High temperature loadcell compensation

Novatech says that it can now offer loadcells that maintain their accuracy figures up to 250 degrees C.

All loadcells have output spans that change with temperature. This causes significant measurement errors particularly if the loadcell is required to operate over a wide temperature range.

The currently used method for compensating for this error in strain gauged loadcells is to use nickel or Balco foil resistors in series with the sensor excitation connections. The method is limited in accuracy by the non-linearity of the resistance change of the foil resistors with temperature.

This non- linearity increases at temperatures above 100 degrees C and foil resistors are not suitable for use at temperatures above 200 degrees C.

Novatech’s new invention compensates for loadcell output span changes with temperature by using passive temperature sensitive elements in the bridge circuit. The temperature coefficient of the temperature sensitive elements is adjusted to be the inverse of the sensor’s uncompensated span change with temperature. Accurate linear compensation can be achieved over a temperature range of -50 to 250 degrees C.

The company claims that this method is inherently more linear than traditional methods that employ nickel or Balco resistors in series with the sensor excitation connections, giving performance specification several times better on span (typically 0.005% output/ degrees C) than most other loadcells currently available for high temperature use. With additional trimming over a range of temperatures of particular interest we would expect to achieve <0.001% output/ degrees C.

Novatech has an international patent application pending for this novel approach to high temperature modulus compensation, which is currently available on 70% of Novatech products.

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