Improvements, in or relating to Pyrometers.
Year: 1888

page_text: Date of Application, 8th. Sept. 1888
Complete Specification Left, 10th Apr., 1889
Complete Specification Accepted, 1st June, 1889,+
Improvements, in or relating to Pyrometers.,
We WILLIAM HARRY GRINDLEY of Tunstall in the County of Stafford; Manu-
facturer and WILLIAM, STONE HENSLEY of Cardiff in the County of. Glamorgan
Demonstrator of Physics, do hereby declare the nature of this invention to be as
follows:-
".
The object of this, invention, is.to, combine and arrange the undermentioned apparatus.
in the following, manner, in order to measure the temperature or change of temperature,
of any form of oven furnace or heated place.
It embraces —
(a). A coil on coils, of platinum or; iridium, wire or. of any other, metal which,
would not melt in the furnace, oven, or other, place, in which the Pyrometer, might
be used.
(b). This coil of, wire is wound on any material, which is a sufficiently, good insulator,
at, the temperature to be measured.
(c). The coil is used as a resistance coil. forming one of the arms or part of one of
the arms of the instrument called a Wheatstone Bridge.
(d). In this bridge; a, balance. is, obtained by means of, a. sliding, contact.. The-
position of this contact which gives a balance, is determined by aid, of any form, of,
sensitive galvanometer or telephone.
(e). The resistance of the coil of wire placed in, the furnace oven or other heated,
place varies with its temperature and this variation of temperature, is determined, by
the variation of the position. of the sliding contact which gives.a, balance this, position.
being shown by the galvanometer or telephone.

page_text: (f). Or the variation of temperature may be determined by directly observing the
deflections of the galvanometer when the sliding contact is kept fixed.
Dated this Seventh day of September 1888.
COMPLETE SPECIFICATION..
Improvements in or relating to Pyrometers.
We, WILLIAM HARRY GRINDLEY, of Tunstall in the County of Stafford, Manu-
facturer, and WILLIAM STONE HENSLEY, of Cardiff, in the County of Glamorgan,
Demonstrator of Physics do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
The object of this invention is to combine and arrange the undermentioned apparatus
in the following manner in order to measure the temperature or change of temperature
of any form of oven furnace or heated place.
It embraces
(a) A coil or coils of platinum, of iridium wire or of any other metal which
would not melt or oxidise in the furnace oven or other place in which the pyrometer
might be used.
(b) This coil of wire is wound on any material which is a sufficiently good insulator
at the temperature to be measured.
(c) The coil is used as a resistance coil forming one of the arms or part of one of
the arms of the instrument called a Wheatstone bridge.
(d) In this bridge a balance is obtained by means of a sliding contact. The position
of this contact which gives a balance is determined by aid of any form of sensitive
galvanometer.
(e) The resistance of the coil of wire placed in the furnace oven or other heated
place varies with its temperature and this variation of temperature is determined by
the variation of the position of the sliding contact which gives a balance, this position
being shown by the galvanometer.

page_text: In the accompanying drawings:
Fig. 1 is a diagram illustrating the manner of working our invention in connection
with five pottery ovens hereinafter generically referrel to as heated chambers the
number (five) being shown only by way of example.
Figs. 2, 3, 4 and 5 are detail views of the arrangement of and preferred 'manner of
constructing the coils located in such chambers; Figs. 6 and 7 are respectively a plan
and an elevation of the combined Wheatstone bridge and switch board the latter of
which is shown in elevation in Fig. 8 Figs. 9, 10, 11 and 12 are sections taken
respectively on the lines a-b, c-d. e-f and g-h of figure 6; Figs. 13 and 14 being
views of the contact-piece or switch used in connection with the switch-board.
The coils A, figure 2, by the changes of temperature and consequently of electrical
resistance whereof will be determined the variations in the temperature to which they
are exposed are each preferably constructed in the manner shown in figures 3, 4 and 5,
Figs. 3 and 4 representing the said coil in a preparatory stage and Fig. 5 being a
view partly in elevation and partly in section of one of the said coils completed.
A is the coil proper which is composed of preferably platinum or iridium wire.
A2 is a core of preferably baked earthenware upon which is formed a screw thread
and in its ends transverse recesses A'. The coil A' is wound around the core A² in
the groove between the screw thread upon it and the ends of the coil are united to
the two preferably platinum leads A and B which as shown in figure 2 will afterwards
be passed through the wall of the chamber Z whose temperature or changes of
temperature it is desired to ascertain, these leads themselves being connected to the
copper leads by which the coils A are connected to the apparatus hereinafter described.
The two joints between the coil A' and leads A³ and B are each located in one of
the recesses A. The coil A', core A2 and adjacent parts of the leads A and B to
preserve them from the injurious effects of the gases are then entirely surrounded with
plastic clay or equivalent material A in the manner shown in figure 5 and the whole
is then baked in an oven or the like until the covering A has become quite hard. On
referring to figure it will be seen that the covering A is so placed around the
core A2 and coil A' (resting as it does on the top of the screw thread) as so leave the
said coil free to expand and contract while at the same time preventing any risk of
short circuiting by any two of the turns coming into contact.
In each of the five chambers represented in figure 1 there are arranged any suitable
number say for example eight of the before described coils as shown in one such
chamber where they are marked 1", 2ª, 3, 4, 5, 6ª, 7 and 8ª four of these coils say
those referred to by the odd numbers being near the floor and the other four near the
roof or other required position.
Through the lead B which in figure 1 is represented in a dot-and-dash line one
terminal of each of the before described coils A¹ is connected so as to form part of
one arm of the Wheatstone bridge C, its other terminal being directly connected to the
switch board D and indirectly through it and the battery E, and galvanometer F to
one of the other arms of the said bridge. This bridge which under our invention is
of an improved construction as shown in Figs. 6, 7, 9, 10 and 11 is formed with a
wooden or other base and two longitudinal ribs C² which form a channel between
them as shown clearly in Figs. 9 and 11 for receiving the elastic conductor 03 04 are
laths secured one on the top of each of the ribs and upon which the preferably
German silver or platinoid wire C³ or C is bedded in insulating material 07. The
employment of the two wires (and C is a convenient form of applying a complete
bridge wire the resistance of which per unit length is different in different parts and
for this purpose they are made, the wire C preferably thinner than the wire C³.
These wires made fast at one end to metal connecting studs C and C and each is
drawn tight by means of a nut C at its other end the said two wires being electrically
connected together by the metal strip (1º of such low resistance as to be inappreciable.
The reason we use as a thicker wire and in consequence a wire of less resistance
than that marked is that the instrument may be more sensitive for those
temperatures for the ascertaining of which the said wire ( will be in use viz. :-the
high temperatures say above 1400° Fah, which of course it is absolutely necessary for

page_text: certain purposes shall be reliably determined. is a carriage which is capable of
sliding on the stationary part-C020 hereinafter generally referred to as the bed C².
The
upper part C of this carriage is preferably of metal and is provided with a fixed
post which is electrically connected to the elastic conductor C, the lower part of
the said carriage may be of metal, wood'or'any other suitable material and is provided
with clamping screws (4. The part (12 carries the metal studs C3 C3 the lower ends
of which as shown in Fig. 9 are preferably tipped with platinum or other not readily
:oxidizable metal the upper ends being electrically connected through the flexible
spring conductors C to the post and consequently to the conductor C³. The
studs and C2 are normally not in contact with the wires beneaththem being held in
their raised position by the springs (15 until they are pressed down by hand so as to
be brought into electrical contact with the wires C and C respectively beneath each.
The carriage carries two pointers (16 for indicating by the relative position of one
or other of them on the scale (17 or 18 the temperature it is desired to ascertain.
The end of the elastic conductor C³ opposite to that connected to the post is
electrically connected through the stud and wire with the binding screw (20
by means of which as shown in figure 1, it is electrically connected with the
galvanometer F which is of any desired construction. The conductor C³ is preferably
in a coiled form so as to provide the elasticity which is necessary to allow the
carriage to be moved along the 'bed C whilst always maintaining electrical
connection between the post Ca and stud 01.
To the stud C to which is attached the wire (as shownjmost clearly in figure 11
is electrically connected the resistance coil which as are also the resistance
coils C3 and C is connected in series therewith these in the drawings merely being
shown diagrammatically. The resistances of the coils 023 and C4 must be equal and
each should be about equal to that arm of the bridge which contains one of the oven
coils when the said oven coil is at that temperature for which maximum sensitiveness
is required, and when the bridge is balanced. The resistance of the whole bridge
wire and must be equal to half the difference between the resistance of one of
the oven coils when at the maximum temperature which the pyrometor is intended
to register, and the resistance of the said oven coil when.at the minimum temperature
which this pyrometer is intended to measure. The resistance of the coil C2 must be
equal to that of the arm of the bridge which contains one of the oven coils,
when the said oven coil is at its minimum temperature and when the bridge is
· balanced.
The stud (by which the coils C and C are united is electrically connected
through the wire and binding screw (27 with one, say the negative pole of the
battery E as shown in Fig. 1, this battery being preferably formed of one or more
Daniell cells of total resistance lower than that of the galvanometer employed and the
stud 28 by which the coils C23-and C4 are joined is connected by the wire and binding
screw to one terminal of the galvanometer F, the other terminal of which as
hereinbefore described is connected to the elastic iconductor C³through the binding
screw C. The end of the coil (24 opposite to that herein described as connected
to the post 28 is connected through the stud 030 to the other or say positive pole
of the battery E and by the metallic conductors D to the mercury containing
(cups D1 D2 D3 D and D which respectively correspond with the chambers
marked 1, 2, 3, 4, and 5 that is to say through the group of mercury cups the
centre one of which is marked D' the temperature of the chamber I will be determined
and similarly with the group marked D will the temperature of the chamber 2 be
determined and so on throughout the series. The mercury cupsid¹ d² d³d d
did and d of each group are each electrically connected by a separate lead.d to
sone end of one of the coils within one of the chambers marked from 1 to 5 the
opposite end of such coil being.as hereinbefore described connected through the lead B
with one arm of the Wheatstone bridge C. Now as there are eight different coils
located at various parts of each of the heated chambers corresponding with the eight
mercury cups marked from d³ to-d" by making contact between any one of the said
cups and the centre cup of its group the circuit will the completed and the current will

page_text: flow through the particular coil corresponding to "that particular cup. The 'means by
which we electrically connect any of one group of the "cups d¹ to with the cup at
the centre of its group consists of the bridge piece or switch D' 'Figs. 13 and 14 the
legs of which are at such a distance apart that they will enter the two said cups.
The galvanometer which we 'prefer to employ in conjunction with the 'before
described apparatus is of the class known as reflecting galvanometers and is preferably
very sensitive in its action its resistance being slightly lower than that of the whole
oven circuit when at its maximum temperature and Fig. 1 is the sciile upon which it
is arranged to reflect a ray of light.
Supposing now with the various parts connected together as before described "it is
desired to ascertain the temperature at the part of the chamber I where the coil I* is
situated. First the switch D is placed so that its 'legs dip one into the cup D¹ and
the other into the 'cup d'. Then with the carriage C placed at any point of the
bed C one of the studs 01 or ( is 'pressed on 'to the wire below it. 'The
connections of the Wheatstone bridge are thus completed, the four arms being as
follows, viz. Ist from the post through the connections D to the cup 'D', then
through the switch D' to the cupid and then through the wire d to the coil [" and
through this coil and the wire B to the post C, and then through the bridge wire
to the point of contact of the studs or 32 pressed down on it as mentioned.
2nd, from the last mentioned point of contact on the bridge wire through the
remainder of the latter to the post and then through the coil C to the post C
3rd, from the post (20 through the coil to the post 4th from the post (128
through the coil to the post (30 Also the galvanometer circuit extends from the
point of contact, of the stud Cor (32 pressed down on the 'bridge 'wire 'through
the conductor to the binding screw C and thence through the galvanometer
and the binding screw 29 to the post C28. Also the 'battery circuit extends from
the post (through the binding screw C.and the battery to the 'binding 'screw
and post 30
Under these circumstances the current coming from the positive pole of the
battery will be divided between the above mentioned several circuits' making up
the Wheatstone bridge, the proportion of the current flowing through each *circuit
depending on the several resistances of each of the six circuits.
Further the direction of the current through the galvanometer and therefore the
direction of deflection of the spot of light on the galvanometer "scale "F when
the stud Coris pressed down, will depend only on the relative resistances of the
four circuits above described as constituting the arms of the bridge.
Further if a certain well known relation exists between the resistance of the arms,
the strength of the current in the galvanometer will be zero and therefore the
deflection of the spot of light on the scule F when the stud Cor is pressed down
And if as described the coils C3 and C4 are equal this will be the case
when the arm containing the coil I is equal in resistance to that containing C22:
will be zero.
If the bridge wire is made of the resistance stated above and if the temperature of
"the coil 1 is "between the greatest and least registered by the pyrometer then a point
must exist on the wire such that if the contact due to pressing down the stud 1 or (33
is made at this point the last mentioned relation between the resistances of the arms
will be satisfied.
If then the stud is upressed down at this point there will be no current in the
galvanometer and consequently no deflection of the spot of light on the scale F
And since the connecting piece is of such low resistance as 'to be "negligable, it
is possible by sliding the carriage (by hand "along the bed to make contact
with one or other of the studs or at any point whatever 'in "the length of
the wire.
Contact is then made at various points of
which on pressing down one or other of the
the spot of light on the scale F.
the wire until by trial a point' is found at
studs for C there is no deflection of
The temperature on the arbitrary scale of the instrument is then read off it once by .

page_text: ..
the position of the pointer C on the scale (Ts if the above mentioned point of contact
on the wire is found to be obtained by pressing down 0 or by the position of the
pointer C on the scale (7 if it is obtained by pressing down C
The trials necessary to obtain the required point of contact on the wire such that no
deflection of the spot of light on the scale F4 is produced by pressing down the
stud are greatly expedited by observing that if the point of contact has been moved
too far along the wire measured from either end the deflection of the spot of light on
making contact will be in one direction along the scale F whereas if the point, of
contact has not been moved far enough along the wire the deflection of the spot.
of light will be in the other direction along F
In a similar manner if it be desired to ascertain the temperature of a particular
part of another chamber say for example the chamber 3 Fig. 1 then the switch D'
is placed so that one leg dips into the cup D3 and its other leg into that cup
which is connected by one of the wires d with the coil located at the particular
part desired.
In order to nullify the effects which the variations in the external temperature
would bave upon the resistance of the copper leads connecting the coils A in the
heated chambers with the bridge C and switch board D we employ carbon; as
the resistance of that substance falls as the temperature rises which is the reverse
property of copper of which the leads B and d are preferably formed the resistancë
of these rising with the temperature. A suitable manner of applying this property
of carbon to our invention consists in inserting in the lead Ban incandescent lamp
as shown in Fig. 1, where the said lamp is marked H the said lamp or its equivalent
being of a resistance about eight times that of the copper leads exposed to the external
temperature, it being understood that the exposed leads B for each heated chamber
should all be of the same resistance. If however the resistances of the leads d, are
not equal then it will be necessary to introduce separate incandescent lamps such
as H in each of the leads d or in some of them, if all are not unequal; or to introduce
further lamps into the lead B these further lamps being placed in parts of the wire B
further from the keyboard than the point at which this wire is divided betwen the
ovens.
In any such case the resistances of the various lamps used must be such that the
total resistance of carbon in any oven circuit is about eight times the resistance of
the copper wire exposed to the external temperature in that circuit.
In some heated chambers it is not so much necessary that the actual temperature
should be known as that there can be ensured a uniform rise of temperature throughout
the firing and that the greatest heat of the chamber should not rise above a certain
maximum nor fall below a certain minimum and these maximum and minimum points
may conveniently be indicated on one or both of the scales C17 C18 Fig. 6 by
red lines.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
1. In pyrometric apparatus a coil of wire wound upon a preferably baked earthen-
ware core and clothed by a covering of earthenware or other like fire-resisting
material constructed substantially as and for the purpose herein described and
illustrated in figures 3, 4 and 5 of the accompanying drawings.
2. In pyrometric apparatus the complete coil such as A substantially as herein
described and illustrated in the accompanying drawings.
3. In pyrometric apparatus the combination with a switch board consisting
essentially of mercury-containing cups such as D' and d¹ to d and switch such as D
of a Wheatstone bridge such as C constructed with two or more wires which are
equivalent to a single bridge wire having different resistance per unit length in
different parts and operated substantially as and for the purpose herein described and
illustrated in the accompanying drawings.

page_text: 4. In pyrometric apparatus the combination with a switch board of a Wheatstone
bridge such as C constructed with two or more wires such as C³ and C substantially
as and for the purpose herein described and illustrated in the accompanying
drawings.
5. A Wheatstone bridge consisting essentially of the resistance coils such as " (22
and an elastic conductor such as C³ wires C and C connections C adjustable
carriage such as C carrying posts or studs such as C13 C1 and (132 electrically
connected together the whole constructed and operating substantially as and for the
purpose herein described and illustrated in the accompanying drawings.
6. A Wheatstone bridge constructed with two or more wires such as C and C
wbich are equivalent to one single wire having different resistances per unit length in
different parts substantially as and for the purpose herein described and illustrated in
the accompanying drawings.
7. In pyrometric apparatus the combination with the metallic leads of carbon for
the purpose of neutralising the effects of variations in the external temperatures
substantially as herein described.
8. The complete pyrometric apparatus consisting essentially of a heated coil leads
Wheatstone bridge switch board galvanometer resistance coils and battery substantially
as herein described.
Dated this 9th day of April 1889.
WILLIAM HARRY GRINDLEY.
WILLIAM STONE HENSLEY.
W. P. Thompson & Boult,
Agents for the Applicants.