The resolution parameter

A key parameter in BiotSavart is the resolution of a conductor. This is how finely the conductor is to be subdivided in order to calculate the magnetic field generated by the conductor. A ten thousand turn solenoid is not recommended to be calculated by summing ten thousand loops. Sufficient accuracy for most purposes is obtained by approximating the solenoid by a smaller number of loops (called elements) that each represent many of the real loops in the solenoid.

The figures below show the elements of a solenoid for several resolutions. The solenoid is 20mm long, 3mm inner radius, and 10mm outer radius. With a wire diameter of 150 micron, packed hexagonally, the number of turns is 7184. The resolutions used in the figures below give a much smaller number of elements. While many people might prefer the very finely divided solenoid, or something even finer, the coarsest solenoid (30 loops) is already a good enough approximation for most purposes, allowing one to calculate fields near the axis of the solenoid to within 0.2%. The main effect of decreasing the resolution is to increase the computation time.

The moral of this story: choose the resolution wisely.

Automatic resolution

Automatic resolution may be specified for solenoid or racetrack, on the Calc tab of the conductor's edit window.

Specifying automatic resolution tells BiotSavart to choose a reasonable resolution based on the dimensions of the object. This resolution is suitable for inductance estimations, but might not be appropriate to your application.