The Standard Penetration Test (SPT) is a test which provides assessment of soil properties and foundation design parameters. The Standard Penetration Test (SPT) is the in-situ soil characterization test, which is most widely used in the Americas. The N_SPT index depends not only on the soil properties and on the SPT sampler characteristics, but also on the energy delivered to SPT sampler during the hammer impact. The amount of energy that is transferred to the sampler depends on many factors, including the test equipment characteristics, soil conditions, and procedures followed during the test. For this reason, different N_SPT index values can be obtained for the same soil. Thus the N_SPT index should be normalized to a standard energy level that is equivalent to 60% of the nominal SPT hammer energy. Thus, it is of great importance to evaluate the actual energy input. The aim of this work is to show a suitable instrumented subassembly developed to assess the amount of energy that is effectively delivered to the sampler during a hammer impact. Results of SPT tests, conducted at the Experimental Research Site of the University of Sao Paulo (USP), showed the suitability of the instrumented subassembly to measure the amount of the energy that reaches the sampler, for the particular conditions. However, it should be verified if these conclusions are valid for tests performed in other situations involving the use of different types of hammer, different soil conditions and different instrumented subassembly positions.