Looking to design an EMF meter - ideas? - Page 1
Forum section: electronics / projects

author: bthoon
author_rank: Newbie
timestamp: October 07, 2011, 08:58:37 pm
content: Hello, folks. I hate to make my first post on any forum a question, but I'm hoping I can get some advice on a new project.I'd like to make a logging, micro controller based EMF meter. I've seen the videos where some folks have used a simple ADC (like the Arduino EMF detector videos) attached to a collector/antenna, but while that shows the PRESENCE of EMR, I'd like to actually measure it.edit for clarification: I'd like to return a milliGauss value to an embedded LCD screen as well as log it to an SD card, not just show relative readings with no calibrated baseline.I'm not sure if there is a simple solution to this, or if complex calibration must be run on any unit that actually returns results in milliGauss.Cost is not really an issue, as we will be producing only about five of these units, which will be both hand-held and placed and left in a test chamber. They needn't be sensitive to 60/50hz, though EXCLUDING those ranges would be nice.We would use existing solutions, but they all lack something we need in one area or another, and frankly we like making our own kit!The final device would need to be sensitive (ideally) to 0.01 mGauss to ~200 mGauss.Any words of advice, even if they're "you can't do it, give up!" would be appreciated! Thanks!

author: InterestedTom
author_rank: Regular Contributor
timestamp: July 29, 2016, 03:37:33 pm
content: I have a similar project but for slightly higher flux densities. If you are still interested you should look at magnetoresistive sensors, there are various ones available. Alternatively you could use a 3 axis mems magnetometer, they tend to provide digital output in uT or Gauss, I'm sure you could find something inexpensive that measures to better than 5%, which is pretty good for measuring magnetic flux density. If you want something significantly more accurate then that is also possible but then you have to start worrying about how good your voltage reference and ADC are.

author: ConKbot
author_rank: Super Contributor
timestamp: July 30, 2016, 05:24:18 am
content: What sort of frequency response range are you looking for? Magnetoresistive sensors are usually good for 50-200khz, depending on the sensor. Being more familiar with RF field strength than low frequency field measurements, 10uG to 200mG is quite the range, (200mG is about 10W/cm^2 in air! )

author: InterestedTom
author_rank: Regular Contributor
timestamp: August 01, 2016, 05:26:11 pm
content: I spotted some Honeywell wheatstone bridge based magnetoresistive sensors that were specified as being good to 5MHz. I have more experience with hall-effect sensors. Given you want to be logging with a microcontroller I assumed you wanted to measure static or low frequency fields. I now realise may well want something with a much broader frequency response.If you want to measure high frequencies then you could use a characterised antenna into a thermal AC to RMS converter. To ease calibration you could use a dipole which can be easily modelled, either analytically or in software. By measuring the dimensions of the dipole you can calculate it's frequency response to electromagnetic waves and generate an inverse frequency response function to be implemented in a filter, either analog or digital with an FPGA (cheaper than a DSP). This will increase your bandwidth but not indefinitely. To achieve your desired resolution you may want to have multiple different gains in the analog front end.