Control System Basics – Isolation

In the final installment of this five-part series, Jon Titus explores the basic elements of a control system. In previous installments, Jon has covered relays, sink vs. source control, PNP vs. NPN logic and open collectors. Q: I don’t like the idea of control signals going from a field device into my rack of expensive […]

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How and Why to Use an Anti-Aliasing Filter

  Q: What is an anti-alias filter, and do I need one? A: At its simplest an anti-alias filter removes unwanted high-frequency signals from the signals you want to measure. Let’s look at why you might need one. When we see a signal on an analog oscilloscope, the signal goes through every voltage shown on […]

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How to Program and Debug RS-485 Networks

  Q: Some of the data sheets for RS-485 devices mention a 9-bit UART protocol. What does it do? A: In a network with many devices you need a way to identify each one uniquely. You don’t want valve-actuator data going to a pump-motor controller! Although most of us think of a universal asynchronous receiver […]

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How to Properly Configure and Wire RS-422 and RS-485 Networks

  Q: Why do the diagrams for the RS-422 and RS-485 buses include resistors at the end of the bus wires and what values do I need for them? A: Signals that reflect from the end of an unterminated bus with a high-enough amplitude can cause problems for other devices that see these reflections as […]

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