Beschreibung
The IET Labs HARS-LX series is the world’s highest accuracy continuously variable decade resistor for the most exacting calibration and test applications. The HARS-LX substituter is a precision resistance source with excellent characteristics of accuracy, stability, temperature coefficient, and power coefficient. All these features serve to make it a laboratory resistance standard, exceeded in performance only by stand-alone standard resistors. Hermetically sealed wirewound resistors are used for 1 Ω steps and over. These resistors are carefully conditioned under power and temperature in order to develop the best stability characteristics. Actual experience has shown them to exhibit a storage stability of better than 5 ppm/year, improving as they age. The low-resistance resistors are constructed with resistance wire with a minimum of copper resistance in series to limit temperature coefficient effects. The resistance substituter has a fixed minimum resistance of 10 mΩ. This is implemented by mechanically limiting the 10 mΩ decade from going below the “1” position. In this manner, no zero resistance subtractions have to be made, and the accuracy given is for the absolute reading. The HARS-LX series employs completely enclosed dust-tight very low contact resistance switches. They feature silver-clad copper contacts and quadruple-leaf silver alloy self-cleaning wipers which keep switch contact resistance to under 1 mΩ per decade, and more importantly, keep switch contact resistance reproducible, insuring repeatable instrument performance. High quality gold plated tellurium copper binding posts minimize the thermal emf effects which would artificially reflect a change in dc resistance measurements. All other conductors within the instrument, as well as the solder employed, contain no metals or junctions that contribute to thermal emf problems. The HARS-LX is designed to allow very convenient maintenance of calibration over time. Most decades can be calibrated without changing components or soldering resistors. The decades for the 100 Ω through 100 kΩ steps are calibrated with convenient trimmers. Trimming of the lower decades is also possible. With a resolution as low as 1 mΩ and a maximum available resistance of over 12.2 MΩ, the HARS-LX Series may be employed for exacting precision measurement applications requiring high accuracy and stability. They can be used as components of dc and low frequency ac bridges, for calibration, as transfer standards, and as RTD Simulators.
