I just have started to use this Joulescope equipment to measure current in one of our low power device having BLE chip. It will have sleep current in uA and during transmission it will have current in few mA (Say as per datasheet maximum peak 9mA).
I was trying to measure same and few query i have after seeing on PC GUI.
What is the current which is getting displayed in CSV file when doing recording? That current is mean current?
Why it is showing Maximum current of approx. +58mA on screen in multimeter view in above image? Which current is this? My device can’t take this much current ever.
In oscilloscope view also it is same, in Auto mode it is showing current in +62mA Max.
Another option is to set your Joulescope to a fixed 18 mA current range (the smallest range still larger than your maximum current). The waveform will then not have any autoranging artifacts.
So, why are min/max confusing? Joulescope is an autoranging shunt ammeter, which means that it inserts a variable resistance between your power supply and target load. The Joulescope shunt resistance, along with your cabling, forms a low-pass filter with your target’s capacitance. On an over-current event, your Joulescope decreases the shunt resistor value very quickly, which decreases the voltage across the shunt resistor. However, your target device’s capacitors must charge up, resulting in a current spike.
For the cleanest waveform, you can select a fixed current range. For the highest dynamic range, you want Joulescope’s autoranging feature. Check out this post for more discussion:
Hi @mliberty, Thanks for follow up. Yes equipment is working well and i am running in the range of as per your suggestions.
But on auto side, i really did not get accurate answer why 60A current is getting shown.
Another query i have related to sampling rate is 500mSec that is fixed or we can change? I am not able to see BLE transmission current in mA and maximum i am able to see only 220uA during transmission while it should be around 3~4mA.
So, i am thinking this will be issue of sampling rate. Let me know if i can change this or other method to measure this?
Hi @mysumithere The default sampling rate is 2 Msps, and you can change it. Select File → Preferences → Device → setting → sampling_frequency. Note that while your Joulescope will always sample at 2 Msps, changing this setting enables downsampling, which can be good for data reduction or noise improvement due to reduced bandwidth.
I am happy to take a look at a capture to see if I can help better explain what you are seeing in “auto” current ranging mode. You can add dual markers to the waveform. Adjust the marker locations to include your entire BLE transaction, then right-click, select Export data. You can then post the file here or email support atjoulescope.com.
Hi @mliberty— Sampling frequency is 2 Msps, i was expecting more so that sampling time will be minimum and we can capture small transition current also.
I will share auto mode waveform.
I have another query, In recorded CSV file time stamp is not getting captured which is little bit hard to decide about the event as per device stamp.
So, is there any option to add date and time stamp in recorded file?
Your Joulescope is advertised as 2 Msps with 250 kHz bandwidth, which allows you to see most everything you can with a modern microcontroller. In most real-world environments, you are bandwidth limited by the bypass capacitance on your device under test. For example, if you target has 10 µF capacitance, then your system will have 250 kHz bandwidth if:
f = 1 / (2 π R C)
R = 1 / (2 π f C)
R = 1 / (2 π 250000 10e-6) = 64 mΩ
Joulescope adds about 25 mΩ, typical. Your cables, connectors, and power supply will add more. In practice, paying for more bandwidth does not normally matter much unless you are connected directly to your chip without any bypass capacitance.
The existing CSV format only records the relative time. However, the default filename is the UTC time as YYYYMMDD_hhmmss. Also note that the relative time is in your Joulescope’s time units which have a ±20 ppm accuracy.
