Hi there!
I'm doing an energy harvester using a buck and battery management IC, Output current is 50uA/ 100mA (min/max), how can i make an logger using T7 pro ?? is any code available for this?. i thinks that using an shunt resistor and programming T7 to save datalog on SDcard is the best option.
Thanks in advance
BR
Julian
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Hardware:
Since your max current is only 100 mA, I would agree that a shunt resistor is the likely option. Presumably you don't want to drop too much voltage across the shunt, so will use a small value such as 1.0 ohms. That will give you a 50 uV to 100 mV signal which the T7 can resolve quite well, but if you want to improve on that, or use a smaller shunt, you should add an op-amp to give you a little gain after the shunt. You could even consider using the LJTCS, but you would short out the thermal fuses and use a smaller shunt than the normal 5.9 ohm.
The other thing you need to consider is common-mode voltage. If you put the shunt on the low side of your load, such that one end is connected to ground, you will just do a single-ended measurement and common-mode is not an issue. If, however, you put the shunt on the high side and do a differential measurement you need to consider if you have too much common-mode voltage:
https://labjack.com/support/datasheets/t7/appendix-a-3-2
Software:
The T7-Pro is capable of standalone datalogging, but first I would consider logging with some sort of host computer, which could be a Windows laptop or something as small as a Raspberry Pi. For more info on standalone logging see here:
https://labjack.com/support/datasheets/t7/sd-card
Hardware:
Vout of instrumentation amplifier in the T7 with differencial voltage of shunt resistor should be referenced to ground of T7, doesnt it ?
Software:
i've read about Sd-card on T7, i agreed with use host, so, there is any script available to log data using an raspberry pi like host? i have to make field test and pc is not a choice.
thanks in advance
br
Julian
Hardware:
Yes, Vout of the internal in-amp is single-ended. The problem I was talking about with a high-side current shunt affects Vin to the in-amp. Example #1 from Appendix A-3-2 would be what happens if you use a shunt on the high-side of a load in a 10V system.
Software:
Using a Raspberry Pi as the host, you can communicate with the T7 over USB/Ethernet. A suggested logging solution would be to performs T7 readings using the Raspberry Pi and logging data to a file on the Raspberry Pi. The T7 uses the LJM programming library. You can find a Raspberry Pi Linux build of it here (Linux arm):
https://labjack.com/support/software/installers/ljm
Code examples for multiple languages can be found here:
https://labjack.com/support/software/examples/ljm
For logging to the T7's SD card instead, you will need to use T7 onboard LUA scripting. Writing/logging to the SD card over USB/Ethernet (Modbus in general) is not supported. For details and an example Lua script (bottom of page), look here:
https://labjack.com/support/datasheets/t7/sd-card