Tag Archives: meter

Why A Professional Digital EMF Meter Should Be Used For a Survey

In my previous post, I commented on a recent phenomena this past year in which a number of customers who had purchased an EMF meter online or elsewhere to do a survey on a prospective property contacted me after finding what appeared to be anomalously high readings and wanted a second opinion.

Every time it was a Trifield 100XE which is easily recognizable with the yellow label, brick-like construction and familiar needle movement which distinguishes it as an analog meter versus the digital EMF versions. The variations in accuracy varied from moderate to extreme when compared with my 3-axis professional grade meter and I began to wonder what was going on.

I recently contacted the manufacturer of the Trifields (AlphaLab Inc.) and one of their electrical engineers cleared up the mystery as to why the readings seemed to vary so wildly. The 100XEs are typically sold as frequency weighted which means that even slightly higher frequency magnetic fields will add even more to the indicated reading than a meter with a “flatter” frequency response. Also, they measure from 40 Hz – 100 KHz which is a VERY broad band for an AC gaussmeter used in a EMF survey for testing the influence of power lines. Typically, for measuring 60 Hz and any relevant power harmonics, an EMF meter that measures in the range of 30 Hz – 3 KHz is a broad enough range and even 30 Hz – 300 Hz will cover 60 Hz plus the 5th harmonic. The strength of the harmonics gets progressively weaker as frequency increases.

60 Hz Power Line Harmonics

60 Hz Power Line Harmonics

In other words, you may have a 3 milliGauss magnetic field at 60 Hz, but a weaker magnetic field at 120 Hz will weight the reading even more strongly and register as 6 milliGauss when in fact it is only 3 mG.  (from an excerpt on the company website) So the standard Trifield 100XE weights the “harmonics” (multiples of 60 Hz such as 120 Hz, 180 Hz, etc.) differently than a flat frequency EMF meter. Ordinarily, any instrument that is frequency weighted has an attendant chart which tells you how much more weight at different frequencies is measured than over the non-weighted frequency point of the meter.

Below is an example of this sort of chart for the Natural EM Meter (blue label) which is very different from the 100XE model. (This was taken from the vendor website – I know the word “frequency” is misspelled)

EMF Meter Frequency Magnetic Field

Natural EM Meter (not 100XE) Frequency Weighting Chart

A little confusing?

Based on my experience, I can interpret the chart, but what I wanted was the chart for the 100XE model Trifield and I could not find it on the manufacturer’s website. This is what initiated the call to the vendor. When I spoke with an electrical engineer, she explained that the 100XE is not particularly accurate (rated as +/- 20% according to the specs on their website) and is not recommended as a reference for any type of serious EMF survey.

Furthermore she went on to explain that even the manufacturer has NO SUCH chart for the 100XE model so you really don’t know what you are reading and how much is due to the 60 Hz magnetic field that you are interested in and how much is distorted or misrepresented by the high frequency harmonics.

And to further dispel another myth, the Trifield is named for the fact that it measures 3 types (tri) of fields: magnetic, electric and radio frequency, NOT because it is a 3-axis meter in every mode as the RF (radio frequency) measurement is only in SINGLE or 1-axis and will alter greatly depending on the orientation of the meter with respect to the RF source.

But I am not disparaging the company at all (they make some excellent equipment for certain applications and their website is very informative) and the 100XE has some viable uses, but it seems to be more towards something more subjective like the paranormal field rather than what a serious EMF consultant would choose for an official EMF testing survey. I DO like the needle movement as it does help you to track slow or fast fluctuations so I do keep a Trifield with me, but the difference is that I know under what circumstances it can be used and also when I would not use it as an absolute for helping a client decide on a property decision because of the proximity of power lines.

EMF Consulting and Safety: On the Importance of Instrument Calibration

When quoting a job or project to a customer, a question that comes up from time to time is:

“Are your meters calibrated?”

An understandable query, but the answer may surprise you.

EMF consulting is a specialty field that most of my clientele have very little familiarity with and it is wise to try and ascertain if you are getting good data for the money paid.

However, my extensive technical experience covering over 25 years in several interdisciplinary fields (including experience and certification in the calibration of instrumentation) has given me a rather unique perspective and stance about the relevance of this question.

My short answer is that as long as it is a digital meter of semi-professional grade or better from a reputable company and is in proper working order from the date of purchase, observing calibration intervals (which are usually a holdover from the old analog days) is not as important as some may think PROVIDED that the meter is known to be initially accurate within a certain % depending on the application. Very often, you can perform a cross-check with other meters and as long as they are in close agreement, that indicates proper operation.

The only exception to this is if:

  • The particular meter/model is known to have serious accuracy / unpredictable performance issues such as one model I discuss on this site.
  • Damage from impact, fluid intrusion or a corroded battery has or is suspected to have caused operational issues to the sensors / internal electronics.

This may sound unprofessional or even contradictory to other post on the importance of using a high quality meter, but I have pondered this issue for a long time and I can give a number of strong reasons for this position:

1) Unless you are doing actual research grade work, (such as in academia or R&D) are calibrating other instruments, or you are performing mission critical work (such as an infusion pump dispensing medication to a patient in a hospital) you simply don’t need the absolute best accuracy to accomplish the mission of the instrument.

Close is good enough for almost any application of EMF surveying.

For instance, if an EMF meter reads 1 milliGauss, (mG) but the true NIST traceable reading is 0.9 or 1.1, being off by 0.1 mG or 10 % should not be the deciding factor between buying a home or not.

2) Readings of magnetic fields, radon and RF naturally fluctuate over time, so what is more important is looking at an average.

3) Different meters have different frequency weightings so no two meters will be in complete agreement anyway.

4) You cannot always trust a calibration sticker. A dirty secret in the industry is that a lot of money is spent on calibrations that are incorrectly performed or not even done at all. I know this as a fact because I have not only had calibration technicians tell me, but I was IN the instrument / radio calibration business myself.

Just because an official looking piece of paper says that a meter is accurate, you are still trusting the honesty of the person / company that certifies the equipment and often there is not a clear “chain of custody” that holds anyone responsible or that the right / qualified individual actually performed said calibration. I am not saying calibration isn’t worth doing, nor am I accusing any calibration company in particular, just that you should maintain a healthy amount of wariness about this issue.

A controversial subject analogous to this is the autograph authenticity industry – try Googling that and I believe you will find some of the stories very eye-opening and sobering as to the real value of an expert’s opinion when volume vs. quality directly impacts the bottom line. And frankly, it is easy to forge a very official looking calibration certification paper for most instruments.

5) Different types of measurements can be very difficult to get accurate because of the physics involved. Not everything is as simple as knowing the speed of a vehicle, for instance. (something which can be measured with excellent accuracy)

For example, received and transmitted RF power is notoriously difficult to nail down due to reflections, constructive / destructive interference, etc. so that getting within 3 dB (or 50 % accuracy) is considered reasonably good and the reading can change depending on your antenna gain, frequency weighting or just moving the instrument a few centimeters to one side.

In plasma physics, if your measurements are within a factor of 2 of calculated values, that is considered valid. In other words if you expected to get 5 and get 8 instead, (a 50% + error) that is still in the acceptable ballpark of even high level research data.

6) Calibration at annual intervals is an old and in my professional opinion for most instruments, unnecessary “feel good” tradition that no longer matches the actual requirements of modern solid state electronics that have a fair degree of drift compensation and stability compared to older, analog devices.

If you have a new instrument made from a reputable manufacturer and after only a year it is found to be significantly off, then I would strongly suspect it was defective / improperly calibrated to begin with.

And this is not just my opinion; a number of modern instruments now manufactured have recommended calibration intervals that are either upwards of 10 years + or are even guaranteed for the life of the instrument barring serious damage such as that from a fall / water immersion, etc. which would probably place the meter in a category of “inoperable and uneconomical to repair” so it would be replaced with a new one anyway.