Intense, time-varying electromagnetic fields with steep gradients in field strength can cause troublesome noise in strain gage circuits. In severe magnetic environments with low signal levels, the noise amplitude may be several times larger than the strain signal from the gage. Micro-Measurements H-Series noninductive strain gages have been specially designed to minimize noise pickup in the gage grid due to electromagnetic fields.

H-Series strain gages consist of two identical grids, with one stacked directly above, and insulated from, the other. The upper and lower grid elements are connected in series so that current flows in opposite directions through the two grids. With this arrangement, noise voltages induced in the grid tend to be self-cancelling. The counter-current principle employed in H-Series gages is particularly effective against magnetic field gradients parallel to the test surface.

H-Series strain gages have been used very successfully in fusion research applications and similar environments with flux densities to 50 000 gauss.

Construction
H-Series strain gages are constructed with two 350-ohm constantan alloy foil grids on a glass-fiber-reinforced epoxy-phenolic carrier. These fully encapsulated gages include closely spaced, heavy copper terminals for direct leadwire attachment. H-Series gages are available in both a single-axis and a delta (0-60-120 degree) rosette pattern. The available S-T-C number is 06.

Adhesives
Micro-Measurements M-Bond 600 or AE-15 adhesive systems are particularly recommended; M-Bond 600 produces the thinnest glueline. Adhesive cure temperature should not exceed the maximum sensor operating temperature of +250 deg F (+ 120 deg C).

Leadwires
In many cases, the leadwire system itself is the principal source of magnetic noise induction in the measuring circuit. Careful attention to details as outlined in Vishay Measurements Group Tech Note TN-501, Noise Control in Strain Gage Measurements , is strongly recommended.

H06A-AC1 Uniaxial; 700 ohms; Special Purpose
H06A-AD3 Delta Rosette; 700 ohms; Special Purpose