Apparatus and method for making decay rate measurements

Apparatus for indicating the rate of decay of oscillation in test objects such as mechanical structures, acoustical enclosures, and electrical circuits which have been suitably excited and providing simultaneous presentation of an adjustable reference decay rate signal for comparison comprising:

• a source of excitation energy for exciting a test object with the excitation energy in such forms as acoustical, mechanical, or electrical energy at a first predetermined point;
• means for terminating the excitation energy;
• means for detecting the excitation response of the test object at a second predetermined point and providing an input signal representative of the excitation response of the test object;
• means for receiving the input signal and producing a signal which is the absolute value of the input signal;
• means for log-converting the absolute-value signal and producing a decaying data signal which is the logarithmic value of the absolute-value signal;
• means for generating and varying a reference signal within a predetermined amplitude range and providing an indication of the value of the amplitude;
• means for integrating the reference signal and producing a reference decay rate signal made variable by varying the reference signal;
• means responsive to the means for terminating the excitation energy for triggering indicator means responsive to the decaying data signal and the reference decay rate signal for producing an indication representative of the decaying data signal from the test object and the variable decay rate for simultaneous comparison.

A method of determining the exponential decay rate of a test object which comprises the steps of:

• exciting the test object at a first selected point;
• terminating the excitation imposed on the test object;
• converting the decay response of the test object due to the termination of the excitation into an electrical input signal at a second selected point;
• absolute valuing of the electrical input signal to obtain an absolute-value electrical signal;
• log converting the absolute value electrical signal to obtain a decaying data electrical signal which is a logarithmic value of the absolute-value signal;
• generating an adjustable reference signal upon the termination of the excitation;
• integrating the adjustable reference signal to produce a variable reference decay rate electrical signal;
• adjusting the reference signal to produce a reference decay rate electrical signal which coincides with the decaying data electrical signal whereby the decay rate of the test object may be determined from the value of the adjusted reference signal.

The method of determining the exponential electrical decay rate in a circuit which comprises the steps of:

• exciting the electrical circuit with an oscillating electrical signal at a first selected point;
• terminating the electrical signal imposed on the circuit;
• detecting the electrical decay response signal of the circuit due to the termination of the electrical signal at a second selected point;
• absolute valuing the electrical decay response signal to obtain an absolute-value electrical signal;
• log converting the absolute-value electrical signal to obtain a decaying data signal which is a logarithmic value of the absolute-value electrical signal;
• generating an adjustable reference signal upon the termination of the electrical signal;
• processing the adjustable reference signal to produce a variable reference decay rate electrical signal;
• adjusting the adjustable reference signal until the variable reference decay rate electrical signal coincides with the decaying data electrical signal whereby the electrical decay rate characteristics of the circuit may be determined from the value of the adjusted reference signal.

The method of determining sound decay rate of an enclosure which comprises the steps of:

• exciting the enclosure with sound at a first selected point;
• terminating the excitation sound imposed on the enclosure;
• converting the sound decay of the enclosure due to the termination of the excitation sound into an electrical input signal at a second selected point;
• absolute valuing the electrical input signal to obtain an absolute-value electrical signal;
• log converting the absolute-value electrical signal to obtain a decaying data electrical signal which is a logarithmic value of the absolute-value signal;
• generating an adjustable reference signal upon the termination of the excitation sound;
• processing the adjustable reference signal to produce a variable reference decay rate electrical signal;
• adjusting the reference signal to produce a reference decay rate electrical signal which coincides with the decaying data electrical signal whereby the decay rate characteristics of the enclosure may be determined from the value of the adjusted reference signal.

The method of determining the exponential vibration decay rate of a structure which comprises the steps of:

• exciting the structure with vibration at a first selected point;
• terminating the excitation vibration imposed on the structure;
• converting the vibration decay of the structure due to the termination of the excitation vibration into an electrical input signal at a second selected point;
• absolute valuing the electrical input signal to obtain an absolute-value electrical signal;
• log converting the absolute-value electrical signal to obtain a decaying electrical signal which is a logarithmic valve of the absolute value signal;
• generating an adjustable reference signal upon the termination of the exciting vibration;
• processing the adjustable reference signal to produce a variable reference decay rate electrical signal;
• adjusting the reference signal to produce a reference decay rate electrical signal which coincides with the decaying data electrical signal whereby the vibration decay rate of the structure may be determined from the value of the adjusted reference signal.