It is tuned to the specific frequency of the signal to be received. It may give a visual or audible indication of the presence of a target line, the location of the line and the depth of the line. A measure of the minimum electromagnetic signal that can be reliably identified by the receiver. This value is typically established in controlled conditions in the laboratory. A feature of the receiver, whereby the relative strength of the signal being received is indicated either visually or audibly.
Visual indications are by means of a digital or analog meter.
Audible indication is by the pitch or loudness of a tone. The signal strength depends on the current in the target line and its depth among other factors. Sonde A small transmitter that emits electromagnetic energy at a specific frequency. This device is pushed into a pipe or duct by means of a rod, and its location is found by means of a receiver. These devices are often used to find faults in sewer pipes.