11
Calibrating Transducers Using the Null Comparison Method
The null comparison method is
frequently recommended by transducer
manufacturers, since it eliminates many of
the variables that can be encountered in the
course of a conventional calibration. The
basic procedure for performing a null
comparison calibration is as follows: The
inputs of a precision standard are connected
in parallel with the inputs of the transducer
under test, and the appropriate source
voltages and/or currents are applied. A
differential meter is connected between the
outputs of the precision standard and the
transducer under test, and the zero and span
settings of the transducer under test are
adjusted until the differential meter dislays
zero. The advantage of this method is that
since the input signals are exactly the same,
the accuracy of the source (and the
equipment used to measure it) are
inconsequential. The calibration accuracy is
dependent only on the individual accuracies
of the precision standard and of the
differential meter.
Precision standards are usually available
from the manufacturers of the transducers,
and typically have accuracies of 0.1%. The
disadvantage of using precision standards is
that for each type of transducer to be
calibrated, a different precision standard is
required. Use of the 1040C eliminates the
need for these various precision standards,
since all of the necessary functions can be
generated from one unit. Also, since the
1040C is a precision source and no external
meters are necessary, the simplicity of the
calibration procedure is about the same as
that of the null comparison method.
