In order to simulate the inputs from a downhole sensor (DHS), RTD type sensors are typically employed, externally heated, and the input provided into an interface unit. At best such an approach provides a solution that is cumbersome and not reliably repeatable. Such temporary inputs seldom provide the equivalent communications protocol verification between the surface controller of the DHS and the external communications device. DHS units commercially available use different register addresses for the requested data, as well as a variation in the number of parameters expected from the DHS itself. The number of parameters may range from 3 to 7 based on the vendor unit selected. In the proposed system, a number of potentiometers are used to provide a variable signal level to the microprocessor, acting as variable parameters from the DHS sensor, the settings of which can be repeated for reliable test or regression test results.