Delay measurement help... - Page 1
Forum section: electronics / projects

author: Sankha
author_rank: Newbie
timestamp: December 15, 2021, 06:27:50 am
content: Hi, I'm sankha from University of Colombo, Sri Lanka . Currently we are doing a projects to measure time delay between two high speed pulses. approximate time delay between the two pulses varies between2 to 10 ns. Any idea of how to move forward?

author: Ice-Tea
author_rank: Super Contributor
timestamp: December 15, 2021, 08:13:46 am
content: Get a good scope?

author: coromonadalix
author_rank: Super Contributor
timestamp: December 15, 2021, 08:22:23 am
content: https://forum.arduino.cc/t/measuring-delay-between-two-pulses-using-millis-and-micros/341893/3

author: Marco
author_rank: Super Contributor
timestamp: December 15, 2021, 08:33:00 am
content: Quote from: Sankha on December 15, 2021, 06:27:50 amRepetitive or single shot?

author: Henrik_V
author_rank: Regular Contributor
timestamp: December 15, 2021, 09:21:40 am
content: Repetitve : part of PLL?Or a fast XOR that loads a cap?Classical instrument is a counter with can measure the A to B interval, KS 53230A ?Depending on the needed resolution / accuracyJust keep in mind that every meter cable is good for ~5ns(A sharp edged pulse source and) a power splitter come in handy to check your setup...Or try to get your hands on a HP 7371A ??

author: Marco
author_rank: Super Contributor
timestamp: December 15, 2021, 10:25:35 am
content: Some PIC microcontrollers have the CTMU, which can be used for time to digital conversion and a whole lot cheaper (though a bit noisier) than fixed function ICs. It also requires a bit more DIY which seems a good thing if you're doing it for a school project.AFAIR Microchip has some documents on the topic, but it might be easier to understand with this project from EDN :https://www.edn.com/use-time-domain-reflectometry-tdr-for-low-cost-liquid-level-measurement-part-iii/

author: Sankha
author_rank: Newbie
timestamp: December 15, 2021, 12:44:14 pm
content: Thx, but i'm working on nanosecond range.

author: Sankha
author_rank: Newbie
timestamp: December 15, 2021, 12:45:22 pm
content: It is single shot.

author: Henrik_V
author_rank: Regular Contributor
timestamp: December 15, 2021, 03:13:28 pm
content: Whst timing resolution do need and/or would like to have ?Using a counter: fast with known uncertainty (spec) but $$using the PIC CTMU (see EDN article): a lot cheaper but need time and some knowledgeSo it seems to be a problem to simply staple coins on, or have some students and a lot of time

author: jmelson
author_rank: Super Contributor
timestamp: December 15, 2021, 03:39:29 pm
content: Quote from: Sankha on December 15, 2021, 12:45:22 pmOh, that makes it harder. Well the classic approach is a FF that is set by the first signal and reset by the second. The output of the FF starts charging a capacitor when true and stops charging when false. Then, you look at the voltage on the capacitor.Jon

author: Marco
author_rank: Super Contributor
timestamp: December 15, 2021, 04:17:14 pm
content: That's exactly what the CTMU does.

author: hgl
author_rank: Regular Contributor
timestamp: December 16, 2021, 12:34:11 pm
content: It depends on which resolution and which repeat accuracy you need.If you want to build it yourself take an AS6501 otherwise buy a time interval analyzer.

author: Picuino
author_rank: Super Contributor
timestamp: December 16, 2021, 06:16:15 pm
content: Quote from: Marco on December 15, 2021, 10:25:35 amhttps://www.microchip.com/stellent/groups/SiteComm_sg/documents/DeviceDoc/en542792.pdfhttps://ww1.microchip.com/downloads/en/DeviceDoc/61167B.pdfYou can reach0.1ns200ps resolution in several models of PIC MCUs.https://ww1.microchip.com/downloads/en/DeviceDoc/30009995e.pdf

author: hgl
author_rank: Regular Contributor
timestamp: December 18, 2021, 02:57:19 pm
content: 0.2 ns resolution are 10 ADC counts at 2ns measuring time.From PIC24FV32KA304 Datasheet :

author: jonpaul
author_rank: Super Contributor
timestamp: December 19, 2021, 08:40:22 am
content: Bonjour,One shot TD in nS..Ps require a very fast analog comparator and counter or multi gHz digital sampling.Cables, connectors and layout are all critical. I would be skeptical of any microP based or home made solutions, results may be impossible to quantify or verify.Such applications are in the nuclear, defense, military, weapons research and testing. EG nuclear devices, one shot laser weapons, EMP, etc.In our research, We used\ dedicated time interval analyzers : the ancient HP 5370B, 5372A, and Yokogawa TA 720 are specifically designed for these measurements but may not have the resolution you require. On ebay.Modern state of the art at Stanford Research (SRS) 25 pS reshttps://www.thinksrs.com/products/sr620.htmlPerhaps Zurich Instruments,https://www.zhinst.com/Hope this is of use to you!Bon chance,Jon

author: Picuino
author_rank: Super Contributor
timestamp: December 19, 2021, 05:01:01 pm
content: Also 0.2ns is equivalent to 6cm at the speed of light. Any length of cable a little longer can alter the measurements.One way to eliminate systematic error is to insert a longer wire for the second input cable. Inject the same signal through the two cables and measure the time shift. That is the time that will have to be subtracted to find the actual time shift between the two input signals.

author: Sankha
author_rank: Newbie
timestamp: December 22, 2021, 12:29:23 pm
content: thx a lot for the information

author: FriedLogic
author_rank: Regular Contributor
timestamp: December 22, 2021, 11:48:09 pm
content: An AMS/Acam GP21 should do this as long as you know when the pulses are coming to within a 4ms or so as that is its maximum timing range. 60ps RMS noise, if that's OK. Cheap little boards with them on ebay, so no QFN soldering required.A TI TDC7201 should do too, but in a BGA package. It has an 8ms timing range, and a little less noise than the GP21. A fair bit easier to set up too - or at least the TDC7200 is, so I would guess this one too.The AMS AS6500 (or AS6501) already mentioned would give better resolution, and a 16s timing range, but you would need to make your own board, or get one of the official eval boards from Mouser etc. at $65 or so.