In this paper a dual-channel pseudo-random signal generator is presented for the calibration of cross-correlators such as cross-correlation-based flowmeters. In this signal generator, the two channels have completely identical hardware structures so that they generate two identical sequences of pseudo-random signals to simulate two signals obtained from the upstream and downstream sensors of a cross-correlator, respectively. Special control strategies both in hardware and software have been implemented in such a way that the control error of time delay between the two channels can be reduced to less than a microsecond. The shift frequency and sequence length of each signal channel and the time delay between the two channels can be adjusted in wide ranges to satisfy majority of practical requirements. The start/stop control of each channel of signal and adjustments of the above parameters are carried out by a micro-controller with a dedicated keyboard and an LED display. The instrument has been evaluated by using a digital storage oscilloscope (Tektronix TDS220). Results obtained show that the control precision of the time delay is better than 0.05% when the time delay is 1ms and over. Comparison with an E+H commercial noise signal generator and an MP noise generator shows that the error of the new generator is much smaller than those of the other two.

The oscillation frequency of a combustion flame that is directly measured from the spectrum of a flame signal often depends on the level of white noise in the signal and the sampling rate. As long as the signal contains white noise, the "true" value of the oscillation frequency will never be known. However, the effect of the white noise and sampling rate on oscillation frequency measurement can be minimized by incorporating a new computing algorithm into the measurement software. The algorithm is developed by making two improvements to the original direct calculation method. One of the improvements is the wavelet-based prefiltering of the raw flame signal. The other is an adaptive truncation of the spectrum of the filtered signal. The improved algorithm is evaluated by using a flame signal that is acquired from an industrial-scale combustion test facility. Results that are obtained are reported and discussed.

In this paper, we present a new flame monitor that uses three photovoltaic cells covering the ultraviolet (UV), visible, and infrared (IR) spectral bands. A gain-adjustable amplifier is incorporated into the monitor so that it is applicable to the coal, oil, or gas-fired flames. Self-checking of the monitor is implemented through cross correlation of the signals from the three cells, and hence, no additional self-checking hardware is required. Both the oscillation frequency and the brightness of the flame are used to monitor flame stability and to detect flame presence as well as sighting-tube blockage. Unlike conventional single-cell flame detectors, the new multicell devices can still be in operation before being repaired, after a cell-failure alarm has gone off. Experiments were carried out on an industrial-scale combustion test facility in order to demonstrate the operability and efficacy of the new flame monitor.

Multielectrode inductance flowmeters were brought forward toward coping with the problem of flow regime dependence of traditional inductance flowmeters. Design of the electrode array is of great importance in construction of a multielectrode inductance flowmeter. The number of electrodes and electrode size are two primary parameters of the array. In this paper, the governing equation of the multielectrode inductance flowmeter was solved using a finite difference method. The chord measurement method was employed to analyze the influences of both parameters on the estimation of mean flow velocity. Based on the quantitative calculation of the influences of the two parameters on measurement error, criteria for the design of the electrode array were presented.