NPN proximity sensor connection.

[Shankman]

Hi,

I am new to LabVIEW, I am trying to connect an NPN inductive proximity sensor to the NI CompactRIO chassis (cRIO-9014). My understanding is that the proximity sensor would give out a digital signal. I have access to the NI9401 module. Can I use a NI 9923 connector to connect the sensor or do I have to get the NI9422 module? The ratings of the sensor are as follows:

Contrinex, NPN NO Embeddable

DW-AD-501-P8

https://www.contrinex.com/product/dw-ad-501-p8/

Input voltage: 10 - 30 VDC

I also have access to an Agilent 6682A power supply which I can use for the source.

Also, while connecting the sensor should I use resistors in between the source and sensor. It would be great if someone could help out with the circuit diagram as well. 

[Henrik_Volkers]

First we have a look into the datasheets: (Bonuspoint for your question, you provided a link 🙂 )

and of the NI9401

the sensor needs a 10V (min) supply, that's more than the spec of the DI input want to see 😉

so yes, you need a resisitor and to be kind to the DI some sort of voltage limiting in the range of 2-5 V.

Voltage limiting in this case could be 3-5 diodes (1N4148 or 400x or ) each good for ~ 0.7V   or a z-diode with 3-5V or (my choice) 1-2 LEDs, number depend on the forward voltage, a typical blue one has 2,7 to 3,5V perfect 🙂

Since you need a external supply for the sensor anyway with 10-30 V ,

+ supply to PIN 1

- supply to PIN3 and COM.

the resistor goes from + supply (and PIN 1) to the PIN 4

the LED (or other diodes) goes from PIN 4   to PIN 3 (+COM)

PIN 4 (+R+LED) to  the DI

The value of the resistor limits the current . 10k Ohm is a good value. Pin 4 (the NPN output , that shortens the pin 4 to pin 3 (- supply and COM) ) also connects to the DI.

(DI for DIOx of 9401)

Before you connect the sensor with the resistor and LED to the 9401, it's a good idea to check the voltages with a multimeter.

Not activ the LED should lit and you should measure a voltage in the range of 2-5 V. With the sensor active the LED should turn off and the voltage should be below 0.8 (better 0.3) V , I expect nearly zero 😉

Another way with just one resistor (4.7-10k) would need one of your DIOs to be configured as an output to source 5V .. see schematic of DIO1 in the fig. . The switch is pin 4 and pin 3 of your sensor.  But another 'Hello World' and a free DIO is worth a LED 😄