Noise equivalent test

The basic test for any IR detector includes measurement of the output (DC or AC) and noise, as well as the calculations of responsivity and the composite figures of merit noise-equivalent irradiance (NEI), noise-equivalent power (NEP), or D. If an assembly includes only a few elements, and if only a few assemblies are to be tested, it is reasonable to make these measurements with simple voltmeters or wave analyzers, and report the results in a tabular form. Higher volume production requires automated data acquisition equipment and graphical and statistical reporting - much like the testing of FPAs. 

Consider the requirement to test a 0.25-in.-long array of PV InSb detectors at a background of 5 X 10 photons/(cm s). To determine whether we will have adequate signal and signal-to-noise ratios, we will need the expected responsivity and noise-equivalent irradiance (NEI) values for the detector. If these are not available from previous tests, we can predict them using the methods of Chapter 4. For our example, assume that the responsivity is 15 x 10 V/[photon/(cm s)] and NEI is 2 X 10 photons/(cm s). 

As indicated before, the maximum entropy approach does not process the measurements themselves. Instead, it reconstructs the data by repeatedly taking revised trial data (e.g. a spectrum or chromatogram), which are artificially corrupted with measurement noise and blur. This corrupted trial spectrum is thereafter compared with the measured spectrum by a x -test. From all accepted spectra the maximum entropy approach selects that spectrum, f with minimal structure (which is equivalent to maximum entropy). The maximum entropy approach applied for noise elimination consists of the following steps ... 

Sensitivity of the instrument, which refers to the system response to small changes in concentration, is determined by the signal to noise ratio (SNR) of the measurement, as well as, the concentration slope. The SNR of each measurement may be considerably smaller than variation between measurements made on different occasions. Measurements of concentration from absolute fluorescent intensity (O) are possible provided that the calibration of the instrument remains unchanged. Reliable fluorescent intensity measurements across different instruments or from repeated measurements with the same instrument are possible only if the above factors can either be eradicated from consideration or be controlled with an experiment independent calibration coefficient. One effective solution proposed the development of a set of standard reference materials (SRMs) for use with identical instruments [9]. Thus, for a particular instrument, the concentration of a test solution can be expressed as a ratio of the fluorescent counts for the test and SRM. Subsequently, it was recommended that the concentration of the test solution could be expressed in molecular equivalent soluble fluorophore (MESF) units. This protocol was developed with respect to the use of flow c) tometers, which can be operated close to the ideal experimental conditions. Despite this, measurements of fluorescent intensity in terms of MESF units stiU have problems, as most fluorescence-based instruments cannot be guaranteed to operate under the same conditions from day to day. 

The noise of the charge-sensitive preamplifier depends on three parameters the noise of the input FET, the input capacitance C , and the resistance connected to the input. The noise can be determined by injecting a charge Q, equivalent to E, into the preamplifier and measuring the amplitude of the generated pulse. Commercial preamplifiers are provided with a test input for that purpose. In general, the noise expressed as the width (keV) of a Gaussian distribution increases as input capacitance increases (Fig. 10.36). 

In preliminary tests performed on the X-ray camera a subarray of 5x5 strips was used to obtain a 25 pixel detector each strip coupled to a hybrid charge sensitive preamplifier (CSP), model CS 507, produced by Clear Pulse (Tokyo) in a modified version with external input FET and a resistive feedback loop CSP is characterised by an equivalent noise (r.m.s.) of about 1 keV. Pulses from CSP... 

System noise temperature The equivalent temperature of a passive device yielding the same thermal noise power per unit bandwidth as the system under test. 

The plot in Fig. 18.45(a) has a high distribution of samples at 0 and avery small number of points occurring at other codes. The distribution is Gaussian, which is what is expected from random noise. From the plot, the noise level is within 3 LSB. The plot in Fig. 18.45(b) is a very noisy DAQ product, which does not have the expected distribution and has a noise greater than 20 LSB, with many samples occurring at points other than the expected value. For the DAQ product in Fig. 18.45(b), the tests were run with an input range of 10 V and a gain of 10. Therefore, 1 LSB = 31 frV, thus a noise level of 20 LSB is equivalent to 620 /xV of noise. 

The optimized eonditions were applied to standard solutions of PAHs eontaining 5.0 ng/mL of eaeh eompound. The pereentages of PAHs reeovered were established by eomparing the peak areas obtained for eaeh PAH with those obtained from the direet injection of 20 pL of standard solutions eontaining an equivalent amount of the analytes. As listed in Table 2 the analyte reeoveries ranged from 87 to 112 %. The intra- and inter-day reproducibilities were also tested the RSD values encountered are listed in Table 3. The limits of detection (LODs), established as the concentration required to generate a signal-to-noise ratio of 3, were < 1 ng/mL (see Table 4). 

A comparative analysis of TPV vs. EPDM with respect to noise reduetion is examined for automotive weatherstrip body sealing apphcations. Specifically, EPDM sponge is eonqjared with JyFlex , a TPV compound of equivalent stiflhess. The study is performed using multiple acoustic tests (road and component), supported by FEA analysis as a diagnostic tool [1],... 

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