Max Kohl A. G., Chemnitz (Germany). 



Supplement to Notice No. 18. 



Simple Experimental Switchboards. 



In addition to being makers of the most complete patterns of experimental switchboards, we 

 ul so manufacture those of a lighter and simpler pattern, which, however, permit of being used in a 

 multiplicity of ways. 



On the one hand they permit of connecting up the apparatus which are being used for teaching 

 purposes (and which are usually intended for working on low pressure) to the heavy current from 

 electricity works; while on the other hand they permit of carrying out those experiments which imply 

 the use of a heavy current, e. g., demonstrating the electric arc. 



The switchboards are accordingly arranged in such manner that it is possible to work with small 



or large current-densities at high or low pressures when the supply is 



obtained from a heavy current system. The condition as regards low 



voltage, which is rendered possible by a shunt method of connecting 



(division of pressure), is particulary important in the case of apparatus 



working with interruption of the current, the contact parts of which 



are burnt out when a high voltage is applied or even when a large 



series resistance is employed, since the full supply voltage prevails 



at the contact parts at the moment of interruption of the current. 

 The switchboards are fitted either with Deprez-d'Arsonval 



precision measuring instruments or with air-damped electromagnetic 



instruments, as desired. The former are rather advisable, as they have 



a uniform scale and are dead-beat. They are only applicable for 



direct current. The electromagnetic instruments possess a scale which 



commences only at approx. 1/5 of the maximum deflection. Smaller 



currents and voltages can thus only be read approximately. On the 



other hand, however, these instruments can b&--used both on direct Fig- 6. l : 10. 



and alternating current. Alternating current, however, is only directly 

 applicable for a few experiments, so that it is usually necessary to trans- 

 form it into direct current. 



The construction of the switchboards may be seen on reference to 

 Figs. 6 and 7. A marble slab is placed on one of the Double Switch 

 Contact Resistances already described, this slab containing the necessary 

 fuses, switches and measuring instruments. The method of connecting is 

 generally in accordance with that described on pp. Ill and 112 of our 

 Price List No. 50, with the exception that the measuring instruments cannot 

 be commutated, and that they give the voltage and current in the 

 apparatus direct. 



The switchboards are designed for fixing on the wall. Directions 

 for use and a diagram of connections are appended to each switchboard, 

 l : 9. The metering instruments have an approx. base diameter of 130 mm. 



Prices. 



7086. Simple Experimental Switchboard, Type EA\, for connecting up to 110 volts D. C., 

 Fig. 6, with Double Switch Contact Eesistance, 39 contacts, 36 ohms; max. permissible 

 load 5 to 30 amps, according to position of Switch Contacts; for taking currents of 

 0.03 to 30 amps, and pressures of 0.3 to 110 volts from the supply ; with Precision 

 Instruments 13. o. 



The marble slab contains: 2 terminals for the supply current ; 2 fuses; 1 main switch; 1 switch 

 lor the shunt; 1 Precision Ammeter; 1 Precision Voltmeter; 2 terminals for connecting up the apparatus. 



7087. -- idem, Type EB\, Fig. 6, style as No. 7086, but for connecting up to 220 volts 

 D. C., with 2 Switch Contacts, 39 contacts, 48 ohms; max. permissible load, 5 to 20 amps, 

 according to position of switch contacts; for taking currents of 0.08 to 20 amps, and 

 pressures of 0.8 to 220 volts from the supply 13. 5. 



M. 18 A e. 



Cl. 6231, 



6234. 



