The present invention relates generally to a device for measuring and memorizing a sensed value. More particularly, the invention relates to a circuit connected to a sensor to measure the maximum values detected by the sensor.
Oftentimes it is advantageous to measure the forces applied to the components of a dynamic system. In some systems, such as those which handle and transport freight, the forces usually are random. In such cases it may be advantageous to know the maximum force applied to the system or to its components during a predetermined period of time. In other systems, forces may be repetitive causing vibrations. Such vibrations may vary in magnitude and frequency. Once again, the magnitude of such vibrations may be of interest.
Various apparatuses for the recording of such information relating to force or vibration are known. For example, inertia devices utilize the concept of single preset trip points. Inertia devices tend to be mechanical, rather than electrical, and are often bulky. Furthermore, inertia devices offer limited information, as each triggering level requires a separate inertia device. Because of their large size and inability to measure various triggering levels, it often is impossible to use the prior art inertia devices in situations where space is limited. In addition, because the prior art devices usually are mechanical, they also are subject to malfunction if excessive forces are encountered.
Alternatively, composite data acquisition systems may be used to record force and vibrational information. Such systems measure and record data electronically, rather than mechanically. They are relatively expensive, are often bulky, and require playback and analysis from system memory devices. Also, the electrical power requirements for composite data acquisition systems are relatively high. Thus, where space is limited, or where the monitoring period is long, these types of devices are impractical.
One example of a composite data acquisition system may be found in U.S. Pat. No. 4,654,634. U.S. Pat. No. 4,654,634 discloses an apparatus for processing a sequence of digital data values with the object of increasing the ratio of signal-to-quantization noise of a digitized repetitive signal in order to enhance resolution. An algorithm for removing noise from a data string is included. The apparatus receives an input analog signal and applies it to a conventional analog-to-digital converter. The digitized waveform data from the analog-to-digital converter is stored in memory and processed according to the algorithm.
Similarly, U.S. Pat. No. 4,856,318 discloses an apparatus for measuring the G forces which occur during an impact and stores the maximum measured value. The impact, or deceleration, force is measured by means of a transducer which may be an accelerometer, or other type of transducer such as a forced balance type, strain gauge, or load cell. Voltage output from the transducer is amplified, its peak value detected, and sent to an analog-to-digital convertor. The output of the analog-to-digital convertor is sent to a display. The operational amplifier disclosed in U.S. Pat. No. 4,856,318 is expressly designed to act as a voltage follower and current amplifier, so that the voltage curve recorded for an impact or deceleration is recorded and then maintained at its peak value. A continuous power source is required for operation, because the display means of U.S. Pat. No. 4,856,318 requires a current flow, and because the voltage signal, which goes to the display and which reflects the peak impact force, must be maintained. Without continuous power, the display of the measured force would disappear, as no current indicating a value would be present. Without the operational amplifier disclosed in U.S. Pat. No. 4,856,318, a peak voltage would reflect an impact but the circuitry would allow the voltage to drop to zero once the apparatus had decelerated to zero velocity. Again, no display would be possible.
None of the prior art devices permit the recording of the maximum acceleration to which an object is subjected by means of a device which does not require power, and which may be visually read at any time following the measuring period. Consequently, if there is a power outage, or if the measurement period is excessively long, resulting in battery failure, the prior art devices will not save the maximum values.