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Looking for a way to measure 12v "on" time...

1K views 9 replies 6 participants last post by  delawarebill 
#1 ·
I'm looking for a cheap way to measure 12v "on" time with .01 sec resolution. My initial plan was to use a hacked stopwatch, which requires completing a circuit to start the clock, opening that same circuit for a short period of time, then completing that same circuit again to stop.

I tried connecting both 87 and 87a of a spdt relay to one leg of the trigger circuit to create the small "open" period needed before the "stop" signal can be accepted. It looks like the small relay i used is just too fast between the contacts, as the stopwatch does not consistantly recognize the "open" event.

Maybe using a larger/slower relay with more inertia in it's movable contact arm would work, but i'd like to see if someone has any other low dollar suggestions that can be assembled using Radio Shack parts?
 
#3 ·
I'm just looking for an inexpensive in-car tool. What i'm actually wanting to measure is the "sweep" time it takes for my engine to run WOT thru an rpm range defined by a digital "window" switch. I'm thinking i should be able to quantify things (like a small change in timing or even wheel alignment) and be able to change the rpm band that i'm measuring to see if the change helps/hurts low rpm vs higher rpm.

I can make what i've got work by using a DPDT relay and manually toggling with a switch between the switched sides of the relay after the window switch comes on, but i would like to eliminate the manual toggling if i can.
 
#4 ·
So what you are saying is that you want to measure the "elapsed time" that your engine takes to run from Idle to WOT or ???
Not real clear here. An oscilliscope is what is needed to measure voltage change in .001 second intervals and greater. Milliseconds, nanoseconds etc, only measured with a scope.
DVOM have a sampling rate and are not acurate enough for a 1 ms on off pulse.
 
#6 ·
LATECH- I want to measure the time it takes to sweep thru a range, for instance 3000rpm to 6500rpm. The window switch in that case would come on at 3000rpm, and go off at 6500rpm. Typical scenario would be to activate the timer during a 3rd gear "pull" starting at an rpm below 3000, then going WOT until the timed range is exceeded, then observe the results. Kind of like a dyno, change something, then repeat the test. Should be easy to quantify if the change helped or hurt with .01sec resolution, the Red Lion timer goes down to .001sec res if desired.

ween- Thanks, i'm ordering a Red Lion timer as soon as i can hear back from a distributor. I don't know what their min purchase is, but Red Lion's website would not let me buy 1 or 2. The direct price was $46/ea
 
#7 ·
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