Hi all, i am looking for a little assistance in a project i am working on for a customer. the short story is i am trying to adapt a flow meter for diesel exhaust fluid to a diesel fuel dispenser. basically the dispenser would see the DEF fluid as another grade of fuel and count the gallons and dollars. my problem is the existing fuel dispenser equipment receives a pulse signal of 5 volts from a pulser that it uses for the diesel fuel. i currently have a flow meter for the DEF fluid that outputs millivolts for pulses. i need to find a way to convert the pulses of millivolts to 5 volts so that the dispenser can recognize the pulses. any suggestions or ideas would be greatly appreciated.

 

A few millivolts isn't much to work with in the electrically noisy environment of automotives.

What power is available to run the circuit?

Will it be mounted under the hood?

What is your skill set for building a small circuit on perf board and enclosing it?

What are the minimum pulse width and maximum pulse repetition frequency?

ak

 

this is not automotive. its a gas station fuel dispenser, no noise and i can supply the 5v or any other voltage from an external power source, i just need it to repeat the signal not in millivolts, i need the signal in 5v. the repetition frequency I'm not sure of, i can gather that data but it would be dependent on the flow of the fluid. most likely very low speed

 

Something like this might work: Millivolt to Voltage Module 70mV to 0-5V 0-10V Linear Conversion Module https://www.amazon.com/dp/B00UTJHPWS/

That’s just an example

 

An LM311 comparator set to trigger on the very small FM pulses. But first be sure that the FM is functioning correctly. Some sensors with an open collector phototransistor give a small pulse unless you add the pull up resistor, then the pulse is 5 volts at least.

 

Would either of you be interested in working with me. I would be willing to pay and I can send you the parts that I want to replicate the signal of

 

What advice I deliver here is free and I have enough to keep me busy otherwise.
If you are really lucky the flow sensor has a light source and a phototransistor and adding a pull up resistor will give the 5 volts pulse just like that. Try a 100K ohm resistor pulling up to 5 volts first and see if that gives 5 volt pulses. use a digital meter to read the voltage..
If not, then you will need the LM311 IC circuit, which is simple, and there is lots of application information available so that you can become an expert on the LM311. But you will also need some soldering skills.
One other thing to provide us with more information is to measure the resistance of the flow sensor output in both directions: meter red to one, black to the other, and then also take a reading with the opposite connections. That will tell if it is a semiconductor device or a magnetic pickup, or something else.