using 6052E card to measure current

[krispiekream]

Hi,

I am very new to implementing hardware with basic measurement in labview.

I have a PXI6052E card.

I believe it has AO of -+10 V.

Does anyone know where or how I can find examples of how to make a basic multimeter with the card?

I want to provide -10V and +10V with 0.04A to a circuit and the read the current for that circuit.

Is it possible?

Thanks

[crossrulz]

You can set the voltage of the AO, but I don't think you can tell the DAQ what the current limit is.  As far as reading current, you are going to need a small current sense resistor on the return of the circuit and measure the voltage across it with an AI.

[krispiekream]

the circuit already has a 500K resistor on it.

V=IR

Assuming it generate 10V and I know the R=500K, I can find out the current.

[krispiekream]

the circuit already has a 500K resistor on it.

V=IR

Assuming it generate 10V and I know the R=500K, I can find out the current.

The reason for the test because if R < 500K then we have a short.

So I want to find out what the current is so I can calculate for R.

[johnsold]

Krispiekream,

Do you understand basic circuit theory?

The AO is a (weak) approximation to a voltage source.  That means that it tries to produce the specified output voltage, regardless of the current bing drawn by the external circuit. The actual circuit cannot produce more than 5 mA without either deviating from the specified output voltage or possibly being damaged.  The actual amount of current drawn is determined by Ohm's law and the external resistance. If the output is 10 V and the external resistance is 500000 ohms, then the current will be 10 uA.

However, as has been pointed out, the device has no method to measure its output current.  One way you could measure the current through the external device would be to connect a resistor in series between the AO pin and the external device.  Using an input of the AI part of the device, measure the voltage at the junction of the series resistor and the external device.  The difference between the voltage programmed at the AO and the voltage measured divided by the resistance of the series resistor is the current flowing.  From Ohm's law you can then determine the resistance of your external device. Make the series resistor larger than 2000 ohms and you cna be sure that a short circuit in the external device will not draw more than the speicified 5 mA from the AO.

Lynn

[krispiekream]

hmmm, in external device, you mean a multimeter?

how would i make this automated?

So using an external device to measure the current, then  to automate this, my external device would need to output the data into the AI of 6052E card?

[johnsold]

Krispiekream,

No.  By external device I am referring to the circuit with the 500000 ohm resistor in it that you mentioned in messages 3 and 4.  The thing you are trying to measure.

You would use the AO to provide excitation to that circuit along with the 2000 ohm resistor I suggested.  Then use an AI channel to measure the voltage at the junction of the 2000 ohm resistor and your circuit.  With some calculations you can determine the resistance of your circuit to approximately the accuracy of the 2000 ohm resistor.

Lynn

[crossrulz]

Here's a KB by NI about using shunt resistors.  It's short, but the information is good.  I haven't explored the other links yet.

[krispiekream]

Great! thanks for the link.

i think its very useful. 

I will look into applying this data.

I'll keep you guys updated on my progress.

thanks!

[krispiekream]

oh, an extra information i have is that i also have a pxi4060

Its a digital multimeter card?

sorry, i am very new in using these cards so i don't know how to use them.