PS081 datasheet(56/155 Pages) AMSCO

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3-33

PSØ81

are not or not perfectly compensated. Mainly in the packaged version of PS081 differences in the

bond wires are not compensated.

Because of the nature of the remaining zero drift, the value of this drift depends on the value of the

strain gage resistor. The lower the strain gage resistor the higher is the remaining drift. E.g. with a

1 kOhm strain gage the zero drift is approximately 1/3 of the drift of a 350 Ohm strain gage with

the same chip.

For best offset drift behavior we recommend the standard full bridge connection. The systematic

offset drift in this mode is approx. ±10 nV/V/K and lies therefore in the 50% limit of OIML 10000.

It is possible to use PS081 in high end scales, please see also Application Note AN018 for further

details.

In all PICOSTRAIN modes the sensor wire resistance is part of the zero drift. To minimize the drift ple-

ase have a close look on the length of these wires to the load cell. The most critical part is normally

the PCB, a few millimeters of missmatch can be well seen in the offset drift. The cable to the load

cell is not as critical because the wires have a much bigger diameter.

A special case is Wheatstone mode. In this mode nearly 100% of the remaining parasitic resistan-

ces are compensated because of the kind of the measurement. Therefore, in Wheatstone mode the

zero drift of PS081 is close to zero and can be improved to < 1 nV/V/K also if the wires are not

matched.

For comparison:

To comply with OIML 3000 specifications the zero drift of the complete scale must not exceed

133 nV/V/K

To comply with OIML 10000 specifications the zero drift of the complete scale must not exceed

40 nV/V/K

Following table gives an overview of the typical offset drift of PS081. To get a good idea of the min./

max. values multiply the typical values by the factor of 3. You get a good estimation over the distribu-

tion of a production lot (not a guarantee).

Typical drift in different modes

Mode

350 Ohm SG

1 kOhm SG

OIML 10000

Fullbridge Standard *

±10 nV/V/K

±4 nV/V/K

±40 nV/V/K

Wheatstone

<±1 nV/V/K

<<±1 nV/V/K

±40 nV/V/K

*with cross-matched traces on the PCB, please refer to below explanation.

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