A Hot Wire Meter of Simple Design 



By C. L. Sears 



IN the construction of the average hot 

 wire meter there are some parts 

 which could be simplified. For in- 

 stance, the device used to bring the 

 pointer back to zero is usually in the na- 

 ture of an arrangement whereby the wire 

 is tightened or loosened, as the case may 

 be. This construction usually involves a 

 special casting which in itself sounds 

 formidable to the amateur. 



The meter to be described is provided 

 with an adjusting member which is easily 

 made and which gives a wide range of 

 adjustment. The case of the meter made 

 by the writer was taken from a damaged 

 voltmeter of the switchboard type and of 

 the size indicated in the dimensioned 

 drawing, Fig. i. While these meter cases 

 are not difficult to obtain, the movement 

 of the hot wire meter could just as well 

 be mounted in a neat wooden case. 



In laying out the case prior to drilling 

 the holes, the builder will facilitate his 

 work if he scribes two diametrical lines 

 at right angles to each other across the 

 back of the case on the inside. With 

 reference to Fig. i, scribe a second line 



The Details of the Case for the Hot Wire Meter. 



one inch above the center line and drill 

 two 3- 1 6-inch holes on this line 4 inches 

 apart or, in other words, 2 inches on 

 either side of the vertical center line. 



This layout is indicated at C D in Fig. i. 

 These holes are to hold the fibre sup- 

 port for the wire. 



Measuring one inch from the inside 



Various Parts of the Hot Wire Meter. 



of the case and one inch to the left of 

 the vertical line, drill a % -inch hole, E, 

 Fig. i. In the sides of the case drill two 

 %-inch holes for the insulating bush- 

 ings and also a 3^-inch hole for the brass 

 adjusting screw bushing as shown at C 

 Fig. i. The insulating support for the 

 wire holders is made from a piece of 

 black fibre J^x2x7*4 inches and is 

 drilled and tapped as shown at A and B, 

 Fig. 2. As shown in the drawing, it is 

 slotted y% inch deep and % inch wide. 

 At C are shown the two wire supports 

 which are made from ^4 -inch square 

 brass stock i% inches long. The three 

 small holes % inch apart on centers are 

 drilled and tapped 4-36 and the large 

 3/i6-inch hole is drilled to clear a 10-24 

 round head machine screw to fasten the 

 supports to the fibre crosspiece. The 

 small holes should each be supplied with 

 screws and small washers. 



At D and E are shown the dial sup- 

 ports for a case of this type. Two of 



135 



