need liquid drop sensor schematic

[loup-garou]

hi all,

can anyone give me a liquid drop sensor schematic, I spent hours googling without finding anyone.

the kind I'm lookin for is that using photodiode pass-band, amplifier , controller and other IC (can be replaced with a PIC microcontroller )

please help me.

thanks in adavnce.

 

[Roff]

hi all,

can anyone give me a liquid drop sensor schematic, I spent hours googling without finding anyone.

the kind I'm lookin for is that using photodiode pass-band, amplifier , controller and other IC (can be replaced with a PIC microcontroller )

please help me.

thanks in adavnce.

What is the liquid(s)? How will the liquid be applied to the sensor?

 

[Mikebits]

What is the liquid(s)? How will the liquid be applied to the sensor?

What! Did you forget your crystal ball again? Or was that a miracle orb...

 

[Roff]

What! Did you forget your crystal ball again? Or was that a miracle orb...

Are you makin' fun of me, or him?

 

[tboydva]

Don't know if this is what your after, but since I've always gotten help and never given any (a perennial newbie), I'll point you to a project I did with a bubble counter. Perhaps these sensors would "sense" a drop of liquid falling (vice a bubble rising)? Anyway, in case it helps: https://www.electro-tech-online.com/threads/successful-project-excitement-and-thanks.40147/

Here's the sensor: **broken link removed**

Good luck!

 

[bryan]

Can't help you with a schematic but it might point you in the right direction. Hospital intravenous peristaltic pumps use a drip sensor to monitor the drip into IV. A photodiode beam is broken by the drip. If this "drip" does not happen within a set period it activates a alarm.

 

[bassnut]

How many drips do you want to count?, or just the presence of one, ie rain. I built one to close an Observatory on sensing rain. Just parrellel up veroboard strips (alternate) and connect to a comparator. The drops short out adjacent strips and triggers an alarm. It does sound like you need to measure something else to do with drips, more detail?.

 

[Mikebits]

How many drips do you want to count?, or just the presence of one, ie rain. I built one to close an Observatory on sensing rain. Just parrellel up veroboard strips (alternate) and connect to a comparator. The drops short out adjacent strips and triggers an alarm. It does sound like you need to measure something else to do with drips, more detail?.

After the strips are shorted out by the drops, how do you measure any subsequent drops?

 

[bassnut]

After the strips are shorted out by the drops, how do you measure any subsequent drops?

LOL, you dont, one drop and its all over, the auto-roof-shut kicks in. By the evening, the veroboard is dry again (or you give it a quick wipe). I suspect now the OP needs something more comprehensive tho .

 

[loup-garou]

hi guys,

thank you all for your replies

The liquid is "sodium bicarbonate", the objective is to count the number of drops passing through a tube (with a low and fixed flow).

there should be, of course, a trasnsmitting diode clocked with a frequency.

1 - if there is no drops the pulses of the transmitting are received by the photodiode (with the exact transmitting frequency)
2 - a drop is detected when there is no signal coming from the photodiode for some milliseconds.


1----> if this remains , an output (alarm of empty tube) should become logically high
2----> the counter should be incremented.


I'm thinking of using a PIC insted of analog circuits.

thanks in advance for your interest.

 

[rjvh]

Hi maybe you can tackle the problem from the other side

If it is sodium bicarbonate than I almost think that it is to control/adapt a PH level in an other liquid

the way you aproach it is to measure the quantity by counting drops

How do you achieve these drops ??

normaly you make use of a dosing pump that is normaly a positive displacement pump so that every cycle it pumps has the same volume (regardless pressure)


if you count the cycles of the pump you have the excact volume what you release(depending of the pump capacity) and the puls is coming from the pump it self

if it is an membrane pump it works with a electromagnetic field that activates the membrane (sort of soilenoid)

if it is a piston pump its a mechanical rotation that can be picked up with a different sensor on the pump it self

what are you trying to control an alarm or an adjustment based on readings from an other sensor in the mixed product

Robert-Jan

 

[loup-garou]

Hi maybe you can tackle the problem from the other side

If it is sodium bicarbonate than I almost think that it is to control/adapt a PH level in an other liquid

the way you aproach it is to measure the quantity by counting drops

How do you achieve these drops ??

normaly you make use of a dosing pump that is normaly a positive displacement pump so that every cycle it pumps has the same volume (regardless pressure)


if you count the cycles of the pump you have the excact volume what you release(depending of the pump capacity) and the puls is coming from the pump it self

if it is an membrane pump it works with a electromagnetic field that activates the membrane (sort of soilenoid)

if it is a piston pump its a mechanical rotation that can be picked up with a different sensor on the pump it self

what are you trying to control an alarm or an adjustment based on readings from an other sensor in the mixed product

Robert-Jan

Hi rjvh,

thank you for answering,

the sodium bicarbonate has a medical purpose (perfusion), I made an error by saying that the liquid flow is constant , cause it can be adjusted by the user and thus, the Drop counter is in reality a flow-meter (this part will be treated by the PIC).

concerning the pump, it its mechanical rotation (a stepper motor running a mechanism as below, with a reducer interfaced between them)
**broken link removed**

your idea is good, but in my opinion, it can be used for checking that the speed of the pump corresponds the actual flow rate (adjusted by the user in the pump board keypad) ,but the liquid drop sensor (or flow-meter) should exists.

 

[rjvh]

The pump you use is a positive displace ment pump the only thing you have to do is counting the rotations

The roller a metal object??

you might use a pick up coil and amplify that to give the signal to the PIC

the only thing that you have to do is measure the volume it gives in a shot and you have pretty accurate the dosed volume over time if you multiply it with the revolutions you count from the motor

Robert-Jan

 

[Mikebits]

How about using a mass measurement. NaHCO3 start weight, let's call it SW. Each drop = n mass. So SW - n mass = drops of NaHCO3.
You could measure SW mass by using a strain gauge pully arrangement.

 

[Roff]

The pump you use is a positive displace ment pump the only thing you have to do is counting the rotations

The roller a metal object??

you might use a pick up coil and amplify that to give the signal to the PIC

the only thing that you have to do is measure the volume it gives in a shot and you have pretty accurate the dosed volume over time if you multiply it with the revolutions you count from the motor

Robert-Jan

But what if the flow is blocked somewhere, or the liquid supply is depleted (empty)? Pump rotation does not guarantee flow.

 

[loup-garou]

hi guys,

thanks again for your replays,

as Roff did say, the use of a drop sensor is appropriate,

by luck , I've found a schematic of a drop sensor used for a blood pump from early 90's,

it is almost what I'm looking for, I named (in red)the OP Amp in the schematic (as my understanding of the synoptic), and I'ill be pleased if someone verify it with me,


some questions about the schematic came into my mind:

-what is the role of the rectifier.
-why the Pass band filter have two stages ? (is it possible to replace it with just one ?)
-why do the comparator compare the output signal with 3.4V
-I simulate the first stage of the pass band filter using ISIS Vsm and the frequency graph response shown a high attenuation (-60Db), what is the reason ?
-what are the parts of the schematic that we can replace with the PIC.


thanks in advance.

 

[Roff]

hi guys,

thanks again for your replays,

as Roff did say, the use of a drop sensor is appropriate,

by luck , I've found a schematic of a drop sensor used for a blood pump from early 90's,

it is almost what I'm looking for, I named (in red)the OP Amp in the schematic (as my understanding of the synoptic), and I'ill be pleased if someone verify it with me,


some questions about the schematic came into my mind:

-what is the role of the rectifier.
-why the Pass band filter have two stages ? (is it possible to replace it with just one ?)
-why do the comparator compare the output signal with 3.4V
-I simulate the first stage of the pass band filter using ISIS Vsm and the frequency graph response shown a high attenuation (-60Db), what is the reason ?
-what are the parts of the schematic that we can replace with the PIC.


thanks in advance.

It's difficult to know where to start when describing a feedback loop, but here goes:
The transmitter and receiver are in a feedback loop which forces the amplitude of the bandpass filter (BPF) to be constant amplitude. It does this with a precision rectifier that develops a DC output equal to the peak amplitude of the BPF output. This is applied to the controller op amp, which is configured as an integrator. If the rectifier output exceeds the voltage on the +input of the integrator, the controller output will decrease. A lower controller output causes the transmitter's output level to decrease, which will in turn cause the BPF output to decrease, closing the loop.
The comparator slicing level (3.4V) is set just below the controller reference voltage (+ input), which is, as I said, also the peak amplitude of the BPF output. The comparator will therefore put out a short pulse at each peak of the 1.2kHz modulation signal. Even a small attenuation of the receiver input, caused by a falling drop, will cause a pulse to be missed, triggering the oneshot.

Regarding your simulation, did you apply power (5V) to your op amps?. If not, that is the reason for the attenuation. Otherwise, post the circuit you simulated.

I don't know if you need both stages of the BPF. You could try it with one.

The PIC question would take a long time to answer, at least for me.

 

[Mikebits]

Here is something that might work for you.
https://www.electro-tech-online.com/custompdfs/2008/12/bio_vision01_kamble_drip_rate.pdf

 

[rjvh]

But what if the flow is blocked somewhere, or the liquid supply is depleted (empty)? Pump rotation does not guarantee flow.

Absolutly a point here

It depents on the proces and the consiquences if this occur

also if you want to spend money on it

I deal a fair bit with water teratment filtration systems and its mandetory for our systems that storage of chemicals or other addetive are monitored

so that if the storage gets emty the system will react with a alarm and a bit furter in time preventive shut down (shut down depents on the health hazard)

same as back wash cycles in filters that can be done on time or on increasing pressure drop in the filter (cloged) or based on the quantity that it handles in a sertain time

Back to the posters problem now

you do have quantity meters that switch a contact at a certain volume pass through
but I never seen them in the low flow applications (drops)

you also have flow meters (worked quite often with them ) but again never seen them in the low flow version

although a ultra sonic might work (theory) I fear that the pipe or hose is first to small and second the flow is still to low for a decent reading

it's also quite expencive way of monitoring

the only thing wat i can think of is a light tunnel that can indeed detect a drop

A trouble spot could be the transparantness of the tube used (use glass it would have the least problems over time)

Lack of light absorption of the liquid (sensetivity of the foto diode in the light tunnel)

Ready product schould also be availible and I would look in the labaratory equipment store

sucsess

Robert-Jan

 

[Roff]

Absolutly a point here

It depents on the proces and the consiquences if this occur

also if you want to spend money on it

I deal a fair bit with water teratment filtration systems and its mandetory for our systems that storage of chemicals or other addetive are monitored

so that if the storage gets emty the system will react with a alarm and a bit furter in time preventive shut down (shut down depents on the health hazard)

same as back wash cycles in filters that can be done on time or on increasing pressure drop in the filter (cloged) or based on the quantity that it handles in a sertain time

Back to the posters problem now

you do have quantity meters that switch a contact at a certain volume pass through
but I never seen them in the low flow applications (drops)

you also have flow meters (worked quite often with them ) but again never seen them in the low flow version

although a ultra sonic might work (theory) I fear that the pipe or hose is first to small and second the flow is still to low for a decent reading

it's also quite expencive way of monitoring

the only thing wat i can think of is a light tunnel that can indeed detect a drop

A trouble spot could be the transparantness of the tube used (use glass it would have the least problems over time)

Lack of light absorption of the liquid (sensetivity of the foto diode in the light tunnel)

That's what I liked about the analog circuit that I analyzed in my previous post. I believe it is very sensitive to small changes in the light path, such as attenuation or diffraction.

Ready product schould also be availible and I would look in the labaratory equipment store

sucsess

Robert-Jan