1925 Volume 28 Issue 96 Pages 153-158
Piezo-electricity of quartz is used to measure the rapidly varying pressure in the cylinder. The electric charge due to the pressure is applied to the grid of a valve, and the plate current which varies as the grid voltage is recorded with an oscillograph. By this method indicator diagrams can be taken with sufficient sensitivity and accuracy even at the speed of 5, 000 r.p.m. or more. Another merit is that the record can be taken at any distance from the engine.