Lecture 30 - Process Control at IMFlash

Representatives from IMFlash will visit to discuss application of process control and statistics in an industrial setting. A couple of the chemical engineering seniors completed internships at IMFlash this past summer and can also attest to the importance of process control in their work.

Homework

  1. Course reading for next class: 11.4 (PDC)
  2. Assignment due by the start of Lecture #31: SP12

For special problem #12, please assume a 4-20 mA signal from the measurement transducer.

From Wikipedia - Current Loop:

For industrial process control instruments, analog 420 mA and 1050 mA current loops are commonly used for analog signaling, with 4 mA representing the lowest end of the range and 20 mA the highest. The key advantages of the current loop are that the accuracy of the signal is not affected by voltage drop in the interconnecting wiring, and that the loop can supply operating power to the device. Even if there is significant electrical resistance in the line, the current loop transmitter will maintain the proper current, up to its maximum voltage capability. The live-zero represented by 4 mA allows the receiving instrument to detect some failures of the loop, and also allows transmitter devices to be powered by the same current loop (called two-wire transmitters). Such instruments are used to measure pressure, temperature, flow, pH or other process variables. A current loop can also be used to control a valve positioner or other output actuator. An analog current loop can be converted to a voltage input with a precision resistor. Since input terminals of instruments may have one side of the current loop input tied to the chassis ground (earth), analog isolators may be required when connecting several instruments in series.

Relate each problem in the context of the overall course objectives.


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