See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/3275911 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 CITATIONS READS 0 698 3 authors, including: Robert G. Olsen Richard A Tell Washington State University Richard Tell Associates, Inc. 154 PUBLICATIONS 2,233 CITATIONS 54 PUBLICATIONS 541 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Book plus power line resonances. View project All content following this page was uploaded by Robert G. Olsen on 31 December 2014. The user has requested enhancement of the downloaded file. SEE PROFILE 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 2510 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 2512 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. View publication stats 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.