding the specified limits as well as by improper handling.

DANGER!

•Use caution when working in the vicinity of powerful radiation sources.

•Persons with electronic implants (e.g. cardiac pacemakers) should avoid

powerful radiation sources.

•Observe the local safety regulations.

•Observe the operating instructions for equipment that is used to generate or

conduct electromagnetic energy.

•Be aware that secondary radiators (e.g. reflective objects such as a metallic

fence) can cause a local amplification of the field.

•Be aware that the field strength in the near vicinity of radiators increases

proportionally to the inverse cube of the distance. This means that enormous

field strengths can result in the immediate vicinity of small radiation sources

(e.g. leak in waveguides, inductive ovens).

•Field strength measuring devices can underrate pulsed signals, particularly with

radar signals in which case significant measurement errors can arise.

•All field strength measuring devices have a limited specified frequency range.

Fields with spectral components outside of this frequency range are generally

incorrectly evaluated and tend to be underrated. Before using field strength

measuring devices, you should thus be certain that all field components to be

measured lie in the specified frequency range of the measuring device.

480846 V2.3 7/09

Introduction

This meter is a broadband device for monitoring high-frequency radiation in the range of

10MHz to 8GHz. The non-directional electric field and high sensitivity also allow

measurements of electric field strength in TEM cells and absorber rooms.

The unit of measurement and the measurement types are expressed in units of electrical

and magnetic field strength and power density.

At high frequencies, the power density is of particular significance. It provides a measure

of the power absorbed by a person exposed to the field. This power level must be kept

as low as possible at high frequencies. The meter can be set to display the

instantaneous value, the maximum value measured or the average value. Instantaneous

and maximum value measurements are useful for orientation, e.g. when first entering an

exposed area.

10MHz to 8 GHz Frequency range.

For isotropic measurements of electromagnetic fields.

Non-directional (isotropic) measurement with three-channel measurement sensor.

High dynamic range due to three-channel digital processing.

Configurable alarm threshold and memory function.

Fundamentals

Electromagnetic Radiation

This meter is used to indicate radiated electromagnetic fields. Wherever there is a

voltage or a current, electric (E) and magnetic (H) fields arise. Examples include the

electromagnetic fields from radio broadcasting and TV transmitters.

Electric Field Strength

This is a field vector quantity that represents the force (F) on an infinitesimal unit

positive test charge (q) at a point divided by that charge. Electric field strength is

expressed in units of volts per meter (V/m).

Use the units of electric field strength for measurements in the following situations:

•In the near-field area of the source.

•Where the nature of the electromagnetic field is unknown.

Magnetic field strength (H) :

This is a field vector that is equal to the magnetic flux density divided by the

permeability of the medium. Magnetic field strength is expressed in units of amperes

per meter (A/m).

Power density (S) :

Power per unit area in the direction of propagation, usually expressed in units of watts

per square meter (W/m2) or, for convenience, units such as milliwatts per square

centimeter (mW/cm2).

The characteristic of electromagnetic fields :

Electromagnetic fields propagate as waves and travel at the speed of light (c). The

wavelength is proportional to the frequency.

λ(wavelength) = c (speed of light)

f (frequency)

Near-field is assumed if the distance to the field source is less than three

wavelengths. For far-fields, the distance is more than three wavelengths. In the near-

field, the ratio of electric field strength (E) and magnetic field strength (H) is not

constant, so measure each separately. In the far-field, however, it is enough to just

measure one field quantity, and compute the other accordingly.

480846 V2.3 7/09

Description

Front Panel Description

(1). E-field sensor.

(2). LCD display.

(3). MAX/AVG

cPress this key to scroll through the following:

“Instantaneous”→“Max. instantaneous” →

“Average” →“Max. average”.

(4) key: Press this key to turn the meter on or off.

(5). UNIT

cPress this key to change the units: “mV/m or V/m”

→“μA/m or mA/m” →“μW/m2, mW/m2or W/m2”→

“μW/cm2or mW/cm2””

dPress and hold this key while turning the meter on

to disable the audible sound. The “ ” symbol

will disappear.

(6). TIME ALARM key:

cPress this key to display date and time.

dPress and hold this key while turning the meter

ON to the alarm setting mode, press the SET key

2 times to exit this mode.

ePress this key for 3 seconds to switch alarm

function On or Off.

(7). XYZ Cal key:

cPress this key to change the sensor axis: “All axis” →“X axis” →“Y axis” →“Z axis”.

dPress and hold this key while turning the meter on to switch the device to the

calibration factor setting mode, press SET key to exit this mode.

(8). SET key:

cPress this key to enter the current data and time setting mode. Press again to exit.

(9 - 12). STWX keys : Used to set current date and time, datalogging interval time,

alarm setting value, calibration factor setting value, or recall data.

(10). MEM key:

cPress this key one time to store one data set to memory.

dPress and hold this key while turning the meter on to enter the clear manually

recorded data mode. Press SET key to exit this mode.

(11). READ key:

cPress this key to switch to the manual data reading mode. Press this key again to exit

this mode.

dPress and hold this key while turning the meter on to disable the Auto Power OFF

function. The “ ” symbol will disappear

10 11

480846 V2.3 7/09

LCD display description

(1). : Auto power off function on / off.

(2). : Audible sound function on / off.

(3). MAX: Maximum measured value displayed.

MAX AVG: Maximum average value displayed.

(4). AVG: Average measured value displayed.

(5). +: Low battery indication.

(6). Units : mV/m and V/m : Electric field strength;

μA/m and mA/m : Magnetic field strength.;

μW/m2 , mW/m2, W/m2, μW/cm2and mW/cm2:

Power density

(7). : Measured value displayed as per selected mode and selected units.

(8). : Stored measured value to memory indication.

(9). : Manual data memory mode indication.

(10). : Manual data memory address number (1~99).

(11). ALM: Alarm function on / off or alarm setting indication.

(12). ▲: Displays when the alarm function is on and the instantaneous measured value

exceeds the limit value indication.

(13). : hh : mm : ss Time displayed.

: YY : MM : DD Date displayed.

(14). CAL : Calibration factor indication or setting indication (from 0.20 to 5.00).

(15). Z : Z axis measured value displayed.

(16). Y : Y axis measured value displayed.

(17). X : X axis measured value displayed.

(18). : Analog bargraph of each axis (X,Y or Z) measured dynamic range

indication for observing trends.

12 34

480846 V2.3 7/09

Operation

E-field sensors

The 3-channel sensor is located at the top of the meter. The three voltages generated

by the sensor are fed back to the meter. In far-fields, an E-field sensor is preferable due

to the greater bandwidth. The E-field sensor frequency ranges from 10MHz to 8 GHz.

The meter is a small portable instrument that measures the electric field in the atmosphere of

the sensor’s surroundings. The measurement of the field is done by moving the aerial of the

sensor in the desired measured environment.

A direct wide band measurement is obtained of the field that the measurement sensor is

subjected to. To find the value of the field emitted by a source of interference, simply

point the aerial towards it and get as close as possible (the value of the field is inversely

proportional to the distance of the sensor/emission source). The operator must take care

not to be between the source of disturbance and the zone to be checked. The human

body shields electromagnetic fields. The E-field sensor is isotropic; it does not require

special handling. It measures the field according to 3 axes without the aerial having to

be moved in the 3 planes. Simply point it at the target to make the measurement.

Explanatory notes

Units of measurement

The meter measures the electrical component of the field; the default units are those of

electrical field strength (mV/m, V/m). The meter converts the measurement values to the

other units of measurement, i.e. the corresponding magnetic field strength units (μA/m,

mA/m) and power density units (μW/m2 , mW/m2or μW/cm2) using the standard far-field

formulate for electromagnetic radiation.

The conversion is invalid for near-field measurements, as there is no generally valid

relationship between electrical and magnetic field strength in this situation. Always use

the default units of the sensor when making near-field measurements.

Result modes

The bar graph display always shows each axis (X, Y or Z) the instantaneous measured

dynamic range value. The digit display shows the measurement according to one of four

selectable modes:

•Instantaneous: The display shows the last value measured by the sensor, no symbol

is displayed.

•Maximum instantaneous (MAX): The digital display shows the highest instantaneous

value measured, the “MAX” symbol is displayed.

•Average (AVG): The digital display shows the average value measured, the “AVG”

symbol is displayed.

•Maximum average (MAX AVG): The digital display shows the highest average value

measured, the “MAX AVG” symbol is displayed.

Max. Hold

Average Actual

Max. Average

Field strength

480846 V2.3 7/09

Alarm Limit Value (ALARM)

The alarm limit value is used to monitor the display value automatically. It

controls alarm indication function. The alarm limit value can be edited in the

display V/m unit.

NOTE:Alarm Limit Function is only used for total three axial value comparator.

Setting the units of measurement

Press the UNIT key to step through the units display.

UNIT

X Y X Y

(a)

UNIT

(b)

(d)(c)

X Y

(a). Electric field strength (V/m).

(b). Computed magnetic field strength (mA/m).

(c). Computed power density (mW/m2).

(d). Computed power density (μW/cm2).

Setting the result mode

Instantaneous result mode is automatically set when the meter is turned on.

Press the MAX/AVG key to step through the results displays:

AVG

MAX

AVG

MAX

AVG

MAX

AVG

AVGMAX

MAX

AVG

480846 V2.3 7/09

Setting the alarm limit value (ALM)

2 2

Power off Hold-on+

1. Press key to turn off the meter.

2. Press and hold the TIME ALARM key, then press key to turn on the meter, the

display then shows “ALM” and “▲” (The Alarm setting mode). The four flashing

digits can now be changed.

3. Press ▼or ▼key to increase or decrease the value.

4. Press SET to store the new setting value and exit.

480846 V2.3 7/09

Setting the alarm function on or off

1. Press ALARM key for 2 seconds to switch the alarm function on or off. The “ALM”

and “ ” symbols in the display indicates that the alarm function is on.

2. When the alarm function is on, the display will show “▲” if the instantaneous

measured value exceed the limit value.

Setting the audible sound function off

When the meter is normally turned on, the audible sound function is on.

1. Press key to turn off the meter.

2. Press and hold MAX/AVG key and turn on the meter again to disable the audible

sound, the “ ” symbol will disappear from the display.

Setting the auto power off function off

When the meter is normally turned on, the auto power off function is on.

1. Press key to turn off the meter.

2. Press and hold READ key and turn on the meter again to disable the auto power

off function; the “ ” symbol will disappear from the display.

480846 V2.3 7/09

Making measurements

Important:

If the sensor is moved quickly, excessive field strength values will be displayed which do

not reflect the actual field conditions. This effect is caused by electrostatic charges.

Recommendation:

Hold the meter steady during the measurement.

Short-term measurements

Application:

Use either the “Instantaneous” or the “Max. Instantaneous” mode if the characteristics

and orientation of the field are unknown when entering an area exposed to

electromagnetic radiation.

Procedure

1. Hold the meter at arm’s length.

2. Make several measurements at various locations around the work place or the

interested areas as described above. This is particularly important if the field

conditions are unknown.

3. Pay special attention to measuring the neighboring vicinity for possible radiation

sources. Apart from active sources, those components connected to a source

may also act as radiators. For example, the cables used in diathermy equipment

may also radiate electromagnetic energy. Note that metallic objects within the

field may locally concentrate or amplify the field from a distant source.

Long-term exposure measurements

Location:

Place the meter between yourself and the suspected source of radiation. Make

measurements at those points where parts of your body are nearest to the source of

radiation.

Note: Use the “Average ” or “Max average” modes only when the instantaneous

measurement values are fluctuating greatly.

Alarm function

Use this feature in the “Instantaneous”, “Max. Instantaneous”, “Average” or “Max.

Average” modes.

When the instantaneous measured value exceeds the limit value, a sequence of

warning beeps will sound.

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