arent those valves anyway inside a metallic housing ?

i doubt a simple conductive sheet might help here,

since it would not shield a magnetic field, (your valve is powerd by DC or ?)

i would try to increase the distance between valve and strain gauges and check if

the effect decreases ...

Since there may be other E/M sources around , separate tests could be performed only for the gauges [ eliminating coils] .

If all, above and previously, suggested fail then the use of EMC complying strain gauges should be used [ according to real needs].

One solution is probably to use Optical Fibers with Bragg Gratings (OFBG). As with strain gages you can measure strains but without any problem as regards the influence of magnetic field. OFBG can be bonded on your valve as for a strain gage and if you use the right glue you can use them even in severe conditions (temp, H%, fatigue,..). I don't know details of your project but keep also in mind that you can also use a composite patch to embedded the Bragg grating if you want to have an complementary protection and/or for specific studies (in this case composite can be used roughly as an amplifier for example or a H% detector,..)

Dear Gyanendra,

local H-fields can be compensated for by using some external windings with compensating currents opposite to the solenoid. The drive current used shall include the low-pass function of the shielding provided by the solenoid's housing. By its position along the solenoid, the dipole can be turned onto a quadrapole yielding 'zero' H-field at certain locations

You'd better use the laser displacement sensor or digital sparkles image corelation method.

Not knowing the dimensions of your problem parts can only lead to a lot of guessing.

Any way here is my 2¢ worth....

The fringing fields from the solenoid that is being coupeled to your strain gauge is probably a low impedance (magnetic dominant)near field. The interference that the strain gauge experiences are again probably from the fringing fields whenever the the solenoid gets energised or de-energised, my guess is that theses are mostly low frequency components. Simple solution is to have a "black out" time in your firmware during these transitions.

The earlier post calls for shielding is correct but thin Aluminium foil are really good for shielding Electric fields in the near field. The most common low frequency magnetic material is soft iron and in many instances silicon-ironl could be a decent substitute although a better shield could be fabricated with mumetal that alloy was something renegated nowadays to engineering history.

Near field magnetic shielding with common silicon-iron would call for a multi layered (to minimize eddy current) custom designed shield that requires 3D simulation that is probably beyond the dream of the average engineering graduate.

You should cover your gauges by layer of resin and then by metal foil to have 'closed metal box' with strain gauge inside. Closed metal box will not have magnetic field inside.

You should cover your gauges by layer of resin and then by metal foil to have 'closed metal box' with strain gauge inside. Closed metal box will not have magnetic field inside.

You should cover your gauges by layer of resin and then by metal foil to have 'closed metal box' with strain gauge inside. Closed metal box will not have magnetic field inside.

Just to complete my previous answer, when I write H% previously it is about relative humidity (not magnetic field) which can have bad effects on strain gauges even if you use a waterproof cover and which have an effect on the OFBG only if you use a cover which is sensitive (mechanically speaking) to the humidity.

If you keep strain gages Tim and Seigei are right. You can encapsulate you strain gauge with a matrix/copper/matrix skin (in first approximation, 0.03 mm copper foil is about 20 times more efficient than a 0.8 mm steel foil at 50/60 Hz). In a near magnetic field, attenuation is, for a part, driven by copper thickness but this influence decrease drastically with the frequency, unfortunately. So you need to increase drastically the copper thickness which is probably not possible if you want to mesure something with your gauge . The second problem is that H(magnetic field) attenuation is mainly driven by the quality of your closing (electrically speaking) between the upper and lower copper foils all around the border of your capsule and mainly at the entry of your gauges cables which need also to be shielded against H field (continuous copper foil, not only a braid) so finally it is really a big problem . It's why, for me, in this case optical fibers with Bragg gratings are really the best choice even if probably you need to invest or rent a specific equipment to interrogate and record data. I will conclude with my best wishes to all RG members for 2014.

I also suggest to use FBGs, as they are no more sensitive to EM fields.

Regards