analog and digital ppt Flashcards
(95 cards)
refers to a category of devices and systems
used for measuring, displaying, and recording analog signals to obtain real-time
data and information about various physical phenomena.
Analog electronic instrumentation
it is a voltage or current whose magnitude represents some physical measurement or control quantity.
Analog electronic instrumentation
play a fundamental role in instrumentation and control systems, serving as the cornerstone for the measurement, monitoring, and regulation of a wide range of physical parameters.
Analog electronic instrumentation
These analog signals offer a
continuous representation of the quantity being measured, making them
indispensable for ensuring accurate control and monitoring of industrial processes.
Analog electronic instrumentation
some common applications of analog electronic signals in instrumentation and Control:
-PID CONTROLLER
-TEMPERATURE MEASUREMENT
-PRESSURE MEASUREMENT
-LEVEL SENSING
-FLOW RATE MEASUREMENT
if the process pressure is ..
75%
what’s its bar and analog input?
7.5 bar and 16mA
if the process pressure is ..
0%
what’s its bar and analog input?
0 bar and 4mA
if the process pressure is ..
25%
what’s its bar and analog input?
2.5 bar and 8mA
if the process pressure is ..
50%
what’s its bar and analog input?
5 bar and 12mA
if the process pressure is ..
100%
what’s its bar and analog input?
10 bar and 20mA
This is an analog signal standard, meaning
that the electric current is used to proportionately represent measurements or command signals.
4 TO 20 mA ANALOG CURRENT SIGNALS
The most popular form of signal transmission used in modern industrial
instrumentation systems.
4 TO 20 mA ANALOG CURRENT SIGNALS
An important concept to grasp with all analog instrumentation is that instruments sending and receiving analog signals
must be compatibly ranged in order to properly represent the desired variable.
are also used in control systems to command the positioning
of a final control element, such as a control valve or a variable-speed motor
drive (VSD).
DC current signals
In these cases, (analog electronic signals) the milliamp value does not directly represent a process measurement, but rather how the degree to which the final control element influences the process.
true
state the cycle of process of analog electronic signal
the process=> measuring device (senses) =>
[4-20 mA PV signal] => controller (decides) => [4-20 MV signal] => final control device (influences) => the process (reacts)
Why 4-20mA and not 0-20mA?
In this case, it would be extremely difficult to identify that either 0mA current is due to open circuit of the transmitter or it is due to no pressure of the fluid. Hence, if the transmitter is calibrated to generate current signal in the range of 4-20mA, the faults like open circuits can easily be detected
Why 4 mA?
instead of zero, to know if there’s a fault and for it to be not a value.
Why 20 mA?
it is not easily disturbed. And the internal resistance of the current source is infinite, and the resistance of the wire in series in the loop does not affect the accuracy, and it can transmit hundreds of meters on the ordinary twisted pair.
Why do we need to convert 4-20mA into voltage?
A current loop requires voltage to drive the current
A 4 to 20 mA current signal represents some signal along a 0 to 100 percent
scale. Usually, this scale is linear,
true
For example, if we were to calibrate a 4-20 mA temperature transmitter for a measurement range of 50 to 250 degrees
C,
we could relate the current and measured temperature values on a graph like ..
linear graph from 50-250
is the type used to represent the
output of a process controller, sending a command signal to a final control
element.
simplest form of 4-20 mA current loop
CONTROLLER OUTPUT CURRENT LOOPS examples
-4-wire (“self-powered”) transmitter current loops
-2-wire (“loop-powered”) transmitter current loops
-Troubleshooting Current Loops
