How EXACTLY do immesion heater tank thermostats work ?

[PEG]

I trust all of you are in good shape,after celebrating the new year

I include the OP.....who raised a glass,4 seconds after the rest of us

 

[RogerJ]

LOL...Thank you PEG and Happy New Year to all on the forum.. In the event last night the clock ws only about 0.1 seconds slow last eve (was reset last Thursday) and I got the the time from Jools Holland anyway..

 

[brianmoooore]

I got the the time from Jools Holland anyway..

Can you anymore, in these days of digital everything?
Back when TV and radio were all analogue, if you listened to Big Ben on any device, the chimes were in perfect sync, and, I assume, accurate.
Nowadays, there's a noticeable difference between devices of the same type, such as TVs in adjoining rooms, radio different again, and if you start adding streamed sources, can be a minute or so behind the others.

 

[RogerJ]

Good point..In the good old analogue days transmission route delay was neglible. Big Ben is maintained by its keepers and no doubt on new years eve is tweaked to be as close as possible to GMT at midnight.. The pips are of course electronically generated by a source fed from a Caesium atomic clock..
I believe the delay via freeview is about 2 seconds.. Cable, Satellite and internet delivery may be a bit longer (and all different) Delay on DAB radio is significant and depends a lot on each radio's decoder (speed ,quality).. On NYE Jools is good enough for me and I reckon I was in sync with all indoor celebrators

 

[brianmoooore]

I regularly watch F1, using feeds from various places for commentary, pictures and data screens. There can be up to 90 seconds difference between identical picture feeds, and anything up to two and a half minutes difference for the other stuff.
Radio Five Live commentator usually says exactly when pit exit light goes green, specifically for the purpose of synchronising their commentary with whatever picture feed you're using.

 

[pc1966]

Some pendulum clocks were extraordinarily accurate, such as these:

Shortt–Synchronome clock - Wikipedia

en.wikipedia.org

 

[pc1966]

If you have the rod already, you could try measuring its electrical resistance and see if it falls in to the range for steel, or is significantly higher as alloys with chrome/nickel tend to be (such as stainless).

If you have a 5A power supply, or a car battery and a headlamp bulb (along with safe means of holding it as it will get HOT!) you can use that to put a decent current along the rod. Then measure the volt drop from two points on the rod (not on the power supply leads or clips) and from a measurement of the cross-sectional area and length you ought to find the material's resistivity. You will need something that can measure a few mV probably, but a cheap-ish multimeter ought to do.

Carbon steel is about 1.43E-7 Ohm.meter, while stainless about 6.9E-7 Ohm.meter, Other cases can be found here:

Electrical resistivity and conductivity - Wikipedia

en.wikipedia.org

EDIT: Just to add some background info about the Kelvin (4 wire) resistance measurement method:

Kelvin (4-wire) Resistance Measurement | DC Metering Circuits | Electronics Textbook

Read about Kelvin (4-wire) Resistance Measurement (DC Metering Circuits) in our free Electronics Textbook

www.allaboutcircuits.com

 

[RogerJ]

Some pendulum clocks were extraordinarily accurate, such as these:

Shortt–Synchronome clock - Wikipedia

en.wikipedia.org

Hi pc1966. I'll address your following post shortly.
The clock stuff: All practiising electrician will know that their craft basically begins with Michael Faraday (Michael Faraday - Engineering and Technology History Wiki - https://ethw.org/Michael_Faraday) - nearly 200 years ago.
Soon after (1841) Alexander Bain patented the first electric clock (Distant Writing - Bain - https://distantwriting.co.uk/bain.html)

A free swinginging pendulum devoid of ANY interference WHATSOEVER will keep good time. In my clock, with the advantage of 21st century electrics, were to be encased in a chamber with a fixed low vacuum it would probably equal the performance of the Shortt/Synchronome. "Interference" in mechanical pendulum clocks, may come from poking the pendulum on every swing and extracting energy to move the hands.

In 1842 Mathtias Hipp came along with a better version (A DIY Free Pendulum, Hipp Toggle master clock. - http://www.rogerj.co.uk/clock.htm)
In 1895 Frank Hope-Jones formed the Synchronome company (Synchronome Clocks history - https://www.synchronomeclocks.com/pages/about-us) and his master clocks, with one second pendulums were in use well into the 1960's - when they finally succumbed to the Quartz crystal and other esoteric resonating sources. Along the way..in 1921, collaboration between Hope-Jones and William Hamilton Shortt produced the time reference you linked too.. Now we all know !!

 

[RogerJ]

If you have the rod already, you could try measuring its electrical resistance and see if it falls in to the range for steel, or is significantly higher as alloys with chrome/nickel tend to be (such as stainless).

If you have a 5A power supply, or a car battery and a headlamp bulb (along with safe means of holding it as it will get HOT!) you can use that to put a decent current along the rod. Then measure the volt drop from two points on the rod (not on the power supply leads or clips) and from a measurement of the cross-sectional area and length you ought to find the material's resistivity. You will need something that can measure a few mV probably, but a cheap-ish multimeter ought to do.

Carbon steel is about 1.43E-7 Ohm.meter, while stainless about 6.9E-7 Ohm.meter, Other cases can be found here:

Electrical resistivity and conductivity - Wikipedia

en.wikipedia.org

EDIT: Just to add some background info about the Kelvin (4 wire) resistance measurement method:

Kelvin (4-wire) Resistance Measurement | DC Metering Circuits | Electronics Textbook

Read about Kelvin (4-wire) Resistance Measurement (DC Metering Circuits) in our free Electronics Textbook

www.allaboutcircuits.com

I have the rod and may attempt to try it. It has also occured to me that if I supported it off the side of a stout board, fixed one end and with a dial gauge at the other..... I could pour boiling water over the rod and see if it expands...
Thank you..I'll follow up the links.. Roger

 

[Avo Mk8]

Roger
Sorry to be a spoilsport - coming back to your original question (Invar or steel), it occurs to me, and no doubt has to you too, that a simple experiment might be worth trying (but only if the length of your thermostat rod will fit in your oven!)
Cut a wire cotahanger to be as close as practicable to the length of the rod, and bung them in the oven at as high a temp as you like! Take them out, stand the pair next to each other and see if they're the same length!!
Or maybe there's a flaw in this scheme

 

[RogerJ]

Roger
Sorry to be a spoilsport - coming back to your original question (Invar or steel), it occurs to me, and no doubt has to you too, that a simple experiment might be worth trying (but only if the length of your thermostat rod will fit in your oven!)
Cut a wire cotahanger to be as close as practicable to the length of the rod, and bung them in the oven at as high a temp as you like! Take them out, stand the pair next to each other and see if they're the same length!!
Or maybe there's a flaw in this scheme

Done ! I left the bitter end of the brass tube on (as a socket) and cut a length of steel fence wire to fit under the conical under face of the "nut" on the other end of the stat rod. the other end was trapped under the nut and screwed down so they lay alogside each other. With other half safely watching Paddington Bear I set the oven to 180 and after 10 minutes put the combination in. The fence wire bowed away from the specimen by 1/4"..soon cooled down to as was. A strong indication therefore that the stat rod is Invar
Simplest ideas !!!!

 

[pc1966]

This is also an interesting run through the history of "time keeping" but phrased as oscillator stability:

http://www.leapsecond.com/ten/clock-powers-of-ten-tvb.pdf

 

[RogerJ]

This is also an interesting run through the history of "time keeping" but phrased as oscillator stability:

http://www.leapsecond.com/ten/clock-powers-of-ten-tvb.pdf

Interesting indeed.. I follow the gist of the sequence OK but I would need to have attended the lecture to understand a lot of the info the slides carried..

 

[johntheo]

Is it possibe that the thermostat is actually a pressure switch with some sort of thermal fluid in the sensing rod, cut a bit off the end??.

 

[johntheo]

No, not a pressure switch.