Thanks again for taking the time to respond and for your time in actually capturing test data to quantify the file size
Based on your feedback there is no question that (finances aside) a 4 channel automotive scope would be an invaluable asset, even as a 'hobbyist' and to be fair I don't think it is expensive for what it appears it can do.
The custom probe option just sounds like the sensor calibration that I would normally put into a data logger setup, can these settings be input as a tabular transfer type function or does it have to be an expression / function such as y = mx + c, I imagine it can be tabular in order to capture something like a non linear NTC thermistor (my likely choice for the temp sensor, as a K type would have poor resolution for the -10 > 60 Deg C range I expect)
For the RPM signal I would really need the ability to capture / display a real transient RPM signal. With the fixed frequency / fixed RPM example that you gave I assume is only useful in a steady state measurement where you manually calculate the RPM or could you reliably derive the instantaneous RPM for the whole data capture as a maths channel and have it visible as an RPM trace?
In the past I have had problems trying to 'piggy back' onto an existing crankshaft sensor on the basis that it has compromised the original signal that the ECU needs to run the engine. How reliable do you find the derived RPM techniques you mention, although I think I would end up short of channels to do this if the RPM is not derived;
1. Battery charge current
2. Alternator output current
3. Battery voltage
4. Battery temp
The current transducer used at the battery -ve cable is something of a dilemma, for the sake of a 1 second event (starting current = 280A) I will end up compromising the resolution for what will be 50A max for say 20 sec at worst and then quickly less than 5 Amps for the remainder of the 3600 seconds.
Another problem has just dawned on me, the TA 167 does an auto zero on power up?, my intention was to have the clamp/s secured in place within the engine bay for the test runs, but they will auto zero on power up when there is in some residual current, I guess I could try and remove the offset after the data is captured but the vehicle has a coolant circulation pump which runs for at least 10 mins after shutdown making it difficult to try and establish a 'zero' current reading to use as an offset.
Here are my latest voltage readings during vehicle start up showing the same lack of logging rate, these tests are using two different battery types, hence the apparent difference in voltage drop during starting.
EDIT: The title looks like -5 deg C, it was +5 deg C, the '-' was just intended as a separator but looks like a negative sign.
All good examples of how those without Pico Scopes see the lower resolution world
Looking back at the Pico Scope Automotive training video which shows a battery test, I notice that this test reports a minimum voltage of 7.64 Volts, I have achieved similar figures during some cold start testing albeit only this low for a couple of tenths of a second, in your experience do most OEM ECU's have enough what I would call a "Capacitive buffer", i.e. sometimes by design and sometimes otherwise there is enough voltage stored in capacitive elements within the ECU that such a voltage drop out doesn't cause an issue due to the short duration of the drop out as the ECU stays 'energized'?