When we talk about proximity sensors, we always think of its output, but what exactly is the output? From a technical point of view, the output of a proximity sensor can be a transistor (PNP or NPN), a relay output, or an analog output(4-20mA for example). Today we are going to cover the difference between transistor and relay output. From this article, you will learn what is a proximity sensor, transistor and relay output in the sensor, and their differences.
What is a proximity sensor?
In short, proximity sensors are used to contactlessly detect the presence of an object within its detection distance. Proximity sensors can be classified into 5 types, namely inductive proximity sensors, capacitive proximity sensors, photoelectric sensors, ultrasonic sensors, and magnetic proximity sensors. For more information, you can check out our article: Proximity Sensor Types: The Most Comprehensive Explanation
What Are Transistor Outputs In Proximity Sensors?
The transistor outputs in a proximity sensor can be PNP or NPN. Both types are based on the switching characteristics of transistors to achieve signal output, but they differ in the way the circuits are connected.
The internal switch of the NPN proximity sensor is connected between the signal terminal and the negative pole. When nothing is approaching, the NPN transistor does not work and the output voltage is high; when something is approaching, the transistor starts to work and the output voltage becomes low. Therefore, if you want the device to start working when something is approaching, you need to connect the device between the output terminal of the sensor and the positive pole of the power supply.
In contrast, the internal switch of the PNP proximity switch is connected between the signal end and the positive pole of the power supply. When there is no signal, the signal output line OUT and the positive pole of the power supply VCC are disconnected, which is equivalent to the output end not being connected to anything; when there is a signal, the output line OUT and the positive pole of the power supply VCC are connected together, and the output voltage is a high level. Therefore, if you want to use a PNP sensor to control a device, you need to connect the output end of the sensor to the device, and then connect it to the negative pole of the power supply to form a complete circuit.
Want to know how to wire the PNP and NPN sensor, please have a look at our this article: PNP VS NPN Sensor: The Ultimate Showdown – Which One Wins?
What Is Relay Output In Proximity Sensor?
Relay outputs are commonly used in 2-wire AC or DC powered proximity sensors. Relay outputs can be powered by either AC or DC, while transistors can only output DC. Relay outputs are designed for high current or high voltage loads.
Differences Between Transistor And Relay Outputs
| Feature | Transistor Output | Relay Output |
|---|---|---|
|
Load Type |
Suitable for DC loads only |
Suitable for AC or DC loads |
|
Load Capacity |
Load voltage: DC 5V to 30V, Load current: 0.2A to 0.5A |
Load voltage: Up to AC 250V/50V, Load current: Up to 2A |
|
Response Speed |
Fast response, typically less than 0.2ms |
Slower response, around 10ms |
|
Lifespan |
Long lifespan due to lack of mechanical contacts, suitable for frequent switching |
Limited lifespan due to mechanical contacts, typically around hundreds of thousands of cycles |
|
Cost |
Lower cost, as it lacks mechanical components |
Higher cost, includes mechanical components |
|
Control Capability |
Suitable for controlling low-current devices, such as indicator lights or small solenoid valves |
Suitable for controlling high-power devices, such as contactors or motor starters |
|
Overload Capacity |
Lower overload capacity, limited ability to withstand inrush current from inductive loads |
Higher overload capacity, can withstand a certain level of inrush current |
|
Application Scenarios |
Suitable for applications requiring fast switching and long lifespan, such as signal lights or small solenoid valves in automation control systems |
Suitable for applications requiring high load current or voltage, such as motor control in industrial machinery |
Conclusion
Now let’s summarize the difference between transistor output and relay output in proximity sensors. Transistor output includes NPN or PNP output, which is mainly used for small DC loads and has three wires, while relay output is suitable for larger loads. Relay output sensors usually have two wires.
Our Lorentzzi proximity sensor transistor output is 200 mA@DC6-36V, if it is relay output, it is 2 amps@AC90-250V. If you are looking for proximity sensors with transistor or relay output, please contact us for the latest price.
