Rif.: Resisive circuit

[EnEng]

Hi everyone,

I have recently been introduced to labview and its capabilies, which seem pretty amazing... i was looking around the we for sample projects to get some experience with data aquisition and was looking for something where i could extract data at specific points with a voltage output reading. I found this example and was looking for some help on how to get started.

My objectives are to build a circuit with ac signal input and measure the ac signal output (V) and compare the change in output voltage to the level of water

-setup arrays? to capture data at a set time interval

(or capture data another way - just know it can be done with arrays)

-produce a graphto show the relationship(Vout vs. Water level)

-indicator indicating the Vout (either continuous or previous measurment output)

Any help would be great, all advice welcome, look forward to learning about this software!

thanks

[Ironman99]

Welcome to the LV world and community, EnEng...

Good starting point!

Just for a better understanding of your needs...

You need help for programming in LV, or for measuring the ac output?

Do you already have some sort of instrument for capturing the ouput voltage?

You need a driver for that instrument. May be you can use a multimeter like 34401

(You can find a driver for it included in almost every version of LV)

From the point of view of programming I would suggest to use a timed loop,

containing the code for reading the measured voltage. You can put the obtained values

into an array, then pass it to a graph chart.

Something like the VI I have write and included in thi s post.

Hope this can help you.

Regards....

[EnEng]

i would appreciate help with the programming too, :S very new to this program, did a basic tutorial but not sure as to how to incorperate a system

how do you simulate a signal, how do i simulate the circuit, how do i capture the signal (out) and display it?

[Pete.Dunc]

Hi EnEng,

There are lots of resources online at NI Support and the Developer's Zone to help you get started.  If you would like some formal training which is much more structured there are several training options.  The help files are usually pretty great too 

Of course you can always post any questions on the discussion forums and we'll do our best to help!

In terms of simulating your application - it looks to me to be a voltage divider (I could be wrong though!) with one fixed resistance and another which varies due to the amount of water, as the conductivity will change.

Check out the following code snippet:

You can copy this into LabVIEW - if you are using the latest version - otherwise I have attached it for an earlier version.  The code is simplified and uses the difference in amplitude to calculate the unknown resistance, you could expand this to include phase if need be.  Come to think of it; if you didn't need phase, then why would we use an AC source?   Additionally there will be an equation which relates the resistance to the actual water level, you will probably find that with the example.

In your final application you will be reading the input and output as voltages, as opposed to simulating - do you have any hardware available to do this?

[EnEng]

Thanks alot peter, I have the  NI mydaq hardware, and will be constructing the circuit in the near future. And yes considering phase is not important i guess it would be wise to use a DC power source.

That answers alot of my questions as to where to start! I will try this out, and expand on it!. My goal with the final user interface is to have a graph of water level vs. voltage out and also incorperate the tank indicator (to show actual representation of what is happening. As well ass numerical values for Voltage in,out, and variable resistance. Also will need to collect the data in some way so ill work on that,

thanks for the advice! If anyone else has anything to add please feel free, much appreciated