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Interaction Between Power Frequency Electric Fields and RF Survey Meters:
Test Protocol and Evaluation of Commercial Meters
Article in IEEE Transactions on Power Delivery · November 2007
DOI: 10.1109/TPWRD.2007.905585 · Source: IEEE Xplore
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2508
IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 4, OCTOBER 2007
Interaction Between Power Frequency Electric Fields
and RF Survey Meters: Test Protocol and Evaluation
of Commercial Meters
Robert G. Olsen, Fellow, IEEE, Richard A. Tell, Senior Member, IEEE, and H. Kenneth Westby, Senior Member, IEEE
Abstract—A radio-frequency (RF) survey meter is often used to
evaluate the safety of human exposure to RF electromagnetic fields.
However, erroneous meter indications occur when the meters are
used in strong, 50/60 Hertz, super low frequency (SLF) electric
fields near electric power facilities. Previously, coupling between
an SLF electromagnetic field and a simple RF survey meter has
been studied. It was shown that SLF coupling can be large enough
for typical electric field values found near power facilities to result
in significantly erroneous readings. In this paper, a protocol for
testing commercial meters is developed. Tests using this protocol
indicate significant potential for erroneous readings near electric
power facilities. Methods to mitigate this problem are discussed.
Index Terms—Electric field measurement, electromagnetic
interference, occupational health and safety, power transmission
line.
NOMENCLATURE
FCC
MPE
RF
SLF
TEM
VHF
Federal Communications Commission.
Maximum permissible exposure.
Radio frequency.
Super low frequency (30–300 Hz).
Transverse electromagnetic.
Very high frequency (30–300 MHz).
I. INTRODUCTION
I
N recent years, communications antennas have been installed on high voltage transmission line towers. Because
of this, transmission line workers are exposed not only to the
expected 50/60 Hz electric and magnetic fields, but also to
radio frequency (RF) electromagnetic fields from the antennas.
As a result, concern about how to properly evaluate worker
safety in the combination of extremely low frequency (SLF,
e.g., 50/60-Hz) and RF electromagnetic fields has been raised.
Assessments of human exposure to RF electromagnetic fields
are often accomplished via direct measurements as opposed to
Manuscript received July 20, 2006; revised October 22, 2006. This work was
supported by the EPRI under Contract EP-P12042C5979. Paper no. TPWRD00398-2006.
R. G. Olsen is with the School of EECS, Washington State University,
Pullman, WA 99164-2752 USA (e-mail: [email protected]).
R. A. Tell is with Richard Tell Associates, Inc., Colville, WA 99114 USA
(e-mail: [email protected]).
H. K. Westby is with the Bonneville Power Administration, Vancouver, WA
98664 USA (e-mail: [email protected]).
Digital Object Identifier 10.1109/TPWRD.2007.905585
theoretical calculations [1]. Given the need for these measurements, instruments to measure RF electromagnetic fields for the
purpose of evaluating safety of human exposure to these fields
have been developed. One example is an RF survey meter that
is used for measuring RF electromagnetic fields throughout a
volume of space occupied by a human.
It has been noted, however, that erroneous meter indications
of the RF electromagnetic field strength occur when broadband
RF survey meters are exposed to strong (typically 1–20 kV/m)
SLF electric fields near power transmission lines [2]–[4]. Such
interference usually results in significantly higher indications
of RF electric field strength than those that actually exist. This
result should not be surprising since SLF electric fields near
power lines can have magnitudes as much as 80 dB larger than
the RF electric fields (typically 100 mV/m to 100 V/m) that
are the target of the measurement [5]. It should be clear that
this significantly stronger SLF field makes the RF measurement
problem difficult.
II. THEORY
A. RF Survey Meter
Most RF survey meters consist of a probe (one or more short
dipoles or small loops), a readout unit and a transmission line
that connects (or isolates) them in appropriate frequency ranges.
A dipole probe responds to the electric field component parallel
to its length while a loop probe responds to the magnetic field
component perpendicular to its area. An example of a simple
dipole probe measurement system is shown in Fig. 1. For this
case, a voltage proportional to the vertical electric field is developed across the probes’ terminals. This voltage is then rectified
by the diode connected across the same terminals. The dc component of the rectified voltage increases with the amplitude of
the incident electric field (at a quadratic or linear rate) and is
used as a surrogate for the electric field that is being measured.
The probe is normally physically separated from the readout
unit in order that the measured field at the probe not be significantly perturbed by the observer’s body (i.e., to isolate the
probe from the observer’s body) [6]. It is not satisfactory to use
a standard conductive transmission line to do this because it can
interact with the field being measured and, hence, may unintentionally “pick up” some of the field and/or perturb the field
at the probe. To resolve this problem, the transmission line is
designed using a highly resistive wire that (at RF) is essentially
transparent to the field [6], [7]. With this modification, the probe
may be substantially isolated from the observer’s body at RF.
The other useful property of the resistive wire transmission line
0885-8977/$25.00 © 2007 IEEE
OLSEN et al.: INTERACTION BETWEEN POWER FREQUENCY ELECTRIC FIELDS AND RF SURVEY METERS
Fig. 1. Simple broadband RF electric field survey meter and the environment
in which it is used.
Fig. 2. Construction of a typical 3-axis electric field probe . Only two of the
three probe elements are visible.
is that it acts as a low pass filter and hence passes the dc component of the rectified voltage across the diode to the measurement electronics in the readout unit with essentially no attenuation. Unfortunately, the resistive wire also allows significant
SLF voltages and currents to pass and hence is partially responsible for the SLF interference problem [8]. In summary, the resistive transmission line isolates at RF but connects at dc and
SLF.
Commercial RF survey meters usually have three orthogonal
probes so that the probe will respond to all three spatial components of the (electric or magnetic) field. An example is shown in
Fig. 2. The outputs of these probes are combined (rms or square
root of the sum of the squares) so that the total probe output is
reasonably isotropic (i.e., independent of the orientation of the
probe).
It is important to note that the meter exists in an environment that includes the RF electromagnetic field, the earth, the
observer, and (because the purpose of this paper is to evaluate
its response to SLF fields) a source of SLF fields. In Fig. 1, the
source above the probe is assumed to be a single-phase power
line above ground with a ground return but in general the source
could be any combination of power lines.
At RF it is usually reasonable to assume that the probe is
isolated from its environment (as argued earlier) and that the
readout unit can be represented as a simple input impedance
2509
Fig. 3. Induced 50/60-Hz currents with stray capacitances and observer effects
identified.
that terminates the two wire resistive transmission line. In previous work [5], however, it was shown that the environment in
which the meter was located was essential to understanding the
50/60-Hz electric field coupling to the device. More specifically
it was shown that unequal currents can be induced on the “relatively long” resistive transmission line by 50/60-Hz electric
fields parallel to it and that this results in an extraneous voltage
across the diode and (since the transmission line passes SLF
signals) hence the input terminals of the readout unit shown in
Fig. 1.
To understand how this coupling occurs, consider the system
shown in Fig. 3. In this figure, a linear circuit (i.e., the diode
is eliminated) is shown that is used to calculate the SLF currents and voltages responsible for interfering with the RF survey
meter’s operation. This circuit includes the source of 50/60-Hz
voltage between earth and the power line and several paths by
which the current can return to the earth. These return paths involve capacitances between the power line and the probe/transmission line as well as parallel paths to the earth through capacitance of the probe/transmission line to earth, the readout unit to
earth and the observer’s impedance to earth. These return currents would not be a problem if the current induced on each
of the two resistive wires was identical since the voltage
would be zero. But the unbalanced termination of the transmission line at the readout unit (i.e., one side connected directly
to the readout unit’s case and the other connected through the
input impedance) leads to unequal currents on the two wires and
. This time-varying voltage is
hence to a nonzero value for
then rectified by the diode and leads to an extraneous dc (as well
as an SLF) voltage at the readout unit’s terminals. Note that,
since the SLF electric fields can be as much as 80 dB larger
than the RF electric field, even a small unbalance in these currents can lead to a significant amount of interference.
Note that the observer is an important part of the circuit. In
fact, the observer’s impedance appears in parallel with the high
impedance parallel capacitive path from the readout unit case to
ground and can in many cases be the limiting impedance.
The amount of “pickup” is proportional to both the amplitude
of the 60-Hz electric field parallel to the resistive wire transmission line and to the length of the resistive wire, and is summarized below.
• In power transmission and distribution line environments,
50/60-Hz electric fields can be as much as 80 dB higher
than the RF electric fields being measured by an RF survey
meter. Thus, even small 50/60-Hz coupling effects can be
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 4, OCTOBER 2007
over the range of bus voltages available. Since vertical electric
field strengths at 1 m above ground level under 500 kV transmission lines are typically less than 10 kV/m [1], the range of
electric fields available under the bus in the laboratory is comparable to that expected when using these meters under high
voltage transmission lines at ground level.
C. RF Testing Apparatus
Fig. 4. Experimental setup with probe on a nonconductive stand.
responsible for noticeable interference with the meter’s operation.
• The 50/60-Hz capacitive coupling to the RF survey meter
causes currents to be induced on the resistive transmission
line.
• The unbalanced input of the readout unit case causes the
50/60-Hz currents to generate an undesired voltage at the
probe’s diode. This voltage is rectified and appears at the
input to the readout unit.
• Observers holding a meter case can increase the “pickup”
because their impedance to ground occurs in parallel with
the very high “stray” capacitive impedance between the
readout unit case and ground.
III. EXPERIMENTAL SETUP
A. Importance of Testing the Entire Measurement System
It is common practice to test RF survey meter probes in a
small test chamber called a transverse electromagnetic (TEM)
cell [9]. When this is done, however, only the probe is being
tested, not the cable and readout unit. As shown earlier, this can
lead to significant uncorrected errors at low frequency. Thus,
the facility used for our tests immersed the entire measurement
system in both the 50/60-Hz and RF electromagnetic fields
B. High Voltage Testing Apparatus
An outdoor high voltage lab was designed and constructed
to expose RF survey meters to an intense 60-Hz electric field
environment. A 230 kV potential transformer (4 kVA, 0–115 V
input) was used to energize 7.0 m of two parallel, connected 7.62
cm diameter conductors separated by 0.38 m and supported 3.7
m above ground. The secondary (low voltage) of the potential
transformer was driven by a 0–245 V, 45 amp variac while the
primary (high voltage) is connected to the bus. A view of this
lab, completely enclosed within a 20 foot tall chainlink fence,
is shown in Fig. 4.
It is possible to make an approximate calculation of the electric field in Fig. 4, but in this study the electric field was measured with a Model EFM 160 (West Stockbridge, MA) SLF
electric field meter. The 60-Hz electric field within 2 meters
above the ground plane was found to be between 0 and 22 kV/m
The RF exposure system consisted of an ICOM IC275A RF
transmitter driving a Mirage B1016 160 watt amplifier that was
connected to a four element vertically polarized Yagi antenna
located 1.3 m above the ground and approximately 2 m from
the location at which RF survey meters were tested. The input
power to the antenna was set so that the incident electromagnetic
, half
field at the test location was approximately 0.5
of the maximum permissible exposure (MPE) limit in the very
high frequency (VHF) band.1 The operating frequency of the
transmitter was set to 144 MHz. This exposure system is shown
in Fig. 4.
D. Pretest Procedure
Before testing any meters, the 60-Hz electric field at 1 m
above ground and under the center of the high voltage bus was
measured to calibrate the electric field against the output voltage
of the potential transformer as measured with a resistive potential divider. Subsequently, the output of the potential divider was
used as a measure of the electric field. The power output of the
amplifier was measured with an inline wattmeter. The antenna
was located on the side of the high voltage bus towards the center
of the yard in order to minimize the effect of reflections on the
field levels at the meter and oriented to minimize reflected fields
at the meter location from the closest part of the fence. The specific point was chosen by measuring the RF field at different
locations and selecting a point at which there was the least spatial variation in the field.
IV. METERS EVALUATED
The majority of instruments evaluated in this project were obtained new, directly from the manufacturers. Requests for loans
of new equipment were made of the manufacturers with the understanding that the instruments would be subjected to a variety of tests for exploring potential 60-Hz interference to RF
instruments interference to their normal operation. It was believed that use of equipment provided directly by manufacturers
would minimize the likelihood of testing defective instruments
that may have been damaged during the course of their previous
use and, hence, would improve the reliability and credibility of
the overall evaluation results. The specific meters used in the
experiment are listed in Table I.
V. EXPERIMENTS
A. Introduction to the Experiments
The purpose of these tests was to document the performance
of commercially available (new and used) RF survey meters in
1The incident field may consist of incident plus reflected waves due to the
fences around the high voltage testing area. This is of no specific consequence
since the probe responds to total incident field.
OLSEN et al.: INTERACTION BETWEEN POWER FREQUENCY ELECTRIC FIELDS AND RF SURVEY METERS
2511
TABLE I
LIST OF METERS EVALUATED.
Fig. 6. Normalized meter reading as a function of the A-1 meter/probe orientation (90 is vertical) in a predominantly vertical 60-Hz electric field.
Fig. 5. PVC pipe apparatus for orienting the RF survey meter with respect to
the (primarily vertical) electric field.
high strength 60-Hz electric fields. Of specific interest were the
effects of meter orientation with respect to the 60-Hz electric
field, 60-Hz electric field magnitude, and resistive transmission
line length on the amount of coupling.
Fig. 7. Normalized meter reading as a function of the A-2 m/probe orientation
(90 is vertical) in a predominantly vertical 60-Hz electric field.
B. Susceptibility as a Function of Meter Orientation (Without
RF)
In the first test, several commercial meters were selected to be
placed in a 60-Hz electric field (i.e., no RF) while the orientation
of the meter with respect to the electric field was varied. The
apparatus used to do this, constructed of PVC pipe, is illustrated
in Fig. 5.
For this test, each meter selected was placed in a 60-Hz electric field that was measured to be 15.8 kV/m in the vertical direcin the horizontal direction (in this case
tion and
horizontal and parallel to the bus). The meter was rotated and
the output noted. Note again that there was no RF electromagnetic field applied for this test. The purpose of this test was to
illustrate the fact that the 60-Hz “pickup” was dependent upon
the component of 60-Hz electric field parallel to the resistive
transmission line.
Since there is a horizontal ( ) as well as a vertical ( )
electric field, the angular dependence will be on the factor
where is the angle with respect to
horizontal. Here, for simplicity, the “expected” result plotted in
Figs. 6–9 is determined by making the following assumptions.
is set to 0 since it is much smaller than
. Second,
First,
. Given
it is assumed that the meter output is proportional to
these assumptions, the “expected” meter output as a function
of the angle (when normalized to its maximum value) should
.
be
The procedure used to test each commercial RF survey meter
was as follows.
Fig. 8. Normalized meter reading as a function of the A-3 meter/probe orientation (90 is vertical) in a predominantly vertical 60-Hz electric field.
1) With the 60-Hz field turned off, the probe/meter was installed on a nonconductive support at an average height of
1 m above the ground plane and under the center of the
high voltage bus (i.e., the same location at which the electric field was measured).
2) The 60-Hz electric field was turned on.
3) The probe was rotated through several steps in angle and
the meter reading was recorded
1) Test of the A-1 Meter/Probe: The results of this test are
shown in Fig. 6. It is clear that the meter reading roughly follows the sine curve as expected. This result is consistent with
the assertion that the meter reading is proportional to the projection of the meters’ resistive transmission line on the electric
field. The reason that the meter reading does not go to zero at
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 4, OCTOBER 2007
presented later. While a shorter probe length may help reduce
low frequency “pickup”, there are other problematic issues such
as operator perturbation of the RF field being measured that may
be significant.
It can be concluded that if the meter is used in a 60-Hz environment, it should be oriented so that the resistive transmission line is perpendicular to the electric field. For points near
the ground 60-Hz electric fields are predominantly vertical, so
the meter and its connecting cable for the probe should be horizontal.
Fig. 9. Normalized meter reading as a function of the B-1 meter/probe orientation (90 is vertical) in a predominantly vertical 60-Hz electric field.
C. Susceptibility as a Function of 60-Hz Field Strength (With
and Without RF)
The procedure used to test the susceptibility of each commercial RF survey meter to 60-Hz electric fields was as follows.
1) With the 60-Hz and RF fields turned off, the probe/meter
was installed on a nonconductive support at a height of 1
m above the ground plane and under the center of the high
voltage bus (i.e., the same location at which the electric field
was measured). For this test, the orientation of the probe and
resistive line was horizontal to simulate the way the meters are
oriented in normal use. A photograph of a typical setup was
shown in Fig. 4.
2) The 60-Hz electric field was turned on and increased
in discrete steps up to the maximum electric field tested
(approximately 15 kV/m). The 60-Hz electric field value and
the output of the meter is noted at each step.
Fig. 10. Experimental setup with probe held by the observer.
0 degrees is that the horizontal electric field is nonzero. It is interesting to note that the ratio of the meter readings (vertical to
horizontal) is approximately 14 while that of the vertical and
horizontal electric fields was approximately 12.
2) Test of the A-2 Meter/Probe: The results of this test are
shown in Fig. 7.
Again, the meter reading roughly follows the sine of the orientation angle except near zero as expected. For this case, the
ratio of the vertical to horizontal meter outputs was 4.
3) Test of the A-3 Meter/Probe: The results of this test are
shown in Fig. 8. In this case the meter reading closely follows
the sine of the orientation angle. For this case, the ratio of the
vertical to horizontal meter outputs was 12.
4) Test of the B-1 Meter/Probe: The results of this test are
shown in Fig. 9.
Although the meter reading generally follows the sine curve,
a note should be made about the response for relatively small
angles. In these cases, the response to the 60-Hz field was not
measurable and hence assigned the value zero. Since the resistive line in B-1 was shorter than those of the other meters, this
result is consistent with the concept developed earlier that the induced voltage on a shorter connection between probe and electronics should be smaller and will be reinforced with data to be
3) Step 2 is repeated with the RF field turned on at a level equal
to one-half of the Maximum Permissible Exposure (MPE)
standard (i.e., 0.5
at 144 MHz). The RF field level
was measured with no 60-Hz electric field present.
4) Steps 2 and 3 were repeated for a meter held by the observer
to determine the effect of the observer on the instrument
output. A photograph that illustrates how this experiment was
done is shown in Fig. 10.
The 60-Hz electric field reported in all of the results to follow
is the vertical (i.e., dominant) electric field. The horizontal electric field to which the meter is responding is approximately a
factor of 12 smaller than this. The meters were tested horizontally since this is the “best” (i.e., minimum “pickup”) orientation
in which they can be used. If the probe was vertical, the results
would have been worse. The vertical electric field was reported
since this is normally the one given when the field is measured
near a transmission line.
1) Tests of the A-1 Meter/Probe: The testing results for the
A-1 meter/probe with the instrument held on a nonconductive
stand and held by the observer are given in Figs. 11 and 12,
respectively.
It is evident that the response of the meter is a quadratic function of the electric field at smaller levels of exposure and a linear
function thereafter. This observation is consistent with the results shown in [8, Fig. 15] when testing the simple probe.
Clearly, the meter reading is affected by the presence of a
60-Hz electric field above approximately 2 kV/m even if the
OLSEN et al.: INTERACTION BETWEEN POWER FREQUENCY ELECTRIC FIELDS AND RF SURVEY METERS
2513
Fig. 11. A-1 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the 144 MHz RF field present. The meter is oriented
horizontally and mounted on a nonconducting stand.
Fig. 13. A-3 meter reading as a function of 60-Hz vertical electric field strength
with and without the RF field present. The meter is oriented horizontally and
mounted on a nonconducting stand.
Fig. 12. A-1 meter/probe reading as a function of the 60-Hz vertical electric
field strength with and without the 144 MHz RF field present. The meter is
oriented horizontally and held by the observer.
Fig. 14. A-3 meter reading as a function of 60-Hz vertical electric field strength
with and without the RF field present. The meter is oriented horizontally and
held by the observer.
meter is mounted on a nonconducting stand. In fact, an electric field above 13 kV/m can produce the same reading as the
RF field by itself. For hand held meters, the 60-Hz field level at
which this occurs is reduced to approximately 9 kV/m. It is also
clear that the observer can have a significant effect on the meter
reading. The difference between 60-Hz only readings with and
without the observer was approximately a factor of two. This
difference was primarily due to an increase in the common mode
current on the resistive transmission line since the observer effect could be “toggled” by having the observer simply touch or
not touch the meter handle when it was mounted on the nonconductive stand. Since the observer did not change position during
this “toggling” (except for a slight movement of the finger), the
body’s perturbing effect on the field (if any) was not a factor.
2) Tests of the A-3 Meter/Probe: The testing results for the
A-3 meter/probe with the instrument held on a nonconductive
stand and the observer are given in Figs. 13 and 14, respectively.
It was initially assumed that since the A-3 probe is a magnetic
field probe (i.e., a loop sensor) it would short out the diode at
SLF and hence not be responsive to 60-Hz fields. However, the
data presented before clearly do not support this. After some
discussion with the manufacturer, it was determined that there
is a capacitor in series with each loop. Hence, the sensor will
not short out the diode at SLF and will be susceptible to 60-Hz
electric field “pickup” observed in our data.
It is also clear that the A-3 probe is even more susceptible
to 60-Hz electric fields than the A-1 probe. More specifically, a
vertical electric field of only 9 kV/m can cause a meter reading
Fig. 15. C-1 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the RF field present. The meter is oriented horizontally
and mounted on a nonconducting stand.
comparable to that of the RF field alone even if the meter is
mounted on an insulating stand. The comparable number for
the A-1 probe was 12 kV/m. Even more notable is the fact that
for 60-Hz electric fields above 2 kV/m, the RF field causes no
change in the meter reading when it is held by the observer.
Finally, this is a good example of how an improperly used
meter might erroneously indicate that the RF fields are well
above the MPE limits even though there is no RF field at all.
In this case an unnecessary RF field mitigation program might
be recommended.
3) Tests of the C-1 Meter/Probe: The testing results for the
C-1 meter/probe with the instrument held on a nonconductive
stand and held by the observer are given in Figs. 15 and 16,
respectively.
2514
Fig. 16. C-1 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the RF field present. The meter is oriented horizontally
and held by the observer.
Fig. 17. C-2 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the RF field present. The meter is oriented horizontally
and held by the observer.
It should first be noted that since the C-1 meter has a frequency response that is shaped like the FCC limits, its output is
in percent of MPE rather than physical units such as mW/cm .
The results shown in the figures shown before indicate that this
probe is somewhat less sensitive to 60-Hz electric fields than
the meters whose results were reported before. For example,
the meter reading for the meter on the insulating stand never
did reach 50% of the MPE for any electric field tested and at a
vertical field of 16 kV/m the RF indication was increased only
40% from 50% to 70%. This result is consistent with the fact that
the resistive transmission line used by Manufacturer C is shorter
than the one used by Manufacturer A and hence less susceptible
to pickup.2 Nevertheless, as expected, an observer held unit is
more susceptible to “pickup.” In fact, the apparent RF field can
be doubled in a vertical 60-Hz electric field of 14 kV/m. This
behavior is consistent with the assumption that the observer’s
impedance to ground causes a greater common mode current
on the resistive transmission line.
4) Tests of the C-2 Meter/Probe: The testing results for the
C-2 meter/probe with the instrument held by an observer are given
in Fig. 17. Above 12 kV, the meter/probe malfunctioned as indicated by a “re-auto zero” message. The test was not repeated with
a nonconductive stand since the results for an observer holding
the meter were relatively immune to the 60-Hz fields.
Note that this meter can be used in several configurations. The
one used for the data of Fig. 17 was without an optional
2The effect of a shorter transmission line on perturbation of the RF field by the
observer was not quantified. In this case, the observer is closer to the observation
point and may perturb the field more.
IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 4, OCTOBER 2007
Fig. 18. B-2 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the RF field present. The meter is oriented horizontally
and mounted on a nonconducting stand.
Fig. 19. B-2 meter/probe reading as a function of 60-Hz vertical electric field
strength with and without the RF field present. The meter is oriented horizontally
and held by the observer with the electronics box just next to the body.
extension cable. With this cable, the meter/probe malfunctioned
at approximately 7.0 kV/m.
5) Tests of the B-2 Meter/Probe: The testing results for the
B-2 meter/probe with the instrument held on a nonconductive
stand and held by the observer are given in Figs. 18 and 19 respectively. Note the log amplitude scale on both of these figures.
It is clear that this meter performs very well compared to the
others in the high 60-Hz field. This is likely due to the fact that
the cable connecting the probe to the electronics is shorter. Of
course, the potential problem with this is that the observer may
be close enough to the probe to perturb the RF field being measured.
The effect of an observer holding the meter with the readout
unit just in contact with the body was investigated. The result of
this test is shown in Fig. 19. Even in this case, there was little
effect of the 60-Hz electric field until the field strength was at 8
kV/m.
6) Testing of A-4 Meter/Probe: The device that was expected
to be the “gold standard” was the A-4 probe with fiber optic
coupling. This was expected since the electronics was self-contained within the probe and no external metallic or resistive cables are used to transfer the output signal to the readout unit.
This device was tested by mounting it on a fiberglass rod and
holding it in the high field region as shown in Fig. 20. The results are shown in Fig. 21.
Recall that the performance of other RF survey meters would
have been worse if their resistive transmission lines were oriented vertically. For the A-4, there is no orientation with respect
to the electric field that is “better” or “worse.”
OLSEN et al.: INTERACTION BETWEEN POWER FREQUENCY ELECTRIC FIELDS AND RF SURVEY METERS
2515
transmission lines. The effect of shorter transmission lines
on field perturbation was not studied.
• A small RF field probe with self-contained electronics and
an output coupled to the readout unit by optical fiber works
well (though not perfectly) in 60-Hz electric fields typically found near power transmission lines.
REFERENCES
Fig. 20. A-4 probe mounted on a fiberglass rod.
Fig. 21. A-4 meter reading as a function of the 60-Hz electric field strength
with and without the RF field present. The meter is oriented horizontally and
mounted on a nonconducting stand.
It is clear that this probe is relatively immune to 60-Hz electric fields. For example, when immersed in a 60-Hz electric field
of 15.7 kV/m, the probe indication of the RF field was approximately 0.05 mW/cm , well below the MPE limit at 144 MHz.
This result is consistent with the fact that it has no resistive transmission line.
VI. SUMMARY
• SLF electric fields associated with power transmission
lines can interfere with RF survey meters used to evaluate
the safety of exposure to RF electromagnetic fields.
• Tests on commercially available meters indicate that 60-Hz
electric fields at levels found near power transmission lines
can cause erroneous readings large enough to exceed established maximum permissible exposures (MPEs) even if no
RF fields are present.
• The electric field that causes erroneous readings is the component parallel to the resistive transmission lines that connects the RF field probe to the readout unit. Thus, this transmission line should be oriented perpendicular to the 60-Hz
electric field for best results.
• The effect is significantly larger if the RF survey meter is
held by an observer rather than mounted on a nonconductive pole.
• Meters with shorter resistive transmission lines are less
susceptible to electric field coupling than ones with longer
[1] FCC, “Evaluating compliance with FCC guidelines for human exposure to radiofrequency electromagnetic fields,” Federal Commun.
Comm., Office Eng. Technol., Washington, DC, 1997, OET Bulletin
65, 97-01.
[2] E. Aslan, “Non-ionizing radiation—measurement methods and artifacts,” in Proc. 39th Annu. Broadcast Eng. Conf., National Association
Broadcasters, Las Vegas, NV, 1985, pp. 645–655.
[3] E. D. Mantiply, “Characteristics of broadband radiofrequency field
strength meters,” in Proc. 10th Annu. Conf. IEEE Eng. Medicine and
Biology Soc., 1988, pp. 889–891.
[4] E. D. Mantiply, “Radiofrequency radiation meter calibration, methods,
and observations,” presented at the RF Radiation and Ultrawide Band
Measurements Symp., Brooks Air Force Base, TX, Feb. 13–16, 1995.
[5] BPA, Electrical and biological effects of transmission lines: A review. Portland, OR, Bonneville Power Administration, 1996.
[6] G. S. Smith, “Analysis of miniature electric field probes with resistive
transmission lines,” IEEE Trans. Microw. Theory Tech., vol. MTT-29,
no. 11, pp. 1213–1224, Nov. 1981.
[7] E. B. Larsen and F. X. Ries, Design and Calibration of the NBS
Isotropic Electric-Field Monitor (EFM-5), 0.2 to 1000 MHz 1981,
Nat. Bureau Std. Tech. Note 1033.
[8] R. G. Olsen and K. Yamazaki, “The interaction between ELF electric
fields and RF survey meters: Theory and experiment,” IEEE Trans.
Electromagn. Compat., vol. 47, no. 1, pp. 86–96, Feb. 2005.
[9] M. Crawford, “Generation of standard EM fields using TEM transmission cells,” IEEE Trans. Electromagn. Compat., vol. EMC-16, no. 4,
pp. 189–195, Nov. 1974.
Robert G. Olsen (S’66–F’92) received the B.S. degree in electrical engineering from Rutgers University, New Brunswick, NJ, in 1968 and the MS and
Ph.D. degrees in electrical engineering from the University of Colorado, Boulder, in 1970 and 1974, respectively.
He is Associate Dean of the College of Engineering and Architecture and the Boeing Distinguished Professor of Electrical Engineering at
Washington State University (WSU), Pullman. He
has been a member of the electrical engineering
faculty at WSU since 1973. During that time, he has been a Visiting Scientist
at GTE Laboratories, Waltham, MA; at ABB Corporate Research, Västerås,
Sweden; and at EPRI, Palo Alto, CA, and a Visiting Professor at the Technical University of Denmark. His research interests include electromagnetic
interference from power lines, the electromagnetic environment of power
lines, electromagnetic wave propagation, electromagnetic compatibility, and
electromagnetic scattering. His work in these areas has resulted in many
publications in refereed journals.
Dr. Olsen is an Honorary Life Member of the IEEE Electromagnetic Compatibility Society. He serves as Technical Editor of the IEEE Electromagnetic Compatibility Society Newsletter, as Technical Paper Committee Chair for the 2006
Portland EMC Symposium and Co–Technical Program Chair of the 2007 EMC
Zurich, Munich, Germany. He is the past U.S. National Committee Representative to CIGRE Study Committee 36 (Electromagnetic Compatibility) and Past
Chair of the IEEE Power Engineering Society AC Fields and Corona Effects
Working Groups. He is also past Associate Editor of the IEEE TRANSACTIONS
ON ELECTROMAGNETIC COMPATIBILITY AND RADIO SCIENCE. His most recent
work has been supported by the Bonneville Power Administration, the Boeing
Defense and Space Group, the Electric Power Research Institute, the National
Science Foundation and the U.S. Navy.
2516
Richard A. Tell (M’69–SM’81) received the B.S. degree in physics and mathematics from Midwestern
State University, Wichita Falls, TX, in 1966 and the
M.S. degree in radiation sciences from Rutgers University, New Brunswick, NJ, in 1967.
Currently, he is President of Richard Tell Associates, Colville, WA. He has 39 years of experience
working on radio-frequency (RF) safety issues, first
at the U.S. Environmental Protection Agency for 20
years where he served as the Chief of the agency’s
Electromagnetics Branch, and since then in his own
scientific consulting business. His specialty areas include RF safety, RF field exposure assessment, antenna analysis, and field measurements. Much of his work
has been in helping clients evaluate compliance with applicable standards and
establish RF safety programs within their companies. His company also produces a line of RF safety signs widely used at antenna sites.
Mr. Tell has been an elected member of the National Council on Radiation
Protection and Measurements and serves as Chairman of Subcommittee 2 of
the IEEE International Committee on Electromagnetic Safety, which has just
published a new Recommended Practice on RF Safety Programs.
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 4, OCTOBER 2007
H. Kenneth Westby (M’06–SM’07) received the
B.S.E.E. degree from the University of Washington,
Seattle, in 1963; and the professional engineering
license from the State of Oregon in 1970.
He was an Electronics Engineer with the Bonneville Power Administration (BPA) from 1963 to
2002. During that time, he was a Lead Engineer for
telecommunications design projects, specializing in
microwave, UHF/VHF radio, fiber-optic systems,
as well as multiplex, wireline communications,
and telephony. He has done extensive work in the
development of RF safety practices for BPA work crews and has conducted
inhouse RF safety training sessions for electrical workers. He has helped
to develop installation standards and safety standards for the colocation of
wireless (cellular and personal communications services) antenna systems
on BPA’s high-voltage transmission-line towers. Currently, he is semiretired,
but continues to be Technical Advisor to BPA for RF safety and other related
topics.