Operation and reference manual for the NIST automated AC-DC calibration systems and software

Abstract

Introduction-3 a glass form. In either case, for higher voltages, the resistor makes the dominant contribution to both the ac-dc difference and the uncertainty of a TVC [16,17]. The NIST Automated Systems for Thermal Transfer Standard Calibrations The present generation of NIST automated thermal transfer standard calibration systems was begun by a prototype system designed by Earl S. Williams and assembled in the early part of the 1980s [18,19]. This system was initially intended for the testing and development of solid-state transistor-based sensors. It became obvious that this automated system was also ideal for routine ac-dc difference measurements as part of the regular NIST calibration service for thermal transfer instruments. Accordingly, it was employed for some routine calibrations in early 1984. Because of the success of this system, a second automated system was assembled and used for routine calibrations beginning in 1985. A third automated system, initially intended for current calibrations, was assembled in 1998, and a fourth in 2000. Because of the availability of highperformance transconductance amplifiers, all four automated systems can be used for both voltage and current calibrations. Although these three automated systems differ in their exact details, all automated ac-dc calibration systems have several common attributes, as shown in Figure 1. All must have highlystable and precise sources of ac voltage or current and dc voltage or current, an arrangement for switching between the ac and dc signals, and a method of monitoring the outputs of the thermal converters with adequate precision. In the NIST systems, the ac and dc signals are provided by separate sources, although in principle, a multifunction calibrator might serve as a single signal source, and the switching is accomplished by relays. The millivolt-level output electromotive forces (emfs) of the thermal converters are monitored using sensitive, low-noise digital nanovoltmeters. The systems also have various arrangements of ac and dc voltmeters and frequency counters to monitor the performance of the system. The calibration systems are controlled by Apple eMac [20] running National Instruments' LabVIEW [21] software. LabVIEW is a graphics-oriented system control package, which acts as a "virtual instrument" (VI) during the calibration procedure, displaying data and results in real time as the measurements proceed. This arrangement is a significant improvement over the older BASIC language-based systems, which, although menu-driven and straightforward to use, nevertheless required the operator to proceed through many screens to operate the system. With the "virtual instrument" concept, the same screen is displayed for the entire calibration run (in most cases) and acts as both the input and output stages of the system.

Automated Multi-Meter Method for the Scaling of Low AC Voltage from 200 mV to 2 mV

“…n: response characteristic varies between 1.6 and 2, depending on the amplitude of the input signal [12]. The factor n is automatically determined for the MJTC and all the µPots individually.…”

Electrical Performance Study of a Large Area Multicrystalline Silicon Solar Cell Using a Current Shunt and a Micropotentiometer

“…It is of a coaxial design; the resistor being a web of wire arranged coaxially about the axis of the shunt. The input terminal is a female UHF connector at one end, and the potential terminal is a male UHF at the other [15].…”

An Improved Design of a Fully Automated Multiple Output Micropotentiometer

“…Sufficient time had been allowed after each current change for the SJTC to reach its final emf value [22]. After completing these four steps, the AC-DC difference (δ) was evaluated at each frequency from the following relation [15]:…”

“…In fact, n is a necessary factor in the equation due to the square law response of the thermal converters. It approximately equals "2" (≈ 1.6 to 2) at rated heater current [22]. At the beginning of the test the value of n must firstly be determined.…”