PicoBNC+ 60 A AC/DC current clamp test

With the introduction of the new 4x25A Automotive PicoScope comes a number of PicoBNC+ accessories. These take advantage of the new and unique connection type on the scope and offer improved performance over existing BNC probes.

One such accessory is the new PicoBNC+ 60 A current clamp (TA473), which can boast of superior resolution during low-current measurements, such as parasitic drain.

The test below covers this challenging measurement procedure using both the new PicoBNC+ 60 A current clamp as well as the existing BNC 20/60 A clamp (TA018).

The procedures for measuring parasitic drain using the TA018 current clamp have been discussed at length within our advanced training feature on parasitic drain.

The article covers the phenomena inherent with all current clamps called “drift”: a term that describes how the current clamp has deviated from zero amps over time.

For example, when zeroing the current clamp prior to measurement at 8 pm (for an overnight parasitic drain measurement test) the clamp may drift from zero by 8 am the following morning. This will become apparent upon disconnection of the current clamp from the vehicle where you would expect the value to return to zero. In reality, the clamp may now be reading 40 mA (disconnected from the cable under test) meaning our true zero is now 40 mA and not 0 A.

When measuring parasitic drain, an error of 40 mA could mean the difference between a pass or fail in the test procedure (if we do not account for the inherent drift of the clamp).

The new TA473 current clamp is by no means immune from drift, as we utilize similar inductive measurement technology. However, the drift has been minimized thanks to the improved screening of the internal magnetics along with superior thermal stability across the operating temperature range (0° C to 50° C).

The benefits of the TA473 for parasitic drain measurements do not stop at minimized drift, far from it. Thanks to the PicoBNC+ connectivity, the probe's settings are automatically configured when the probe is connected to the scope, the clamp is auto-zeroed, the bandwidth limit is activated and the probe ranging is carried out automatically with no user-switching required.

The most practical benefit of all is, without argument, that the TA473 is powered by the Scope/USB connection, abolishing battery anxiety and, in worst-case scenarios, erroneous measurements.

Errors in overnight parasitic drain measurements may result in a delayed customer hand-over by up to 24 hours, not to mention the valuable workshop space consumed by a standing vehicle.

Below, we apply both the TA018 and TA473 to measure parasite drain via a fused jump lead between the battery negative lead and battery negative post.

In the following screenshot, you can see the parasitic drain measured by the TA473 on Channel A and the TA018 on Channel B.

Note how the clamps are at zero prior to the test and then removed from the cable under test after testing is completed to confirm that they remain at zero. While this capture is only 90 seconds in total, the same zero validation technique should be used before and after overnight parasitic drain measurements so that you can compensate for inherent drift if necessary.

Conclusion:

Both the TA018 and the TA473 are more than capable of measuring parasitic drain. However, the TA473 makes this challenging measurement technique a lot smoother thanks to:

  • The automatic probe identification and configuration
  • The automatic range-setup upon connection (no external switching)
  • The automatic application of bandwidth limit
  • The minimal clamp drift
  • The improved immunity from environmental noise (screening)
  • The improved signal quality thanks to superior shielding
  • Being powered via the Scope/USB
  • The wider jaw (12 mm), which increases non-intrusive measurement possibilities 

Cutting through the technical jargon above, we can summarise the PicoBNC+ 60 A current clamp in just 3 words: Easy to use.