Compression column load cell with compensation for off center loading errors
Simple and inexpensive electrical compensation for off-axis and off-center loading sensitivity is possible in compression column load cells having a pair of compensation strain gages in series with each of the main strain gages in the load cell. The compensation gages are connected in series with their associated main strain gage. Each set of one main strain gage and two series connected compensation gages form one bridge arm in a strain gage bridge. Two compensation gages meet at each bridge corner, and are shunted by a common trimming resistor. The loading sensitivity compensation works for both conventional fixed axis load cells and Rocker Pin load cells.
1. A compression column strain gage load cell comprising:
four main strain gages distributed around a periphery of a compression column, and arranged to alternately measure longitudinal and transverse strains in the compression column;
a pair of compensation strain gages associated with each of said main strain gages, said pair of compensation strain gages arranged in parallel alignment with and symmetrical to said main strain gage and having a substantially lower resistance than said main strain gage; and
each of said main strain gages being electrically connected between said pair of associated compensation strain gages.
2. A compression column strain gage load cell according to claim 1 , wherein said four main strain gages and associated compensation gages are connected to form a bridge circuit with two compensation strain gages at each bridge corner, and further comprising trimming resistors shunting each pair of two compensation strain gages at each bridge corner.
3. A compression column strain gage load cell according to claim 1 , wherein each of said main strain gages comprises two parallel strain gages arranged symmetrically with respect to said pair of compensation strain gages, and wherein all of said strain gages are formed as one composite strain gage.
4. A compression column strain gage load cell, comprising:
a compression column having four bonding surfaces arranged in a square pattern centered on the axis of the column;
four first strain gages bonded to said bonding surfaces and arranged alternately to measure longitudinal and transverse strain;
a pair of second strain gages arranged symmetrically to each of said four first strain gages and connected in series with said first strain gages, said second strain gages having substantially lower resistance than said first strain gages, and said four sets of one first and two second strain gages being connected to form a bridge circuit with two second strain gages at each bridge corner; and
trimming resistors shunting two second strain gages at two or more bridge diagonals.
5. A compression column strain gage load cell according to claim 4 , wherein the center part of the compression column comprises four separate columns arranged symmetrically around the axis of the load cell.
6. A compression column load cell according to claim 4 , wherein the center part of the compression column is hollow.