Gauss measurement

Gauss meter for measuring pemf
We are often asked if one can buy a low cost EMF meter and check these Gauss values?

Some manufacturers of PEMF devices make unsubstantiated claims about the field strength intensities of the PEMF devices they manufacture and write confusing statements for Gauss, or milli Tesla, or micro Tesla's.

 

How is one able to understand what the real Gauss values are and why these are important?

How can someone start to compare between the Gauss claims made of the various PEMF devices?

 

Can these measurement devices be used for obtaining the objective Gauss values for PEMF devices and coils?

In this very long page you will find explanations on how Gauss measurements for PEMF devices should be made and why.


How NOT to measure Gauss values for PEMF devices


There are many inexpensive EMF meters for Gauss measurements on the market creating confusion about to perform correct Gauss measurements for intensities generated by PEMF devices. These Gauss meters start at $30 and expectations should match the price tag.

First of all these Gauss meters are designed to measure electromagnetic fields created by cell phones, radio waves, micro waves, power lines, antenna radiation, Wi-Fi detection etc. etc.

Then there are $1,000 Gauss meters used for measuring magnetic field strength of permanent magnet materials, motors, speakers, magnetic sensors, magnetic transducers and other machines and instruments.


Use ghost meter for pemf Gauss measurements?
Popular Gauss meters are also used by people who are interested in paranormal activities and use them for ghost hunting.

 

They assume that ghosts changes electromagnetic fields and that Gauss meters can be used to detect these movements, thus calling them ghost meters.


This does not however mean that even expensive Gauss meters can be used for measuring PEMF intensities because measuring very fast PEMF pulses is very difficult.

Placing such a meter in a strong, low frequency, pulsing electromagnetic field like a high intensity PEMF device, it reacts abnormally because the electronics inside are completely overloaded, making correct Gauss measurements not possible.

Gauss meters measure the rate of changes in electromagnetic fields. The reading on these meters depends on the frequency range of the electromagnetic changes.


There are different kinds of Gauss meters: frequency-weighted and non-frequency-weighted.


Gauss meters consist of an inductor coil connected to an amplifier, while an AC oscillating magnetic field will create a very small current inside the inductor coil. This signal is then amplified, filtered and rectified in a DC voltage. The measured signal frequency is then proportional to the displayed magnetic field strength.

 

Note that the sensitivity of the meter depends on the frequency of the electromagnetic field! 


Frequency-weighted Gauss meters


Inexpensive Gauss meters are usually frequency-weighted because non-frequency weighted technology is only used in more expensive meters. These Gauss meters measure frequencies over a very wide range and they will not give a true electromagnetic value because the higher the frequency to be measured, the higher the value “measured”. These values cannot be relied upon as being accurate and sometimes measure a Gauss value hundreds of times higher than it actually is. This is the reason why these frequency weighted meters are factory calibrated for Gauss values at 50 or 60 Hz.


Gauss meter frequency response

  Sensitivity of such Gauss meters may sometimes be proportional in a specific frequency range, then become linear in the next frequency   range and then even be reversed in the following frequency range!




Non-frequency-weighted Gauss meters


Gauss meter frequency response 2
  Non-frequency weighted Gauss meters give a fairly flat frequency response, regardless of the frequency.

 These instruments are accurate for laboratory work, because they show more or less the real field strength instead of a frequency    dependent strength. 


pemf peak Gauss meter
So how about Gauss meters for measurement of fast PEMF pulses? Well we purchased such a peak Gauss measurement device specially designed for this purpose and started testing it.


In communications with the manufacturer of the device we received the following information. The measurement coil has a 1” diameter single-turn detector loop while at the same time writing that this is a Helmholtz coil. Because a Helmholtz coil always consists of two exact identical coils placed symmetrically along the same axis, a single loop can never be a Helmholtz coil so we decided to look further.

When asking about the calibration procedure the manufacturer wrote: A 1000 Gauss reference magnet is used in which the coil is pulled out to record the peak.


Then we looked into the way the peak measurements are recorded. As we already expected, an electronic (sample-and-hold circuit) is used. The manufacturer claimed that the device is able to measure individual pulses as short as 1 microsecond.



grab pemf pulse  
Hold pemf pulse

In electronics a sample and hold circuit is used to “grab” a signal and then “hold” the signal for displaying the measured information. Inexpensive devices make use of such electronic sample and hold circuits.


Such a circuit is created by charging a capacitor with the sampled signal and then holding this charge for a while to allow for a read out. Because the charging time of a capacitor is non-linear, only the linear part of this charging curve can be used, otherwise a complicated anti-logarithmic amplifier must be used to correct measurement failures. Alternatively, the capacitor charge is compared to values in a preset table with similar inaccuracies. This limits the measurement abilities drastically and the higher the peak value of the PEMF pulse the larger the measurements mistakes.

There are several problems measuring maximum PEMF peak values. During the measurement, a time window is opened to grab the PEMF pulse. What happens with such meters is that during the measurement time (possibly around one second) a time window is opened to let the PEMF peak value through to the sample catching mode and thus creates another source for critical Gauss measurement mistakes.


These additional smaller pulses are then added to the previous peak value when more than one of the ringer pulses pass through this time window. The following smaller pulses are now added to the previous value completely distorting the peak Gauss value results and show much higher Gauss values than actually generated. 


for pemft ringer wave form




Look at the actual pulse form of a PEMF device inside the applicator coil at the left. A ringer signal consists of a series of pulses slowly fading out during each individual pulse.






Ringer wave form measurement for pemft
Because of the time the measurement is made in addition to the first maximum peak pulse value also pulses in the blue area are measured if the measuring window is too long.


These smaller pulses are then added to the previous peak value when more than one of these ringer pulses pass through the measuring window. The following smaller pulses are now added to the previous value completely distorting the peak Gauss value results by showing a substantial higher Gauss value on the meter than generated.



Because we are only interested in the maximum PEMF peak value of a single pulse and not the accumulated energy inside the fading pulse, we can never be sure that the real maximum peak value of such a PEMF pulse is measured, if the above measurement method is used!


Conclusion: Can an inexpensive Gauss measurement device be used for defining the maximum intensity of a PEMF device? The answer is no!


Now the next question is how the maximum intensity of a PEMF device should be measured, because some manufacturers make wild and unsubstantiated Gauss value claims, far exceeding reality.



Hall sensor for PEMF measurements


How to measure Gauss values for PEMF devices


The only reliable Gauss measurement method requires a visualization of the PEMF pulse, while simultaneously quantifying the Gauss value. For this purpose our company uses of the following measurement method, based on purely scientific methods.

Hall sensor for Gauss measurement of pemf devices


A Hall effect sensor is a transducer where the output voltage changes depending on changes of a magnetic field. 

A Hall probe has a magnetic field sensor that passes electrical current when the sensor is perpendicular to a magnetic field. The stronger the field the more current passes through the sensor. 


Oscilloscope to visualize pemf pulse for Gauss measurements


To make correct Gauss measurements for PEMF devices a measurement procedure based on this Hall effect must be used, where the PEMF pulse is measured and visualized on an instrument called an oscilloscope, all at the same time. 





Gauss measurement design



For this it is necessary to use a sophisticated measurement instrument with a laser calibrated linear Hall sensor, with temperature and offset compensation. The output voltage of the Gauss measurement device is proportional to the magnetic flux density through the Hall sensor plate. The temperature and offset compensations result into stable magnetic characteristics for the power supply voltage. This includes stabilizing changes that may occur in temperature, like temperature increase because of the pulse currents in the PEMF coils.


The Hall sensor measures constant and low frequency magnetic flux densities accurately. The device voltage output is proportional to the magnetic flux density passing vertically through the sensitive area of the Hall sensor.




Single pemf pulse waveform




The actual magnetic field strength measurement procedure is performed by placing the Hall sensor on the PEMF coil while at the same time showing the maximum pulse signal on the screen of the oscilloscope.





Gauss measurement of pemf pulse



Because the field strength measurement is derived through a special electronic voltage amplifier for stability, the measured output signal consists of a positive and negative part, while the PEMF pulse itself is positive only.




PEMF Gauss measurement pulse




The picture at the right side shows an example of  a PEMF frequency of 1 Hz, with a 50% duty cycle and the measured real Gauss magnetic field intensity is 496 Gauss = 49.6 milli-Tesla.