Opening Time (OT) or latency is measured as the difference of the start of the current rise on channel #1 to the “knee” and coinciding 1st oscillation on channel #2. The Closing Time (CT) or latency is the difference of the Current off line on channel #1 to the 1st downward closing oscillation on channel #2. It is easiest to hit the hold button on the scope once you have a clean sample to measure these 4 events from. Once you have the OT and CT times, subtract CT from OT to get an overall or net latency time for the conditions you are currently testing under, which can vary with changes in voltage or pressure, etc. It must be noted that the actual flow during OT and CT can’t be assessed from the physical latency times alone, but basically there will be a deficit of flow during the OT that is partially offset by a small amount of additional flow gained during the CT. The actual flow deficit during OT and CT is better assessed by the dynamic flow latency test described later. Net Latency is typically calibrated in the ECU as a set of pulse width offsets vs. injector voltage, to be added (it’s always an offset, not a coefficient) to the final pulse width.
|I am speechless that this sort of stuff can be sold!|
For the actual flow tests, there are many ways to run these tests and J1832 only makes suggestions for the sake of accuracy, but is vague on prescribing exact finite test cycles, so you will need to find a work path that fits best for accuracy in the attributes you are interested in. That said, for static flow tests, simply turn on the timer for 60 seconds of static flow, that’s about as fancy as it gets. The dynamic flow testing is where things get a bit more muddled. My preference for the dynamic flow test is to do a 50% duty cycle of 5ms of on time and 5ms of off time for a total run time of 120 seconds (which equals 60sec.of total on time). This requires you to set the signal generator to 100Hz (confirm this on your scope as 10ms of period) and run it thru the timer set to 120 seconds of test time.
|Opening Time Latency (OT) can be seen in both waveforms as the “Knee” on channel #1 and as the 1st up cycle on channel #2. The Closing Time Latency (CT) can only be seen on channel #2 as the 1st down cycle after power is shut off.|
For consistency, run this test twice per injector, the 1st run is to normalize the injector; the 2nd run will be used to get the Dynamic flow value. Now if you want to make a simple correlation between the physical latency and the flow latency as a percentage of the 5ms dynamic flow time, first divide the total physical latency (in milliseconds) by .05 (Example: if total latency is .96ms then .96/.05=19.2%). To get the dynamic flow latency as a percentage of static flow (so it can be compared to the physical latency as a %), subtract from 1 the dynamic flow quantity (5ms PW at 50%D.C. for 120sec.), divided by the static flow quantity (60sec at 100%D.C.) and multiply the total by 100 or: Dynamic Flow Latency %=100(1-(dynamic flow / static flow)).