Automation in Environmental Engineering Lecture notes 2
-
Upload
patryk2000 -
Category
Documents
-
view
12 -
download
0
description
Transcript of Automation in Environmental Engineering Lecture notes 2
Automation in Environmental Engineering
dr inż. Patryk Wójtowicz
Signals
• Signal is a variable that conveys the value of a parameter (information) between the elements of a system
Signal types by physical form
General classification of signals
Signal
Analogue
Discrete Pulse
Analogue signals
• Analogue signals are continuous in nature • Analogue signals may vary over some finite
range and may have any value within that range (determined by a physical phenomenon)
• Most process signals are analogue
Discrete signals
• Discrete signals have two or more states. At any point in time, may only exist as one or other of those states
• Discrete signals are used to convey status information such as auto/manual, on/off, open/closed, running/stopped
Analogue vs digital
Pulse signals
• Pulse signals consist of trains of pulses, each pulse being equivalent to a fleeting discrete signal.
• Pulse signals are typically associated with rotary devices such as turbine meters or agitator shafts
• A known number of electrical pulses are generated with each revolution. Counting of the pulses with respect to time yields an average shaft speed
Standard signal ranges
• Signals have some standard ranges. • Compatibility of input and output signals
enables systems to be configured from off-the-shelf elements
barg – gauge pressure
Signal interpretation
• Knowledge of the behaviour or calibration of the elements and of the nature of the signal is necessary to determine the value of the parameter being transmitted
• Determine temperature reading assuming linear calibration (see diagram below)
Signal interpretation
• Analogue signals have a non-zero lower limit to their range to enable zero valued signals to be distinguished from faulty ones (4 – 20 mA signal while 0 mA = fault)
Signal processing - Linearity
• Signals which are linear are easy to interpret
• In practice non-linear input-output relationships prevail
• A basic strategy of control system design is to eliminate nonlinearities
Linearization - example
Orifice (ISO 5167)
orifice flow coefficient
mass flow rate
General instrument or function symbols
General instrument or function symbols contd
Symbols according to DIN 30600 and ISO 14617
Symbols according to DIN 30600 and ISO 14617
Symbols according to DIN 30600 and ISO 14617