Digital Multimeter

The HP 3457A is a versatile digital multimeter. It can measure DC voltage, AC voltage, AC and DC currents and the resistance over a wide range of values. The math operation facility can manipulate or modify a set of measurements before display. The STAT operation can perform up to five running calculations on the present series of measurements and stores the results. It evaluates the standard deviation, time-mean, number of samples, upper reading and lower reading. These facilities can be used to measure mean temperature and the RMS value of the temperature fluctuations with the constant current mode of the hotwire anemometer.

Spectrum Analyzer

The digital spectrum analyzer used in the present work (Advantest R9211E) employs the Fast Fourier transform (FFT) algorithm for determining the signal statistics. Wide band as well as high sensitivity measurements can be performed in the frequency range of 10 mHz-100 kHz and input voltages of 1 Vrms-31:6 Vrms. The analyzer has four different modes of operation. The waveform and spectrum modes are important ones generally used in turbulence measurement. In waveform mode the spectrum analyzer does on-line measurement of the time signal, followed by calculations of the histogram (PDF), autocorrelation and cross-correlation functions. In the spectrum mode, it measures power spectrum and the complex spectrum. It has various options such as Math, Setup, Device and Copy. The Math menu does arithmetic operations between two arrays and integration and differentiation of an array. This facility can be used for the measurement of average of product of two-wire signals. All traces shown on the screen can be stored on a floppy and processed whenever required. These facilities have helped in standardizing the measuring procedures linked to the HWA.