In-vehicle current measurement

Why is vehicle current measurement important?

There are a number of reasons for investigating current draw in a vehicle. ECUs can fail functionally for a number of reasons such as software glitches, hardware failures, load variations, cold weather conditions and mechanical wear.

Measuring the current to one or a small number of ECUs is a useful technique that can be employed to identify system issues.

What is a typical current measurement range?

There is a very wide range of currents in a modern vehicle, ranging from microamps to hundreds of amps and covering as much of this range as possible is important, within practical limits.

How can I measure current on my vehicle without cutting wires?

Because cutting into the harness cables of any kind of vehicle can be expensive and likely to introduce reliability issues – even before release to ‘job 1’ during development – a system that avoids modifying the cabling is preferable.

This is where in-fuse measurement systems offer best-in-class solutions.

What is an “in-fuse measurement” ?

An in fuse measurement solution is a hardware solution that can replace a vehicle fuse, such as a mini-fuse, ATO or MAXI fuse, with a device that can provide sensitive measurement in the space normally taken by the fuse.

High density with few high current wires

Using in-fuse holder measurement and CAN communications to deliver the current values can reduce heat, the use of copper and improve density – even for high-end vehicles.

Example of a high-end multi-point fuse measurement system

What test cases can be covered using this technique?

Multiple test cases can be covered using this technique, including ECUs failing to communicate due to power supply perturbations, power down issues, stuck relays, software functionality issues, corroded connections, incorrect wiring and shorted harnesses.

So what is a “practical measurement range”?

Solutions such as our Sens-X fuse point-of-measurement devices have a very wide dynamic range, and can offer usable current measurements from around 1mA up to 50amps (with resolutions as low as 50uA). This is available on the same device with no range switching, low noise and response rates sufficient for the test cases required.

Is current all you need?

No.  Knowing the current is the primary goal, however, your system can benefit from knowing the voltage at both sides of the fuse to identify voltage supply (or wiring) issues, as well as fuse-based voltage drops which may be compounding low voltage issues.

What other features can improve this application?

Measuring current should take as little current as possible from the fuse itself – taking 10uA or less is considered acceptable at a nominal 12V battery voltage.

Using high-speed CAN communications for the current and voltage values can enable modern CAN-based vehicle systems to correlate current measurements with vehicle bus communications. This allows CAN logging to enable timestamped verification of systematic functional issues.

Providing a (ground) reference point for voltage measurement close to the fuse box – but independent from the instrumentation ground – can help measurement accuracy.