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Suitable data logger - Cold cranking behaviour

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Suitable data logger - Cold cranking behaviour

Postby Spencer_D » Tue Feb 03, 2015 7:01 am

Hi there,

Initially I was considering a TC08 to log both temperature and voltage inputs, but I don't think it will be suitable

The requirement is to monitor a vehicles start up behaviour, cold cranking and battery voltage, RPM and temps

x5 k type
x1 Cold Cranking current - TA167 Current clamp input via PP264 terminal board
x1 Vehicle battery voltage - PP264 terminal board (with voltage divider)
x1 RPM input signal (maybe not essential but is preferable)

The obvious question would seem to be logging rate in order to properly capture;

Inrush current transients at start up
RPM signal transients

What is the maximum logging rate for something like the TC08 and is this an 'aggregate' logging rate, i.e. does the unit divide the aggregate logging rate by the number of active channels. For instance if the unit could log 100 samples a second and 4 channels were active then 25 samples a second per channel?

Do you have a device which can be used as an RPM pickup?

My guess is needing to capture the transient inrush current and transient RPM behaviour will not be possible with a TC08, along with the total number of channels required, but if you could advise what is most suitable.

All of the data collected has to synchronous and 'aligned' so any combination of units would need to 'synch' with each other.

Thanks
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Re: Suitable data logger - Cold cranking behaviour

Postby Karunen » Mon Feb 09, 2015 2:28 pm

Hi Spencer,

Each channel of the TC-08 has a 100 ms conversion time. With all channels enabled it would take 900 ms to get a new value from the first channel (Cold Junction also has 100 ms conversion time).

Unfortunately we do not have a device that could work as a RPM pickup.
PicoScope 6 some maths ability(e.g duty cycle and frequency) but the TC-08 is not compatible with PicoScope 6.

Do you know how fast you need to collect data for?

It might be better using a PicoLog 1000 (https://www.picotech.com/data-logger/picolog-1000-series/multi-channel-daq) as it is a bit faster. (PicoLog 1000 is compatible with PicoScope 6)

You can use the TC-08 with the PicoLog 1000 using the PicoLog software. But the values returned from the Tc-08 will change slower.

Kind Regards,
Karunen

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Re: Suitable data logger - Cold cranking behaviour

Postby Spencer_D » Tue Feb 10, 2015 10:00 am

Thank you for your response,

Yes I have been slowly bringing myself up to speed with the various options

I had come to the same conclusion as you as regards the TC-08, (Once I got my head around what conversion time meant)

I think I have found a suitable RPM 'pick up' but this has an 'open collector output' and I think would really need to be fed into a digital input in order to derive engine RPM as a result of the pulse frequency from the pick up. Or would need additional circuitry to convert the frequency into an analogue voltage?

The capture rate of the data needs to be high enough to properly plot the shape of the current drawn by a starter motor during initial start up (So I guess something like the default rate used in the Pico automotive battery test routine?) My guess is 20 S/s as a minimum probably more to be safe. (Actually I'm sure the automotive battery test rate is much higher in order to capture AC ripple etc...)

However the same current will still need to be measured after the engine has started as this will now represent the charge current going into the battery, but could easily be captured at a much lower rate 10 S/s during this period at it should be much less transient?

So the voltage measured by the current clamp (and hence data logged) will change sign between the battery starting the car and then being itself charged by the alternator.

Also battery voltage, battery temperature would need to be measured simultaneously

Current from the alternator output would need to be measured simultaneously

So in summary: (Ideally...)

Digital input for RPM (7000 RPM max)
Analogue input for 'Battery current' measurement - Needs to be able to deal with +/- 0.5V (o/p from current clamp) (20 S/s minimum)
Analogue input for 'Alernator current' measurement - 0 to 2.5v (10 S/s minimum)
Analogue input for battery temp measurement in the range -10 to 60 Deg C


Logging duration could be up to 1 hour and ideally the logging rate should be comfortably above 20 S/s (with all channels simultaneously logged) just so I can increase the logging rate if necessary.

I could possibly try and seperate the engine 'starting' event from the 'vehicle running' event - to try and overcome the requirement for the +/- 0.5 voltage analogue input (So it became just a 0 to 2.5V input), but could the TA 167 current clamp be used in 200A setting during start up (-250A to -280A) without any negative effect on the clamp or generating any measurement offsets as a result to try and get better resolution?

Even when I am just logging the battery charging current, the current clamp needs to be in position while the engine cranking takes place otherwise I will miss the maximum current peak charging the battery which occurs as soon as the starter motor stops.

The automotive 4 channel Picoscope option would I think be capable of measuring all the above inputs but could it log them to a PC for up to 1 hr for analysis after the data has been captured? I will post a similar question on my Automotive section thread.

Cheers
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Re: Suitable data logger - Cold cranking behaviour

Postby Karunen » Thu Feb 12, 2015 12:05 pm

Hi Spencer,

I believe Steve has answered your question on the other post.

For others looking for the other post is can be found herehttp://www.picoauto.com/support/topic10423.html.

Kind Regards,
Karunen

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