Temperature probe settings

[Brian71583]

I feel like I am either an idiot or using the wrong search terms because this has to have been asked before.

In setting the temp controller settings… Temp threshold is the temperature you want the tank set at correct, say 78.

What is hysteresis? I have an understanding of what the term is but am having trouble comprehending what kind of number I would apply to that understanding. I’m also further confused because the little search results I’ve found are for other controllers and apparently use a time for hysteresis rather than a temperature.

lastly what is the consensus on the reliability of using pi as a temp controller? I’ve read differing points of view. I have two sensors and two heaters. I planned on setting heater 1 slightly higher than planned. Say 81, and letting reef pi controller it. Then I was going to leave heater two set just below where I have reef pi set at as a low backup.

 

[Doctorgori]

hysteresis is the amount of variance before triggering either on or off, say 5 degrees up or down before shut on or off…for temps I use 1 degree plus or minus, within a degree is fine, I wouldn’t stress over keeping it dead on 78F or whatever….

 

[Brian71583]

Awesome, thanks. My confusion was I didn’t know it was a variance up OR down and thought it was just one but couldn’t figure out which it would be.

 

[flagg37]

hysteresis is the amount of variance before triggering either on or off, say 5 degrees up or down before shut on or off…for temps I use 1 degree plus or minus, within a degree is fine, I wouldn’t stress over keeping it dead on 78F or whatever….

My understanding is that hysteresis will control how much time between repeatedly turning on/off. Longer periods will help to keep components from wearing out from too many cycles.

 

[Brian71583]

That is my understanding with other controllers but the reef pi settings call for a temp not a time.

 

[Doctorgori]

My understanding is that hysteresis will control how much time between repeatedly turning on/off. Longer periods will help to keep components from wearing out from too many cycles.

couldn’t have said it better lol
…basically it’s so you don’t wear the equipment out trying to maintain a narrow parameter of whatever…

 

[Sean Clark]

lastly what is the consensus on the reliability of using pi as a temp controller? I’ve read differing points of view. I have two sensors and two heaters. I planned on setting heater 1 slightly higher than planned. Say 81, and letting reef pi controller it. Then I was going to leave heater two set just below where I have reef pi set at as a low backup.

From what I have seen, heaters fail on as much as they fail off. I would use the pi to control both heaters but with different settings. The higher back up heater can control itself but be shut off by the pi if it gets too warm. The lower set heater can be controlled by the pi to cycle and maintain temp. Set limits to shut either off incase of a fail on situation.

 

[wizzlebippi]

My understanding is that hysteresis will control how much time between repeatedly turning on/off. Longer periods will help to keep components from wearing out from too many cycles.

Hysteresis is the technical term for the slop inherent in mechanical or analog electrical systems. With respect to an analog heater, it's the temperature difference between when the bi-metallic strip completes the circuit and when it opens it. Digital control systems often need to have hysteresis built in to prevent constantly toggling on and off, which is what you're defining here.

Personally, I define the temperature range I'd like the tank to remain within and let the heater manage its self within that range. This alerts you to heater failure if it's constantly bouncing off the limits, and allows some level of temperature control after a heater failure.

 

[Ranjib]

Hysteresis is pretty clear technical definition, but various nuances in how its used in different control systems.

For reef-pi it was used to reduce flapping or repeated equipment on/off. When defined reef-pi will not change the equipment state till the hysteresis threshold is breached. This allows some swing (slop) in the target threshold, but significantly reduces the equipment state change frequency (hence higher life span). In reef-pi hysteresis is always represented in the sensor value, not time. For example a temperature controller with 78F target and 0.2 hysteresis will allow temperature swing 77.8 to 78.2, i.e reef-pi will not turn on the heater (when its off) even if the tank temperature falls below 78, it will wait till 77.8 and then switch on heater. Same way it will not turn off heater even if the temperature goes to 78.1 (above 78), reef-pi will wait till the temperature becomes 78.2, and then turn it off. While introducing this feature that goal was to improve equipment life span (by avoiding frequent equipment switching) and to bring parity with similar systems. It was just incidental that the community member who brought this up referred it as hysteresis, and i felt its ok.

let me know if you have any other questions.

 

[fulltang]

Hysteresis is pretty clear technical definition, but various nuances in how its used in different control systems.

For reef-pi it was used to reduce flapping or repeated equipment on/off. When defined reef-pi will not change the equipment state till the hysteresis threshold is breached. This allows some swing (slop) in the target threshold, but significantly reduces the equipment state change frequency (hence higher life span). In reef-pi hysteresis is always represented in the sensor value, not time. For example a temperature controller with 78F target and 0.2 hysteresis will allow temperature swing 77.8 to 78.2, i.e reef-pi will not turn on the heater (when its off) even if the tank temperature falls below 78, it will wait till 77.8 and then switch on heater. Same way it will not turn off heater even if the temperature goes to 78.1 (above 78), reef-pi will wait till the temperature becomes 78.2, and then turn it off. While introducing this feature that goal was to improve equipment life span (by avoiding frequent equipment switching) and to bring parity with similar systems. It was just incidental that the community member who brought this up referred it as hysteresis, and i felt its ok.

let me know if you have any other questions.

Curious what hysteresis you use personally?

 

[Ranjib]

Curious what hysteresis you use personally?

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