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