A monitoring arrangement monitors the operation of a cleaning-in-place system which is operable to remove contaminations, deposits and other impurities from the internal walls of a container. The CIP system comprises a pipe for extending into the container through a wall portion of the container, and a nozzle head for ejecting liquid into the container in a predetermined pattern. The monitoring arrangement comprises a sensor unit with a sensing surface responsive to liquid impact for enabling the sensor unit to emit a sensor signal indicative of the liquid impact. The sensing surface is elongated and configured to extend along a perimeter of the pipe when the sensor unit is mounted at the wall portion of the container. This enables improved performance of a processing unit that obtains and processes the sensor signal for monitoring the operation of the CIP system.