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'Therrbstats
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57
strips of different metals, f0r example steel
together face to face alongtheir length. When a temperatùréChànge
occurs both metals expand:_aud the composite strip bends as a result
of differential expansion. An electrical contact is carried at the end ‘
{
of the bending strip and this meets another on the fixed part of the
thermostat body to form a sensitive switch, The bending strip
’
pre-tensioned by an adjusting screw so that when it is at or below
'
the minimum required temperature the fixed and moving contacts *
touch, and when it is at the maximum temperature required the
-
contacts move apart. The difference between these two temperatures
-is called the ‘differential’ of the thermostat and in high quality
equipment is only a few degrees.
_'
'
‘
Adjustment for the desired temperature is carried out by altering
'
'
the tension on the bi-metallic strip by means of a precision screw " '
A small magnet is usually fitted next to the,cOntact
'
,
so that as the moving contact approaches"thefixed'one it is snatched
"
quickly-into contact, and similarly when trying to move away itis
released s—uddenly after acquiring a
This provision
reduces arcing at the contact points and thus maihtains them in good
_
f l _—
condition.
‘
'
'
.
-
Aquarium,thermostats are usually designed to fit either inside,
wholly or partially immersed in the water, or outside, fitted
’
__
against the glass side so as to sense the water temperature thr0ugh
‘
the
glass. So-called submersible »thermostats are "designed to be
totally immersed if required, and when adjustment is neededîthe
'
thermostat body must be removed fr0m its protective-*‘ftu_be(after
’
.
the poWer supply) in order “to reach the 1nternally
fitted adjusting screw. This type of thermoStat isfquite smalland
'
cannot usually carry as
Current as other
models are sold as submersible it is a Wise precaution to
top
'
above the water level, particularly after»«thefbung has been removed :
and replaced several times for adjustmentS. Theyare
makers supposedly set for .'an approximate temperature butthis
should not be blindlÿ_ relied_ ’on, and the best results will be achieved
if the thermostatis adjusted to_ the partiCularrequ‘irem6n‘tshôf'the_
.
environment.
'
'"
w,Immersible;thermostats are also available with an external adjuster
Some models
this type”
notbefully _
_,5Esubmerged or water may enter around the adju-éting‘
They
maybe susceptible to dripping and
thescrewor Spindle bearing the adjusting
?
and as it , is in contact withathe bi—metallic «strip inside it is electticallÿ
:
‘
'_
‘
‘
“
'
’
L_;_
'
‘
J
‘
,{
'
"
‘
,
‘
_‘
-
'Therrbstats
’
’
'
j
_
57
strips of different metals, f0r example steel
together face to face alongtheir length. When a temperatùréChànge
occurs both metals expand:_aud the composite strip bends as a result
of differential expansion. An electrical contact is carried at the end ‘
{
of the bending strip and this meets another on the fixed part of the
thermostat body to form a sensitive switch, The bending strip
’
pre-tensioned by an adjusting screw so that when it is at or below
'
the minimum required temperature the fixed and moving contacts *
touch, and when it is at the maximum temperature required the
-
contacts move apart. The difference between these two temperatures
-is called the ‘differential’ of the thermostat and in high quality
equipment is only a few degrees.
_'
'
‘
Adjustment for the desired temperature is carried out by altering
'
'
the tension on the bi-metallic strip by means of a precision screw " '
A small magnet is usually fitted next to the,cOntact
'
,
so that as the moving contact approaches"thefixed'one it is snatched
"
quickly-into contact, and similarly when trying to move away itis
released s—uddenly after acquiring a
This provision
reduces arcing at the contact points and thus maihtains them in good
_
f l _—
condition.
‘
'
'
.
-
Aquarium,thermostats are usually designed to fit either inside,
wholly or partially immersed in the water, or outside, fitted
’
__
against the glass side so as to sense the water temperature thr0ugh
‘
the
glass. So-called submersible »thermostats are "designed to be
totally immersed if required, and when adjustment is neededîthe
'
thermostat body must be removed fr0m its protective-*‘ftu_be(after
’
.
the poWer supply) in order “to reach the 1nternally
fitted adjusting screw. This type of thermoStat isfquite smalland
'
cannot usually carry as
Current as other
models are sold as submersible it is a Wise precaution to
top
'
above the water level, particularly after»«thefbung has been removed :
and replaced several times for adjustmentS. Theyare
makers supposedly set for .'an approximate temperature butthis
should not be blindlÿ_ relied_ ’on, and the best results will be achieved
if the thermostatis adjusted to_ the partiCularrequ‘irem6n‘tshôf'the_
.
environment.
'
'"
w,Immersible;thermostats are also available with an external adjuster
Some models
this type”
notbefully _
_,5Esubmerged or water may enter around the adju-éting‘
They
maybe susceptible to dripping and
thescrewor Spindle bearing the adjusting
?
and as it , is in contact withathe bi—metallic «strip inside it is electticallÿ
: