Inductive proximity sensor reading

[Nryk]

Hi everyone,

I need to get the output signal from an inductive proximity sensor PNP NO. I have a cDAQ-9188 and a NI-9215 module but I am not pretty sure if it is possible to get the signal with this module. If not, I would like to know what kind of module I need.

Thanks.

[Dennis_Knutson]

The 9215 senses voltage so if your sensor outputs a voltage signal, you are probably set to go. Since you did not specify the make and model of the sensor, or the type of output, or provide the manual, pretty hard to help you.

[Nryk]

Sorry, the sensor is from Pepperl + Fuchs, model NBB0,8-5GM25-E2. The voltage supply has to be between 10 and 30V but I have no clear neither the type of output nor the range of it. I have read that this type of sensor are normally used with an actuator, but what I want is to connect it with the cDAQ to monitorize the signal.

Please see attached the specifications of the sensor. 

[johnsold]

According to the specifications that device is a switching device. The output depends on the supply voltage you connect and the load circuit.

It appears that the switch will conduct when the target is closer than 0.8 mm or less, depending on the target material. If you use a power supply of 10 V and a load resistor of 1000 ohms, you should be able to use your DAQ device to detect the presence of your target. If your power supply is higher than 10 V, use two resistors as a voltage divider for the load.

Lynn

[Nryk]

Ok, thank you very much! I'll think about it.

[Nryk]

Hi again,

I’ve been thinking about including a 1000 ohms resistance if the power supply is 10V but I cannot find the reason of it. As NI9215 has +-10V input range (and there is also a voltage drop because of the sensor), why do I need to use a resistance? And if the voltage supply is higher than 10V, why do I have to include a voltage divider? I attach the scheme of the circuit I am considering (The resistances are provisional in function of the answer I get). Please let me know if I am wrong. Thank you so much again.

Enrique.

PS: My NI9215 has BNC terminals instead of screw ones, so if I am not wrong, the input should be differential instead of single-ended, shouldn’t be? Does it affect to my circuit?

[johnsold · Accepted solution]

Enrique,

You need to think in terms of current flow as well as votlage drops.

The sensor acts like a switch. It connects the output line (the one you have shown connected to R1) to the V+ line when the target is sensed. If you had no resistor, it would be short circuiting the power supply from V+ to V-. The likely result would be the destruction of the sensor.  By connecting R1 and R2 as shown below some current will flow from the sensor output to ground when the target is present. This will cause a voltge drop across R2 which is then measured by the NI 9215.  The values of R1 and R2 are chosen so that the maximum voltage across R2 is less than the 10 V limit fo the DAQ device. For a 10 V power supply R1 could be zero ohms (a wire in place if the resistor). If the power supply is 24 V and R1 is 1000 ohms, then R2 would be 1500 ohms.

Since the negative side of the input to the DAQ device is at the power supply negative point (ground), single ended input configuration is appropriate.

Lynn

[Nryk]

Thank you very much Lynn, I was I little bit confused about voltage drop and short-circuiting as you noticed. The scheme has been very helpful for me. Now all is clear. Thanks again.