Symbol in Schematic: Termostat switch, adjustable?

[Erik Baigar]

Dear Electronics experts,

in the schematics of an old intertial navigation system (origin is
Ferranti in the UK and it must have been designed between 1960 and
1970) I came accross a symbol I do not understand completely:

http://www.baigar.de/electronics/INU/thermostats1.jpg

shows the part of the schematic where A-X6, B-X3 and
B-X2 are the questionable symbols. These must be some
type of thermostatic switch (i.e. closed below a certain
temperature and open above). The purpose of these is
to maintain the case of the unit at a certain temperature
in energizing resistive heaters when neccessary.

My question is the following: Do the numbers (e.g. 80-85C in
A-X6) mean,

(a) that the switches are adjustable in this range
(no hysteresis)
(b) there is a hysteresis of 5C (i.e. switch opens at 85C
and closes again below 80C).
(c) or the accuracy is 5C, i.e. the switch is definitively
closed blow 80C and open above 85C with unpredictable
sate inbetween?

So what does the 5/10C mean in switch C-X1 in the following
excerpt?

http://www.baigar.de/electronics/INU/thermostats2.jpg

Maybe this is a typo and should read 5-10C?

Thanks for reading this,

best regards,

Erik.

 

[Ross Herbert]

:
ear Electronics experts,
:
:in the schematics of an old intertial navigation system (origin is
:Ferranti in the UK and it must have been designed between 1960 and
:1970) I came accross a symbol I do not understand completely:
:
:http://www.baigar.de/electronics/INU/thermostats1.jpg
:
:shows the part of the schematic where A-X6, B-X3 and
:B-X2 are the questionable symbols. These must be some
:type of thermostatic switch (i.e. closed below a certain
:temperature and open above). The purpose of these is
:to maintain the case of the unit at a certain temperature
:in energizing resistive heaters when neccessary.
:
:My question is the following: Do the numbers (e.g. 80-85C in
:A-X6) mean,
:
: (a) that the switches are adjustable in this range
: (no hysteresis)
: (b) there is a hysteresis of 5C (i.e. switch opens at 85C
: and closes again below 80C).
: (c) or the accuracy is 5C, i.e. the switch is definitively
: closed blow 80C and open above 85C with unpredictable
: sate inbetween?

Without knowing the brand/model of the bi-metal switches it could be either of
the above. If the switch has an adjustment slot then it is probably variable
over the stated range but if it isn't adjustable then the temp range is probably
a nominal switching temperature when heated. With bi-metal switches it is
difficult to produce the elements with a precise switching temperature unless
they have an adjuster. Very much like there would be on your electric frypan.

:
:So what does the 5/10C mean in switch C-X1 in the following
:excerpt?
:
:http://www.baigar.de/electronics/INU/thermostats2.jpg
:
:Maybe this is a typo and should read 5-10C?

Same answer as above. You need to know the device make and type to be able to
check.

:
: Thanks for reading this,
:
: best regards,
:
: Erik.

 

[Lostgallifreyan]

http://www.baigar.de/electronics/INU/thermostats1.jpg

I think those are fixed value bimetallic switches for protection. They're
designed to switch within a narrow range. Whether the variance is
hysteresis or inaccuracy is not important so long as it will switch within
the specified range.

I don't think that A-Xn stuff is a switch rating at all, it looks related
to the numbering of the heaters, so is probably a scheme to identify parts
in the design.

 

[Ross Herbert]

::
:> http://www.baigar.de/electronics/INU/thermostats1.jpg
:
:I think those are fixed value bimetallic switches for protection. They're
:designed to switch within a narrow range. Whether the variance is
:hysteresis or inaccuracy is not important so long as it will switch within
:the specified range.
:
:I don't think that A-Xn stuff is a switch rating at all, it looks related
:to the numbering of the heaters, so is probably a scheme to identify parts
:in the design.

Well, it should have been obvious to you that I wasn't referring to the circuit
designator as the temperature rating. Of course the A-Xn stuff is not the temp
rating. But the 40 - 45C (for example) subscript IS the temperature rating of
the switch, and that is what I was referring to.

 

[Ross Herbert]

:
ear Electronics experts,
:
:in the schematics of an old intertial navigation system (origin is
:Ferranti in the UK and it must have been designed between 1960 and
:1970) I came accross a symbol I do not understand completely:
:
:http://www.baigar.de/electronics/INU/thermostats1.jpg
:
:shows the part of the schematic where A-X6, B-X3 and
:B-X2 are the questionable symbols. These must be some
:type of thermostatic switch (i.e. closed below a certain
:temperature and open above). The purpose of these is
:to maintain the case of the unit at a certain temperature
:in energizing resistive heaters when neccessary.

You might also care to investigate the product range of one of the most common
brand of thermostat switches to see if the items you have match any of them.

The Klixon brand (owned by Sensata) make various types of temperature sensitive
circuit breakers and switches. Specifically, their bi-metal thermostats made
under the Airpax brand name
http://www.airpax.net/site/utilities/eliterature/pdfs/Airpax_TSP_shortform_0805.pdf

If you don't recognise anything in this catalog then do some more digging on the
Klixon web pages http://www.sensata.com/products/controls/thermostats.htm

 

[Erik Baigar]

Without knowing the brand/model of the bi-metal switches it could be either of
the above. If the switch has an adjustment slot then it is probably variable
over the stated range but if it isn't adjustable then the temp range is probably
a nominal switching temperature when heated. With bi-metal switches it is
difficult to produce the elements with a precise switching temperature unless
they have an adjuster. Very much like there would be on your electric frypan.

Thank you Herbert, this is interesting information. At the moment
I can not reach the switches since the unit is still in the sealed
vessel protecting the delicate mechanics from dust. But if I am
going to open it, I will be able to have a closer look to the switches.

 

[Erik Baigar]

You might also care to investigate the product range of one of the most common
brand of thermostat switches to see if the items you have match any of them.

The Klixon brand (owned by Sensata) make various types of temperature sensitive
circuit breakers and switches. Specifically, their bi-metal thermostats made
under the Airpax brand name
http://www.airpax.net/site/utilities/eliterature/pdfs/Airpax_TSP_shortform_0805.pdf

If you don't recognise anything in this catalog then do some more digging on the
Klixon web pages http://www.sensata.com/products/controls/thermostats.htm

Many thanks for these links, too - I will compare the switches I will
see with these
and see whether this enlightnes me...