Hello,
At our university lab we somebody needs to build a gas phase chemoreactor. for this purpose he bought a cFP-2120 with a Relay module, a thermocouple module and last but nog least a DO-403 sinking output module.
One of the most important things the cFP needs to do is control and the temperature of 5 separate saturation units; These are basically just 1 litre metal vessels filled with compounds such as ethanol, hexane and various other solvents. Temperature of these saturators needs to be fairly precise becaus this is what determines compound concentrations in the reactor feed.
Previously we used dedicated PID controllers like the ones from eurotherm or watlow for control of these saturators.
Now I am planning on using the labview PID addon for handling the temperature control and this is where my problem starts; The heating device is a standard resistor wire in a metal casing, connected to the 220V AC mains. This heater can be switched on or of using a solid state relay which takes 24V DC input. Because of this I wil need my PID output to control a pulse width modulation type process in order to achieve proper control of my system.
I noticed that many examples regarding PWM (like the one attached) seem to be based on built in counter support on various DAQ devices sold by NI. NI also sels dedicated PWM modules or counters for FieldPoint. However, we currently do not have any more funds left to actually buy one of these.
I am therefore looking for a way to achieve the same result using only our DO-403 module to drive the solid state relay. The only thing I cannot figure out is how I can reliably generate some sort of pulse train to achieve my PWM. Is this at all possible or does an application like this really need a dedicated hardware component to generate this sort of signal? (Is there a risk of the fieldpoint falling over itself if I use something like the signal generation VI's?)
Any help would be greatly appreciated!!