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What's the difference between sensors and relays?

Someone who is far from the topic, the question may arise: what is the difference between the sensor and the relay? Let's answer this question. Sensor and relay things are fundamentally different. If the sensor is essentially measuring means, relay switching means. As you can see, the difference is quite significant and generally principled.


The sensor's task is to produce a signal indicating the current measurements. While the information coming from the sensor is transferred for processing, transformation or storage in a convenient form, but is not available to the observer or the equipment itself.

Sensors are electronic or mechanical, they usually serve to measure any physical quantity and convert it into a different physical quantity, convenient for equipment or staff. For example, the value of the measured temperature (thermocouple) or magnetic induction (Hall sensor) can be converted into a certain voltage or current.

Widely used sensors in various scientific studies to check settings, telemetry, and quality control in various tests.

Automated control system and a system where it is necessary to obtain information about dimensions, are inconceivable without sensors: system control processes or devices, system control and alarm.

Such quantities as velocity, pressure, displacement, temperature, voltage, flow rate, concentration, current and frequency converted into optical, electrical or pneumatic signals, convenient for measurement, conversion, registration, transfer, and store information about the current state of the system or object control or management.

Electronic sensor, for example, composed of sensor and Converter, where the main characteristics are the measurement range, sensitivity and accuracy.

Historically, the sensors are integrally associated with the measuring apparatus and techniques of measurement as a whole: barometers, thermometers, speedometers, flowmeters, etc.

The term "sensor" is a General concept, which has been strengthened in connection with the distribution of automatic control systems where the sensor is part of a logical chain: the sensor control device the Executive body the object management.


Relay is essentially a key, electronic or solenoid, designed for switching, opening and closing the electrical circuit in response to the input stimulus to the relay. This input action can be both electric and nonelectric.

When you say "relay", usually mean the solenoid that is the device, opening or closing contacts at the time of filing to the relay coil voltage, which generates in the winding a current which in turn generates a magnetic field, leading to mechanical movement (attraction) ferromagnetic armature relay.

The anchor is connected to the mechanical contacts, and is moved together with them, leading to a short or open external circuit. Were widespread before the special relay used as a switch for the turn signals in automobiles.

The main part of the solenoid at all times were and still are: electromagnet, armature and switch. The electromagnet is a relay coil wound on a ferromagnetic yoke. The anchor acts as a plate of magnetic material, it is via the pushers acts on the contacts.

The term "relay" is usually called a variety of devices, the switching contacts in response to a change in some input variable, not necessarily electric.

So, there are "thermal switch" that reacts to temperature change, "photo switch" that responds to the light level, "acoustic relays" responding sound. In fact it is the sensors that are connected to the relay and interacting with them according to a specific algorithm.

The word "relay", sometimes referred to as timers, for example "timer" the timer is connected in circuit with any device, and enables/disables it at time intervals counted by electronic timer that only sends the input signal to the relays for its operation.

For example, the indoor fan runs for a few minutes, then shuts off and turns back on in a few minutes you can say that the timer controls the relay action.

There are on the market and a class of semiconductor switches, called solid state relays. These devices operate similar to a solenoid relay is supplied the input signal and the device switches the working circuit.