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Fundamentals of Analog Control in MicroLogix Programmable Controllers**

This guide explains the basics of analog signals and their significance in control systems using MicroLogix packaged controllers. Unlike discrete signals, analog signals represent continuous physical variables like temperature, allowing for an infinite number of states. The document also covers analog input and output interfaces, including how analog devices translate these signals using analog-to-digital and digital-to-analog converters. Furthermore, it provides insight into input/output wiring, signal ratings, and resolution considerations necessary for accurate measurements in various industries.

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Fundamentals of Analog Control in MicroLogix Programmable Controllers**

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  1. Programmable Controller BasicsAnalog Control MicroLogix Packaged Controllers

  2. What is an Analog Signal?g I/O Analog Signal: The representation of numerical quantities by the measurement of continuous physical variables.

  3. Answer Unlike Discrete signals, which have only 2 states (ON and OFF). Analog signals can have an infinite number of states. Temperature is an example of an analog signal. This signal is constantly changing by infinitesimal amounts. A change from 700F to 710 F degrees is not just a 10F change but a infinite number of smaller fractions of that 10F.

  4. S Analog input interface 0000000000000000 PLC Word/Bit file of Memory T Continuous Signal Analog to Digital Converter Analog Input Signals Analog Input Interface:Translates the continuous analog input signals into discrete values with in the PLC. (analog to digital converter)

  5. Analog Input Devices • Flow Transducers • Humidity Transducers • Load Cell Transducers • Potentiometers • Pressure Transducers • Vibration Transducers • Temperature Transducers

  6. Analog input Signal ratings • Voltage Range • 10V dc • 0 to 10V dc • 0 to 5V dc • 1 to 5V dc • Current Range • 20 mA • 0 to 20 mA • 4 to 20 mA • Unipolar: Positive voltage only • Bipolar: Positive and Negative

  7. S Analog Output Interface 0000000000000000 PLC Word/Bit file of Memory T Continuous Signal (voltage or current) Digital to analog converter Analog Output signals Analog Output Interface:Translates the discrete values of the PLC into continuous analog output signals. (digital to analog converter)

  8. Analog Output Field Devices • Analog Valves • Actuators • Chart Recorders • Motor Drives • Analog Meters • Pressure Transducers

  9. Analog output Signal ratings • Current Range • 0 to 21 mA • 0 to 20 mA • 4 to 20 mA • Voltage Range • 10V dc • 0 to 10V dc • 0 to 5V dc • 1 to 5V dc • Unipolar: Positive voltage only • Bipolar: Positive and Negative

  10. Resolution Resolution:The smallest detectable increment of measurement This is a reference to the accuracy of the A/D converter. 15bit = Signal/32767 (0 to 32766 steps) 14bit = Signal/16384 (0 to 16383 steps) 13bit = Signal/ 8192 (0 to 8193 steps) 12bit = Signal/4096 (0 to 4095 steps) Example: 12 bit resolution with +10 volt signal. 10Vdc/4095 = 2.4mV per step Example: 15 bit resolution with +10 volt signal 10Vdc/32766 = 305uV per step

  11. Resolution Calculating number of counts per unit. Using a temperature range of 00 to 1000.To determine the counts per degree with 12 bit resolution. Example: Total Counts / Total Degrees = Counts Per Degree 4095/100 = 4.095 Example: Counts Per Degree x Units per step = Units per Degree 4.095 x 2.4mV = 9.8mV

  12. Terminal Block 1 Channel 1 2 Analog device 3 4 Channel 2 5 Analog device 6 7 COM Input/Output Wiring Single ended: All analog channels share the same common 1 2 3 4 PLC 5 6 7 8 9 10

  13. 1 COM Analog device Channel 1 2 COM 3 Channel 2 Analog device COM 4 COM Input/Output Wiring Differential: All analog channels have individual commons Terminal Block

  14. Channel 1 Transducer Transmitter Field Devices Transducer: Converts the field device variable (pressure, temp) into a very low electrical signal. (current or voltage) 1 Process COM 2 Senses physical signal COM Low Level signal current/voltage 3 Amplified signal compatible with analog interface COM 4 COM Transmitter: Amplifies the signal to an interface rated signal (4-20mA, 0-10v)

  15. AnalogTarget Customers • Vertical markets: • SCADA Industry (New installations and existing A-B installations) • Water/Waste Water • Oil & Gas • Electric Power • Process Industry • Food Industry • General Industry machinery applications

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