Temperature and humidity control with USB-6008 DAQ

[Fatsat]

Hello,

This is a project for school where I have to control the environment for a plant in a veranda.

I have to do the following:

- Control the temperature

I use a PT100 for the measuring. 

When the temperature gets too cold, I have to raise it by activating heat resistors (not sure if this is the correct translation). 

When it gets too hot, I have to open the roof of a little veranda using a little DC-motor (I can give specifications if needed)

- Control humidity

Using a HIH 4000 for measurement. 

Same thing as for the temperature, lower humidity by closing the roof, etc etc.

- Control irrigation

Using a DC30A-1230 pump for puming the water.

I have to control these by using a USB-6008 DAQ card. My knowledge of labVIEW is pretty low, that's why i'm asking it here.

I can provide you guys with pictures, more specific details, anything. Just ask.

Thank you!

[Aaron_W.]

The place I would start would be to break down each signal and determine whether the input and output signals are analog or digital. Then you should determine the following:

Acquisitions:

What amplitued of a signal will you need to sample?

What frequency do you need to sample?

What's the resolution you need to know? Do you need to know if temperature changes by 1 degree C? What's the change in your signal that you need to detect for your smallest temperature change. The 6008 is a lower cost DAQ module so it doesn't have the greatest accuracy.

Generation:

What type of signal are you trying to generate?

What amplitudes?

What current is required to drive the motors? Where do you plan on supplying the current from?

I would break up the project into these areas and then work on getting each to work separately. We can suggest some example programs within LabVIEW to get you started. The Example Finder (Help >> Find Examples) works wonders. There are also some good help guides for LabVIEW such as the Learn LabVIEW in 3 Hours tutorial.

[Fatsat]

The precision of the temperature and humidity readings do not have to be specific at all. It's just a simulation, nothing for industrial purposes (the veranda is very small, easy to hold and replace).

So this basicly means that for example below 20°C is referred as cold, and above that is referred as hot. So nothing specific there. This is probably also the reason why my school has given me the cheap DAQ module, as you stated.

As for the other two areas you asked me about for the acquisition part, could you be a little more specific? By amplitude, do you mean the maximum voltage these components can handle? As mentioned, i'm not familiar with projects like these.

Now for the generation part I have the same question about the amplitudes as stated above. The current required is about 75 mA. This will be supplied from an external power source. All the sensors and components are actually all in place and just need to be connected to the right circuit and later configured correctly using labVIEW (but don't worry about the circuits though, I've got most of them covered already).

As for example programs or guides, i've read alot of tutorials and guides for projects like mine, but most of them use some formula they've prepared thremselfs and which I don't really understand.

This is one of the tutorials I'm talking about:

https://forums.ni.com/t5/Example-Code/Measure-Temperature-using-a-RTD-myDAQ-and-LabVIEW/ta-p/3996486

Thank you for already responding so quickly, I hope we can make something out of this!

[Aaron_W.]

Let's start with the RTD, this is not going to be as easy with a 6008 as what it would with other modules. To start you will need a current source to excite the circuit. Look at the white paper called Understanding and Choosing RTDs here on the NI Website. You will take a differential measurement across the sensor to determine the voltage drop across the sensor. Since you will be applying a known current, you should be able to calculate the resistance. There should be a datasheet with the sensor that will give temperature readings for different resistances.

Next, there was a good discussion on some issues when using the 6008 to take a temperature measurement with a RTD. Understand that the 6008 is not overly accurate, so maybe that's not a problem, just giving you all of the details I have found.

For the generation side of things, you will not be able to drive the motor with the 6008 by itself. It can only drive 5mA. You will need an external source and then you will need to use the 6008 as the control signal. This could be Analog or Digital, it just depends on the circuit that controls the motor and what you have setup.