infra-red liquid level detector

[fantabulous68]

infrared water level detector

The design useful in liquid level or proximity detection. It should operate by detecting the distance from the target by reflection of an infra-red beam. It should safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range should be variable, from a couple of cm. to about 50 cm.

Parts:

R1_____________10K 1/4W Resistor
R2,R5,R6,R9_____1K 1/4W Resistors
R3_____________33R 1/4W Resistor
R4,R8___________1M 1/4W Resistors
R7_____________10K Trimmer Cermet
R10____________22K 1/4W Resistor


C1,C4___________1µF 63V Electrolytic or Polyester Capacitors
C2_____________47pF 63V Ceramic Capacitor
C3,C5,C6______100µF 25V Electrolytic Capacitors

D1_____________Infra-red LED
D2_____________Infra-red Photo Diode (see Notes)
D3,D4________1N4148 75V 150mA Diode
D5______________LED (Any color and size)
D6,D7________1N4002 100V 1A Diodes

Q1____________BC327 45V 800mA PNP Transistor

IC1_____________555 Timer IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________7812 12V 1A Positive voltage regulator IC

RL1____________Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm

J1_____________Two ways output socket

Device purpose:

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.
Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.
Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off the LED and the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.
Notes:

* Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
* Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
* R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.
* The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
* Avoid sun or artificial light hitting directly D1 & D2.
* Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
* If you are needing a similar circuit driving 3 LEDs in sequence, also suitable as a parking aid, click here



could som0ne plz provide a more detailed description of what the comparator is used for. What will the cct do with the relay and without the relay. Any other methods of implementing this project? microcontroller? a brief cct description is provided at:

[http://www.redcircuits.com/Page41.htm][/img][/url]

 

[Thanhlongbin]

infrared liquid level sensor circuit

I do not think this circuit can detect the distance from the target. It can detect if there is some target in distane <50cm only.
Non-contact distance mearsurement (or liquid level) with resolution about cm requires more complex signal proccessing algorithm and real-time computing platform.
So this's a simple proximity detector.
In this circuit, the comparator is to reduce noise from far target reflection. Without the relay, the only LED D5 can indicate that there's any target in range or not. The relay can be used to drive external alarming devices (lamp, buzzer,...) or registering devices (datalogger, counter,..).
I think some thing can be enhanced:
1. Transmition frequency (carrier) should be higher with value about a IR TV remote control to reduce AC line noise (50/60Hz) as weel as noise from external lighting sources. The transmitter may work in pulse modulation mode to save energy.
2. In the receiver, a narrow band pass filter is useful

 

[FvM]

infrared liquid level sensor

I agree with Thanhlongbin. Level measurement by optical reflection intensity can't be considered a reliable method because of various disturbing effects, particularly fluid movement, and dirt or condensating conditions affecting the optical path.

Laser TOF (time of flight) or FMCW optical radar would be a reliable method, but obviously much more complex.

 

[fantabulous68]

infrared emitter and receiver threshold level

Thanks for the feed back guys


My design project is an infra red liquid level detector
These are the specifications:
The design should be useful in liquid level or proximity detection. It should operate by detecting the distance from the target by reflection of an infra-red beam. It should safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range should be variable, from a couple of cm. to about 50 cm.


I wanted to use the circuit that i posted. Any suggestions on approaching the design?

 

[FvM]

infra red water level indicator.pdf

I think you understood, that the doubts are basically related to the involved sensor physics rather than the eletronic design.

In my opinion, the project specification isn't clear enough. You can specify the process enviroment in a way, that a simple
intensity measurement can work. But in the general case, it won't.

Another method, to implement an optical distance measurement is a triangulation design. Usually multiple optical detectors or a
linear array are used in this case.

I don't, expect that a TOF or FMCW "radar" design should be considered for the project. But your instructor or whoever
defined the project specification should be able to clarify the point.

 

[Thanhlongbin]

infrared liquid level detector

FvM wrote quite right!
Your project technical requirement is far from completed.
B'cause I have some experience in Optical distance measurement, so I can share with you somethings:
1. Accuracy: You have defined a distance range to measure (1cm-50cm), but it's not enough. You need an expected accuracy. Sub-mm accuracy is not real. Check out it from your Instructor.
2. Optical measurement methods: The first idea is to measure time delay between IR transmitting and receiving pulses. It's so called single pulse method. With light velocity of 3E+8 m/s, at max distance (0.5m) you can get max time delay about 3.3 ns because light pulse travels double distance. This time duration is hard to measure and nothing to say about accuracy!!!
There's an another methode so called "phase measurement" may fuffil your tech. requirements. In this method, IR source (IR laser diode or LED) is modulated AM with modulation frequency F0~30MHz. Instead of time delay said above, you have to measure phase delay between IR transmitting and receiving analog signals. To do that, both of signal are multiplied with a heterodine (internal sinewave oscillation with frequency exactly equ F0-3KHz). After narrow band pass filter at 3KHz, you have 2 new 3KHz (F1)signals with the same phase delay as the 2 above.
For example, with time delay Delta_T0=3.3ns @ 30MHz, you have:
Phase delay=2pi*F0*Delta_T0=2pi*F1*Delta_T1
Delta_T1 is time delay @ 3KHz (F1)
=> Delta_T1=10000*Delta_T0=33 micro-second!!!
Using time counter with clock F0 (30MHz), you easily measure Delta_T1 with accuracy 33ns i.e distance accuracy about 500mm/1000=0.5mm!!!!
Of course this is only theoretical limit when the liquid face is an ideal fixed-flat IR reflecting mirror and and there's no any side reflection!
In real working environment you have to build a physics-mathematical model to estimate affect of noise and other side effect phenomenons.
Good lucks

 

[fantabulous68]

infrared liquid surface detection

Thanx for the help, its much appreciated.

Every design starts with a breakdown of functional modules. So thats were im starting. If i use the circuit i posted, would this be an appropriate corresponding breakdown of the design?

Push button-refers to the power supply being on

 

[fantabulous68]

infra-red level detector

specialist interview:

Does any1 have an insight into what it takes to produce and sell infra red liquid level detectors?

could you plz assist me in conducting a feasibility study on infra red liquid level detectors


Feasibility:

The Market Feasibility
The Technical Feasibility
Financial Feasibility


Thanx

 

[ark5230]

build tank level detector

YES I do have a very useful suggestion. Just stop thinking along these lines. If you are able to understand the details given by 'Thanhlongbin' you would realize the complexity of implementation of Phase sensitive detection.
With ordinary approaches like one shown in the diagram, the best way is to switch to something like ultrasonics and not the IR or Visible part of the e-m spectrum. The timings corresponding to distances in question can not be handled by simple means and needs knoledge of several advance areas.

 

[Thanhlongbin]

feasibility liquid level indicator

Dear Fantabulous68,
It seems to be something mis-understanding in terminology so called "distance (or liquid level) detection". Previously I thought you want to measure some distance from detector to the nearest targets (liquid face). I was wrong! You do not need it ! Sorry for my mistake.
I suggest you need only to detect if the target (or liquid level) is in pre-defined distance range from the detector then send a alarming signal to another devices or equipments. Is that right?

 

[FvM]

lcd anode cathode connection

I understood, that the intended application is a level switch with up to 50 cm adjustable distance. Unfortunately, it has to deal basically with the same issues as a continuous level measurement. Optical waveguides are a common solution for liquid level switches, but I won't designate the method contactless.

 

[Thanhlongbin]

best way to measure the liquid level

Dear FvM,
As I now, for such application with liquid level, there're some classical methods like: pressure measurement, resistive or capacitive detection,..All of them require a mechanical and/or electrical "contact". So another methods which is based on optical or ultrasonic wave are naturally called "non-contact". It may be not an official scientifics term.
I agree with you that level detection "has to deal basically with the same issues as a continuous level measurement". But I think the first one is more simple and available than the last one especially if detection does not require high accuracy.

 

[FvM]

how infrared water level detector works

My comment was about simple optical methods rather than level measurement in general. I doubt, if the presented method can work even for low accuracy requirements.

The original circuit has been intended for solid surfaces distance measurements and low distances.

 

[Thanhlongbin]

ac fluid level sensor

My comment was about simple optical methods rather than level measurement in general. I doubt, if the presented method can work even for low accuracy requirements.

I hope with 20% accuracy (50cm+/-10cm) it can work!

The original circuit has been intended for solid surfaces distance measurements and low distances.

I would say:
The original circuit has been intended for target detection with solid surfaces and low distances.
It remembers me the vehicle counter in the gateway.

 

[fantabulous68]

infrared water level sensor circuit

"I suggest you need only to detect if the target (or liquid level) is in pre-defined distance range from the detector then send a alarming signal to another devices or equipments. Is that right?"


yes that is right Thanhlongbin




It is a constraint that i use infra red. I cannot change that specification given to me ark5230

Added after 8 minutes:

thanks to every who takes der time to view my topic and contribute. i am trying to get a clear understanding b4 i start this project

 

[kender]

infrared water level detector using

So, it looks like the plan is to sense the intensity of the IR reflected by the face of the liquid. Then make a threshold comparison with some intensity that corresponds to 50cm. IMHO, such distance can't judged with a reasonable resolution.

I propose a disproof of concept experiment (should take less time than putting together a block diagram). Take a IR LED and an IR protodiode/photottransistor (receiver). Put them on a breadboard and turn the whole thing upside down. Place it 50cm above a bath tub. Measure signal out of a receiver. Repeat at 40cm and 60cm. How much does the signal change? How much noise do you see?

 

[Thanhlongbin]

level detector schematics

I propose a phys. model so:
Almost of comercial IR LED produce IR beam with beam divergence about 10-20 degree. Ignoring all the IR absortions in short distance, IR intensity can be shown as a simple function of the distance.
Let say: L= optial travel path length. I(L)= IR intensity at L.
=> I(L)=k*1/L^2. When k is some constant.
Let L shifted some dL value.
=> dI=- (k*2/L^3)*dL= - 2* (k*1/L^2)*dL/L= -2*I(L)*dL/L.
=> dI/I(L) = -2*dL/L.
With dL/L =+/-10% => dI/I = +/- 20% ! That's enaugh large value for simple detection!
Have I done a mistake somewhere?
The matter is left :
1. Choose necessary IR LED with conus divergence beam form.
2. Choose IR Photodiode (PIN) with small aperture
Optical transmision power (of LED) and optical sensivity (of PIN PD) are coresponding to the distance of detection.I think a pair IR LED/PD from any TV IR remote control can be used.

 

[FvM]

liquid surface detection led

Wouldn't say mistake, but some issues aren't considered in your estimation.
- The reflection coefficient of the liquid surface is typically very low, e.g. 2% in case of an air-water interface. This means, you may get considerably stronger reflections from the tank bottom.
- You must assume a plane and completely clean liquid surface.

My conclusion is: You are most likely able to build demonstration system, that works under ideal conditions. But the method is effectively worthless for most real measurement problems.

 

[kender]

alcohol sensor circuit diagram

- The reflection coefficient of the liquid surface is typically very low, e.g. 2% in case of an air-water interface. This means, you may get considerably stronger reflections from the tank bottom.

There's possibility that the liquid will absorb IR on its way to the bottom, so that the receiver gets a weak 2% reflection, but doesn't get a stronger (98%) reflection from the bottom. Depends on the liquid (?) and the distance to the bottom (?).

 

[Thanhlongbin]

infrared water level sensor

-Let's take a look to reflection from the tank bottom which is made from 100% reflective material (ideal mirror!) and placed at distance >10cm from air/liquid surface.
Google says that water absorption is about 10dB/cm @IR wavelength 800-1100nm (typical for cheapest near IR LED/Laser).
After reflecting from tank bottom and transmitting through liquid/air surface again , IR intensity is a absorpted >10dBx20 = 200dB (20cm is double travel distance).
In compairision with 2% surface reflected intensity (about -17dB) the tank bottom effect can be ignored.
Google also says almost types of oil have higher near IR absorption than water.
The situation may a bit change with a alcohol liquids. Who has some infor. with alcohol, please inform us.
At least, Fantabulous68 can limit application scope with water and oils.
- If surface is not plane but has curvature radius more than 50cm, all the calculation are still valid.
- Mixed water/oil surface seem to reflect better than clean water surface.