Controlling external light levels by monitoring temperature of a solar panel

[Neil Sampson]

Hi there,

I am carrying out a project where I have a solar panel with a light shining down on the panel to mimic sunlight. Further there is a temperature sensor on the surface of the panel to monitor the temperature. The output of the solar panel is connected to a LabJack U12 interface card, together with the temperature sensor.

Within LabVIEW 6.1 I am able to dim the external lights above the solar panel, via one of the analogue outputs on the interface card (with the aid of some external circuitry as well). I am also able to monitor the temperature of the external sensor within LabVIEW.

What I would like to achieve is the external lights being dimmed to some safe voltage
(such as 3 volts) if the temperature from the sensor exceeds 47C, until the solar panel cools down to a safe temperature. When this occurs the user should not be able to have control over the dimming of the lights via the control on the front panel. After the panel has cooled down to say 35C, the user should then be able to have full control over the dimming of the lights again. Please note that I have a fan cooling the solar panel surface at all times.

Any help on this matter would be greatly appreciated. Please find my vi so far.

Thanks in advance,

Neil.

[Dr._Imad]

You probably can do that
when the temperature exceeds 47C, set the knob setting programatically (local vraiable or property_node_Value) to the safe voltage and disable the knob (property_node_disabled : 0 enabled, 1 disabled, 2 disabled and greyed out). Then the operator cannot change the knob setting.

When the temperature drops to 35C, enable knob

[Neil Sampson]

Dr. Imad,

Thanks for the quick reply to my question. I have carried out the instructions that you advised. Basically I have the problem of keeping the knob disabled and greyed out until the temperature of 35C is reached from the maximum 47C. The knob is disabled and greyed out when the temperature reaches 47C, but as soon as the temperature falls below 47C, the knob becomes enabled, set at 3 volts. I am unsure how to program my application to keep the knob disabled until the temperature reaches 35C.

Another question I would like to ask is whether it is possible to store the last voltage at which the lights were set to, before the temperature reaches 47C, the knob disables, and goes to 3 volts? After the temperature reaches the 35C, I
would like the program to return to the value of the last voltage applied to the lights, say 4.5volts

Thanks again, and please find my modified vi attached.

Neil.

[Liz F]

Neil,

I think that a great solution to your problem would be the use of a state machine. I went ahead and created an example state machine that accomplishes what you want to do with the use of property nodes. You could use this structure to make changes to your program to implement your exact application.

Please take a look at the VI I created and let me know if you have any further questions. Have a great day!

Liz Fausak
Applications Engineer
National Instruments

[Neil Sampson]

Hi Liz,

Thanks for taking the time out to help me with the problem. The vi you gave me is perfect for the application. I never thought about using a state machine for this, but it seems to be the most methodical way for solving this type of problem!

Thanks again,

Neil.