Sensors- How to and why? - Outputs type
Sensor output types
1. NPN Output
- Description: NPN (Negative-Positive-Negative) output refers to a type of transistor configuration commonly used in electronic circuits. In the context of sensors, an NPN output will connect to the negative ground when activated.
- Application: In sensors like photocells, inductive, and ultrasonic types, NPN outputs are often used in systems where the control logic operates on a ground reference. This makes them suitable for many industrial automation systems.
Definition: In a sinking configuration, the sensor output connects (sinks) the load to the ground. When the sensor is activated, it completes the circuit by connecting the load to the ground, allowing current to flow from the positive supply through the load to the sensor.
In Practice: For a sensor with an NPN output (which is a type of sinking output), upon activation, the sensor connects the load to the ground. The current flows from the positive supply through the load and 'sinks' into the sensor.
When the NPN output is off sensor output is effectively floating, so you can get strange voltages, if not connected to a load.
2. PNP Output
- Description: PNP (Positive-Negative-Positive) output is another transistor configuration. Unlike NPN, a PNP output connects to the positive voltage when activated.
- Application: PNP outputs are common in sensors for environments where the control logic requires a positive reference. They are particularly useful in systems where grounding is an issue or in certain safety-related applications.
Definition: In a sourcing configuration, the sensor output provides (sources) the voltage to the load. When the sensor is activated, it connects the load to the positive supply voltage. This is akin to the sensor 'pushing' current through the load to the ground.
In Practice: In a sensor with a PNP output (which is a type of sourcing output), when the sensor detects the target (like an object for a photocell or a metal for an inductive sensor), it will connect the load to the positive voltage. The current flows from the sensor to the load and then to the ground.
When the PNP output is off sensor output is effectively floating, so you can get strange voltages, if not connected to a load.
3. Push-Pull Output
- Description: Push-pull outputs can actively drive an electrical load either to the supply voltage (push) or to the ground (pull). This type of output offers both sourcing and sinking capabilities.
- Application: In sensors, push-pull outputs are versatile, providing compatibility with both PNP and NPN input logic. This makes them suitable for a wide range of industrial applications.
(Sourcing and sinking) ( PNP + NPN )
4. NAMUR Output
- Description: NAMUR outputs are designed to comply with the NAMUR NE43 standard, characterized by low signal levels. They are intrinsically safe, making them ideal for hazardous areas.
- Application: NAMUR outputs are used in sensors that operate in explosive or hazardous environments, ensuring safety and minimizing the risk of ignition.
5. TTL (Transistor-Transistor Logic) Output
- Description: TTL outputs use transistors to perform logic gates and operate at lower voltage levels, typically 5V.
- Application: In industrial sensors, TTL outputs are often used for communication with microcontrollers and digital circuits, where low voltage levels are required.
6. HTL (High Threshold Logic) Output
- Description: HTL, or High Threshold Logic, operates at higher voltage levels than TTL, typically around 24V.
- Application: HTL outputs are used in industrial environments with longer cable runs and where higher noise immunity is required, such as in large machinery controls.
7. RS422 Output
- Description: RS422 is a standard for serial communication that allows for higher data rates and longer cable lengths compared to RS232.
- Application: In sensors, RS422 outputs are used for digital communication over longer distances and in environments with significant electrical noise, ensuring reliable data transmission.