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CAN Test Box

can test box


Continuing with our mission to make vehicle diagnostics easier and faster…the new CAN Test Box gives you easy access to the 16 pins of the diagnostic connector that is fitted to all modern vehicles. Depending on the configuration of the vehicle, this may allow you to check power, ground and CAN Bus signal quality. With the test leads supplied you can connect your PicoScope lab scope to the CAN Test Box to monitor signals such as the CAN High and Low. More.....

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Attention all
Automotive Scope Users

Pico Automotive Scope software now sports a new Waveform Library browser.
Must own PicoScope to view.
See details here


We have just posted a few new Automotive Tutorials and Case studies Here is the latest:
Honda Rattle

New Kvaser white paper discusses ways to maximise CAN’s efficiency in next generation vehicles

By using a Virtual CAN Bus, we separate the control task from other tasks. The distributed embedded control system can be developed using standard CAN Controllers and transceivers in a traditional way with well proven tools.

Other tasks such as encryption, transmitter authentication, re-flashing, etc. can be developed by experts in these fields and carried out by using other protocols. With modern technology, the different tasks can run in parallel and simultaneously communicate on the same physical layer.

It is a great advantage to separate the control problems from other problems. The control problem can be solved once and for all by the control experts and other problems by experts in their respective technology fields.


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Engine Management

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Testing Digital MAF Sensors

(with Frequency Outputs)

By Alan Tong

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Most Mass Air Flow (MAF) sensors have analogue outputs that typically vary from 0.5 V  to 4.5 V  (0 V  or 5 V  is an error condition). The output of these sensors does not, however, change linearly with air flow - scaling and corrections need to be applied by the ECU. A typical output from a non-turbo engine is shown in figure 1 below:

figure 1

Figure 1

Some modern MAF sensors contain digital electronics so that the scaling and corrections can be made within the sensor, thus improving accuracy. The output of these sensors is a changing frequency. A typical scope trace looks like this:

figure 2

Figure 2

Whilst you can see the frequency changing with airflow, it is not as easy to test the sensor. One partial solution is to measure the current drawn by the sensor (the so called "Massey method"). A typical trace is shown below:

figure 3

Figure 3

The blue trace shows the frequency output and the red shows the current drawn. The change in current drawn is only a few mA so it stretches the limits of what can be measured with the 60 A  current clamp, even when set to the 20 A  range.

figure 4

Figure 4

To get the trace below, we wrapped the wire carrying the current through the jaws of the current clamp 5 times as shown in figure 4.

This "amplifies" the current 5 times so, although the scale shows 1A, the actual range is 200 mA. We also switched on the low-pass filter to further clean up the signal.

The current clamp method will only work with hot-wire type sensors where the current drawn by the sensor is proportional to airflow. It will not work on Bosch-type hot-air film sensors or the AC Delco "coldwire" / inductive sensor as with these sensors the current does not change with airflow. Clearly a better way of testing these airflow sensors is to have an option to plot the changing frequency against time. This allows us to look at the same signal as the ECU.

An option to measure frequency against time has now been added to PicoScope software (version 6.4.28 onwards). A trace from a turbocharged diesel vehicle is shown below. The vertical scale is in frequency.

figure 5

Figure 5

There are a few points to note. Firstly this option is only available on the PicoScope 4000 range of automotive scopes, as it requires hardware resources not available in earlier products. Secondly, in PicoScope 6.4.28, the frequency measurement is a bit sensitive to noise. This will be addressed in future releases. Frequency measurement is enabled from the AC/DC drop-down menu.


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