Symbol in Schematic: Termostat switch, adjustable?

: :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: : :

: :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? : :

: :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.

Ross Herbert wrote in news: snipped-for-privacy@4ax.com:

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 wrote in :news: snipped-for-privacy@4ax.com: : :>

: :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.

: :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: : :

: :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

If you don't recognise anything in this catalog then do some more digging on the Klixon web pages

probably

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.

the

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