| 摘要 |
A high resolution digital test instrument is provided which has particular, although not exclusive, utility in testing the inductance and inductance changes of wire loops which are embedded in roadways and which are incorporated into vehicle presence sensing systems. The test instrument provides a simple means for determining the sensitivity of the loop to vehicles of different sizes; as well as for determining whether the loop inductance is susceptible to drift, whether open circuit or short circuit conditions exist, whether there are intermittent circuit breaks, and a variety of other conditions. The instrument includes frequency counting circuitry which counts, on a selected time basis, the output frequency of a Class C oscillator. The frequency of the oscillator is determined by the combined loop and lead-in inductance together with the lead capacitance of the loop circuit being tested. The pulses generated by the oscillator are cyclically counted over a selected time period, and the results are displayed as a frequency measurement.
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