Redundant Temp Controls?

I'm wondering. I was researching into the Johnson Controls unit, and in the PDF document from the Johnson Controls site, there is this warning:

Quote:

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Originally Posted by http://cgproducts.johnsoncontrols.com/MET_PDF/125188.PDF

IMPORTANT: The A419 Series Temperature
Controls are intended to control equipment under
normal operating conditions. Where failure or
malfunction of an A419 Series Control could lead to
an abnormal operating condition that could cause
personal injury or damage to the equipment or other
property, other devices (limit or safety controls) or
systems (alarm or supervisory) intended to warn of
or protect against failure or malfunction of the A419
Series Control must be incorporated into and
maintained as part of the control system.

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The document does state that the unit will shut off in the case of a sensor failure, and will also shut off in case of a program failure.

However, this unit is relay controlled, and relays can stick in the closed position.

So with the Johnson Controls unit, at least, the only way to ensure safety is to use two units - one as the main unit, and a second one set a couple degrees higher so that it will shut down the primary unit if it fails.

I couldn't figure out what the Ranco and HerpStat units use for voltage control. Do either of those use solid state switching as opposed to a mechanical relay switch?

Here's what I found for Ranco:
http://www.icca.invensys.com/uniline/d/d71.pdf

And for HerpStat:
http://www.spyderrobotics.com/produc...ual_online.pdf

Interestingly, HerpStat makes no claim that the unit will shut off in the event of a program failure.


So, any thoughts on redundancy of temperature controls? Considering a BP can live over 20 years, I think one could assume that the risk of a temperature controller failing in that time frame is fairly high. So does anybody think the cost of an extra unit to maintain redundancy is justified, or is it okay if a snake is exposed to a 125 degree strip of flexwat for several hours (the time it may take for you to get home from work and notice the temperatures are way high)

Absolutely. Whenever possible you should use a backup thermostat for redundancy and fault tolerance. I've been advised to use an on/off (like a ranco or johnson's or any cheaper brand) as a backup for a proportional. In fact, I am setting mine up this weekend (now that I got a new probe for my second herpstat).

I like the proportional output of the HerpStat controller, but the fact they make no claims as to program error detection bothers me a little. But then again, in my experience program fault detection rarely detects program faults.


Right now I'm leaning towrds a HerpStat with a Johnson Controls backup.

I use Herpstats and love them. I know there have been debates in the past so I will say it works for me. Others might like other brands better :)

Quote:

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Originally Posted by jglass38

I use Herpstats and love them. I know there have been debates in the past so I will say it works for me. Others might like other brands better :)

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Nothing wrong with being an advocate for a product that works well for you!

ROCK ON! :D

-adam

Quote:

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Originally Posted by Adam_Wysocki

Nothing wrong with being an advocate for a product that works well for you!

ROCK ON! :D

-adam

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Oh no doubt there. More and more I see different things that work for different people. This holds true with thermostats, feeding, enclosures, etc. Like you say, if your BP eats, craps, sheds and breeds (or something like that :) ) then all is good in the world. There is no one right way.

for the johnsons and rancos, that statement is geared for for hvac equipment. they are basically saying to use limits and sensors to cut off equipment and don't rely soley on the thermostats. example if one was used for a drink cooler/walkin fridge type you would use a limit set or made to the lowest temp acceptable and that would be a safety or backup circuit to turn off compressors/fans if the thermostat should fail. same could be said for high temp applications. some fan motors and compressors cost on the thousands and you want additional safety/limit devices to protect them.

vaughn

Quote:

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Originally Posted by kavmon

for the johnsons and rancos, that statement is geared for for hvac equipment. they are basically saying to use limits and sensors to cut off equipment and don't rely soley on the thermostats.

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True, but would not one of these controls being stuck on be harmful to a snake? Whether you're frying a $1000 motor or slow-roasting a $30 ball python, either one would be bad.

Quote:

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Originally Posted by TraconSnake

True, but would not one of these controls being stuck on be harmful to a snake? Whether you're frying a $1000 motor or slow-roasting a $30 ball python, either one would be bad.

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Without a doubt. Even though that wasn't what they were referring to (Johnsons and Rancos were not created for reptiles), it makes sense to heed the advice and backup your tstat. Flexwatt can hit 130 degrees no problem. More than enough to seriously burn a snake.

i agree, a stuck control would be bad. some people use 2 thermostats. one set a little higher as a backup to run power to the main stat. any control can fail or break, if it is man made it can happen!



vaughn

maybe i should look into temp limits and make a limit relay combo that would cut power to the stat or heat tape! i could be rich! lol one dime at a time lol all kidding aside i'll check out some limits and see what i can come up with, off the top of my head about 20 bucks in parts and some wire should do it. maybe less...



vaughn

Quote:

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Originally Posted by kavmon

maybe i should look into temp limits and make a limit relay combo that would cut power to the stat or heat tape! i could be rich! lol one dime at a time lol all kidding aside i'll check out some limits and see what i can come up with, off the top of my head about 20 bucks in parts and some wire should do it. maybe less...



vaughn

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How would that work? I know NOTHING about electric except not to stick paper clips in the electrical outlets (learned that the hard way). :rolleye2:

basically you find a temp limit that opens on rise. most limits have fixed temp settings like designed to open at 110f for example. some have adjustable settings. you would wire this either on the power to the stat or on the power wires to the flexwatt. basically the limit will open on high temp and stop flow of current to stat or flex. next time i'm at the parts store i'll poke around. a limit similiar to this one would work

http://americanhvacparts.com/Merchan...ry_Code=fl-tdf this one closes on temp rise, one that opens the circuit on temp rise would be easier to install and wire in. i can get those for around 10 bucks.


vaughn

Interesting stuff. I think anything that will work is worth the effort and money.

The way you can self build a circuit is fairly simple. What you do is you take a temperature probe which is basically a thyristor in a protective housing. Youl could actually probably just get a bare thyristor and enclose it in some heat shrink. This would work since we won't be exposing it to extreme temperatures.

The thyristor is basically a resistor which varies resistance based on temperature. What you do is put a voltage on this and feed it into an Operational Amplifier (Op-Amp) circuit hooked up as a comparator. On the other input of the op-amp would be a trimpot wich you would set as a trip point. The output of the op-amp would go to a power transistor wich would activate/deactivate a relay with sufficient current capacity to handle up to 5A. (I think the flexwatt uses 1.5A if I recall correctly)

Once it's hooked up, you would adjust the variable resistor to "set" the trip point where the relay would be de-activated.

Dang, now you got me thinking. Perhaps I can build this and just buy one temperature controller! A better alternative would be to use a high power transistor as an on/off switch so that a mechanical relay would be un-necessary.

Really, when I think about it, what you're paying for in these temperature controllers is a digital display and easy adjustment of it's trip point. But for this application, all we have to do is set it once, and just use our cheap Acu-Rite thermometers to gague temperature.

I'll look into this...

i will still use my helixs' on all my racks! i was mainly just thinking of a high limit for safety. using a line voltage limit which is basically a thermal safety as a backup. i'm going to sell these to jamie and cash in big time!!! lol



vaughn

Quote:

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Originally Posted by kavmon

i will still use my helixs' on all my racks! i was mainly just thinking of a high limit for safety. using a line voltage limit which is basically a thermal safety as a backup. i'm going to sell these to jamie and cash in big time!!! lol



vaughn

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Hahah..Sign me up for 12 of them!!