Chris Wilson Posted August 1, 2011 Share Posted August 1, 2011 I know quite a few people here are into electronics, so maybe worth me posting this here. I am after a clip on current clamp for my oscilloscope, around 0 to 40 amp rating. One was on Ebay the other day, was bid over retail and didn't even hit the reserve, I felt sure it would go quite cheap... Thanks. Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 1, 2011 Share Posted August 1, 2011 Hi Chris I've been looking for something similar myself recently. I've had my eye on the PP264 from Pico for a while. I've not come across anything close to it for automotive type work. It'll do both AC and DC; it also has a 20 kHz bandwidth which will come in handy for fast transients in ingition systems. Cheers Andy Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 1, 2011 Author Share Posted August 1, 2011 That's the unit I was after myself, I have bought a few Pico accessories, and I have seen that clamp cheaper form the US, on Ebay, but high carriage costs make it dearer, once landed here. I may just bite the bullet and get the Pico one. I use these accessories on a none Pico USB scope, and miss the pre set channels that the Pico Automotive units offer, I have to cheat and look at the help illustrations in the demo Pico software, read the voltages and set ups off the screen shots and try and set my scope up the same way Usually it works OK. Thanks Andy. Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 4, 2011 Author Share Posted August 4, 2011 Just found a PP264 (without the Pico logo) on Ebay and grabbed it with a cheeky buy it now offer. I'll let you know how I find it. Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 9, 2011 Share Posted August 9, 2011 All this talk of current clamps motivated me to pull my finger out and buy one. I went for the Pico one in the end; it arrived today. One of the first things I went to measure was the ignition dwell time with the stock ECU and stock coil packs. I was quite surprised by the waveform I measured: It appears that the stock igniter is regulating the coil current at around 6.6A. I didn't expect to see this. As a quick comparison I hooked up a single channel igniter to a stock coil and drove it with a standalone ECU. It appears that this igniter is also limiting the current, but to a lower value of 5.4A: I believe on your Skyline you chose to replace the stock Nissan igniter with a couple of 3-channel igniters (I came to the same conclusion for my standalone build). If you're desperate to play with your new current clamp would you mind clamping it around a wire going to a coil pack and posting the current waveform you see? If the 3-channel igniters are limiting the current I need to re-think my system. Cheers Andy Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 9, 2011 Author Share Posted August 9, 2011 It's not arrived yet, I have paid for it but the vendor only returns from his hols today. I will try this ASAP for you Andy. What `scope are you using? Would you mind telling me if my `scope, linked below, has many disadvantages compared to a Picoscope Automtive `scope, save for no pre configured set up files for one click automotive diagnostic settings? Mine: http://www.dataman.com/webpages/prod...w.aspx?pid=727 Picoscope Automotive: http://www.picoauto.com/diagnostic-scopes.html Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 9, 2011 Share Posted August 9, 2011 Thanks Chris. I use a PicoScope 3204. It's a little underpowered for the embedded electronics work I do but more than capable for automotive work. The only thing that lets it down is the low max input voltage of +/- 20V. When used with a x10 attenuating probe this only gives you a +/- 200V range, unsuitable for hooking up to ignition coil primaries or mains powered circuits (340V peak). I've got around this by buying a couple of x100 attenuating probes from a seller on ebay which are rated to 1.2 kV. It's a good job too - when I was measuring the stock coil primary voltage, I saw voltages of 450V when the coil current was cut, peaking at 750V when the spark started. I didn't realise Dataman made oscilloscopes! I only know them from their EPROM programmers. The model you have looks like quite a capable scope, better than the Pico Automotive scope in most areas, especially sampling rate and bandwidth. The Pico has a 12 bit resolution vs. the Dataman's 8, but in my experience I've never needed better than 8 bit resolution on a digital scope. The biggest advantage that the Pico scope has is it's sampling buffer - It can store 32M samples compared with 8k on the Dataman. I'm a big fan of large buffers on digital scopes as they are invaluable in finding glitches in digital logic circuits. However, I don't think they are as valuable in an automotive environment. Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 9, 2011 Author Share Posted August 9, 2011 Thanks for that Andy. You seem very clued up on electronics, I may badger you again On my Dataman there is software attenuation, yet they also sell attenuated probes for it. I have to say changing the software attenuation doesn't seem to do anything noticeable though. I suspect I am misunderstanding its function. Does it mean I use these variable settings WITH a physical attenuated probe, or instead of one? Ta! Would you say my `scope is adequate for automotive stuff, I'm sure it's infinitely more capable than the user? Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 9, 2011 Share Posted August 9, 2011 The "software attenuation" function is for use with attenuated probes. Back in the Good Old DaysTM if you used an attenuated probe, the signal you saw on the screen would be different to the signal that you were measuring. For example, if using a x10 probe you probed a 20V DC signal, your scope would show 2V DC. You would have to remember to multiply the signal by 10 in your head to get the real signal. There are a few reasons you may want to use an attenuated probe: one being to look at signals that are greater in amplitude than your scope can handle, another is when you want to measure particularly sensitive circuits - attentuated probes have a higher input impedance and draw less current from the circuit being tested at the cost of a lower signal to noise ratio. With the advent of digital scopes, you no longer have to perform the multiplication in your head - the scope can do it for you. Basically you need to set the "software attenuation" to match the attenuation of your probes. Here, even though the 20V original signal is attenuated to 2V at the input of the scope, the software will display a 20V signal. It's important to ensure that the software is set to match the attenuation of the probes to ensure that you aren't misled by the measurements. Many probes have a x1 / x10 selector switch; it's easy to lose track of which setting each probe is on. The scope you have is more than capable for automotive work! The signals encountered in the automotive world aren't particularly demanding for an oscilloscope. Even full-speed CAN bus can be viewed with a bandwidth of 2MHz. The features I concentrated on when selecting a scope for automotive use were the physical robustness of the scope, how user-friendly the software was and the different triggering options. Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 10, 2011 Author Share Posted August 10, 2011 Wow, fantastic detailed answer, I understand completely now. I will buy a couple of different attenuated probes, so I can cover most bases. I need to get more into `scope usage, I am slowly seeing how damned useful they are. When my probe arrives I'll try and capture some screen shots of the Skyline coils on the Bosch 3 way igniters for you. I need to see if I need an attenuated probe though, for ignition coil readings Thanks again. Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 16, 2011 Author Share Posted August 16, 2011 My clamp arrived yesterday, and this is a screenshot of the clamp on it's most sensitive setting, on coil number one coilpack lead. I have also included a screenshot from Motec's i2 data analysis software showing this engine running about 1900 RPM, you can see the dwell figure in mS in the RH column. HTH. Link to comment Share on other sites More sharing options...
Andy Blyth Posted August 16, 2011 Share Posted August 16, 2011 Thanks for that Chris! It certainly seems that you're not getting the current plateau that I was seeing. Things are looking good for the 3-channel igniters! Just for reference, how many mV per Amp was your probe set to? On mine, the most sensitive setting is 100mV/A. This is just to see what the peak current your coils are drawing before the spark. Cheers Andy Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 16, 2011 Author Share Posted August 16, 2011 It's the exact same clamp as Pico sell, set to the 20 AMP range (100mV/A) This was the one I grabbed: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=300584210597&ssPageName=STRK:MEWAX:IT Don't forget these are aftermarket Skyline coils though... The blue Splitfire ones: http://www.hioctanedirect.com/index.php?main_page=product_info&cPath=25&products_id=232 Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 16, 2011 Author Share Posted August 16, 2011 The igniters I am using are the Bosch ones in the screenshot below. I can get them trade a lot less than Motec sell them. I did consider getting the 4 channel ones and having 2 spare channels in case one went down, or if I wanted to use them on a V8 sometime in the future. The three channel ones are standard equipment on the straight six 2.8 and 3 litre rear wheel drive Volvos, some late 960's and all S90 and V90 models if you want to try some from a breaker. They are under the intake manifold. Link to comment Share on other sites More sharing options...
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