Convert NPN to PNP sensor using relay

[Tomasz_Kowalczyk]

Hello Jobar 1933!

Did you manage to solve the problem? Was any of the advises helpful?

[Jobar1933]

Using a 20k resistor instead of the 2.2k indeed reduced the voltage at the digital input down to about 8.2V from a 24V power source.

However when measuring between the digital input and ground with an oscilloscope, it remains at 8.2V and doesn't change even when my whole system is running. I've tried many different sample time, none showed anything. That sensor range is 37-917 Hz, meaning 27-1.1 ms.

Edit: Message posted at the same time as Tomasz_Kowalczyk, no sorry still not solved 😞

[Henrik_Volkers]

How does the signal on the scope look like if you measure only the sensor with a pull up without connection to the DAQ? 

Connected between 24V GND and pulse out.

You should see nice triggerable pulses on the scope.

HAve you tried another DI (just in case it's broken)

The sensor range is one thing ,as noted in the spec, but how long are the pulses?

[Jobar1933]

Thanks again for the support, and sorry for the delay.

So I doubled checked the sensor wiring, its all good.

Then I connected the sensor to 24VDC+ and 24VDC-. I then connected the SIGNAL wire to my oscilloscope, and the oscilloscope earth to the 24VDC- and I have added the 20kohm resistor between SIGNAL and 24VDC+.

No matter what sample time I set the on the oscilloscope, the signal stays at 24V. I've tried 2 different sensors, with the same result. I am really starting to wonder if either my sensors are dead, or if I am really stupid and not seeing what's wrong here. Electrics is not really my field but this is really basic!

Confused.

[Henrik_Volkers]

check the connector and cable..

try it with single  wires, the bare end wrapped around the connector pins

[JB]

The datasheet of the flow sensor says this :

Output NPN Sinking Open Collector @ 20mA Maximum

(1 to 2.2K Ohm Pull-Up Resistor Required)

Do you get the expected signal if you go back to a 1-2.2K resistor ? Only flow sensor, without DAQ. 

[Jobar1933]

So I had time to test this, and it still won't work even using a 2.2k resistor.

The value I get between the signal output and ground stays at 24V.