Is this a heat detector?

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steve66

steve66

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Illinois
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Engineer
I've seen quite a few of these. IMO they look like a bell.

But from the locations I've seen them in, I assume they are older style heat detectors.

Just to confirm my hunch is right, is this what older heat detectors looked like?

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Hold a heat gun to it and see what happens. If it is a heat detector then it will sound.
 
A closer match is the Simplex 4255-1. I think they are all derivatives of the Chemtronics 500 series detectors, the 501 being the most popular.
 
construct said:
I think it's an old Edward's fire alarm. Edwards Signaling has been around since 1872. Here's a link on their company history:

https://edwards-signals.com/index.cfm?pg=21&level=50&sid=0
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GrayHair said:
That's an old Rate-of-Rise detector, probably a combination Fixed Temperature/Rate-of-Rise. Saw them a lot in warehouses.
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Could be either one really, they can look similar. The simple tell would be that if it's an older Edwards Adapt-A-Bell unit, that dome is the bell and will ring if you tap it. If it's a spot heat detector, that's the chamber cover and it will not ring like a bell.
 
jumper said:
A quick image google search seems to support that. Good job.
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I agree, and more proof that great minds think alike:

Prior to this post, I did a couple of image searches, but didn't find anything to match. But adding "old edwards heat detector" did the trick.

:D
 
I believe the ones I'm running across are still active and operational.

I doubt any of the modern electronic heat detectors will last as long.
 
steve66 said:
I believe the ones I'm running across are still active and operational.

I doubt any of the modern electronic heat detectors will last as long.
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Many modern addressable heat detectors use RTD's, sometimes in pairs. That's a pretty bullet-proof technology.
 
gadfly56 said:
Many modern addressable heat detectors use RTD's, sometimes in pairs. That's a pretty bullet-proof technology.
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Maybe, but as soon as you say "addressable", I think electronics, semiconductors, and microprocessors, and such. Eventually, that will probably die from heat or surges.

I think these heat detectors have probably been in use for 70 years, and they probably have an another easy 70 left. I'm guessing they are nothing more than a fusible chunk of metal that melts at a specific temperature - probably a lot like a motor overload.

I don't think anything addressable will last that long.
 
steve66 said:
... electronics, semiconductors, microprocessors, and such. Eventually, that will probably die from heat or surges.
...in use for 70 years, ... I'm guessing they are nothing more than a fusible chunk of metal that melts at a specific temperature - probably a lot like a motor overload.
I don't think anything addressable will last that long.
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Everything we build has a failure mode. Semiconductor systems are as reliable as they're designed to be, which can be highly reliable. (or not; history provides many examples)
(for example, FADEC aircraft engines and ETOPS airliners, which would have been unthinkable in the era of carburettors and magnetos.)

For example: Using a fusible link as a heat detector can provide a false indication if there's a short in the cable anywhere between the detector and the alarm panel, but whatever goes wrong with an addressable detector or its cable, it will always not reply to an inquiry and the alarm panel will always be aware of the failure. And I'd rather have an alarm panel that continuously diagnoses the sensors than one that lasts for 140 years.

Full-Authority Digital Engine Control
Extended Two-engine OperationS (aka. Engines Turn Or Passengers Swim)
 
gadfly56 said:
Many modern addressable heat detectors use RTD's, sometimes in pairs. That's a pretty bullet-proof technology.
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steve66 said:
Maybe, but as soon as you say "addressable", I think electronics, semiconductors, and microprocessors, and such. Eventually, that will probably die from heat or surges.

I think these heat detectors have probably been in use for 70 years, and they probably have an another easy 70 left. I'm guessing they are nothing more than a fusible chunk of metal that melts at a specific temperature - probably a lot like a motor overload.

I don't think anything addressable will last that long.
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I kind of agree with steve66. What is bullet proof about the addressable unit is if you lose communication you get a trouble signal and something will likely fail before it is 50-70 years old. I still see those old units like OP is asking about in schools sometimes. Especially in storage areas or attics that need heat but not smoke detection.
 
kwired said:
I kind of agree with steve66. What is bullet proof about the addressable unit is if you lose communication you get a trouble signal and something will likely fail before it is 50-70 years old. I still see those old units like OP is asking about in schools sometimes. Especially in storage areas or attics that need heat but not smoke detection.
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The rate of rise units are easily tested if they are accessible by step ladder. Rub your hands together to warm them up and put your palm on the dome. The delta T is sufficient to set them off.
 
GrayHair said:
That's an old Rate-of-Rise detector, probably a combination Fixed Temperature/Rate-of-Rise. Saw them a lot in warehouses.
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That's exactly correct. The fixed temp only ones have the little dimple in the center painted white if it's a 136 degree unit and white w/ black dot if it's a 190 degree unit. The fixed temp ones are a one shot deal if you trip them but the rate of rise units are resetable if you use the hand friction method as previously described. You can also look at the label on the side of the unit.
 
kwired said:
I kind of agree with steve66. What is bullet proof about the addressable unit is if you lose communication you get a trouble signal and something will likely fail before it is 50-70 years old. I still see those old units like OP is asking about in schools sometimes. Especially in storage areas or attics that need heat but not smoke detection.
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Yes, these are in several schools.


gadfly56 said:
The rate of rise units are easily tested if they are accessible by step ladder. Rub your hands together to warm them up and put your palm on the dome. The delta T is sufficient to set them off.
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Don't tell the kids that!!:D
 
steve66 said:
Yes, these are in several schools.




Don't tell the kids that!!:D
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Hah! That didn't even cross my mind until you said that.:D It would be pretty fool proof too; there's nothing to indicate which of the dozens/scores/hundreds of detectors went off. Makes it hard to try and backtrack to find the culprit.
 
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