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Question about oscilloscope

Hi , i am a beginner at using the scope for car diagnostics , so i was looking to buy something within the budget i looked online found hantek 8 channels but it said its 8 analog channels , some other scopes saying its 4 digital channels , so i was wondering what is the difference bet. Analog and digital channels ??

Regards

I had an earlier version of this long ago

http://www.testequipmentdepot.com/tektronix/oscilloscope/4-channel-digital-phosphor-oscilloscope-100mhz-tbs2104.htm?ref=gbase&gclid=CjwKCAiA3vfgBRB9EiwAkfpd3CdgRPJZ_TRl-YhsvS-yKVGZ7cMZhRLKDpIy36R4UF6dxhPh0hGLAhoCLAYQAvD_BwE

and found that 4 channels were all that was ever needed then and also had this
Snap-On scope at the time

https://www.ebay.com/p/Snap-on-Vantage-Pro-EETM303-Scope-Meter-Component-Tester/1122111159?iid=254035360160&chn=ps

and for the beginner it can save a lost of time in set up and operation but many times the controllabillity of ranges and viewing related inputs simultaneously made the tektronic more useful. Plus the lab scope is not programmed to be dedicated to current automotive applications and so will never need upgrading.

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And re analog and digital, that refers to the operation of the scope itself and I feel sure that any analog scope would use an old cathode ray tube while digitals use flat screen ‘digital’ monitors. I would be surprised if analog oscilloscopes are available that can be easily used on an automobile. The old Sun Electrics were analog but they are all antiques now and very limited in their functions.

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Analog scopes basically use CRT screens, basically a bench unit that has the settings/adjustments on the same panel as the display… Signals were modified using resistors and amplifiers then sent to a cathode ray tube for display. This was the “old” method for scopes much like an old television. Today everything has gone digital, even the new bench units. The digital scopes make snap shots of the signal very very quickly, then put all the snapshots/samples together to draw the signal on the screen.

For automotive applications, it is recommended to have at least 4 differential channels (In my opinion). Honestly, I prefer 6 but as the channel count climbs, so does cost. Differential simply means the scope measures the voltage diff between the positive and negative/ground probes for each channel. Some scopes tie all of the negative/ground leads together which can corrupt certain signals when multiple channels are used. Perfect example would be looking at analog/VRS crank position and cam positions signals at the same time. Obviously today with variable cam timing, being able to review crank and cam signals simultaneously is very important for some vehicle diagnostics.

Having fully differential channels will also help reduce channel “Cross talk” when looking at ignition or injector driver pulses. Cross talk is simply when you see the electrical signal of one channel displayed on another… There are multiple reasons this can happen but having the channels fully isolated reduces the chanced significantly. I can say the use of non isolated channel scopes on current diesel engines will not go well as the injector control use high and low side drivers. For you to see the injector pulse, the scope must measure the positive injector drivers and negative injector driver. If the scope channels share grounds, the LOW side injector drivers would be shorted together… This cause measuring issues plus have the potential to fry equipment.

Another benefit to Digital scopes is that the user can make recordings/snapshots of signals on most modern units… This is very nice when trying to capture glitches or build yourself know good/bad signal library. Digital is the way you likely will be find yourself going. You will want to also pay attention to scope sample rate, voltage range and the number of bits per channel. Sample rate is how fast the scope is collecting data. A scope too slow will be unable to see some signal glitches or may cause some actual good signals to look glitchy. For example, when looking at a modern day digital/Hall type crank sensor on a high resolution trigger wheel (60 tooth) the signals will look pitiful even at idle on a scope that does not sample fast enough.

The voltage range is important because you don’t want to fry your hardware by over voltaging. Keep in mind, when looking at an ignition coil primary signal. Voltages may exceed 200 volts, Fuel injectors as well will have high fly-back voltages. Modern diesel do exceed 200V. From experience 200V should be the MINIMUM voltage range you should consider for an automotive scope.

I am rambling, so time for me to shut up. Back to your question, make the investment in a good digital scope.

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I wanna thank " Rod_Knox " & " jgree " for that much informations i got but you misunderstood me somehow what got me confused is i found a scope has 2 digital channel & 2 analog channels in the same scope so my question was what are the differences bet. These channels in the same scope ??

Here is what i am talking about : https://s.click.aliexpress.com/e/b1yXt8SM

Regards

Aliexpress? Run…Run Away!!! Guaranteed to be the cheapest crap available. Just my opinion.

https://www.amazon.com/dp/B019R7790A/ref=cm_sw_r_cp_apa_i_012hCb50F4JR6

Just being battery powered would be a deal breaker for me. This all but assures it will be dead or near dead just when I need it. It also looks like it comes with a USB cord but no AC adapter for it, so unless you have/buy one your tied to a pc also. I would spend the extra for a better unit. Again just my opinion.

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What do you recommend ??

Looks for something that has the features @jgree142 and @Rod_Knox mentioned and either AC powered or can be connected to the car battery. Other than that I only have my opinions which are unfortunately bias against anything on aliexpress. Just never had any luck with them. Sorry I can’t be of much help

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o-scope "Analog channels " usually means it works just like scopes have worked since they were invented, the crt display shows the signal volt vs time as it occurs. “Digital channel” means the signal is sampled (a/d converted at an appropriate number of samples per second for the bandwidth) and stored in the scope’s memory chips, before it is displayed. There are advantages and disadvantages with each. But for automobiles, the differences would be minor for most situations, so focus on getting a good quality instrument for cheap. A used 2-channel analog scope from craigslist at around $100 is probably best compromise, bang for the buck, for auto diagnostic use.

The only advantage of a digital channel (for auto use) would be when the signal your are interested in isn’t repetitive. An example for that might be for diagnosing a fails to crank situation. A digital channel would be able to record the “start” signal from the ignition switch, and the “start” signal to the starter motor, and the voltage to the starter motor main power input, all for a single start attempt. But the same thing could be done with an analog channel, just a little more cumbersome.

I see quite a few used o-scopes priced from $40 to $100 on CL right now. There’s an old antique looking Heathkit version for $75, that would be perfect for auto use if it still worked. For another $40 you even get a signal generator.

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One big difference is loading. Analog sensors load a circuit, that is they draw some current while measuring the signal. Because of this, they actually change the signal by a tiny amount. That change varies by the amount of loading. A cheap sensor can load a circuit quite a bit where a high quality (expensive) sensor will not load as bad. The advantage to an analog sensor is real time data and a potentially higher frequency response.

Digital sensors have almost no load so do not affect the signal at all. But digital sensors are limited by their sampling rate. They need at least two samples per cycle of the signal. As they approach their limit on frequency response, some distortion of the signal can occur.

Flat screen displays ultimately convert the signal to a digital format for display in most cases so I’m not sure why they would bother with an analog sensor.

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