The Cello GSM Level Recorder combines the Siemens Milltronics ultrasonic level sensor and the Technolog Cello GSM/SMS Data Logger. The result is a battery-powered level measurement system with remote communications.

Traditionally, ultrasonic sensors and GSM modems have been mains powered, since both devices consume significant power during operation. The Cello GSM Level Recorder utilises Technolog's power-saving techniques to provide up to 3 years’ battery life.

The system comprises two parts: the ultrasonic sensor and the GSM data logger, which are connected via a 10m cable. This allows the sensor to be mounted directly above the surface of the material to be measured and the Cello to be housed in a more convenient location.

The sensor houses the ultrasonic transducer and temperature sensing element. The sensor emits a series of ultrasonic pulses from the transducer. Each pulse is reflected as an echo from the material and is sensed by the transducer. The echo is processed and filtered to help discriminate between the true echo from the material and false echoes. The time for the pulse to travel to the material and back is temperature-compensated and then converted to distance.

The numeric values are read by the Cello and recorded in memory at predetermined intervals. Periodically, such as every day, the recorded values are transmitted by SMS (text message) to a host computer or to the Internet. The SMS usage is dependent upon several factors, including the recording interval and data send frequency. Typically the system will use one SMS per day. In the event that one or more measurements are outside preset parameters, the Cello will immediately send an alarm message, which can be received by email, SMS or an alarm banner on the host computer.