Hello,
I am trying to measure very small field changes in the earth's magnetic field at a distance of about 2ft to detect ferromagnetic objects a distance, so I am using the DRV425 in high sensitivity mode to see if I can achieve the desired level of sensitivity with this part. However, when I start increasing my Rshunt value from 100 OHMS (which is the default value in the eval board) to say 330, I get an increase in noise in Vout. In relation to this observation, the response to this question mentions "If you would like to shied the earth's magnetic fields or any other stray magnetic fields you will need to place a material that is magnetic around it" and furthermore, section 8.2.1.2 (pg 25) of the datasheet states "The high sensitivity of the DRV425 may require shielding of the sensing area to avoid influence of undesired magnetic field sources (such as the earth magnetic field). Alternatively, an additional DRV425 can be used to perform difference measurement to cancel the influence of a static magnetic field source, as shown in Figure 68."
So really two methods are recommended to deal with the elimination of any static field sources that would contribute an error to low field changes
1) Shield using magnetic material, I'm assuming some type of mu-metal or soft ferromagnetic material
2) Use two DRV425 in differential mode to capture the difference between their respective outputs
Now the questions...
Question 1: What type of materials have you used or can recommend to shield the DRV425?
Question 2: The geometry of the shield has large influence on the effectiveness of being able to divert lines of flux. Can you recommend a shield geometry that is effective at shielding against interfering static field while still allowing measurements to be made
Question 3: You mention using the simulation software FEMM to calculate the fields. Do you have an example of this that you can share since I am having difficulty setting this up in this software
Thanks in advance,
E
