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

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Dear all,
I first have to state that I dont have lot of experience with electronics but I hope the information I will supply will be adequate to understand the source of my problem.
I am using the Cynergy UF Series flow sensor(Datasheet attached)
I use the sensor in NPN pulse mode and have connected the signal output to the Vcc with 10K Ohm resistor as suggested. I use one power supply.

I power up the sensor with 24V. However the signal outputs 8V in relation with the ground ( isn't it supposed to be 24V?). When the sensor is running the high is around 8V and the low around 7V.

It never goes close to zero. Using the oscilloscope I can see the pulses when water flows through it. Additionally, the led indicators are lit according to the datasheet.

However I want to use the signal as input in a digital module that recognizes from 2V to 5.5V as High and anything lower than 0.8V as Low. Lowering the Vcc voltage doesn’t help since the difference between High and Low is always lower than 1V and the signal is of no use.

Do you have any workaround on the issue? I don’t understand why the Low doesn’t get to ground.

I attach a schematic with the connections. (I am using a standard breadboard)
Please let me know if you require any extra information
Thanks a lot in advance for your help

Kind Regards,
Kostas
 

Attachments

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
Is anything connectd to the signal pin except the 10k resistor and the 'scope?
Hey Albert, No there is nothing else connected to the signal except the 10K resistor and the scope. All the voltage drop is across the 10K resistor as I just measured. Whatever value of pull up resistor I use I still gate a voltage drop of the order of 15V to 16V.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
I don't understand your breadboard connections but it should be wired as below.
You will also need to reduce the signal for 5 volt logic using R2.

Thanks for the reply sghioto . I left the 10K resistor as it is and connected the signal with the ground with a 2,7K resistor but the output voltage range of the signal remain the same between 7 and 8 V.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
You need to show the connections circuit overleaf mentioned in the data sheet.
Hey crutschow, the connection circuit is shown in the second page of the datasheet. I tried to implement both configurations with 1 and 2 power supplies but still not able to get a usable output signal
 

djsfantasi

Joined Apr 11, 2010
7,626
Why can’t you use a differential amplifier, to look at the voltage difference between the lowest output voltage (set with a voltage divider) and the actual sensor output. This would give you 0V (or very close) if the difference was close to zero; and amplify the 1V difference to a value above the logic threshold. I found example circuits by googling “op amp subtractor”, given that I was looking to reduce the lowest sensor output to zero volts. The first result was a differential amplifier. I expected to need another circuit to amplify the 1V difference to a logic threshold. I was pleased that the differential amplifier did both. Note, I have not used this design practically. So, I’m just providing an idea.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
So, in your diagram, which sensor wire is red, which is blue, and which is black?
In my diagram the blue is the green cable in the middle designated as signal,the red is the orange one designated as + sensor and the black is the bottom black designated as ground sensor. The yellow cable designated as ground goes to the ground pin of the digital module and the other green cable on the left designated as signal goes to the signal pin of the digital module.
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
So the signal wire is connected to the digital module?
With that wire disconnected what voltages do you get?
Yes the signal is connected to the digital module so I read the values through LabVIEW.
I get a value of 8V between signal (green in my picture) and ground (yellow in my picture) when I apply a boltage of 24V across VCC and ground. However I assume I would expect 24V since signal is connected to Vcc with the pull up resistor. But for some reason the voltage falls 16V across the pull up resistor.
 

AlbertHall

Joined Jun 4, 2014
11,218
Do you have a multimeter?
If so disconnect the signal wire from the digital module and measure the signal voltage with the multimeter.
 

sghioto

Joined Dec 31, 2017
2,332
If you are interfacing with 5 volt logic you should use the Orange output wire as it's output says 0 to 5 volts.
I believe the correct wiring is:
1617663077833.png
 

Thread Starter

Kostas Kourbetis

Joined Apr 5, 2021
18
If you are interfacing with 5 volt logic you should use the Orange output wire as it's output says 0 to 5 volts.
I believe the correct wiring is:
View attachment 234629
Thanks for the recommendation sghioto, that would be the last resort if nothing else works out. I try to make it work with the Pulse Output since this configuration is supposed to give the highest performance according to the manufacturer.
 
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