6
b. Unstable zero due to changes in lead resistance with ambient temperature.
c. Span errors when the indicator is "calibrated" by shunt-calibration of arms external to the
indicator.
All the above effects are proportional to the ratio of the lead resistance to the gage ( or
bridge arm ) resistance. Using relatively heavy leads ( AWG #18 or 1 mm diameter ) will
minimize errors; this is especially important when using the 120Ωcircuit. However, if the
purpose is to simulate an actual gage or transducer installation, use lead-wires of the
same size and length as would be used in the actual installation.
Good zero stability with temperature requires complete symmetry in the total bridge. To
achieve this with the quarter or half bridge, use nearly identical wires for all leads (size
and length) and keep them grouped together to minimize temperature differentials.
CALIBRATOR SET-UP
2-4 Rotate the switch to "0".。
2-5 Apply bridge excitation. Excellent stability will be achieved with normal excitations ( up
to 7V on AE-120 or 10V on AE-350 ). Maximum permissible excitation ( AE-120 10V
and AE-350 15V, respectively ) may produce some warm-up drift; readings should not
be recorded until stable, which may take up to a couple minutes at each selected output
under extreme conditions.
2-6 If it is anticipated that readings on half and full bridge will be taken through zero ( that is,
both POLARITY buttons will be used ), check that "+0" and "-0" both yield the same
reading. If not, adjust ±ZERO slightly to achieve this.
INDICATOR SET-UP
2-7 Where an initial zero or bridge balance control is provided on the indicator, it would be
normal practice to set this to achieve a zero reading so that data need not be corrected
for initial offset.
Note: An unbalance of up to 50με ( 0.025 mV/V ) can be encountered with theAE
Calibrator where no indicator balance control is used.
2-8 Set the indicator scale factor as desired.
a. A strain indicator would usually be set for a gage factor of exactly 2.000 to achieve
direct-reading calibration. If it is set for any other gage factor, data reduction will be
necessary (see paragraph 2-9).
b. A transducer indicator may read directly in mV/V, percent input for a fixed or settable
span, or it may read directly in engineering units (pounds, Newton, etc.) for a selected
transducer. Any indicator above can be accurately calibrated with the AE calibrator,
although some simple data reduction is generally necessary (see paragraph 2-10).
