A recorder is a measuring instrument that display a time varying.Signal in a form easy to examine and re-examine,perhaps long after the original signal has ceased to exist.In other word a recorder is a device whose function is to record the value of quantity as it is being measured.Such device may include graphic recording devices,computer printers,tape recorders,or cathode ray tube.

Recording preserves the experimental data in a manageable and usable form.A recording system is very useful as (i)It preserves information which could be obtained at any instant from indicating instruments and (ii)It gives informations about waveforms and transient behaviour or phase relationship in different parts of a circuit.

A recorder records electrical and non-electrical quantities as a function of time or relates two signals to each other.Electrical quantities,such as current,voltage etc.,can be recorded directly while non-electrical quantities,such as pressure,temperature,speed,flow etc.,are recorded indirectly by first converting them into the form of electrical signal with the help of sensors or transducers.

Recording devices are of two types namely (i)analog recorders and  (ii) digital recorders.