Zeroing load cell data

alex · 2006-03-29T12:08:44+00:00

Dear Group,Please look at the Figure 1 and read the question below: y | * * * * ------ Load cell calibration data | * * | * * | *-- Pt. a * 0 |______________* --Pt. b ______ x | | Figure 1In Figure 1 you have a set of load cell data. The thing is, thebeginning and end points (Pt. and Pt. b) are above the "y" axis andaway from the "x" axis i.e. they are not zeroed.The following function was written to fix this problem, but it has aninherent flaw. The flaw can be demonstrated by Figure 1, point a > b,the script subtracts the gap between Pt. a and the "x" axis but thisonly adds the problem onto the end of Pt. b. How can you solve eitherthe problem with this script or the problem in general?function [zeroed_x,zeroed_y] = zero_xy_v2(x,y),length_x = length(x);a = x(1); %first value of xb = x(length_x); %last value of x%-----------------------------%Zero "X_axis"%-----------------------------zeroed_x = x;% if a == b,%% if a == 0,% zeroed_x = x;% elseif a > 0,% zeroed_x = x - a;% else %a 0)),% zeroed_x = x - b;%% elseif ((a > 0) & (b == 0)),% zeroed_x = x - a;%% elseif ((a 0)),% zeroed_x = x - (b + a);%% elseif ((a > 0) & (b 0) & (b > 0)),% if a > b,% zeroed_x = x - a;% else %b > a% zeroed_x = x - b;% end%% else %((a b,% zeroed_x = x - a;% else %b 0, zeroed_y = y - a; else %a 0)), zeroed_y = y -...

Mar 29, 2006 22 Replies

Rate this thread:

miles 20 years ago

In what way? The ASCII graph had no values associated with it so the actual nonlinearity % is unknown. Generally a load cell plot shows an error from a straight line. Y-Axis being the error as a % of fullscale and X-Axis being the force. If the graph shown was simply load vs output then I agree the error would appear to be rather large.

The original OP's question appears to have never been answered. Normally when a load cell is calibrated the results are normalized with the initial zero reading subtracted such that zero load = zero output. A load cells zero reading is arbitrary since mounting methods etc. can shift the initial zero considerably. A load cell calibration therefore typically shows span.

I work for Interface Inc. who manufactures load cells and have written the calibration software they use and sell.

Vote

Jerry Avins 20 years ago

Miles,

You're jumping into the middle of an abandoned thread. The graph was represented as output, not error. The foldback it shows is the unusual behavior I had in mind when I said that functioning load cells don't do that.

The curve turns out to have been invented for the purpose of illustrating an ill-formed linearization question and is unrelated to any reality. The rest of the thread is a fine illustration of a sci-fi writer's dilemma.

Jerry

Vote