Digital-electronic control mechanisms

Digital-electronic control mechanisms and apph-ances are the mainstays of modern industry, mainly because of the precision with which processes and... 

Another essential component in the functioning of automated processes and servomechanisms is the feedback control systems that provide self-regulation and auto-adjustment of the overall system. Feedback control systems may be pneumatic, hydraulic, mechanical, or electrical in nature. Electrical feedback may be analogue in form, although digital electronic feedback methods provide the most versatile method of output sensing for input feedback to digital electronic control systems. 

Digital microfluidic architecture is under software-driven electronic control, eliminating the need for mechanical tubes, pumps, and valves that are required for continuous-flow systems. The compatibility of each chemical substance with the electro-wetting platform must be determined initially. Compatibility issues include the following (1) Does the liquid s viscosity and surface tension allow for droplet dispensing and transport by electrowetting ... 

Traditionally controllers were complex mechanical devices operated pneumatically and many pneumatic controllers still exist in industry. More recently, analogue electronic controllers have been used but these are now superseded by various digital control devices (see section 7.7.6). Details of controller hardware operation are given by Johnson. The controller compares the signal representing the measured value with the setpoint (i.e. desired) value of the variable. The control action depends on the control mode selected for the controller. 

Servomechanisms used in automated systems check and monitor system parameters and adjust operating conditions to maintain the desired system output. The principles upon which they operate can range from crude mechanical levers to sophisticated and highly accurate digital electronic-measurement devices. All employ the principle of feedback to control or regulate the corresponding process that is in operation. 

Mossbauer spectra are usually recorded in transmission geometry, whereby the sample, representing the absorber, contains the stable Mossbauer isotope, i.e., it is not radioactive. A scheme of a typical spectrometer setup is depicted in Fig. 3.1. The radioactive Mossbauer source is attached to the electro-mechanical velocity transducer, or Mossbauer drive, which is moved in a controlled manner for the modulation of the emitted y-radiation by the Doppler effect. The Mossbauer drive is powered by the electronic drive control unit according to a reference voltage (Fr), provided by the digital function generator. Most Mossbauer spectrometers are operated in constant-acceleration mode, in which the drive velocity is linearly swept up and down, either in a saw-tooth or in a triangular mode. In either case. 

One of the key controls for audit trails is the linking of the electronic record with the audit trail. It must not be possible to modify audit trails access rights to audit trial information must be limited to print and/or read only. The combination of authentication, digital certificates, encryption and ACLs, provides the technical mechanisms needed to control the access to audit trail files. 

Digital computers were first built at Harvard University (Aiken s53 Automatic Sequence Controlled Calculator, Mark I, 1939-1944) and at the University of Pennsylvania by Eckert54 and Mauchly55 (Electronic Numerical Integrator and Calculator, ENIAC, 1946) they used vacuum tubes instead of the cumbersome and slow mechanical switches. ENIAC morphed into an Eckert-Mauchly design of BINAC, which was sold to Remington Rand and became Univac I. 

Already in the mid-1960s, there was rich potential of applying such experiments to the determination of concentrations but even more to the elucidation of reaction mechanisms and kinetics coupled to electron transfer at an electrode was recognized. Today the resulting Knear sweep or cyclic voltammetries are employed as simple, flexible routine techniques in particular as sophisticated means to solve chemical and mechanistic problems. The combination with computer control, ultramicroelectrodes, and digital simulation has further contributed to their success. 

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