I have no explanation for the 10.86V out....if your supply is 12.00V and the diode across relay was installed with the polarity as shown?
I bread-boarded the circuit, with 1Meg instead of 980K and 1.5K instead of 1.2K...what I had handy. With a 12.00V supply the high output was 11.99V and the low output was 0.55V.

All resistors can be 1/8W or greater, and the capacitor can be 15V or greater.

Ken

 

The maximum continuous voltage that the resistors and capacitor can be exposed to is VCC, or 12V in my circuit. Therefore, the capacitor should have a voltage rating greater than 12V. The maximum continuous power dissipated by the resistors is P=(Vcc*Vcc)/R. For the 100K resistor (12*12)/1000000=1.4mW, (12*12)/47000=3mW for the 47K resistors, and (12*12)/10000=144mW for the 10K. The 10K is there for static protection, and since I never expect it to be exposed to even 12v continuously, I'll go with 1/8W or greater for it too. Except for physical size, there is no downside to using 1/4W resistors in this circuit.

Ken

 

While searching for the component resistance for R1 i was finding anti surge resistance of 0805 package(1/4W,5%,0805) what is the difference between this anti surge resistor and normal resistor (i found another one of 1206 ,1/4W,5%).Which one will be suitable to use and why .I was not able to find the smd equivalent of IN4007 and IN4148 diode can u give suggestions abt the same where can I find these and there part no,vendor .Is there an easy solution of locating this on a more appropriate site.

I have not dealt with "anti surge" resistors. I would just use normal resistors. For the surface mount diodes look for 1N4007 and 1N4148...not IN4007 and IN4148. Since you haven't listed your location in the world in your profile, I can't make any suggestions for vendors that you might have access to.

Dear Kmoffet one more help is required from your end .In this circuit is it possible to reverse the logic at the output Kindly give some suggestions .In this if I want to detect water at 12V and for fuel it shows VCC-0.7 or floating voltage is it possible to do the same by incorporating additional component at the output or I can use any solid state relay instead of changing this circuit at the other end to meet this requirement.This s also one thing I wanted .

I don't understand your distinction between "12V" and "Vcc". You make no distinctions in the attached schematic. Normally, in the circuits you and I have posted Vcc=12V. Do you have a "written" specification from your"customer"?

If instead of 10K in the previous circuit if I use 1K will this affect the functionality ?Which one will be more appropriate to use since u told that 10K is for protection purpose from continuous 12V supply.

The higher the value of R2 in my schematic the better. Why do you want to make in lower?

 

RS Electronics India http://in.rsdelivers.com/product/vishay/byg10m-e3-tr3/diode-standard-rectifier-1kv-15a-sma/7003885.aspx Since you have to buy in quantity, you can use the same diode for D1, D2, and D3.

Still waiting for a distinction between +12V and Vcc. ???

Ken

 

Payal

Why don't attach the images to the Forum database. This would make things much easier

Are you going to make this circuit and sell it...or is it a prototype.

 

Dear KMoffett,

There is no distinction as such the range of VCC supplied by customer is between 10.5 t0 16V max I have choosen 12V supply.Is it possible to reverse the logic by putting some logical not gate ?I tried with the same the circuit of yours using LM311 there is reversal of logic but for LM741 circuit there is no reversal at output I tried to simulate that for values below 115kOhm o/p is 11.3 (i.e for water detected) and above 120kohm (fuel detected)it is 5.22 though it should have been between the range 0.5 to 1.6Max can you suggest what I can do in this circuit using LM741 to reverse the thing tht is when fuel detected it should be open voltage and for water it should be near about 0.I need suggestion fast since my customer is in dare need of a suggestion .Waiting for your kind reply please again find enclosed the circuit for which reversal of logic is required.

The LM741 is bad choice for a comparator. Why do you want to use that circuit? The relay in the LM311 output gives you the option of Vcc (+12), ground (0.0V), or float when water in detected or not...just a matter of how you wire the contacts. Wire the N.O. contact to ground and the common contact to the customer's circuit...water=0.0V...no water=open.

Ken

 

I'm going to make assumptions here.

1. The customer's input is internally pulled high (10-16V) by a resistor, and needs an open collector signal to pull it low with water, and floating with no water.

2. You would rather go all solid state, rather than use a relay.

The attached circuit should do that. It should work...but...I haven't bench tested it yet. Maybe tomorrow, if I have time.

Note the swapped inputs on the LM311. Q1/R6/SW1 is used to latch the detector ON if water is momentarily detected. Since SMD resistors are only sold in batches, I changed some values so you only need two different ones.

If I'm making the wrong assumptions, let me know.

Ken

 

Dear Kmoffet,

Please find here enclosed the full vehicle side circuit diagram in upper side of this pic 1 .Our water in fuel sensor is located in place of switch.In this when water is detected(0V) in fuel the switch will close LED will glow and buzzer will sound.When fuel is detected switch will remain open and water in fuel will show no indication and buzzer would not produce any sound am I right in this explanation ?if wrong please correct me .In second down side of this picture my customer has done slight modification he has placed the sensor 12V and just changed the connections here and there.This sensor which they have mounted in second place it is working on logic that when water is detected it shows a logic high that is 12V and when fuel is detected it will show a 0 V .What they want is to reverse this logic of sensor that is when water is detected it will show a 0V and when fuel is detected it will show a 12V is this possible ? without using external components like solid state relay just by changing slight connections of these components external to water in fuel sensor is it possible to reverse the logic of the same?kindly let me know whether it is possible without knowing circuit diagram of water in fuel sensor and whether the same is possible or not . Waiting for your advice .
Thanks in advance

1. Are we talking about two different sensors in the same tank?
2. In the second schematic, their buzzer will always be ON when the IGN switch is on.
3. To reverse the logic without external components you would have to rewire the buzzer so it's in parallel with the indicator. But, that assumes that the second sensor can handle the current requirement of the indicator and buzzer. And, that the indicator and buzzer are only used for the second water sensor (The isolation diode on the buzzer in both circuits makes me wonder if it has other functions.)

It feels like we're shooting at a moving target.

Ken

 

I tried to connect buzzer in parallel with the indicator but the thing is not working in that case when water is detected that is 12V the indicator will glow and buzzer will produce a sound . While in second case when fuel is detected that is 0V indicator will not glow and buzzer will not produce any sound am I correct in my explanation ?

You're confusing me. Which circuit are you referring to?

Even it feels to me it is not possible we cant change the logical working by just rewiring he wants reverse that is 0V for water detected and 12V for fuel detected.

I agree. At minimum you would need one transistor and one resistor.

Ken

 

Are you still looking at using the LM311 circuit also?

Ken

 

Changing the output to an N-channel MOSFET will easily handle well over 1A current sink. If this is going into "heavy equipment vehicles", than the battery supplies are more likely to be 24V, not 12V. The absolute maximum voltage rating on the LM311 is ~36V. Because motor vehicles are very noise and punishing electrical environments, it would be necessary to add more protection circuitry than I have shown. With the proper protection, there should be no long term maintenance of the circuit. I don't know that there would be any long term maintenance issues with the sensor probe. As an aside, do you need the latching feature that I added?

Ken

 

I added C2/D3/R6/D4 to protect the sensor circuit from reverse and over voltage spikes. C1 was moved to stop the output from flickering ON momentarily when the power is applied.

Ken

 

Sure...just want clip any positive spikes to a range of >18V (highest battery supply) and <36V (max comparator VCC).

Ken

 

1W is fine.

Ken

 

Dear KMoffett,

I was thinking you have provided protection circuit consisting of zener diode and all at the output of ic but i think this should be with the unregulated power supply that is 12V the protection circuit you made .consisting of zener diode and capacitor .

Perhaps you misread the schematic. The Zener D3 and the capacitor C2 are not connected to the output Pin 7 of the IC. They are connected between Pin 8 and Pins 1&4, across the power supply to the IC. Note the connection dots.

I was facing one more trouble while i was connecting buzzer at output of drain of NCV8402 mosfet the switching does not takes place it shows 12 V with water and fuel both while i connect the buzzer terminal to output of LM311 IC switching takes place .what is the probable reason for that.

Was the buzzer in place of the unmarked resistor on the right side of the schematic?
Test just the MOSFET. With the buzzer between +12V and the drain, the source connected to ground, and the gate disconnected from IC's pin 7, will the buzzer sound if +12V is connected to the gate?

Ken

 

C1 can be in either position and bypass electrical noise to either fixed rail, ground or +12V. In the Pin-3-to-ground position, when the power is turned on, there is a "momentary" indication that water is present even if there isn't any. In the Pin-3-to-+12V position, when the power is turned on there is only an indication if water is present. I noticed this in the earlier, latching version of the circuit. It's just a blink of an LED or whatever your output is.

The "fault" could be considered a "feature" if you say it's to indicate that the detection circuit is active.

I have no specific "justification" for the 0.1uF value. It's a frequently used value for noise bypass capacitors in many circuits. I do not know the spectrum of the electrical noise that you will find in your specific application. Since the detection of water represents essentially a DC signal, You could go with a much higher capacitance value like 1.0uF or 10uF. Therefore, it's up to you.

Ken

 

The reason I moved C1 is so the lamp does not briefly flicker ON when power is first applied to the circuit.

With C1 connected between pin-3 and ground, when power is turned on C1 briefly holds Pin-3 to 0V. This would seem like water was present and light the lamp. C1 would quickly charge up, the lamp would go out, and the circuit would respond correctly to the presence or absence of water.

With C1 connected between pin-3 and +12V, C1 would briefly hold pin-3 to +12V when the power is turned on. This would seen as if there were no water present and the lamp would not light. C1 would quickly charge and the circuit would respond correctly to the presence or absence of water.

There is no time-hysteresis built into this circuit. Briefly contacting water will only briefly light the lamp. That's why I included a latching function in an earlier schematic. I think hysteresis would require additional circuitry. What would be the desired time delay?

Ken

Perhaps moving C1 back to the pin-3-to-ground position and increasing its value might get hysteresis you need. I can't bench test it right now.

 

i caan bench test it can you give me suggestion what to check and how if you tell me the procedure I can do the same at my end

Use the last circuit, except move C1 back to between pin-3 and ground. Increase C1 from 0.1uF to 1.0uF or 10uf. Touch the sense electrodes to water very briefly and pull them out. Does the output of the comparator change right away or do you have to hold the electrodes in the water for a period of time before the output changes? Once the output changes and you remove the electrodes from the water, does the output change right away, or does it take some time...the time-hysteresis.

can you explain me latching function step wise what will happen when water is detected and when fuel is detected .how much time delay will be taken care by this latching function.Please explain me latching function in detail since i do not have idea about it.

Look at my schematic in post #46. When water is detected the output at pin-7 goes to high. This causes current through R6 to turn on Q1. Q1 shorts pin-3 to ground. This acts like there is water between the electrodes, even after the water is gone. The lamp will stay on continuously. To clear the water detection indication, you have to press the momentary switch SW1. This shorts Q1's base to ground, turning off Q1, and letting pin-3 return to the non-water detection level. If the electrodes are still in water then pressing SW1 does nothing and the indicator lamp stays on.

Ken

 

Here's a modification. Q2/R6/C3/D3/C2 form a timed-latch. When the electrodes touch the water the indicator will light and stay on for about 30 seconds. It will remain on for the 30 seconds even if the electrodes are no longer touching the water during that time. If the electrodes touch the water for longer than 30 seconds, the indicator will stay lit until they are removed from the water.

Ken

 

OK, put the 10uF capacitor in the +12V-to-pin-3 position.
You get:
1. no turn-on indication.
2. immediate and extended indication if the electrodes contact water.
3. continuous indication if electrodes are in water.
4. several seconds of extended detection indication after electrodes are removed from water.

Changing the value of C1 will change the indication extension time. 10uF=~7 sec. ... 22uF=~15 sec. ... 47uF=~30 sec.

The Q2/R6/C3/D3/C2 circuit additions were to provide a very long indication extension time of intermittent water detection. If the above times are OK with you, then just move C1 and don't use Q2/R6/C3/D3/C2.

Ken