You may have just purchased an emf meter from an unreputable brand and wondering how it is actually giving you the correct readings. If this is your case, the answer is you have to run a calibration.
However, EMF meter calibration can cost you not a little amount of money. You have to send them to a calibration lab and let some metrologists calibrate them for you. This process can take time, meanwhile, you need it soon.
On this page, we are going to discuss some DIY ways of emf meter calibration that you could do just in your house. If you are looking for the methods or steps like what it does in the lab calibration, then this post is not for you.
Why Calibrate the EMF Meter?
The main reason for calibration are to ensure the reliability of the instrument so that it can be trusted.
Aside from that, the calibration itself let us know the level of accuracy of the instrument and verify that the readings agree with a known reading/standard.
Afterward, surely, the measurement error can also be identified.
If the readings are outside the acceptable range (the error is too large), the instrument must be modified or simply replaced.
DIY Calibration of An EMF Meter
Before we go further calibrating the EMF meter, it’s important to acknowledge the basic thing to use the emf meter. EMF meters can be the single or tripe axis meter model; you can read about it here on how an EMF meter works. Due to how it works, the sensor within the instrument is kept perpendicular to the magnetic field so that the proper measurement is taken.
Asides, you need to know what things to calibrate. Since EMF detectors are instruments to detect magnetic field strengths, electric field strengths, and RF fields, we will do separated calibrations for each measurement.
Therefore, you have to know the unit readings of each measurement. An EMF meter presents its readings in µT (micro-Tesla), mT (milli-Tesla) or milli-gauss for magnetic field strength, V/m for Electric Field Strength, and mW/m2 for RF readings. It has a sensitivity of 0.1 milligauss or 1 V/m.
1. Calibrating Magnetic Field Sensor
The calibration process is done by measuring the magnetic field of a known source and in this case we will assume that the source is an electric meter outside a residential or commercial unit.
The measurement is taken 1 foot and then at 2 feet distance from the electric meter. Typically the strength is 2 milligauss and 7 milligauss respectively. A 5-10% error rate is negligible for home applications. Surely, when using it for R&D purposes the device needs to be professionally calibrated.
2. Calibrating Electric Field Sensor
The process is pretty much similar for the Electric Field strength sensor calibration.
Basically, the user can use house wirings or electrical appliances as the source of ELF. House wirings have a typical electric field strength of less than 0.1 KV/m, and electrical home appliances are in the range of 0.02 to 0.2 KV/m within a 1-foot radius. Again a 5% error is negligible if the device is being used for household purposes.
3. Calibrating RF Sensor
Radio frequency calibration takes over at higher frequencies than the ones encountered in dc and low-frequency ac calibration. RF meters or sensors inside EMF meters cannot be calibrated manually with the aid of using an individual and must be calibrated by a consultant in a lab.
RF power and a measure of how effectively it combines or transfers from a source to a load are two critical properties. Mismatch errors contribute significantly to measurement uncertainty in RF calibration. These are caused by the output and input matching of the device, as well as the cables and connectors used to connect the device. In order to reduce these sources of error and uncertainty, the use of high-quality measurement technology connectors and cables and their careful handling is essential.
Signal generators, level generators, function generators, power meters, test receivers, spectrum analyzers, RF and microwave counters, network analyzers, audio analyzers, oscilloscopes, and digital multimeters are typical instruments in a classic RF calibration system. However, none of these devices are specifically designed for calibration; instead, they are all general-purpose test tools used throughout the system. Signal generators cannot provide the power required for RF calibration. Therefore, they must be used in conjunction with power meters and calibrated step attenuators to achieve the correct level and damping accuracy. When low harmonics are needed, e.g. when calibrating spectrum analyzers, external filters are required. Signal sources with low phase noise behavior are also required for the calibration of high-performance spectrum analyzers.
Alternative: DIY EMF Meter Calibration for the RF Sensor
A home calibration method is also available but it is bound to be filled with inaccuracies and errors. The procedure includes using an RF generator capable of producing frequencies in the Megahertz range or greater, along with an RF transmitter used for transmitting the signal. A known frequency signal will be transmitted and measured from different locations in the room. Make sure to take the transmitter antenna’s specification in consideration. The procedure is too complex for someone with little to no science or research background and is super expensive to set up. It involves lots of instruments and requires complex mathematical calculations. The room the device is being calibrated or tested also plays an essential role such as EMF disturbances in the room may affect the manual calibration process. High testing facilities are usually shielded from these external EMF disturbances.
Calibration of any measuring instrument is a tedious and difficult task for someone with little to no technical background. However, most recent and advanced EMF meters do come with calibration certification from the manufacturer. It is always recommended to test your EMF meter or any other measuring device using a known source to make sure if it’s functioning properly or not. In case of malfunctioning replacing the device is the most suitable option. You can also check our guide on the best EMF meters, meant for general, home and office use.