Pulse Output Flow Sensor doesn't output a Low around 0V

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Do you have a multimeter?
If so disconnect the signal wire from the digital module and measure the signal voltage with the multimeter.
I just measured it. When the module is disconnected I measure the full of voltage of the Vcc for the signal voltage(24V). When the digital module is connected I measure 8V as I said previously.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
If you are driving the digital module input directly from the sensor output, the signal is perhaps being clamped to the digital module's supply rail voltage by input protection circuitry.
Hey Alec_t. I get the behavior described above also when the digital module is not powered, so I guess this is not the case except if I am not understanding correctly what you say.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Please try the 5V output.
I will do that, I was trying to make it work with the Instrumentation Amplifier INA 122P but no success until now. I can choose the voltage I want to output to the but still the voltage difference between ouptut and reference pin of the amplifie is close to 1V when the flow meter is operating,so no improvement.
 

Alec_t

Joined Sep 17, 2013
11,984
Is your power supply output floating, or is it connected to ground? Is your scope probe grounded? Do your sensor and digital module share a ground connection?
Your schematic is incomplete. Please show us how everything is connected.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Is your power supply output floating, or is it connected to ground? Is your scope probe grounded? Do your sensor and digital module share a ground connection?
Your schematic is incomplete. Please show us how everything is connected.
Hey Alec, I am using an output floating power supply. My scope probe is grounded and the digital module shares a ground with my sensor. I now used the 0-5 VDC output as AlbertHall suggested with an analog module. It seems to work even though it is quite inaccurate, but should be fine for the needs of the application. Now i want to use a filter to get rid of the Noise coming from the mains. The signal looks like the picture below (with black background) when there is no flow. Do you guys have any tips of how I should implement a simple filter to get rid of the noise present on the signal (noise also visible in the scrennshoot from the excel sheet that shows the flow per min)?
 

Attachments

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
So now it depends on just how everything is connected.


Seconded: Please show us how everything is connected.
So here are the connections(picture attached) . The sensor signal is on the same row with the pull up resistor, even though it is not clear on the photo. The green cable (signal towards digital module) is connected to pin 16 of NI 9401 (https://zone.ni.com/reference/en-XX/help/373197L-01/criodevicehelp/ni_9401/) and the black cable (Ground towards d.module) is connected to pin 3 of NI 9401.
The NI 9401 is connected to embedded to a cRIO 9074 controller.
 

Attachments

LesJones

Joined Jan 8, 2017
3,102
This table shows that the inputs on the NI-9401 are TTL level inputs. TTL inputs tend t float high. It also suggests that the common for the inputs is NOT connected to ground so your negative should be connected to one of the "COM" connections on the 25 pin "D" connector. Are you sure that you have DI01 configured as an input ? Can you post a picture that includes ALL of the wiring including the the connections to the NI-9401 and the flow sensor.

Les.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
This table shows that the inputs on the NI-9401 are TTL level inputs. TTL inputs tend t float high. It also suggests that the common for the inputs is NOT connected to ground so your negative should be connected to one of the "COM" connections on the 25 pin "D" connector. Are you sure that you have DI01 configured as an input ? Can you post a picture that includes ALL of the wiring including the the connections to the NI-9401 and the flow sensor.


Hey Les, thanks for the reply. The common is connected to the ground at pin 3 as shown on the 3rd picture of the attachment. Pin 3 is the cable described as "Ground towards d.module" in the 2nd picture.
The first picture shows the 3 cables coming from the sensor and ending on the board on picture 2(red is plus, black is ground and green is signal). A DSUB cable connects the pins shown in picture 3 to the digital module shown in picture 4. DI01 is configured as input in LabVIEW. Do you have a more clear idea of what's the configuration now?
 

Attachments

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Hey Alec_t, sorry for the picture. I clarified it in a previous email saying " The sensor signal is on the same row with the pull up resistor, even though it is not clear on the photo". It is actually connected on row 15 along with the pull up resistor but it is not visible in the photo.
 

LesJones

Joined Jan 8, 2017
3,102
I still can't follow the path of all the wires between the components. I can't see any blue wire that should be the output from the flow sensor. Post #33 looks like a number of separate photographs rather than one overall photograph.

Les.
 

AnalogKid

Joined Aug 1, 2013
9,070
Still not clear to me:

What is the relationship between connections A, B, C, D, E on your drawing, ans wires Red, Blue, Black on the document? What is the function of each of the connections A-E?

ak
 
Top