Thermostat Lab

[Kevinand]

Hi guys,

im relatively new here, and a little new to labview.

Ive done a few small things in it but now i would like to do something a little more complex.

Here is a link to a lab i found at some university and i would like to try to do this as i have most of the components, its relativly cheap and its seems like a practical project.

http://www.ece.mtu.edu/faculty/btdavis/courses/mtu_eet3131_s08/labs/Lab_8.Closed_Loop_Development_wi...

I dont have that exact thermistor, but have one relativly close, so ill just make the necessary adjustments to the labview....

The main question I have is how can I alter the control loop of this application in order to have two set temperatures(control limits)... instead of a set temperature and a hystoresis value.

(eg set temp limits to 19 and 22 deg Celcius) so that the furnace would kick on at 19 until it reached 22 andthen shut off)

Another question is dont understand the what they mean by thermistor power resistor couple? can someone explain

here is the labview schematic

can you explain the logic of what is circled in green?

Thank you... much apprciated as i am kinda new!

Kevin

[RavensFan]

Just change the hysteresis control to your upper limit and eliminate the addition.

1.  Logical OR.  You want the furnace to be on if the control scheme says turn it on OR you want to manually force it on with the override.

2.  Logical AND,  You only want the furnace to be on if #1 is true AND you have enabled the furnace.

"Celsius" is the correct spelling

[Kevinand]

much thanks... that answers all my labview questions.

But what about the thermistor power resistor couple... ive been trying to look up what its purpose is in tis circuit.

obviously the thermistor is to measure the temp change and control the system but what about the power resistor, or is this part of the same thing, i am confused

[RavensFan]

I didn't look at the circuit, only the LabVIEW code.

I don't know what exactly a thermistor power resistor couple is.

Is the power resistor actually the heating element of the furnace?  The thermistor is coupled to that in order to read the temperature of the heating element?

[Kevinand]

I am not sure. I wasnt under that impression, but this is all the lab says about the Relay and power resistor.

"The role of the LU5 relay and the transistor is to allow the digital I/O of the NI_DAQ to
turn on and off a high-current power resistor. The NI_DAQ digital I/O is not able to
supply enough current to warm the power resistor, but using the transistor and the relay,
the digital I/O is capable of switching significant current."

and where do i find the daq assistant block in labview?

[RavensFan]

But that paragraph doesn't even mention the thermistor or why it is coupled to the power resistor.

DAQ assistant is under Measurment I/O >> DAQmx palette.  Also Express >> Input palette.  But you need to have the DAQmx drivers installed.

[Kevinand]

yes, realized i dont have the drivers, will ass when i am on labview station at school.

thanks alot, i will consult with my prof on this and see if we can get it working after i build the circuit

Is there a way i could collect data regarding the usage tme of the furnace for system monitoring... ex. capture the furncae run start times and run stop time to determine the length of usage?

that would be a good addition to this project

[RavensFan]

Sure.  You can use boolean logic to detect the change from on to off on the furnace and write a stop time to a text file, and detect the change from off to on and write a start time to a file.

[Kevinand]

last question, where do i find that green arrow, in the final part of the schematic, whats it called.... it looks like some sort of feedback node..cant seem to find it

[RavensFan]

Yes.  It is a feedback node.  It is under the structures palette.