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Abstract
There are several designs of instruments and various techniques
for measuring the a.c voltage. The a.c-d.c thermal transfer standards represent the common method for measuring the a.c voltage accurately in
terms of the d.c voltage. The single junction thermal converter (SJTVC)
is widely used as a.c-d.c thermal transfer standard. It is to be noted that the SJTVC is mainly an active electric resistor (heater) whose
temperature is sensed by a standard thermocouple element. This device
has an input which is either a.c current or voltage and an output signal
represented by the output voltage of the thermocouple. This thermal converter suffers from many drawbacks such as, it has low d.c output
voltage requiring accurate milli-voltmeter to measure it which its
accuracy and resolution at this range of d.c voltage is very small. This
leads to high uncertainty and not very high accuracy of a.c voltage
measurement. Also, the SJTVC is limited in usage at the high frequencies
which is higher than or equal to 100 kHz.
These drawbacks are studied and treated in this thesis through fabricating of modified designs TVCs. The suggested solution depends on three different electrical connections of a number of new single junction vacuum thermocouples their heaters leads gathered in three groups; Series, Parallel and Series/Parallel arrangements. The modified TVCs are implemented entirely in National Institute for Standards (NIS), Egypt to improve the capabilities in ac voltage measurements. Referring to the above description of the SJTVC, these designs cover a range of voltage from 200 mV to 1000 V at frequencies from 20 Hz to 100 MHz but they are calibrated to 100 kHz only due to technical limitations. As a
result of the steadily increasing demand for high accuracy a.c voltage
measurements at high frequencies, single junction vacuum thermocouples (UHF-type) will be used in these new designs. This type of thermal elements will be used to replace of the conventional type of the thermalelement.
Also, in this thesis a trial is made to fabricate a.c voltage standard sources which benefit from the advantages of the thermal element and depend on its theory. The a.c voltage is obtained by designing two a.c voltage standard sources one at 1V and the other for the 10V a.c. The higher voltage level of 10V can be theoretically used but due to certain technical limitation it is used in the range of 5V only. This is in a way similar to the d.c voltage standard sources (the solid-state voltage source
and the saturated standard cell) which have a 1V and 10V d.c voltage standard sources and the other ranges are obtained by using voltage dividers.