Hi Everybody!
I'm Lisa and new here going to UCLA summer prep class in EE off campus. Need a little help on my homework assignment. So please please help me.
How to view 12V automotive relay voltage transient with an Oscilloscope!
I have a 5 pin 12V 30amp automotive relay and need to capture the transient voltages created when the magnetic field collapses in the coil. How do I make the connections with the oscilloscope to be able to capture these voltage transients?
I connected my scope to pins 86 and 85 and can see the voltage rise and fall from the power supply but not the transient spikes across the coil.
The assignment is capture the voltage transients with the scope both with a suppressor circuit and without - just a high switching diode on the coil in reverse bias to pins 86 and 85 and then adding a Zener Diode in series with the switching diode across the coil to pin 85.
My oscilloscope is set at 100ms @50v trigger set at edge (dual) and DC coupling and measuring Rise and Fall time with Peak voltage.
My DUT relay is setup with DC Power supply set at 12V DC with 200ma positive connected to SPST switch connected to PIN 86 of relay and PIN 85 to GND. No other PINS are connected.
I put the oscillscop probe on PIN 86 and can see the voltage rise and fall as I manipulate the switch but no voltage transients show on the oscillscope when I power off at the switch - no diodes are connected accross the relay coils.
My classmates are just as clueless as I am!
Thanks Guys!
Hi Everybody!
I'm Lisa and new here going to UCLA summer prep class in EE off campus. Need a little help on my homework assignment. So please please help me.
How to view 12V automotive relay voltage transient with an Oscilloscope!
I have a 5 pin 12V 30amp automotive relay and need to capture the transient voltages created when the magnetic field collapses in the coil. How do I make the connections with the oscilloscope to be able to capture these voltage transients?
I connected my scope to pins 86 and 85 and can see the voltage rise and fall from the power supply but not the transient spikes across the coil.
The assignment is capture the voltage transients with the scope both with a suppressor circuit and without - just a high switching diode on the coil in reverse bias to pins 86 and 85 and then adding a Zener Diode in series with the switching diode across the coil to pin 85.
My oscilloscope is set at 100ms @50v trigger set at edge (dual) and DC coupling and measuring Rise and Fall time with Peak voltage.
My DUT relay is setup with DC Power supply set at 12V DC with 200ma positive connected to SPST switch connected to PIN 86 of relay and PIN 85 to GND. No other PINS are connected.
I put the oscillscop probe on PIN 86 and can see the voltage rise and fall as I manipulate the switch but no voltage transients show on the oscillscope when I power off at the switch - no diodes are connected accross the relay coils.
My classmates are just as clueless as I am!
Thanks Guys!
Hi lisa can you tell me the pin configuration of 5 pin automotive relay.
Sent from my SM-J700F using Tapatalk
no diodes are connected across the relay coils.
NGG
For this you need a DSO and use Single shot capture.
Setup @ 10V/div and say 100ms/div.
You want to see on the display just the 12V across the coil and as it's DC you won't need the Trigger level anywhere special to see it.
Now set the trigger level above the 12V and engage Single shot mode. The trace should disappear and remain hidden until you remove the 12V supply and the resultant back EMF will take the hidden waveform above the Single shot trigger level creating a triggered event and display it on the display.........ready for you to capture on a USB stick as a screenshot to show off to your buddies later.
To do this, take the positive wire from your power supply, and attached it to the common pin of the relays contacts (pin 30 for std automotive relay) then loop a wire from the normally closed contact output (pin 87a) to the coil input pin (pin 86) and finally from the coil output (pin 85) back to the power supply negative terminal.
NGG
For this you need a DSO and use Single shot capture.
Setup @ 10V/div and say 100ms/div.
You want to see on the display just the 12V across the coil and as it's DC you won't need the Trigger level anywhere special to see it.
Now set the trigger level above the 12V and engage Single shot mode. The trace should disappear and remain hidden until you remove the 12V supply and the resultant back EMF will take the hidden waveform above the Single shot trigger level creating a triggered event and display it on the display.........ready for you to capture on a USB stick as a screenshot to show off to your buddies later.
To make it easier for the scope to lock on to the waveform, you can easily set up your relay to "switch itself" so it sits there turning on and off rapidly. This will generate some very big voltages indeed (if there are no additional voltage suppressing components fitted), enough to give you a bit of a shock if you touch it in fact!
To do this, take the positive wire from your power supply, and attached it to the common pin of the relays contacts (pin 30 for std automotive relay) then loop a wire from the normally closed contact output (pin 87a) to the coil input pin (pin 86) and finally from the coil output (pin 85) back to the power supply negative terminal.
When you turn on the power, current flows into the coil, causing it to energise, but when it does, it opens it's contacts, which breaks power to the coil, so it closes again. This cycle repeats at the fundamental mechanical frequency of the relay (typically 10 to 20 Hz).
NGG
For this you need a DSO and use Single shot capture.
Setup @ 10V/div and say 100ms/div.
You want to see on the display just the 12V across the coil and as it's DC you won't need the Trigger level anywhere special to see it.
Now set the trigger level above the 12V and engage Single shot mode. The trace should disappear and remain hidden until you remove the 12V supply and the resultant back EMF will take the hidden waveform above the Single shot trigger level creating a triggered event and display it on the display.........ready for you to capture on a USB stick as a screenshot to show off to your buddies later.
You were right - I did what you said and it worked the only thing I had to do was speed it up - to slow at 100ms. When you get a chance can you explain as to why it did not matter where the Trigger Level sat at?
I liked your way the best as the only trace I needed to see was the Transient voltage and capture to Matlab for analysis.
I got my Delta's and and inputed to Matlab and turning in my assignment!
NGG
For this you need a DSO and use Single shot capture.
Setup @ 10V/div and say 100ms/div.
You want to see on the display just the 12V across the coil and as it's DC you won't need the Trigger level anywhere special to see it.
Now set the trigger level above the 12V and engage Single shot mode. The trace should disappear and remain hidden until you remove the 12V supply and the resultant back EMF will take the hidden waveform above the Single shot trigger level creating a triggered event and display it on the display.........ready for you to capture on a USB stick as a screenshot to show off to your buddies later.
You were right - I did what you said and it worked the only thing I had to do was speed it up - to slow at 100ms. When you get a chance can you explain as to why it did not matter where the Trigger Level sat at?
I liked your way the best as the only trace I needed to see was the Transient voltage and capture to Matlab for analysis.
I got my Delta's and and inputed to Matlab and turning in my assignment!That was for when you were in the process of finding the 12V level.........it's DC and the scope will show it without the need for a trigger...........while in Auto trigger mode.
If the Single shot did indeed capture something @ 100ms and the sweep signaled it was Stop'ped, even if the sweep speed was too slow to see the detail, while Stop'ped you increase the timebase speed to examine the detail.
Such is the power of a DSO.
Welcome to the wonderful world of DSO's.
Enjoy your journey.