Constant Sampling Time Research Articles

Continuous monitoring of ozone in air by reflectiometry

A porous cellulose tape containing silica gel as an absorbent and impregnated with a processing solution that includes potassium iodide, starch, buffer solution, glycerin and methanol was developed for the detection of ozone in air. When the sample is passed through the tape, ozone is absorbed on the surface of the tape, and reacts with potassium iodide to form a colour stain. The intensity of the colour stain is proportional to the concentration of ozone at a constant sampling time and flow rate, and was recorded by measuring the intensity of reflected light (555 nm). The detection limit was 5 ppb of ozone with a sampling time of 60 s and a flow rate of 400 ml min–1. The sensitivity of the tape could be maintained for at least 1 month when stored in a desiccator. Reproducibility tests showed that the relative standard deviations of the response (n= 10) were 2.4 and 4.2% for 0.2 and 0.05 ppm of ozone, respectively. No interference was observed from ethanol (1 vol.-%), acetone (1 vol.-%), trichloroethylene (1 vol.-%), carbon dioxide (4.9 vol.-%), carbon monoxide (100 ppm), sulfur dioxide (30 ppm), hydrogen chloride gas (5 ppm), acetylene (120 ppm) or ammonia (40 ppm). The relative intensities of chlorine, nitrogen dioxide and hydrogen peroxide gas were 25, 2 and 1.1% of that of ozone, respectively.

Development of a monitoring tape for phosgene in air

A porous cellulose tape impregnated with a processing solution that includes 4- p-nitroben-zylpyridine, N-benzylaniline and methanol is a highly sensitive means of detecting phosgene and maintains stable sensitivity for at least three months in air in a desiccator. When the sample including phosgene was passed through the tape, the color of tape changed to red. The degree of color change was proportional to the concentration of phosgene at a constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). The detection limit was 6 ppb for phosgene with a sampling time of 60 sec and a flow rate of 400 ml/min. Reproducibility tests showed that the relative standard deviation of response ( n = 10) was 2.6% for 0.2 ppm phosgene. No interference was observed from ethanol (1 vol.%), trichloroethylene (1 vol.%), acetone (1 vol.%), carbon dioxide (4.9 vol.%), carbon monoxide (100 ppm), nitrogen dioxide (100 ppm), sulfur dioxide (50 ppm), hydrogen chloride gas (5 ppm), chlorine (3 ppm), acetic acid gas (24 ppm), ammonia (40 ppm), or benzyl chloride (20 ppm).

Development of a monitoring tape for ammonia gas in air by fluorescence detection

A porous cellulose tape impregnated with a processing solution that includes Eosine Bluish, p-toluenesulfonic acid, glycerin and methanol is a highly sensitive means of detecting ammonia gas in air. The monitoring tape for ammonia gas is based on the change in fluorescence intensity of a pH indicator (Eosine Bluish) put on the tape. Exposure to the sample including ammonia increased the pH of a solution existing in the tape. The compound produced with ammonia gas shows an excitation maximum at 460 nm and a fluorescence maximum at 550 nm. The degree of the change in fluorescence intensity was proportional to the concentration of ammonia gas at a constant sampling time and flow-rate. The tape could detect 0.1 ppm of ammonia gas at a sampling time of 40 s and a flow rate of 400 ml/min. No interference was observed from carbon monoxide (100 ppm), carbon dioxide (4.9%, v/v), nitrogen dioxide (100 ppm), sulfur dioxide (50 ppm), acetone (1%, v/v), ethanol (1%, v/v), trichloroethylene (1%, v/v), chlorine (3 ppm), or hydrogen chloride gas (5 ppm).

Development of a Monitoring Tape for Formaldehyde Using Hydroxylamine Sulfate and Methyl Yellow

A porous cellulose tape impregnated with a coloring solution that includes hydroxylamine sulfate, Methyl Yellow (pH indicator; pH 2.9-4,0, red—yellow), glycerin and methanol has been developed to provide a highly sensitive means of detecting formaldehyde gas. Formaldehyde reacts with hydroxylamine sulfate to produce sulfuric acid. When a sample including formaldehyde was passed through the tape, the color of the tape changed from yellow to red. The degree of color change was proportional to the concentration of formaldehyde at a constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). No interference was observed from carbon monoxide (100 ppm), nitrogen monoxide (50 ppm), nitrogen dioxide (105 ppm), carbon dioxide (4,9%), hydrogen (100%), hydrogen sulfide (32 ppm), or hydrogen fluoride (6 ppm). The response of acetaldehyde and propionaldehyde were one fortieth and three-hundredths of that of formaldehyde, respectively, Reproducibility tests showed that the relative standard deviation of relative intensity (n=10) was 3.4% for 4 ppm formaldehyde. The detection limit was 0.1 ppm for formaldehyde at a sampling time of 5 min and a flow rate of 400 ml/min.

Development of a monitoring tape for ammonia gas in air using Rose Bengal

A porous cellulose tape impregnated with a processing solution containing Rose Bengal, p–toluenesulfonic acid, glycerin and methanol was found to be a highly sensitive means of detecting ammonia gas, and is stable on exposure to air. When the sample including ammonia was passed through the tape, the colour of the tape changed to red. The extent of the colour change was proportional to the concentration of ammonia gas at a constant sampling time and flow rate and was recorded by measuring the intensity of the reflected light (555 nm). The tape could be used to detect down to 0.1 ppm of ammonia gas with a sampling time of 60 s and a flow rate of 400 cm3 min–1. Reproducibility tests showed that the relative standard deviation of the relative intensity (n= 10) was 2.8% for 0.6 ppm of ammonia. No interference was observed from ethanol (1 vol.-%), trichloroethylene (1 vol.-%), acetone (1 vol.-%), carbon dioxide (4.9 vol.-%), nitrogen dioxide (100 ppm), sulfur dioxide (50 ppm), acetic acid gas (24 ppm) or hydrogen chloride gas (5 ppm). The relative intensities of ethanolamine and triethylamine were 1.04 and 1.6 times greater, respectively, than that of ammonia.

Development of a monitoring tape for hydrogen chloride gas using Metanil Yellow

A porous cellulose tape impregnated with a processing solution that includes a pH indicator (Metanil Yellow; pH 1.2–2.3, red-yellow), glycerin and methanol is a highly sensitive means of detecting hydrogen chloride gas and is stable on exposure to light. When the sample including hydrogen chloride was passed through the tape, the colour of the tape changed from yellow to red. The degree of colour change was proportional to the concentration of hydrogen chloride gas at a constant sampling time and flow rate. The degree of colour change could be recorded by measuring the intensity of reflected light (555 nm). The detection limit was 0.1 ppm for hydrogen chloride gas with a sampling time of 40 s and a flow rate of 400 ml min–1. No interference was observed from ethanol (1 vol.-%), propan-2-oI (1 vol.-%), acetone (1 vol.-%), carbon dioxide (4.9 vol.-%), nitrogen dioxide (100 ppm), sulfur dioxide (50 ppm), acetic acid gas (24 ppm) or hydrogen fluoride gas (6 ppm). The relative intensities of hydrogen bromide and gaseous nitric acid were one quarter and one eighth of that of hydrogen chloride, respectively.

DMA transfer method for wide-range speed and frequency measurement

A frequency measurement method based on both pulse counting and time measurement during a constant sampling time is presented. The content of a free-running timer is transferred by a direct memory access (DMA) to a memory location after each rising edge of an input pulse, so the DMA transfer counter serves as a pulse counter. Several sources of measurement errors are discussed in detail. The DMA method is suitable for real-time speed control system with an integrated DMA controller. >

Speed measurement using the improved DMA transfer method

A wide-range speed measurement method using the direct memory access (DMA) transfer of a content of the timer to the memory is presented. The DMA method is based on both pulse counting and time measurement during the constant sampling time. The hardware configuration and algorithms for a microcontroller implementation are also presented. The proposed method is suitable in systems using microcontrollers with integrated DMA controller and timers. Limitations and sources of errors are discussed in detail.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Digitization Noise in Power Spectral Analysis

Abstract It is well-known that the digitization noise variance is Δ2/12 for a continuous time series sampled with the signal resolution Δ. It is also generally accepted that this variance often has a white-power spectral density. We have examined in detail under which circumstances this is the case for turbulent media and found that for a joint Gaussian signal x(t) with variance σ2{x} and a Taylor microscale λ the digitization noise is indeed white if (Δt/λ)(σ{x}/Δ) ≳ t, where Δt is the constant sampling time. Otherwise, the digitization noise tends to be concentrated at lower frequencies. White spectral noise with known variance is easily removed, so from a practical point of view Δt should not be too small.