sync to RPM

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littleozfella
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sync to RPM

Post by littleozfella » Tue May 19, 2020 1:34 pm

Hi all. Is it possible to link the traces to sync with engine RPM.. IE I am using an engine dyno and I want to display 2 cycles of the engine on the scope then when I increase the rpm the same data stays on the screen, so I guess you can say the time scale is linked to RPM to keep the same display.. I hope that makes sense.. the scope and laptop are inside the cell, I can't keep changing the X axis ms/div scaling. Basically I am reading pressure sensors in spark plugs for knock. Cyl pressure and crank position traces.
Cheers
Mick

matt07181986
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Re: sync to RPM

Post by matt07181986 » Tue May 19, 2020 5:31 pm

I am sure the guys at Pico will link you to a more thorough explanation but I have a few suggestions. You could use something like the cam, crank, or ignition pulses to create a math channel and graph the RPM. That way you could trigger off the RPM signal. You could also use the optical pickup that is available for the NVH kits, you do not need the NVH kit to use the optical pickup. Pico has a video on YouTube in the NVH series, I recall them covering how to graph RPM.

Martyn
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Re: sync to RPM

Post by Martyn » Tue May 19, 2020 5:33 pm

If you go to Tools->Math channels and create a new maths channel

T*freq(A)

then you need to change the X axis so it uses this math channel and not the normal Time one. You can do this in the menu which is accessible when you right click on the display area.

One of the team will probably post an example soon, I am on a phone so this is from memory.
Martyn
Technical Support Manager

littleozfella
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Re: sync to RPM

Post by littleozfella » Wed May 20, 2020 3:10 am

Hi Guys, thank you for your quick reply. Martyn, I guess the channel (A)in the formula is Input A so could be any of the inputs (B,C,D). I would also guess this input needs to be a frequency consistent to what I want to sync to, RPM in my case. If I use a Tacho output from the ECU this should be sufficient I think??
Cheers
Mick

Steve Smith
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Re: sync to RPM

Post by Steve Smith » Wed May 20, 2020 6:31 am

Hello Mick and thank you for the posts.

You are correct, the letter in the math channel refers to your input. (A) being Channel A,so you can if you wish use any of your scope inputs that are capturing a frequency relative to RPM

Assuming you have a crankshaft position signal on channel A (or optical signal as Matt referred too) you would create the Math Channel T*freq(A) This could also be T*freq(B) etc.if your speed signal uses Channel B

When creating the Math Channel formula, click on the "Down arrow" in the image below to find "Time"
IMAGE 1.png
Image 1
To now set the math channel as your X Axis as Martyn referred to, you can use the Right Click Option within PicoScope 6 or click on Views > X Axis > and scroll down to find your math channel (See below)
IMAGE 2.png
Image 2
I hope this helps, take care......Steve

littleozfella
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Re: sync to RPM

Post by littleozfella » Wed May 20, 2020 6:52 am

Fantastic guys, thank you all. Steve my Crank signal is 60-2 so the frequency won't be constant and in any case I am using a motorsport ECU so I can simply configure a Tacho output. I would think that will be easier solution.
Cheers
Mick

Steve Smith
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Re: sync to RPM

Post by Steve Smith » Wed May 20, 2020 12:26 pm

Hello Mick, 60-2 will create a rapid drop in the frequency and could play havoc when using a frequency math channel on our crank (It is worth a try though as we have below)
Image 1.jpg
Image 1
Resolution is key and you could try T*Crank(A,60)

If you can configure an output that would be even better as you have control over the pulse count per revolution

I hope it helps and please let us know how you get on

Take care.......Steve

littleozfella
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Re: sync to RPM

Post by littleozfella » Sat May 23, 2020 5:11 am

Hi Steve,
Well success to a point. I have tacho setup with 4 pulses per ENGINE cycle so 2 pulses per Rev. The data synchronises to a point.. The data tends to "float" a little across the screen. while the size of the channels requested remains (ie 1 engine cycle) the channel data tends to jump a little across the screen making the viewing a little difficult. I think this is because of the channel rate. Unfortunately the highest value I can use is 3 pulses per RPM, I will try your 60-2 maths on Monday. Unfortunately these are my only Hz based options, the only other option I have I can generate a duty table that would give a duty proportional to RPM, say 10% at 1000 RPM, 100% at 7000 RPM, channel rate 100Hz. (I can use from 13hz to 10,000hz) I am not sure if this is a possible solution. This would be derived from a PWM control base table.
cheers
Mick

Martyn
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Location: Cambridgeshire

Re: sync to RPM

Post by Martyn » Sat May 23, 2020 7:41 am

Can you post a data file so we can look at the setup?
Martyn
Technical Support Manager

littleozfella
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Re: sync to RPM

Post by littleozfella » Sat May 23, 2020 8:21 am

Please find attached..

cheers.
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