What is a relay tester?
Generic test devices capable of supplying currents (and also voltages) to relays and testing their performance based on current settings and trip timing.
The obvious simple is someone who tests relays
however, I think you might want something more. in order to test a relay, you need a power supply providing the correct voltage for the relay coil. you then need an element connected to the relay contacts to indicate that a circuit has been created or opened. It can be a multimeter using the scale of restance or a battery and a light that turns on or off depending on the type of relay.
there are semiconductor electronic relays of which I have no experience, but the principle is the same.
it is a problem of nomenclature.
A relay is one of many electromechanical or semiconductor devices in which low-voltage low-voltage can be used to switch much higher voltages and currents. but in the language of the switchboards, it is used to refer to a protective relay which is a complex device that is connected to voltage and current transducers and external devices (such as buchholz relays) to monitor the charging a circuit breaker and trigger charging a wide range of fault conditions.
So a relay tester can be
a device that uses relays to generate a stimulus to test elements such as power supplies or a simple logic,
or that uses relays to simulate the actions of the installation for the debugging programs Plc
a device to measure switching action, switching speed, flight time, synchronization of the differential contact, etc., of a simple relay.
an endurance tester used to approve the type of a relay design based on the number of sample switching cycles
a very specialized device for testing protection relays in arrays, including aspects such as current injection, voltage drop / power failure and response time.
context is everything, and the question is vague.