An off-duty Sydney police sergeant who was found guilty of using her rank and authority to avoid being randomly breath tested by a junior colleague has been jailed in a Sydney court.

Sarah Louise Johnston, 50, drove away from the RBT site without having been tested after a short conversation with the rookie officer at North Sydney on January 8, 2016.

The sergeant drove away from the RBT site without having been tested after a short conversation with a rookie officer. Credit:Max Mason-Hubers

She wept in the dock on Friday as Judge Christopher Hoy sentenced her to 16 months in jail with a non-parole period of 12 months.

"I consider the offender's conduct was disgraceful," he said at the Downing Centre District Court.

AAP