7 replies to this topic

[Heckler511]

So I just got my Labjack today, and I've just finished readin through the entire user's guide.  Well, I still don't think I know how to do a very simple task, like read a voltage in off a battery.

 

From my reading, here's what I would try.  I would wire one side of the battery to AIN0 and one side to GND?

 

Please advise.

 

Thanks!

[LabJack Support]

Yes, just connect the +battery to AIN0 and -battery to GND.  Assuming the voltage will be less than 10 volts.

 

The only complication for something like this would arrise if -battery was already referred to the U6.  For example, if -battery was connected to some chassis ground, which was connected to earth ground, which was connected to computer ground, which was connected to USB ground, which was connected to U6 GND.  Even that would likely not be a problem, but would warrant some more thought.

 

http://labjack.com/s...s-guide/2.6.3.4

[Heckler511]

I'm just going to keep asking stupid questions as I re-read the user guide. 

 

It says the VSs are outputs for the usb power (5 volts).  How can I use a DMM volt meter to read the output voltage on the VS?

 

Thanks!

[Heckler511]

Thanks!  And then if I wanted to read the voltage in off of another battery (two batteries at the same time), could I hook the +battery up to AIN1 and the -battery up to the same GND as before?

[LabJack Support]

 

 

It says the VSs are outputs for the usb power (5 volts).  How can I use a DMM volt meter to read the output voltage on the VS?

 

Connect the +DMM to VS and the -DMM GND.  To guarantee a good reading, you need to make a secure connection with the screw-terminals clamped down.  Just touching the screw heads usually does not work, especially if the screws are loose.

 

 

 

 

And then if I wanted to read the voltage in off of another battery (two batteries at the same time), could I hook the +battery up to AIN1 and the -battery up to the same GND as before?

 

It depends whether the batteries are referred to each other.

 

Example:  If you just have 2 batteries sitting on your desk not connecting to anything or each other, they are floating.  Since they are floating, you can connect both -battery signals to U6 GND, and thus you are defining both -battery terminals to be at the same potential.

 

Example:  If the batteries are connected in parallel, then both -battery terminals are already connected together, and you just need one connection from either to U6 GND.

 

Example:  If the batteries are connected in series, then the -battery terminals are referred to each other but are not the same.  Say you have 2x 9V batteries connected in series ... that means one of the -battery terminals is at a potential 9 volts higher than the other.  A way to handle this would be to make a connection from between the 2 batteries to U6 GND.  Then connect the lower -battery terminal to AIN0 and measure about -9 volts, and connect the upper +battery terminal to AIN1 and measure about +9 volts.  With more batteries you might get into using differential inputs to measure the voltage across each cell, but still need to consider the voltage on each AINx terminal compared to GND.

[Heckler511]

Thanks for all the help!  So far you've been extremely helpful in getting me started using this new Labjack.

 

I have a few more questions:

 

I am confused by the term "differential inputs," and the positive and negative talk... To me this sounds like it means I should be able to hook up a 1.5v battery to two AIN channels.  And maybe see +1.5v on AIN2 and -1.5v on AIN1, for example?  I see this idea referenced a little further in the talk of 4-wire sensor with 2 signal wires (positive and negative). 

 

I've got a LJTick-CurrentShunt, and look forward to measuring a device which outputs a 4-20mA current loop!

 

I have a sensor that requires 8.5-40 VDC for power.  Do you think I could power the device with Labjack if I use the LJTick-DAC, and does the LJTick-DAC plug into the FIO terminal blocks?

 

Do people use the digital I/O as inputs to read voltages or outputs to power devices?  It says they are factory set as inputs, but where in the software can I make them inputs and read those values?  Perhaps I'm a little confused as to what the digital I/Os actually do.

 

Thanks again!

[LabJack Support]

See if the following helps to clarify Different versus Single-Ended (which is not really related to unipolar/bipolar):

 

http://labjack.com/s...l-analog-inputs

 

The LJTick-DAC can provide up to 10V, but only a few milliamps.  If you need to provide a power supply in the 8.5-40V range, and don't want to add an external supply, you can use some sort of little switcher that boosts 5V to 12V.  We have used the CC1R5-0512SF-E from TDK (Digikey 445-2448).

[Heckler511]

Thanks again for the help!