Sinking and Sourcing PLC Inputs with PNP NPN Sensors

Summary

This video explains the crucial concepts of syncing and sourcing in PLC systems, focusing on how to determine the right type of sensor for different PLC inputs. Tim clears up common confusion around NPN (sinking) and PNP (sourcing) sensors, discussing the different ways they work with PLCs like the Allen Bradley 1769 L16 and L24 models. With practical wiring examples, the video guides viewers through understanding sensor requirements, helping them determine whether to use sourcing or sinking sensors based on the PLC’s configuration. The video also addresses common viewer questions and offers valuable insights for industrial automation systems.

Takeaways

• 😀 Syncing and sourcing can be confusing because different PLC manufacturers define these terms differently.
• 😀 PNP sensors are sourcing sensors, meaning they send power (positive voltage) to the PLC input.
• 😀 NPN sensors are sinking sensors, meaning they receive power (sink current) from the PLC input.
• 😀 For PLC inputs that are sinking, you need a sourcing sensor (PNP). For sourcing inputs, you need a sinking sensor (NPN).
• 😀 The 90% of major PLC manufacturers define syncing and sourcing consistently, but a small percentage of manufacturers do the opposite.
• 😀 Check your PLC manual carefully to understand whether it uses sinking or sourcing inputs and outputs for correct sensor matching.
• 😀 The basic setup for syncing and sourcing circuits involves ensuring that the positive side of the sensor connects to the correct PLC input terminal.
• 😀 Contact closures (e.g., push buttons, limit switches) are simple to wire with either sinking or sourcing configurations depending on the PLC input.
• 😀 It’s crucial to understand the sensor type and the wiring for each PLC model, as some allow for mixed configurations (e.g., L24 can handle both sinking and sourcing).
• 😀 When wiring PLC inputs with PNP and NPN sensors, always refer to the sensor’s specific configuration—PNP for sourcing and NPN for sinking.
• 😀 NPN sensors might be faster and more suitable for high-speed applications, though the choice between NPN and PNP should be based on the specific application and PLC setup.

Q & A

What is the main topic of the video?

The main topic of the video is about syncing, sourcing, NPN, PNP sensors, and how to determine the correct type of sensor needed for your PLC input.

What is the confusion around syncing and sourcing that the video addresses?

The confusion arises from varying definitions of syncing and sourcing by different PLC manufacturers. Some manufacturers define these terms differently for inputs and outputs, which leads to misunderstandings.

How do PLC manufacturers typically define syncing and sourcing?

Most PLC manufacturers define syncing and sourcing the same way, but about 10% of manufacturers define them differently. In some cases, even the same manufacturer may define these terms differently for inputs and outputs.

What is the difference between NPN and PNP sensors in terms of sourcing and syncing?

A PNP sensor is a sourcing sensor, meaning it sends power out (positive). An NPN sensor is a sinking sensor, meaning it sinks power (negative). This is the fundamental difference between the two types of sensors.

What are the main configurations of PLC inputs and outputs discussed in the video?

The video discusses two types of configurations: the Allen Bradley 1769 L16, which has sinking inputs and sourcing outputs, and the 1769 L24, which can have either sinking or sourcing inputs and outputs.

How does the Allen Bradley 1769 L16 PLC work with sensors?

The Allen Bradley 1769 L16 has sinking inputs, which means it needs a sourcing (PNP) sensor. Its outputs are strictly sourcing, so it requires a sinking (NPN) load.

What should you do if the sensor is already specified for an application?

If the sensor is already specified, you must adjust the wiring to match. For instance, if you have a sourcing sensor, you'll wire the PLC inputs to be syncing. If you have a sinking sensor, you'll wire the PLC inputs to be sourcing.

How do you wire a contact closure to the PLC?

For a sourcing PLC input, you wire the contact closure to the sensor and connect the PLC input to the sensor, with the other side of the contact closure connected to the negative power supply. For a sinking PLC input, the power is sent to the sensor, and the other side of the sensor connects to the PLC input.

Why is it important to understand the sensor type (PNP or NPN) when wiring PLCs?

It’s essential to understand the sensor type because the wiring configuration depends on whether the sensor is sourcing or sinking. Using the wrong type can cause incorrect operation or failure of the system.

Which sensor type (PNP or NPN) is better for high-speed applications?

NPN sensors are often used in high-speed applications because they can operate faster, though this is based on the assumption that NPN sensors are faster. There is no definitive proof presented in the video regarding the speed difference.