Hello! I'm currently hard at work on a PID fermentation temperature control program. I am coding the algorithm that translates a PID output into a time proportioned window for full on/full off control of my heating element. If you are unfamiliar, time proportioning is essentially a very slow PWM over 'macro' timescales (in my case currently a 10s window). I plan on using a 4 channel solenoid relay board but I have a question about switch speed with the physical relays. I know that for very fast switching applications SSDs are preferable but I need clarification on exactly how fast 'very fast' is.
I am not interested in the theoretical limits but rather what the maximum safe switching rate would be for the physical ones. Currently, the way I have it coded (without a minimum), the shortest possible runtime for the heating element would be 1 ms. In reality, it will probably be ~100ms or more depending on how long it takes for my code to loop once. I also will need to control the fridge compressor (restraints on compressor on/off times will mean very slow switching either way). Should i go SSD instead? Thanks in advance, cheers!
The answers to the questions you are asking are what datasheets were made for. We can't answer your questiions without knowing WHICH relay you are asking about. If you know that , you can look up the information yourself in the datasheet. http://jumperone.com/2011/10/using-relays/
Most relays have switching times around 10 to 20ms. Switch off can be longer
with a free-wheel diode.
Heating water is a very slow process, you can probably stretch that 10s period to
a minute even (unless your heater is over powered for the application and causes
surface boiling!).
Well here is the datasheet for the relays on my board:
operation time is 10ms max
release time is 5ms max
what I am confused about is that there are two maximum switching rates:
mechanical - 300operations/min
electrical - 30operations/min
is this implying that the mechanics of the relay would allow faster switching but I will be limited by how fast the electronics act?
i realize the response time of my system is likely much larger. the reason for my short 10s window currently is because I am using Brett's PID library and the newSampletime variable type is an int. because the units are ms, a max int of 32767 is only ~33 seconds! It is not a complicated library, so i will probably just modify it but for now I am still working on my program as a whole. until i get around to it, i just upped the window size to 30s.