Digital transmitter

Adding digital transmitter calibration factors to transmit a controlled variable in % ... 

Some digital transmitters have a pH span adjustment defined as follows ... 

The ultrasound system should have more independent channels and allow the transmitter pulse to be individually adjustable in width and amplitude, and an increased frequency range for the logarithmic amplifier was desired. The digitization should be improved both with respect to sampling rate and resolution. 

C = transmitter D = signal transmission E = analogue-to-digital converter(A/D) F = digital-to-analogue converter (D/A) ... 

In order to meet their initial requirements, several manufacturers have developed digital communications capabilities for communicating with smart transmitters. These can be used either in addition to or in lieu of the 4-20 milliamp signal. Although most manufacturers release enough information on their communications features to permit another manufacturer to provide compatible instruments (and in some cases provide an open communication standard), the communications cap ihty provided by a manufacturer may be proprietaiy. 

Coupling digital controls with networking technology permits information to be passed from level-to-level within a corporation at high rates of speed. This technology is capable of presenting the measured variable brom a flow transmitter installed in a plant in a remote location anywhere in the world to the company headquarters in less than a second. 

Digital Field Communications An increasing number of valve-mounted devices are available that support digital communications in addition to, or in place of, the traditional 4—20 mA current signal. These control-valve devices have increased functionality, resulting in reduced setup time, improved control, combined functionality of traditionally separate devices, and control-valve diagnostic capabihty. Digital communications also allow the control system to become completely distributed where, for example, the process PID controller could reside in the valve positioner or in the process transmitter. 

The battery-powered electronics acquire and store sonic waveforms. Under the control of a downhole microprocessor, the transmitter is fired, and four receiver waveforms are simultaneously digitized at 12 bits and added to a signal stack. The transmitter firing is done in bursts at the rate of 10 Hz, which allows minimum movement while stacking. 

Figure 2.2.9 shows a typical portable MRI console. The MRI console consists of a digital system (PC), MRI transceiver, 3 channel gradient driver and rf transmitter. 

In this expression, x is the independent variable of measurement, whether it be wavelength, wave number, or other parameter. The quantity UM(x) is the flux, as measured by the spectrometer, after it has passed through the absorbing sample. The quantity BM(x) represents the flux that has passed over an identical path but in the absence of an absorbing sample. The term Dm(x) represents any additive offsets that might be introduced by stray flux, errors in electronic amplification and digital conversion, or other causes. We call the resulting measured transmittance TM(x). 

Less expensive instruments give a direct readout of absorbance and/or transmittance in analog or digital form. These instruments are suitable for single-wavelength measurements however, if a scan of absorbance vs. wavelength (Figure 5.4) is desired, some type of device to display the spectrum must be available. 

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