Selection of proximity sensors - npn(sinking?) vs. pnp(sourcing?) perhaps for the NI-9403?

[jdude]

I need to select proximity sensors and was thinking of using the 9403 with my compact DAQ chassis.  Can you help me better understand the 9403?  The data sheet says it is compatible with 5V TTL logic devices.  So does this mean I need npn or pnp sensors?  Any other prox. sensor selection tidbits are welcome.

Thanks!

[Chris_W.]

Hi ncdoody,

The specification of “TTL compatible” simply refers to the fact that it is able to read logic levels using the TTL standard, Low = 0V –  0.8V and High = 2.2V – 5V.  Whether you get a sensor that uses NPN or PNP transistors is not really relevant. Most of the transistors used these days are NPN. The most important thing to pay attention to is specification of the output for the proximity sensor,  and whether it outputs a TTL signal. This is the factor that will determine whether that particular sensor can be used with the 9403. Here is some information about TTL (Transistor-Transistor Logic).

Chris N White
High Speed Products Group

Message Edited by Chris W. on 10-30-2008 12:50 PM

Message Edited by Chris W. on 10-30-2008 12:50 PM

[jdude]

Thanks Chris...

So it doesn't matter whether the sensor is sinking or sourcing?  Is the 9403 neither sinking nor sourcing? 

Please excuse my inexperience.

[Chris_W.]

No worries. The important thing here is that this module is simply reading a voltage from the sensor with reference to the ground of that sensor. This means that this module is always going to be a sinking device, and will be always be sinking small amounts of current from that sensor. This means, that your sensor is going to be powered externally and we will simply be reading the output voltage from it. Here is a link to a knowledgebase article about sinking and sourcing current. I hope this helps to clarify.

Chris N White

High Speed Products Group