A type of transducer, ultrasonic sensors can convert an electrical signal into ultrasound waves. However, they can also be used to operate in the reverse fashion, if desired. Because this type of sensing device can both transmit and receive, it is regarded as a type of transceiver. Passive ultrasonic sensors are commonly used in industrial settings. Operating in a similar way to microphones, they sense ultrasonic noise that might be present and report this to a datalogger or a computer, once the sound has been converted into an electrical signal. Conversely, active ultrasonic sensing equipment generates a high-frequency sound wave and then evaluates the echo it receives, a little like a sonar system. By determining the amount of time that has elapsed between sending a signal and detecting its echo, it is possible to work out the distance between the device and any object nearby that might be causing audible reflections. Used in this active way, ultrasonic sensors are often referred to as proximity sensors. Made by companies such as Honeywell and Pepper+Fuchs, sensors such as these offer a wide choice of acquisition ranges, from just a few millimetres to several metres. Many ranges come with a choice of operating voltages, as well as various connection types, such as M12 and M8 plugs.