I want to know what is difference between NPN & PNP sensors & what kind of sensor (NPN/PNP) is better use.
Thanks in advance,
Dear majid, let discuss about sinking and sourcing sensor.
Sinking sensors allow current to flow into the sensor to the voltage common, while sourcing sensors allow current to flow out of the sensor from a positive source. For both of these methods the emphasis is on current flow, not voltage. By using current flow, instead of voltage, many of the electrical noise problems are reduced.
When discussing sourcing and sinking we are referring to the output of the sensor that is acting like a switch. In fact the output of the sensor is normally a transistor, that will act like a switch (with some voltage loss). A PNP transistor is used for the sourcing output, and an NPN transistor is used for the sinking input.
for more details write to me:
I'm a little confused about "A PNP transistor is used for the sourcing output, and an NPN transistor is used for the sinking input".
I drew an image of a sensor with current flowing into it (sinking sensor); and another with current flowing out of it (sourcing sensor). I'm confused about "sourcing output" and "sinking input". Can you explain further?
It is confusing, not the least because they use conventional current flow rather than electron flow which reverses the sense of source/sink. It's easiest to think of it in these terms. With a positive supply voltage, a normally biased PNP will have its emitter more positive than its collector. So, a PNP output with an open collector will pull a load positive towards the supply voltage when conducting. This gives what is called a sourcing output. The NPN case is opposite so it's collector will take a load towards ground when conducting. That's why PNP and NPN are sometimes used instead of sourcing/sinking, because they are not ambiguous at least with open collector outputs. Inputs get a little more confusing as some can be strapped to be either sinking or sourcing. In general, a sinking input is one that needs to be pulled up towards the positive supply to be true. And a sourcing input is one that needs to be pulled toward ground to be true. So a Sourcing output would normally be used with a sinking input and vice versa. This all assumes positive logic.
I didn't think this was a physics forum. Conventional flow vs. Electron flow ... That's taking the explanation a bit too far! :o)
I am an electronics type, steeped in semiconductor lore. I am not an electrician. Conventional flow doesn't work for semiconductors but, conventions are conventions.
An NPN or sinking output accepts voltage and sinks it to ground to complete the circuit. A PNP or sourcing output sources voltage and the external circuit sinks it to ground to complete the circuit. A sourcing circuit would be drawn as voltage->switch->load->ground. A sinking circuit would be drawn as Voltage->load->switch->ground. In these cases, the switch could be a transistor.
Hope this helps,
NPN needs current and PNP supplies current. that's sinking and sourcing.
sinking means something it will take and sourcing means to provide source to something.
> An NPN or sinking output accepts voltage and sinks it to ground to
> complete the circuit. A PNP or sourcing output sources voltage and
> the external circuit sinks it to ground to complete the circuit. A
> sourcing circuit would be drawn as voltage->switch->load->ground. A
> sinking circuit would be drawn as Voltage->load->switch->ground. In
> these cases, the switch could be a transistor.
The best explanation Bill. Well done!!!
Very good explanation on the sinking and sourcing. So, please correct me if I'm wrong... Meaning to say, for a wiring of field device in a DCS system... Normally the field device screen will be floating and the instrument earth shall be grounded at the System marshalling cabinet at the IE bar. Does this mean that the field device is a sourcing output and the input module is a sinking input?
Thanks in advance guys.
In pnp transistor n-type material is sandwiched between two p-type materials. Where as in npn transistor p type material sandwiched between two n type materials..
in pnp transistor holes are the majority charges carriers & electrons are minority carriers. In npn transistor electrons are majority charge carriers & holes are minority charge carriers
for me to easy remember,
Output NPN sensor is Negative (0Volt), and need positive (+24Volt or whatever voltage supply) to make output working. so in the circuit I Pull up (sourcing) output sensor.
for PNP type sensor the output is Positive (+24Volt), and need negative (0volt) to make output working. so in the circuit I pull down (sinking) output sensor.
I have an application to test the sensors and state, about 30 sensors per test. Some machines use PNP and some use NPN. The control and Logic will be via a programmable Logic controller and the preferred input device will change logic state on voltage/current rise. Does anyone know of an interface that would accept NPN and output it like PNP or vice versa?
Many (opto)isolators will do that, but I'll confess I don't quite understand whether we're talking input or output.
Many PLCs have both PNP and NPN inputs available. Often times it is just a matter of how you wire to the input as the inputs can work either way.
worst case is you might need a pull up resistor and invert the logic in the PLC.