Dimension ( W-D-H ) 110 mm x 115 mm x 50 mm / 4_1/4" x 4_1/2" x 2" LABOR Low-Level DC-AMPERE METER SIEMENS & HALSKE / Germany (1930) ******************************************************************** CLASS 1 300 μA / 160 mV / 533 Ω 0.3 mA ; 1 mA ; 3 mA ; 10 mA Housing is made of bakelite - Original state: No seal was broken! EXTENSION OF THE MEASUREMENT-RANGE WITH A HOME-MADE »TWIN-SHUNT« ... -------------------------------------------------------------------- 3 mA ==>> 30 mA & 10 mA ==>> 100 mA The right picture shows the inside ... Experiments with HELIPOTS & WHEATSTONE BRIDGE resulted in: The [ 30 mA ] 3 mA Range needed a 21.0 Ω resistor as shunt, made out of selected 33 Ω // 39 Ω ; The [ 100 mA ] 10 mA Range needed a 6.7 Ω resistor as shunt, made out of selected 12 Ω // 12 Ω . "How to find the value of a SHUNT ?" -------------------------------------------------------------------- When you want to expand (eg.) the 10 mA-Range to 100 mA-Range, than let a 10 mA current go through the instrument: It shows FULL SCALE. Now connect an EXPERIMENTAL RESISTOR (= "SHUNT") parallel to the instrument until it shows a 10-times reduced current = 1 mA. This is the value of the searched SHUNT! ( "Fine tuning" recommended if another Lab-A-Meter with right ranges is available. ) What "SIZE" (= Watt ) the SHUNT has to have ? ≥ 0.1 W ! U = R*I ; P = U*I = R*I2 ===>> 6.7 Ω * ( 9o mA )2 < 70 mW impressum: ******************************************************************** © C.HAMANN http://public.BHT-Berlin.de/hamann 11/14/09 |