Heater Control

[hookes2]

Hello Everyone,

Please I have a furnace which I want to control the rate of heating of the heater. I have the following hardware: cDAQ 9172, NI 9211, NI 9474 and a K-type thermocouple. The specificatio of the heater is as follow:

Maximum Temp: 1600

Voltage: 240 Volts

Watts: 4500

Amps Max: 43.6

Thanks!

[Brandyn]

What specifically are you asking for? You need help creating the application? Help interfacing with hardware? 

[apok]

you want us to write the code for you? what have you done so far? have you check the shipped vi examples? it seems you want to daqmx acquire (AI) temp, software controlled PID and control (DO) the heater's fan,cooling and heat...post your vi and what problems you see with it

[Brandyn]

In the future if you can give more description on what exactly you are looking for, then people can give better help.  If you are looking for someone to write the application then that's a different conversation. I'll be more than happy to write it for a fee off course :). 

[hookes2]

Thanks you all,
I have written a code to acquire temperature from the thermocouple using the NI 9211. I have also been able to log this into a file and also control the rate of logging. The code for that is working fine. My challenge is controlling the heater. I am aware the NI 9474 being a DO output would be useful for doing that. I need some assistance on how to write the code and also integrate it with the hardware.

[Brandyn]

What voltage does the heater control need? For example your DO card will put out 5V but the heater inputs may need 24V. 

[hookes2]

Thank you Brandyn,
The heater requires 240V, 43.6A and the power is 1600W. The NI 9474 gives a output of 24V.

[RavensFan]

Obviously your DAQ card isn't going to put out the voltage or current you need to drive a heater.

So what piece of hardware do you have that can control the voltage and/or current going to the heater?

[hookes2]

Thank you RavensFan (Knight of NI),
Apart from the cDAQ and the modules, I do not possess any other hardware. I was hoping all these would be sufficient for me to work on the furnace. This is just the prototype I am building and I thought what I have together with some few external circuits will suffice. If there is need for some special hardware, I might just purchase them when I want to design the real system.

[RavensFan · Accepted solution]

The simplest form of control in terms of hardware would be a relay that can handle the voltage and current to turn on and turn off the high voltage/current going to the heater.  Then your LabVIEW code would drive a digital output on the DAQ card that could turn on/off that bigger relay.  Simplest control would be strictly on/off.  You could also use a pulse width modulation scheme that will cycle the relay on and off at a rate.  So theoretically 50% on time and 50% off time would be approximately 50% of the heating power.  You could use a PID control setup to determine what the duty cycle of your waveform should be an any given point in time.