Choosing a scope

Frank Massey scopes out what technicians should look for when picking a oscilloscope

By Frank Massey | Published:  18 April, 2018

Having just completed a foundation oscilloscope course this weekend, it became very apparent that a large number of technicians in our industry lack good advice in both choosing and using cutting edge diagnostic tools.

So this topic is dedicated to my favourite friend – the oscilloscope. This year, June to be exact, will be my 50th year in automotive engineering, so I have witnessed first hand how mechanical systems and electronics have evolved.

Adapt and change
I don’t agree with all that’s happening, with autonomous self-drive a clear example. I do however agree in the way we must adapt and change. My diagnostic career began with analogue or moving beam scopes. My first experience with digital scopes was a disaster. The Crypton Cudos not only failed regarding signal integrity, it also caused a probing reaction in sensitive circuits, like Lambda and some crank angle sensors.

This led to a fateful decision in seeking a competent oscilloscope from the electronics industry. I owned various Fluke and Tektronix scopes, before moving to the Pico range. During years of research into high performance scopes I became unpopular with most automotive diagnostic scope providers.

Going digital
So, what is a digital oscilloscope, how do they work, how do you choose one, and what ancillary accessories are important?

  •  Performance
  •  User interface
  •  Industry standard connectivity
  •  Software support
  •  Cost

Performance is critical. Bandwidth is the maximum frequency of the incoming signal that can be reproduced without a reduction of signal integrity. It must be ten times the input signal frequency. Assuming high speed can at 1MHz, the minimum specification should be 10 MHz. The minimum standard set by professional scope manufacturers is 20MHz. This is often compromised with multiple channels that divide the AC/DC conversion. This means that selecting multiple channel input can divide bandwidth, so check specs carefully. Test leads can also reduce bandwidth ensure they match or exceed the scope bandwidth. A lack of bandwidth will distort signal amplitude, edges will disappear or become distorted and high frequency changes will not be resolved.
A digital scope takes multiple samples of the incoming waveform, stores them, and then reassembles them as a visual image. The higher the sample rate,  the more detail you have. Unfortunately, if the bandwidth or sample rate is to low you will get an image that is not a true representation. This is called aliasing.

Critical tools
The three critical tools of a digital scope are:

  •  Acquisition
  •  Storage
  •  Display

These are different ways the sampling is applied to the incoming signal:

  •  Acquisition tools
  •  Sample mode
  •  Peak detect
  •  High resolution
  •  Envelope
  •  Average

Storage is often the deal breaker, as scopes must be both fast and have vast storage capacity. I own a fabulous 2.5GHz Tektronix digital phosphor scope. It offers a two thousand five hundred million bandwidth, but has a very limited internal memory. Therefore, I use a Pico scope. It is fast and utilises the PC memory. Job done.

Display; Interface; Connectivity
How the data is displayed on the digital monitor is very important, as is having  the tools available to enhance or change its appearance. Pico has a 12bit resolution offering exceptional clarity. Do not confuse clarity with accuracy as some scopes offering visual clarity lack signal integrity.

User interface is achieved through  the knobs and buttons that you use to manipulate the scopes controls. My Tektronix scope has manual buttons and switches whereas the Pico has virtual buttons. They both do the same job. The important feature
here is that are they simple and unambiguous.

Universal connectivity is a big help too. Does the scope offer BNC ports? If it does then the world is your oyster. These are the industry standard, offering a wealth of accessories. Many automotive tool manufacturers offer their own non-standard ports restricting your flexibility and offer costly and limited accessories.   

The accessories options are wide and extensive so let’s explore what is vital and what’s advantageous.
Test leads; High frequency signals demand 10.1 attenuation with 10meg Ohm resistance.  The bandwidth is vital and must match or exceed the scope range. 1.1 leads are fine for most automotive applications; However, consider how you are
going to probe various automotive sockets. Colour and length help working flexibility.

Current measurement is the holy grail of load bearing circuit evaluation. They range from 2k amps down to milli amps. Pressure measurement offers a unique insight into mechanical functionality in real time. All our compression testing is conducted with a running engine. Turbo boost and control evaluation exposes discrete errors. Vibration and noise measurement is the new kid on the block, well not quite. Other industries have been relying on its importance for many years. Our gifted Royal Navy submariners can monitor and identify target vessels thousands of miles away from sound waveform signatures. Everything we take for granted in a vehicle is based on frequency signatures. Measure them identify them and accurately predict their status.

To conclude, the subject is enormous. I have been a pioneer for over 30 years and I am still learning. a final word of advice before you choose a scope demand the full spec sheet. If it does not exist there is a good reason.
Walk away!

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  • Train in vain?  

    You’re never too old to learn, as they say. Well in this industry they should say you are never too old to stop learning. If you do stop learning, you might never catch up, and then where will you be?
    In June, like much of the industry we were at Automechanika Birmingham. As always it was highly illuminating. We are not going to give you a full lowdown on the event here though. If you want that, turn to page 30 where we have all the info you are ever likely to need. There is one aspect of it we would like to cover though – change, and what the impact can be.

    During our three days at the show, we noted all the new technology, factoring in electric vehicles and hybrids, as well as all the ongoing developments within the internal combustion engine. EVs and hybrids might take up the column inches, but it is conventional powertrain vehicles that make up the majority on the roads still, and will continue to do so for some time. It might sound like stating the obvious, but it was made very clear that nothing will stay the same forever, so businesses that work on vehicles (that means you, dear readers) need to make sure they keep up to date.

    We’re not telling you anything you didn’t know. It’s just one of those situations where you walk through the various halls, and remember that all that development you spend all your year writing about is a tangible thing, that you can go and touch and see.

    Off-topic; On-message
    While we were at the show, we were able to speak to a wide range of industry figures. One tries to stay focused on the key issues in these sorts of interviews, but during our sit-down (on surprisingly comfortable stools considering their vertiginous height) with IMI chief executive Steve Nash, we went a little off-topic. We were supposed to be talking about Automechanika Birmingham, and you can see that in the show feature, but we ended up talking about the history of the sector and where technology is going.

    "The IMI will be 100 years old in 2020,” said Steve. “There is a real parallel in what was happening then, and what is happening now. 100 years ago,  just after the First World War we had seen that natural explosion in technology that wars create. Before the war, cars were very noticablely horseless carriages. By the 1920s you had sophisticated cars, and it was no longer appropriate to have the local blacksmith tending to them, which is what happened. This is why we were set up.  It was to try and introduce some professional standards to the industry.

    “Fast forward 100 years and we are there again at the quantum point we were then, where the technology is moving rapidly ahead of the people in the industry, and we have got to move rapidly to keep up. I don't think it is appropriate to ask people to engage with potentially lethal high voltage electrics without knowing they are properly equipped and trained."

    Steve added: "If you look at Volkswagen, they are quoted as saying that from 2019 they will bring out a new electric vehicle to somewhere within one of their ranges every month. We are moving into a different era, and the skills have got to move with the times."

    Move with the times indeed. It’s a lot to take in, but no challenge is insurmountable. While the various technological marvels and new products on show might seem too much to deal with, if you make sure you regularly undertake training to develop your skills, you should be able to keep up and get a handle on it all.

    Through the show, there were many seminars available for free. Some were in Aftermarket’s very own Seminar Theatre, as well as in the various other dedicated venues. Considering the extent of development going on in the sector, we wonder sometimes why these sorts of sessions are not completely overrun by businesses looking to stay up to date. Obviously not everyone can attend, you need to stay up to date.

    Continuing professional development (CPD) is something you need to pursue. Training is not just for the young. It is vital for existing technicians, to stay young in mind and attitude.

    We regularly talk about training, as regular readers know. We have a standalone section that covers it every month (pages 62-63 in this issue while we have your attention), where we discuss and cover training, both in terms of outcomes and available courses. You don’t just need ongoing training because of changes to vehicle construction and engine type either. MOT requirements mean testers need to undertake annual training, and the new MOT regulations that came into force in May have only reinforced this.

    Top idea
    Training can take you a long way. We recently held the finals for Top Technician and Top Garage. One thing that we always notice at the semi-finals and the finals of Top Technician is that when you are talking to the contestants, training comes up constantly. They will tell you about all the courses they have been on, and all the skills development they pursue. If they come up across a difficult problem they will research and follow it through to its successful conclusion. Accessing training and looking to find the route case of particularly interesting problems are both goals for participants. CPD is a mantra and a passion here.

    This might not always be the best use of time and resources in the moment, but they see it as an investment in the future. It will pay off later for them. Clearly when you are looking at the bottom line and trying to keep pushing forward and push jobs out the door this cannot always be the priority. However, if you can factor this kind of thinking into your day and follow up with training, you will be heading in the right direction.

    In the end, it’s all investment whether it is a spanking new piece of kit, or training to enable you to work on the latest vehicles. Equipment will always need to be replaced in the end, sad as it is to admit when you have bought the latest doohickey that really will help you, but knowledge breeds knowledge, sparks new ideas, and helps you and your business grow. Put your money where your life is, and get to it.


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