Figure 2-1.
AC voltage calibration using AC-DC transfer technique
2. Dependent on the type measurement required at the secondary transfer level by
the AREA TMDE SUPPORT TEAM (ATST), you may use one or all of the following
instruments which are addressed in this lesson: the Model 540B Thermal Transfer
Standard, Model 1395 Coaxial Thermal Converter Set, and the Model B7842 Thermal
Converter Set.
3. The Model 540B, together with the Model A54-2 Voltage Plug-in Unit (both of
which are pictured in Figure 2-2), constitute an AC-DC Thermal Transfer Standard.
As previously mentioned, these instruments are used for measuring unknown AC
voltages and calibrating AC voltage sources. The unit has 14 ranges of input from
0.5 volts to 1,000 volts.
It is furnished with a solid-state galvanometer,
internal DC reference, search meter, and battery power supply.
A voltage
protection circuit protects all internal circuits from damage as a result of over-
voltages of up to 1,500 volts on any range.
a. The instrument features an input impedance of 182 ohms/volt in all voltage
modes. The galvanometer does not require special mechanical orientation for proper
operation and is no more fragile than any normal meter movement.
The circuit is
equipped with an internal calibration circuit that provides easy and rapid
calibration of meter deflection sensitivity representing 0.1 percent and 0.01
percent at any input. The accuracy depends on the range in use and the frequency
of the AC voltage being measured and varies from 0.2 percent to 0.01 percent. The
thermocouple reversal error (explained in Lesson 1) is less than 0.01 percent of
input at 100 percent of rated current or voltage and less than 0.3 percent at 50
percent of rated current or voltage.
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