Span and Offset Compensation by Software

Temperature Independent Loadcells & Scales just by Software Compensation

• No need for a offset compensation resistor on the load cell
• Span compensation resistor does not have to be precise

The sensitivity of a loadcell depends on temperature. It is also affected by the elasticity of the loadcell (e-module), the strain gain factor (k-fator), and other such phenomena.  The sensitivity usually increases at higher temperatures, and the drift may reach 5% / 100°C.  This is often unacceptable, even for basic scales.
Today this error is typically reduced by adding a compensation resistor to the loadcells .

PICOSTRAIN devices like the PS021 solve these problems in a very elegant manner. The PS021 provides the mathematical post-processing to correct the results without any mechanical modification of the loadcell. When the residual error of the sensitivity and the final offset are known, it is possible for the PS021 to to correct the errors by software.

By means of the multiplication factor TKGain, the compensation effect of Rcomp can be increased (>1.0) or decreased (<1.0).  In case Rcomp on the loadcell is mismatched and has a wrong value, it is possible to modify the final compensation effect by multiplication.

A second correction constant, TKOffs, is introduced to take care for the temperature effect on and by the offset.  After the full calculation of the compensation, the strain is now independent from temperature. There is no offset drift caused by the initial offset in combination with the compensation resistor and also the offset temperature drift itself is eliminated .

Simplification of Loadcell & Scale Production

As a consequence there is no more need to trim the loadcell to zero offset! The user just writes the measured offset value into the TKGain register of the PS021. The mathematical operation is already integrated into the PS021.

Inside the PS021 the final result is calculated as: