Rookie with a new project

[Welshy141888]

Hi all
First time post for me.

I am currently trying to design a circuit where i can measure the time an object is between a laser and sensor. I would need the timer to start as soon as the object breaks the beam and stops as soon as the object is removed. Possibly an LED to indicate the timer has started.
I am a total rookie at this but it would come in handy at work.
Any advice or information would be very well appreciated.

Thanks
Paul

 

[chemelec]

One way:
Aim Laser at a Photo Diode or Photo transistor.
Output of Photo Diode output is Normally High with Light on it.
Connect an Inverter to this, So Output goes High when Light is Blocked.
Connect this output to run a digital Timer.

NOTE: The Photo Diode or Transistor Needs to be in the back of a long TUBE or PIPE, To BLOCK Normal LIGHT from hitting it.

 

[Reloadron]

Without more detail this will be pretty generic but if the object travels a known or contained path you can use a photo transistor, photo diode or similar to detect when the light beam is broken and returns and then simply measure the time interval. You let the sensor develop a pulse and measure the time interval of the pulse. All you are doing is a time interval measurement. As to the measuring device? A Google of Time Interval Meter will bring up dozens of hits of various panel meters in standard 1/8 DIN and 1/4 DIN sizes and ranges and accuracies so you can decide what you want based on the approximate time you plan to measure. You can also roll your own but I suggest buying a turn key off the shelf solution. The more that is known about your exact project the better the suggestions will be.

Ron

 

[chemelec]

My Thought was to just trigger a CHEAP Timer from a "Dollar Store".
I have bought Numerous timers for $1.00 ea.
With a Little THOUGHT, they are Good for many applications
However, this assumes a Minimum of 1 Second Time intervals.

 

[Welshy141888]

Thanks for the replies.

I have seen a few circuits on youtube but they seem to over complicate it instead of just a photodiode and timer.

To give you more of an insight to what i need from it. I will be using this to calibrate flow cups, when calibrating flow cups you need to measure the time it takes from when the oil starts to flow through the orifice to when it stops. The timer has to read to 0.1 seconds or better. The oil is high viscosity oil so will not let a laser through, therefore breaking the beam

 

[Reloadron]

OK, I get it, you want to calibrate or test what I called Zahn Cups or Flow Cups. The cups are used to measure the centistoke viscosity of oils, resins, varnish, paints or whatever based on the orifice size on the bottom of the cup and the temperature of the fluid under test, generally to within 0.1 degree F. You need to accurately resolve .1 second. The time measurement, if I remember is the efflux time or something like that. We did the cups according to some ASTM standard. Been some years since I was n that rodeo. We just used a stopwatch to certify the cups with a standardized viscosity oil at a prescribed temperature. We also used certified pin gauges to check the hole diameters in the cups.

If you want to do this electronically I guess it should work. I might be concerned with the standard oil sticking to the sides of the tube possibly effecting the time. I guess that could be worked around. With your added information here is what I would think about doing. You will need to fabricate some sort of test fixture or jig. I would look for a pyrex short glass tube or any glass tube having the ID (Inside Diameter) that you want or need. I would run a piece of black heat shrink tubing over it to sleeve it. Take a small "C" Clamp and place your IR Emitter and Detector on the anvils, they can be mounted in two small blocks of wood. Based on the distance you can select a photo sensor pair of emitter and detector that can easily be clamped onto the tube.

I would just buy an off the shelf timer like those I mentioned earlier. I would start with an IR Emitter and Detector similar to the below:

Ron

 

[Welshy141888]

Thanks for the reply Ron.

I will get this built then try put it in to practice, good to get a response from someone who has working knowledge of what i'm looking to do.
This is the way the powers at be are looking to do them then eventually go down the route of auto logging to a computer.

I appreciate the help.
Paul

 

[Reloadron]

Hi Paul and no problem. Your mention of auto logging the data got me to thinking. Should you go that route or plan to there may not be any need for an actual meter or counter to measure the time interval, it could simply be charted. The chart would reflect the time. Yeah, been there and done that years ago with the Zahn Cups. Mostly measuring the viscosity of certain resins and varnish used in a motor impregnation process, manufacturing motors.

If this will eventually become automated I would think doing it with a focus on that now unless they have deep pockets. The trick is getting a fixture or jig made and finding suitable sensors.

Ron