Operate time of Relay

[Sandeep Km]

I need to find the operate time of Relay with and without contact bounces.
I configured MSP 430 timer and port interrupt to find out time taken for first low to high
transition on contact.Since relay contact bounces several time, i am not sure
the port level interrupts give exact operate time without bounces...Is there any way to find operate time with bounces?View attachment otrt.BMPView attachment otrt.BMP

 

[KlausST]

Hi,

(if you wait low-to-high. Is it an NC contact, or are you cenncted to VCC?)

You didn´t show your schematic. use relatively low ohmic resistors.

With bounce: LAST time low to high transition.
Wait 100ms to timeout your measurement.


Klaus

 

[Sandeep Km]

https://obrazki.elektroda.pl/3979440500_1417515698.jpg


Please find the attached image.
relay is driven from p2.0 using a mosfet bs170. P2.4 is configured to detect low to high transition interrupt.
P2.4 is internally pulled down. P2.4 connected to mosfet common contact while NO contact is pulled high..

 

[KlausST]

Hi,

driving the relay is OK.
Mind that D1 makes the relay slowly releases. But you don´t need to care if you measure activation timing.

*******

R2 as series resistor is not necessary. (it slows down timing and lowers voltage levels.)

To improve timing you need an external (P2.4 of ucontroller) pulldown resistor. Maybe 1k.
This helps speed up timing.

***
What does this mean?

P2.4 connected to mosfet common contact

please show this in your schematic.


Klaus

 

[Sandeep Km]

Hi,

Sorry that was a mistake.. I just meant P2.4 is connected to relay common contact.
Is there any way to get timing points enough to plot contact bounces ...?

 

[KlausST]

Hi,

from your description you only need to know the timing to the first low to high transition and the last low to high transition.
The transitions inbetween are not of interest.

I´d use a timer capture input.
it freezes the timer value at the desired transition.
to recognize the first transition you need some non retriggering (if possible) capture. So if the first transition is recognized the value is freezed and an interrupt is requested.
Within the ISR read the captured value and activate the capture function as soon as possible - now with retriggering (if possible).
Then wait (about 100ms) and read the last captured value.

If there is no possiblility for non retriggering capture, then read the captured value as soon as possible.

With a retriggering capture you don´t need to read all events, only the last one is valid.


I don´t know your relay, but i expect the first transition in about 10ms, and the last in maybe 13ms (for small signal relays. both timings referred on starting to activate relay)
From the first to the second transition i expect the longest gap in time. Maybe 1ms. Then i´d expext it to speed up from one transition to the next until bouncing stops.
This is just an expectation without having true experience.

Just of curiosity you could save ALL capture events in SRAM to get a clue about the timing and the number of bounces and the complete baviour.

Good luck

Klaus