readout will be positive. Should the left cell have the lower amplitude,
the resulting EMF will be negative. Under perfect conditions, both readings
should be equal in amplitude, except the one would be a positive 6
microvolts and the other would be a negative 6 microvolts. However, as you
will find, the two readings will seldom be equal in amplitude.
The
difference in readings is due to residual voltages present in the
measurement system.
This residual will either add or subtract from the
measurement.
Thus, you can see that by changing the cells' positions, we
can detect this error introduced by the measurement system which would not
be apparent if only one measurement was made. Although the manufacturer may
have taken special care in the design of the measuring system, it is
impossible to completely eliminate residuals.
By the use of the series
opposition measurement technique we can, however, detect and compensate for
these residuals in the processing of the data obtained from the
measurements.
Learning Event 3:
DESCRIBE THE US ARMY VOLT PROGRAM
1.
Figure 3-3 indicates an ideal flow of the volt within the calibration
system. It indicates an ideal traceability chain from the "Legal Volt" at
the National Bureau of Standards (NBS) to the lowest level of the Army
Calibration System.
2.
Before continuing with our discussion of the Army Volt Program, the
following terms should be understood.
a. Transport standard. A group of standard cells used to compare the
unit of voltage maintained at one location to that maintained at another
location. A transport standard can either be used to calibrate a reference
standard or to disseminate the volt from the reference standard to other
lower level standards.
b. Reference group.
A designated group of cells used only for main-
taining the volt in a calibration facility. This group is not normally used
in performing routine calibrations.
c. Working group. A designated group of cells which may be used as a
standard for performing routine calibrations in a calibration facility.
d. Observation.
A noted occurrence involving a measurement with a
standard or test system.
An observation is the simplest piece of
information (data) that has independent significance in a calibration.
e. Run.
A sequential group of observations in a test procedure or
measurement design.
f. Army Calibration Facility (ACF). An Army activity that is assigned
the mission to provide US Army Area or Internal Calibration Laboratory
Calibration and Repair Service.
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