(a) Digital signal Analog signal input Binary output 94 Chapter 5 Basics of PLC Programming • The valve is initially open 100%. • As the fluid level in the tank approaches the level preset point, the processor modifies the output to degrade, closing the valve to 90%, 80%, etc., adjusting the valve to maintain a set point. may produce significant errors as the signal is processed. Analog signals must be coded into digital signals before they can be processed by the PLC. An analog-to-digital converter (ADC) converts analog input signals to digital signals. A digital-to-analog converter (DAC) converts digital output signals to analog signals. Analog applications are present in many forms. Figure 5-54 shows a typical use of analog control for a tank-filling process. The operation of the circuit can be summarized as follows: • The processor controls the amount of fluid placed in a holding tank by adjusting the percentage of the valve opening. Analog output Valve Level sensor Processor Analog input PLC Analog I/O Module Level Preset Point Figure 5-54 Analog control for a tank-filling process. Figure 5-53 Digital and analog signals. 1 0 0 1 1 ADC (b) Analog signal (c) Analog-to-digital converter (ADC)
Petruzella_ProgrammableLogicControllers__5e
To see the actual publication please follow the link above