Glitch Detector - Page 1
Forum section: electronics / projects

author: David_AVD
author_rank: Super Contributor
timestamp: June 09, 2013, 12:48:08 pm
content: At work we seem to find ourselves working on equipment with intermittent faults fairly regularly. Sometimes the fault may only show up very briefly and only once every few hours. This mean that standing there watching a meter is not really practical.So... I was thinking of making a small tester that would accept a DC voltage (say in the range of -50 to +50V DC) and have adjustments for low and high thresholds. Somewhat like a logic probe, it would also have a pulse detect (with small piezo) and latched LED indicator (with reset button) to show that an event had occurred.The tester needs to be portable (battery powered) as sometimes the equipment is on-site with limited access. The idea is to hook it up to the suspect voltage line, set the thresholds, press the reset button, walk away and check back later (or when it beeps).Maybe a multichannel unit would be handy with individual event indicators so a few lines could be monitored at once and reduce the time required to track down the fault.I don't think we need to log the actual voltage(s) in any great detail, just get an idea if they are staying withing range when the fault occurs. I'd probably rather keep the detection as simple window comparators as they would be well suited to catching brief events that sampling (with a micro) may miss.Has anyone been down this path before?

author: SeanB
author_rank: Super Contributor
timestamp: June 09, 2013, 02:13:04 pm
content: Power supply supervisor IC's do this as a part of their operation. Built in window comparators, pulse detection and an alarm output along with an ADC and multiple inputs to monitor typically 5 rails and give a temperature sensor as well.All you need is to normalise the inputs to the range the IC needs with a resistive divider, and they have inputs for both positive and negative input voltages.

author: David_AVD
author_rank: Super Contributor
timestamp: June 09, 2013, 09:31:40 pm
content: It needs to be adjustable and cover the range of +/- 50V with separate low and high limits. That may be asking a bit much from a supervisory IC.

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 12:54:18 am
content: So, basically what I need is a simple window comparator, but I thought I'd post here to get some ideas on the most useful way to set the thresholds in the field.As I wanted to make this portable, I was thinking of using AA cells so I'd have a single 6V or 9V rail with Vcc/2 for the input 0V ref.One idea was to (variably) scale the input voltage and compare it to +/- 1V (or so) fixed references. I'd actually have to scale it twice to feed the low and high comparators separately so I could set the thresholds independently.

author: notsob
author_rank: Frequent Contributor
timestamp: June 10, 2013, 01:15:37 am
content: Back in my mainframe days we had a quick and dirty glitch capture board 'home made' - was just TTL latches with half a dozen leds on it. I like where you are headed with this, these references may help if you haven't already looked at them.http://www.freepatentsonline.com/6751079.htmlhttp://www.google.com/patents/US20030226082Cheers

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 01:28:49 am
content: We had a LED scoreboard recently where the display was intermittently flickering. Access was difficult and it was hard to look at the display whilst wriggling wires, flexing boards, etc. Being able to monitor a line and have an audible cue (beep) when the line glitched would have been great.