DC signals TM172

[otrotabi]

Out of curiosity, I hardly ever do this, I decided to hook up my old oscilloscope trying to find out why I am not receiving the right signal from a turbine type flow sensor. 

I guess there´s a step down converter inside the PLC to give 5V DC. Is this an expected signal from this 5V DC output? I do not care about the ripple but I was wondering if output is fine. Pressure sensors take power from this signal and they work just fine, so I do not suspect this is the reason why the flow sensor is not working fine. The AC ripple period is about 50 microseconds.

24V dc output signal seems fine.

I do not expect any in-depth comments, I am just wondering if anyone has ever checked this. My oscilloscope is a little rusty and so are my electronics skills, so maybe I am doing something wrong here.

[Bastian_Schmitz]

Did you use 24V AC as power supply of the TM172?

If yes try 24V DC. I had a few years ago problems with a 5V ratiometric sensor.

This one give not back a suitable value if the controller was supplied with AC, but with DC everything works well.

The smoothing of the voltage may not be sufficient in this particular case.

[otrotabi]

It is a switch type 24V DC power supply in this case, though I do power up wtih 24VAC many times, so I will keep the reference to the ratiometric sensor in mind.

[FedericoM]

Hi,

have you checked if the 40mA that can be provided by the 5Vout are enough for the sensor?

[otrotabi]

Actually I disconnected the flow sensor and the 5V output signal remained the same. I ended up with this signal you can see in the picture because I because when I first hooked up the scope I got an unsteady signal so I started to play with the scope to see what the signal actually looks like. 

I would like to try using DI1 or DI2 as fast digital inputs and 24 V instead of what I am doing now. How do I read frequency ? Do I need to count pulses or there is an easier solution ?

[FedericoM]

Hi,

you can map the variables related to frequency and pulses of fast digital input as in the attached picture.

The frequency is the one of the last period, so you might need to post filter it.

[otrotabi]

No. It does not help enough. I could not find any information in the manuals on how to use this. I will open a new post for future reference. Thanks.