BAIRD &L TATLOCK (LONDON) LTD. 



220 



Thermo -Electric Couples, copper constantan. In steel tubes with terminal heads. 

 For use up to 500 C. (Exactly similar to Fig. B but with steel instead of porcelain tubes.) 



5555 T Length of steel tube, 13 inches (330 millimetres) . . 



5556 T ,, 27 ,, (690 ) . . 



5557 r 39 (1000 ) . . 



5558 T ,, 51 ,, (1300 ,/ ) .. 



5559 T 66 (1680 ) .. 



5560 T Steam-pipe pattern copper, constantan thermo-couple. With bent stem as in 

 Fig. 9, screwed with a J in. gas-thread for screwing directly into steam-pipes, boilers, etc. 

 The stem projects about 3 in. into the main so that it can be used with any pipe over 

 4 in. internal diameter 



Connecting Leads. 



General. For connecting from the thermo-couple to the millivoltmeter two connecting wires or " leads " 

 are necessary, and lor this purpose it has been customary to use a single " twin-core " cable containing 

 two insulated copper wires. With a thermo-electric pyrometer as already described and using such leads the 

 temperature actually indicated is the difference in temperature between the hot end and the cold end or terminal 

 head of the thermo-couple. Therefore, as the temperature at the cold end of the couple varies, the readings will 

 vary, although the temperature of the hot end may remain constant. This makes it necessary either (i) to make 

 provision for keeping the temperature at the cold end of the couple constant, or (2) to apply corrections to the 

 readings as this temperature varies, or (3) to neglect the point and put up with the inaccuracy thus introduced 

 into the readings. To get over all these difficulties we have introduced our Peake's Patent Compensating Leads. 



Peake's Patent Compensating Leads. These leads are intended for use with the platinum series of thermo- 

 couples and are made up in the form of a " twin-core " cable, one wire of which is copper and the other a special 

 low resistance alloy. By their use the " cold-junction " of the thermo-couple is transferred from the couple 

 to the indicator or recorder and changes in temperature at the terminals of the couple do not affect the readings in 

 the slightest degree. The reason for this is that the thermal electromotive-force given by copper against the special 

 alloy is the same as that given by platinum against the platinum alloy used in the thermo-couple. Experiments 

 show that this compensation is correct for any temperature of the thermo-couple terminals up to 300 C. 



The usefulness of these leads is at once apparent. The fact that the temperature of the head of the pyro- 

 meter itself within the limit of 300 C. does not affect the readings of the pyrometer at once obviates 

 the necessity of water-cooled heads with all their attendant disadvantages and also allows of the employment 

 of shorter pyrometers. Another very real advantage is the fact that pyrometers may now be inserted vertically 

 through the roof of a furnace when formerly they had to be used horizontally because, in the vertical position, 

 the heads would have been overheated and thus serious errors would have been introduced. 



The leads used with couples of platinum, platinuhi 10% indium, are, of course, slightly different from those 

 used with platinum, platinum 10% rhodium, and, when ordering leads only, customers should state with what 

 type of couple they are to be used. 



The leads have the same resistance per yard as our ordinary copper leads and can therefore be installed to 

 replace existing leads, the only point to be noticed being that the alloy wire which is the thicker of the two must 

 be connected to the platinum or terminal of the thermo-couple, whilst the copper wire, which is the thinner one 

 and is covered with red insulation, must be connected to the platinum alloy or + terminal. 



Peake's Compensating Leads. 



5561 T Flexible braided pattern, for general use . . . . 2/- 



5562 T but enclosed in flexible steel 



sheathing, to stand rough usage .. .. .. .. 3/- 



5563 T Lead-covered pattern, for permanent installations where 

 moisture may be present . . . . . . . . 2/- 



5564 T Asbestos covered pattern, in flexible steel sheathing, for 

 use in hot positions . . . . . . . . . . 4;. 



For fitting coloured tangs on both ends of any of the above leads add 3/-, or on one end only, 1/6. 



Ordinary Copper Leads. 

 5565 1 Braided and compounded pattern, twin core . . . . . . per yard 008 



5566 T Lead-covered pattern, twin core .... 008 



1000 



