Abstract:The practical method for precise penetration rate measurement in a short time and the instrument design have been specially discussed in this paper. Considering the defects of the penetration rate meters available, via the balanced design in consideration of service life, costs, accuracy and reliability, a kind of penetration rate meter has been put forward. The meter consists of a magnetic clutch, a gear box and a raster disk system to pick up the signal. The meter has the following advantages-it might measure a low speed with higher accuracy; it could disengage automatically without being divorced from the driving device during tripping rods at high speed: it has a circuit of rotary direction discrimination and of repeated counting prevention so as to eliurinate error caused by rod vibration.

Key words: penetration rate measurement, instrument design,  magnetic clutch,  gear box,  raster disk