Low pass filters

The Chebyshev low pass filter shown in Fig. 3.53 was constructed in all three simulators as well as in hardware. The circuit values in Fig. 3.53 were used in all cases. A MathCAD file that was used to design the Chebyshev low pass filter is located in the Chebyshev directory of the CD, which accompanies this book. This file can easily be modified to accommodate designs that use a Sallen-Key circuit for each stage of the filter (see Fig. 3.54). The schematic of the circuit that was used in each simulator is shown in Fig. 3.53. The measured breadboard results are shown in Fig. 3.55, and the simulated results are shown in Figs. 3.56, 3.57, and 3.58. 

Simulator File name Maximum attenuation Run time (s) 

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The obtained signal is filtered with a low-pass filter having the cut-off frequency of 5Hz and a slope of 6 dB/octave. Since we are working with e.m.f modulus, the phase lag does not influence the control. 

The image generated by the image intensifier was found to be very sensitive to noise and to reduce this effect, a low pass filter was included. This filter has greatly improved the final 3D... 

In order to get an extremely high resolution and a small dead zone" (after the transmitter pulse) single amplifier states must have a bandwidth up to 90 MHz ( ), and a total bandwidth of 35 MHz (-3 dB) can be reached (HILL-SCAN 3010HF). High- and low-pass filters can be combined to band-passes and provide optimal A-scans. All parameters are controlled by software. 

The HILL-SCAN 30XX boards enable ultrasonic inspections from 50 kHz (concrete inspections) to 35 MHz (inspection of thin layers) with a signal to noise ratio up to 60 dB. The gain setting range of the receiver is 106 dB. High- and low pass filters in the receiver can be combined to band-passes, so that optimal A-scans are displayed. 

After the signal emerges from the lock-m amplifier it still contains a considerable amount of noise. Most of the noise contributions to the signal can be eliminated by passing the signal tlirough a low-pass filter. The filter tune constant is a measure of the cutoff frequency of the filter. If accurate linewidth and g-factor... 

The resolution of the analog I/O channels of the controller vaiy somewhat, with 12-bit and 14-bit conversions quite common. Sample rates for the majority of the constant sample rate controllers range from I to 10 samples/second. Hard-wired single-pole, low-pass filters are installed on the analog inputs to the controller to protect the sampler from aliasing errors. 

Low Pass Filter Two chambers are connected by a choke tube or pipe. At least one of the chambers should be connected to the compressor cylinder. Figures 13-lB and 13-lC. Melton offers a standardized, simple design that is useful for some types of package compressor arrangement. 

Figure 13-1B. Low pass filter. Two equal (usually) surge chambers connected by a choke-tube. This type of fii-ter does not have to be a common vessei as shown here. See Figure 13-1C.

Compressor Suction and Discharge Drums Design Method—Acoustic Low Pass Filters... 

After the anticipated disturbing frequencies have been determined, it is necessary to begin the sizing of the filter system. The cutoff frequency should be set at least one cycle per second below the lowest frequency to be filtered. The base frequency is determined from compressor speed and should be determined at the lowest anticipated compressor speed for variable-speed compressors. The following equation is used to determine cut-off frequency for a low-pass filter ... 

Melton, J. E, Low-Pass Filter Design for Gas Compressors Reduces Pulsation, Oil and GasJournal, p. 149, June 23, (1980). 

The signal before digitization is sufficiently low-pass filtered so that noise is below 1 mV at the digital volt meter (DVM). 

Low-pass filter A filter used for selecting coherence orders >/>. 

The main problem has been a methodological one. The patch clamp analysis of single channels views the world of channels through a very small analytical window [10]. A single channel event (opening) needs to be sufficiently long-lived and sufficiently large to be picked up within the current noise band under optimized conditions, and with the low-pass filter set to say 2 kHz. The open time needs to be close to a millisecond and the current amplitude close to 0.5 pA to permit detection. 

Fig. 40.28. Effect of a low-pass filter, (a) original Gaussian signal, (b) FT of (a), (c) Signal (a) filtered with V() = 10. (d) Signal (a) filtered with Vo = 20.

Fig. 40.32. Deconvolution (result in solid line) of a Gaussian peak (dashed line) for peak broadening ((M i/,)prf/(H vi)G = 1). (a) Without noise, (b) With coloured noise (A((0,1%), Tx = 1.5) inverse filter in combination with a low-pass filter, (c) With coloured noise (A (0,1 %), Ta = 1.5) inverse filter without low-pass filter.

The shaip cutoff at the limits -i and t, as illustrated by the boxcar function, often occurs in the frequency domain. In this case the boxcar acts as a low-pass filter in applications in electronics. All frequencies below [l] areunaltgEed, in this ideal case all higher ones are suppressed. 

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