High-precision measurement and control facility for electrical-resistivity experiments in an He i i environment

A control and measurement system is described that provides direct digital output of the electrical resistance of a metal sample with an uncertainty of < or =5 x 10(-9) Omega at 1.7 K with a linearity of +/-0.04%. In addition, the system allows in situ isochronal and isothermal annealing experiments to be performed with DeltaT< or =0.1 degrees C and Deltat< or =3 s between any two temperatures. With the exception of two commercial instruments, all devices were made with readily available components.