A proving unit adapted to verify the operation of a separate voltage measurement device, the voltage measurement device including a housing having a probe portion, the proving unit comprising: a housing having a sensor receiving portion adapted to receive the probe portion of the voltage measurement device during a proving operation; an alternating current voltage source that, in operation, is adapted to provide an AC voltage at an AC output node; a contact AC/DC positive port that is accessible to a test instrument probe of a separate contact voltage measurement device; AC-to-DC converter circuitry that, in operation, is adapted to receive an AC voltage as input and outputs a DC voltage; at least one AC/DC switch (170, 174) that, in operation, is adapted to selectively electrically couple the AC output node of the AC voltage source either directly to the contact AC/DC positive port, or indirectly to the contact AC/DC positive port via the AC-to-DC converter circuitry; a field sense conductor disposed within the housing at the sensor receiving portion of the housing, wherein the field sense conductor is electrically coupled to the AC output node; a mode selection switch; and a controller operatively coupled to the mode selection switch, the AC voltage source, and the at least one AC/DC switch (170, 174), wherein, in operation, the controller is adapted to: receive, via the mode selection switch, a selection of a mode of operation, the mode of operation comprising at least a DC voltage mode or an AC voltage mode; control the at least one AC/DC switch (170, 174) based at least in part on the received selection of the mode of operation; and cause the AC voltage source to provide an AC voltage at the AC output node. a housing having a sensor receiving portion adapted to receive the probe portion of the voltage measurement device during a proving operation; an alternating current voltage source that, in operation, is adapted to provide an AC voltage at an AC output node; a contact AC/DC positive port that is accessible to a test instrument probe of a separate contact voltage measurement device; AC-to-DC converter circuitry that, in operation, is adapted to receive an AC voltage as input and outputs a DC voltage; at least one AC/DC switch (170, 174) that, in operation, is adapted to selectively electrically couple the AC output node of the AC voltage source either directly to the contact AC/DC positive port, or indirectly to the contact AC/DC positive port via the AC-to-DC converter circuitry; a field sense conductor disposed within the housing at the sensor receiving portion of the housing, wherein the field sense conductor is electrically coupled to the AC output node; a mode selection switch; and a controller operatively coupled to the mode selection switch, the AC voltage source, and the at least one AC/DC switch (170, 174), wherein, in operation, the controller is adapted to: receive, via the mode selection switch, a selection of a mode of operation, the mode of operation comprising at least a DC voltage mode or an AC voltage mode; control the at least one AC/DC switch (170, 174) based at least in part on the received selection of the mode of operation; and cause the AC voltage source to provide an AC voltage at the AC output node. receive, via the mode selection switch, a selection of a mode of operation, the mode of operation comprising at least a DC voltage mode or an AC voltage mode; control the at least one AC/DC switch (170, 174) based at least in part on the received selection of the mode of operation; and cause the AC voltage source to provide an AC voltage at the AC output node.