Input circuit

Figure 3-54 Typical ac and dc input filter circuits (a) ac input filter circuit for a single or universal input power supply (common-mode EMI filter shown) (b) a voltage doubling ac input circuit for 110V and 220V ac inputs (c) single dc bus input filter.

Instruments with a balanced input circuit are available for measurements where both input terminals are normally at a potential other than earth. Further problems arise due to common-mode interference arising from the presence of multiple earth loops in the circuits. In these cases the instrument may need to be isolated from the mains earth. Finally, high-frequency instruments, unless properly screened, may be subject to radiated electromagnetic interference arising from strong external fields. 

The EDISEN- method allow the compensation of static input capacities Cm 200 pF only by a resistor Rc vs. GND at the input of the Ee102 . This resistor discharge during every sampling cycle a constant quota Cc of the sensor capacity C N.Xo, so the input circuit of the IC has not to discharge Cc. 

Reliable operation of the system is ensured by the ability of the Detonator Module to continuously monitor the input circuits and the detonator output circuits, to supervise the coil and wiring of the solenoid valve or squib, as well as to perform a self-test procedure to allow verification of other critical circuits. 

Power for the control panel should be provided with a suitable uninterrupted power supply (UPS). The panel will provide a DC current to field detectors. This power will enable the panel to monitor all input circuits, output circuits, and trouble signals within the detectors, such as shorts, ground faults, and detector disconnects. It will also provide an AC powering signal to field output devices. All output circuits should be similarly supervised for trouble. An example alarm and detection control panel is shown in Figure 7-18. 

Cr Cr- l Capacitance of amplifier feedback circuit in hard-wired system generating PI action Capacitance of voltage input circuit in hard-wired system generating PD action i, etc. Elements in Routh-Hurwitz array F (farad) F (farad) M L-2T[Pg.731]

The key element of this amplifier is a phase sensitive detector. It demodulates the frequency of interest and produces a signal, which is a function of the phase angle of the input signal. The input circuit of a lock-in amplifier is properly adjusted to achieve the ability of the devise to recover signals that are overloaded with -> noise. 

By analyzing separately a single-input circuit, superposition allows us to analyze linear circuits with more than one independent source. For example, Figure... 

The main compromise within all circuit designs is the sensitivity. The signal from the sensor at minimal speed has to exceed Utrigger= 35 V with a tolerance of A Utrigg, = 7 mV. To gain more input signal the passive part of the input circuit has to be designed carefully. Typical values are shown in Fig. 7.9.3 and Fig. 7.9.4. 

The input circuit of an ECU for active wheel-speed sensors has to provide... 

The basic corrosion instrumentation requirement involves the measurement of potential difference. Currents are measured as the potential across a resistor (R ) as shown in Fig. 1.2, where the potential difference is again determined with an operational amplifier. More sophisticated measurements such as polarisation characteristics and zero resistance ammetry involve the use of potentiostats which again use operational amplifiers in a differential mode. The potentiostat is an instrument for maintaining the potential of an electrode under test at a fixed potential compared with a reference cell, and the basic circuit is similar to that for potential measurement with the earth return circuit broken to an auxiliary electrode in the electrochemical cell. Such a circuit would maintain the potential of the test electrode at the reference cell potential. This potential may be varied by inserting a variable potential source (V ) in the input circuit as shown in Fig. 1.3. The actual cell potential (V ) and the current required to polarise the test electrode to this potential may be measured using the basic circuits shown in Figs. 1.1 and 1.2 respectively. 

Input Circuit Input Module Common Circuitry X p Main Processor Common Circuitry Output Module Common ( rcuitry )p Output Circuit ... 

Each "input circuit" contains the electronics required to read one sensor input. The "input module" subsystem includes all the electronics common to all input channels on a module. The "main processor" encompasses all components common to any PLC function. The "output module" subsystem contains all components common to the output channels on one module. The "output circuit" consists of the components needed to interface to one final elements device. 

OR the analog input circuit of the safety PLC fails dangerously. 

The sensor subsystem will also initiate a trip if either of the pressure transmitters (Gate G12) indicates an overpressure. The individual pressure transmitter failures are represented by Gates G18 and G19. G18 indicates that any dangerous failure of a pressure transmitter, its associated impulse line or the associated input circuit of the safety PLC will cause a gate failure. The PFD can be represented by approximate simplified equations. For Gate G18 ... 

Gate 6 accounts for the pressure switch, the impulse line and the connected safety PLC digital input circuit. The simplified approximation for gate 6, PFD is ... 

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