Looking for ideas how to make an event sequence tattletale circuit - Page 1
Forum section: electronics / projects

author: Bob773
author_rank: Newbie
timestamp: July 29, 2024, 06:11:57 am
content: I work on industrial equipment and sometimes intermittent anomaly or component failures can be very difficult to troubleshoot. (What happened first?, second?, etc) I have an idea to build a tool that could be attached to monitor a minimum of 4 signals and left on a job site for an extended time until the failure occurs, then would indicate the sequence that the 4 signals occurred. Input signals in my case would just be switched 12vdc power or relay contact closures. I have used 2 latching relays to determine which of the 2 happened first… but my ideas for 4 inputs using relays gets quite complicated. I occasionally use a scope set with single trigger when I know I can recreate the fault, but it’s not feasible to leave unattended and hope that it triggers properly a month later. Does anybody know of a chip that would easily perform this operation? I am sure it’s possible with logic gates, but I can’t quite recall all that I learned 20 hrs ago. Thanks

author: ebastler
author_rank: Super Contributor
timestamp: July 29, 2024, 06:26:01 am
content: I think some more information would be required before we can make recommendations. What time resolution do you need for the captured signals? For how long do you need to record them? Are digital signals enough, or do you think analog glitches could occur and need to be captured?I understand there is a defined trigger condition (on one or any of the monitored lines?) which starts a recording -- but maybe you need to see some timebeforethe trigger event too? Can there be multiple events over the duration of the unit's deployment, and you need to capture them all? Do you need time stamps ("wall clock time") for recorded events?

author: Bob773
author_rank: Newbie
timestamp: July 29, 2024, 07:08:14 am
content: My original idea was actually super simple, just a box with rows of LEDs to indicate which input happened first, second, third. I think digital inputs are all that is needed. Response time of 15-20 milliseconds should be quick enough, but faster would be good too. It would be a one shot device that needs manual reset after triggered. Here is a real work example: a Diesel engine is shutting down on “low oil pressure” fault. I could monitor the oil pressure switch, the fuel supply solenoid, the power to the governor, and the fault indication output. The device would reveal if another module is cutting off fuel supply or if the engine control is initiating the fault erroneously.

author: ebastler
author_rank: Super Contributor
timestamp: July 29, 2024, 07:21:02 am
content: Ok, at that time resolution (milliseconds or fractions of milliseconds) I would definitely use a microcontroller to do the monitoring, store the data and drive a display. Any Arduino-style off-the-shelf board should work; the Arduino environment makes them easy to program in case you are not too comfortable with this stuff. Most of them bring a USB port which you can use to download data, and have flash and/or EEPROM storage on board where a data record could be stored semi-permanently to allow the board to be powered down after it has made a capture.If normally all of the monitored inputs remain at rest, a change of any input could trigger a capture. But you could also continuously capture all inputs in a circular buffer, and then stop recording once the critical fault indicator becomes active. That would let you see a time span before the critical event.Probably best to use optocouplers to isolate the microcontroller inpus from the engine relays.

author: Psi
author_rank: Super Contributor
timestamp: July 29, 2024, 08:10:55 am
content: There are off the shelf data loggers that could do this, if you don't want to build something.You just need one that can be setup in the right mode so it time-stamps IO changes, instead of polling and recording every sample in realtime.And maybe enable auto-erase old memory feature.